Satellite-borne microwave radiometers provide essential measurements to study the surface melt state of ice sheets. Therefore, selecting suitable microwave radiometer data is critical to characterize the spatial distr...Satellite-borne microwave radiometers provide essential measurements to study the surface melt state of ice sheets. Therefore, selecting suitable microwave radiometer data is critical to characterize the spatial distribution of surface melt. In this study, we investigated the Greenland Ice Sheet and evaluated the usefulness, as climate indicators, of data acquired by microwave radiometers onboard the F17 satellite of the United States of America Defense Meteorological Satellite Program(DMSP) and the Soil Moisture and Ocean Salinity(SMOS) satellite of the European Space Agency. First, surface melt was simulated using the DMSP dataset as input for a brightness temperature threshold algorithm, the Microwave Emission Model of Layered Snowpacks(MEMLS2), and the SMOS dataset as input for the L-band Specific MEMLS(LS-MEMLS). For accuracy evaluation, the simulation results were then compared with surface melt estimates derived from air temperature measurements at Automatic Weather Stations and from ice surface temperature measurements from the Moderate Resolution Imaging Spectroradiometer(MODIS) satellite-borne instrument. Our results show that global(over Greenland) MEMLS2 simulation performance(overall accuracy 83%) was higher than that of LS-MEMLS(overall accuracy 78%). However, in southeastern Greenland, MEMLS2 omission error was markedly higher than that of LS-MEMLS, whereas LS-MEMLS could detect longer-lasting surface melt than MEMLS2. This analysis showed that DMSP-based surface melt simulations are more accurate than SMOS-based simulations, thereby providing a data selection reference for surface melt studies of the Greenland Ice Sheet.展开更多
As the world’s top two economies,the United States(U.S.)and China face a number of similar water resources problems.Yet,few studies have been done to systematically compare policies and approaches on water resources ...As the world’s top two economies,the United States(U.S.)and China face a number of similar water resources problems.Yet,few studies have been done to systematically compare policies and approaches on water resources management between China and the U.S.This study compares water resources policies of China and the U.S.in the areas of national authority,water supply,water quality,and ecosystem use of the water to draw lessons learned and shed light on water resources management in China,the U.S.,and the rest of the world.The lessons learned from the comparison include six aspects.1)New paradigms of people-water harmony and a water-saving society are urgently needed to address the pressing water crisis and achieve the United Nations Sustainable Development Goals(UN SDGs).2)A comprehensive,consistent,forward-looking national policy is necessary to achieve sustainable use of water resources.3)Empowerment of river basin commissions with comprehensive authority over the integrative management of air,land,water,and biological resources in the river basin could significantly enhance the benefits and effectiveness of economic development and environmental protection.4)Expansion of water exchange through market mechanisms among water users promotes efficient and beneficial water uses.5)Use of water for ecosystem services should be an integral part of water resources management.China has set up a national blueprint for achieving ecological civilization;maintaining appropriate amounts of flow in rivers and lakes for maintenance of wildlife and fisheries and ecosystems should be institutionalized as part of this national strategy as well.6)By sharing their rich experiences and lessons in water resources management,economic development,and ecological protection with other countries,China and the U.S.can help the world to achieve global human-water harmony and the UN SDGs.展开更多
The thermal infrared channel (IRS4) of HJ-1B satellite obtains view zenith angles (VZA) up to ±33°. The view angle should be taken into account when retrieving land surface temperature (LST) from IRS4 data. ...The thermal infrared channel (IRS4) of HJ-1B satellite obtains view zenith angles (VZA) up to ±33°. The view angle should be taken into account when retrieving land surface temperature (LST) from IRS4 data. This study aims at improving the mono-window algorithm for retrieving LST from IRS4 data. Based on atmospheric radiative transfer simulations,a model for correcting the VZA effects on atmospheric transmittance is proposed. In addition,a generalized model for calculating the effective mean atmospheric temperature is developed. Validation with the simulated dataset based on standard atmospheric profiles reveals that the improved mono-window algorithm for IRS4 obtains high accuracy for LST retrieval,with the mean absolute error (MAE) and root mean square error (RMSE) being 1.0 K and 1.1 K,respectively. Numerical experiment with the radiosonde profile acquired in Beijing in winter demonstrates that the improved mono-window algorithm exhibits excellent ability for LST retrieval,with MAE and RMSE being 0.6 K and 0.6 K,respectively. Further application in Qinghai Lake and comparison with the Moderate-Resolution Imaging Spectroradiometer (MODIS) LST product suggest that the improved mono-window algorithm is applicable and feasible in actual conditions.展开更多
Integrated assessment models and coupled earth system models both have their limitations in understanding the interactions between human activity and the physical earth system. In this paper,a new human–earth system ...Integrated assessment models and coupled earth system models both have their limitations in understanding the interactions between human activity and the physical earth system. In this paper,a new human–earth system model,BNUHESM1.0,constructed by combining the economic and climate damage components of the Dynamic Integrated Model of Climate Change and Economy to the BNU-ESM model,is introduced. The ability of BNU-HESM1.0 in simulating the global CO2 concentration and surface temperature is also evaluated. We find that,compared to observation,BNU-HESM1.0underestimates the global CO2 concentration and its rising trend during 1965–2005,due to the uncertainty in the economic components. However,the surface temperature simulated by BNU-HESM1.0 is much closer to observation,resulting from the overestimates of surface temperature by the original BNU-ESM model. The uncertainty of BNU-ESM falls within the range of present earth system uncertainty,so it is the economic and climate damage component of BNU-HESM1.0 that needs to be improved through further study. However,the main purpose of this paper is to introduce a new approach to investigate the complex relationship between human activity and the earth system. It is hoped that it will inspire further ideas that prove valuable in guiding human activities appropriate for a sustainable future climate.展开更多
The surface roughness characteristics(e.g., height and slope) of sea ice are critical for determining the parameters of an electromagnetic scattering, a surface emission and a surface drag coefficients. It is also imp...The surface roughness characteristics(e.g., height and slope) of sea ice are critical for determining the parameters of an electromagnetic scattering, a surface emission and a surface drag coefficients. It is also important in identifying various ice types, retrieval ice thickness, surface temperature and drag coefficients from remote sensing data. The point clouds(a set of points which are usually defined by X, Y, and Z coordinates that represents the external surface of an object on earth) of land fast ice in five in situ sites in the eastern coast Bohai Sea were measured using a laser scanner-Trimble GX during 2011–2012 winter season. Two hundred and fifty profiles selected from the point clouds of different samples have been used to calculate the height root mean square, height skewness, height kurtosis, slope root mean square, slope skewness and slope kurtosis of them. The root mean square of the height, the root mean square of the slope and the correlation length are about 0.090, 0.075 and 11.74 m, respectively. The heights of 150 profiles in three sites manifest the Gaussian distribution and the slopes of total 250 profiles distributed exponentially. In addition, the fractal dimension and power spectral density profiles were calculated. The results show that the fractal dimension of land fast ice in the Bohai Sea is about 1.132. The power spectral densities of 250 profiles can be expressed through an exponential autocorrelation function.展开更多
Slope farmland is an important component of farmland resources in China.The utilization and change of slope farmland have significant effects on ecosystems,and understanding the impact of slope farmland change on ecos...Slope farmland is an important component of farmland resources in China.The utilization and change of slope farmland have significant effects on ecosystems,and understanding the impact of slope farmland change on ecosystem services(ESs)is critical for effective land utilization and ecosystem protection.This study aims to analyze slope farmland changes in China between 2000 and 2020 and quantify the impact of these changes on ESs by the use of a land use dynamic attitude study,and an ecosystem services value(ESV)equivalent.Results show that the area of slope farmland in China was mainly concentrated on slopes of 2°-6°,and exhibited a downward trend between 2000 and 2020.There were significant differences in the spatial distribution of the farmland,which was mainly located in the Taihang,Qinling,Wushan,and Xuefeng mountains.ESV increased by$179.235 million due to the conversion between slope farmland and forest,grassland,and construction land from 2000-2010.Conversely,from 2010 to 2020,ESV decreased by$2613.919 million due to the conversion of forest and grassland to slope farmland as well as the conversion of slope farmland to construction land.展开更多
In this paper,we investigate the influence of the winter NAO on the multidecadal variability of winter East Asian surface air temperature(EASAT)and EASAT decadal prediction.The observational analysis shows that the wi...In this paper,we investigate the influence of the winter NAO on the multidecadal variability of winter East Asian surface air temperature(EASAT)and EASAT decadal prediction.The observational analysis shows that the winter EASAT and East Asian minimum SAT(EAmSAT)display strong in-phase fluctuations and a significant 60-80-year multidecadal variability,apart from a long-term warming trend.The winter EASAT experienced a decreasing trend in the last two decades,which is consistent with the occurrence of extremely cold events in East Asia winters in recent years.The winter NAO leads the detrended winter EASAT by 12-18 years with the greatest significant positive correlation at the lead time of 15 years.Further analysis shows that ENSO may affect winter EASAT interannual variability,but does not affect the robust lead relationship between the winter NAO and EASAT.We present the coupled oceanic-atmospheric bridge(COAB)mechanism of the NAO influences on winter EASAT multidecadal variability through its accumulated delayed effect of~15 years on the Atlantic Multidecadal Oscillation(AMO)and Africa-Asia multidecadal teleconnection(AAMT)pattern.An NAO-based linear model for predicting winter decadal EASAT is constructed on the principle of the COAB mechanism,with good hindcast performance.The winter EASAT for 2020-34 is predicted to keep on fluctuating downward until~2025,implying a high probability of occurrence of extremely cold events in coming winters in East Asia,followed by a sudden turn towards sharp warming.The predicted 2020/21 winter EASAT is almost the same as the 2019/20 winter.展开更多
Soil erosion is one of the most serious environmental issues constraining the sustainable development of human society and economies.Soil compound erosion is the result of the alternation or interaction between two or...Soil erosion is one of the most serious environmental issues constraining the sustainable development of human society and economies.Soil compound erosion is the result of the alternation or interaction between two or more erosion forces.In recent years,fluctuations and extreme changes in climatic factors(air temperature,precipitation,wind speed,etc.)have led to an increase in the intensity and extent of compound erosion,which is increasingly considered in soil erosion research.First,depending on the involvement of gravity,compound erosion process can be divided into compound erosion with and without gravity.We systematically summarized the research on the mechanisms and processes of alternating or interacting soil erosion forces(wind,water,and freeze-thaw)considering different combinations,combed the characteristics of compound erosion in three typical regions,namely,high-elevation areas,high-latitude areas,and dry and wet transition regions,and reviewed soil compound erosion research methods,such as station observations,simulation experiments,prediction models,and artificial neural networks.The soil erosion model of wind,water,and freeze-thaw interaction is the most significant method for quantifying and predicting compound erosion.Furthermore,it is proposed that there are several issues such as unclear internal mechanisms,lack of comprehensive prediction models,and insufficient scale conversion methods in soil compound erosion research.It is also suggested that future soil compound erosion mechanism research should prioritize the coupling of compound erosion forces and climate change.展开更多
This special edition of the Journal of Geodesy and Geoinformation Science(JGGS)presents a curated selection of papers that offer novel techniques in the realm of intelligent interpretation of remote sensing images.In ...This special edition of the Journal of Geodesy and Geoinformation Science(JGGS)presents a curated selection of papers that offer novel techniques in the realm of intelligent interpretation of remote sensing images.In recent years,tremendous efforts have been made across a wide spectrum including theory,models,algorithms,applications and datasets,etc.Such advancements have demonstrated their stunning performance in a variety of remote sensing topics spanning from general challenges like remote image classification and object detection,to highly specialized tasks such as autonomous situation awareness and disaster response.Moreover,such achievements have redefined disciplinary boundaries and also reshaped our education.展开更多
Rainfall was witnessed for the first time at the highest area of the Greenland Ice Sheet on 14 August,2021.The thermodynamic mechanisms supporting the rainfall are revealed by ERA5 reanalysis,in-situ and satellite dat...Rainfall was witnessed for the first time at the highest area of the Greenland Ice Sheet on 14 August,2021.The thermodynamic mechanisms supporting the rainfall are revealed by ERA5 reanalysis,in-situ and satellite data.We find that a strong southward intrusion of the polar vortex favored the maintenance of a deep cyclone over Baffin Island and an amplification of anticyclonic circulation over the southeastern ice sheet,which pumped warm and moist air toward Greenland from anomalously warm waters south of Greenland.Across a wide swath of the ice sheet,atmospheric uplift maintained above-melting and rainfall conditions via condensation and enhanced downward infrared irradiance.Without the low-level liquid clouds,the spatial extent and duration of the rainfall would have been smaller.Over the ice sheet topographic summit,the air temperature from the ground to 250 hPa level was~2℃higher than the previous record set on 12 July,2012.Such events may occur more frequently with the decreased temperature contrast between the Arctic and the mid-latitude regions that drives highly amplified jet streams.Thus,this extreme event serves as a harbinger of a more likely wet surface condition across all elevations of the ice sheet.展开更多
Two parallel sets of numerical experiments(an ozone-hole simulation and a non-ozone-hole simulation) were performed to investigate the effect of ozone depletion on surface temperature change using the second spectral ...Two parallel sets of numerical experiments(an ozone-hole simulation and a non-ozone-hole simulation) were performed to investigate the effect of ozone depletion on surface temperature change using the second spectral version of the Flexible Global Ocean–Atmosphere–Land System model(FGOALS-s2), focusing on the eastern Antarctica(EA) continent in austral summer. First, we evaluated the ability of the model to simulate the EA surface cooling, and found the model can successfully reproduce the cooling trend of the EA surface, as well as the circulation change circling the South Pole in the past 30 years.Second, we compared the two experiments and discovered that the ozone depletion causes the cooling trend and strengthens the circumpolar westerly flow. We further investigated the causes of the EA surface cooling associated with the ozone hole and found two major contributors. The first is the ozone-hole direct radiation effect(DRE) upon the surface that happens because the decrease of the downward longwave(LW) radiation overcomes the increase of the downward shortwave(SW)radiation under clear sky. The second is the cloud radiation effect(CRE) induced by ozone depletion, which happens because the decreased downward SW radiation overcomes the increased downward LW radiation in the case of increased cloud.Although the CRE is theoretically opposite to the DRE, their final net effect makes comparable contributions to the EA surface cooling. Compared with the surface radiation budget, the surface heat flux budgets have a much smaller contribution.We additionally note that the CRE is basically ascribed to the circulation change.展开更多
Land surface hydrothermal conditions(LSHCs) reflect land surface moisture and heat conditions, and play an important role in energy and water cycles in soil-plant-atmosphere continuum. Based on comparison of four eval...Land surface hydrothermal conditions(LSHCs) reflect land surface moisture and heat conditions, and play an important role in energy and water cycles in soil-plant-atmosphere continuum. Based on comparison of four evaluation methods(namely, the classic statistical method, geostatistical method, information theory method, and fractal method), this study proposed a new scheme for evaluating the spatial heterogeneity of LSHCs. This scheme incorporates diverse remotely sensed surface parameters, e.g., leaf area index-LAI, the normalized difference vegetation index-NDVI, net radiation-Rn, and land surface temperature-LST. The LSHCs can be classified into three categories, namely homogeneous, moderately heterogeneous and highly heterogeneous based on the remotely sensed LAI data with a 30 m spatial resolution and the combination of normalized information entropy(S’) and coefficient of variation(CV). Based on the evaluation scheme, the spatial heterogeneity of land surface hydrothermal conditions at six typical flux observation stations in the Heihe River Basin during the vegetation growing season were evaluated. The evaluation results were consistent with the land surface type characteristics exhibited by Google Earth imagery and spatial heterogeneity assessed by high resolution remote sensing evapotranspiration data. Impact factors such as precipitation and irrigation events, spatial resolutions of remote sensing data, heterogeneity in the vertical direction, topography and sparse vegetation could also affect the evaluation results. For instance, short-term changes(precipitation and irrigation events) in the spatial heterogeneity of LSHCs can be diagnosed by energy factors, while long-term changes can be indicated by vegetation factors. The spatial heterogeneity of LSHCs decreases when decreasing the spatial resolution of remote sensing data. The proposed evaluation scheme would be useful for the quantification of spatial heterogeneity of LSHCs over flux observation stations toward the global scale, and also contribute to the improvement of the accuracy of estimation and validation for remotely sensed(or model simulated) evapotranspiration.展开更多
The great challenges of sustainable development highlight an urgent need to systematically understand the mech-anisms linking humans and nature.Resources and Environmental Sciences are a broad and practical discipline...The great challenges of sustainable development highlight an urgent need to systematically understand the mech-anisms linking humans and nature.Resources and Environmental Sciences are a broad and practical discipline focused on coupled human and natural systems.They aim to study the formation and evolution of resources in the earth system,the drivers of various environmental problems,processes and relationships between resources and the environment,particularly under the combined impacts of natural conditions and human activities.The major resources and environmental problems drive the discipline development;international science programmes guide the direction of the discipline;interdisciplinary and transdisciplinary integration promotes new branches of the discipline;and technological progress results in a research paradigm shift.Facing the critical research re-quirements of strengthening trans-and interdisciplinarity,breaking through the key technology,targeting major environmental and disaster issues,and supporting sustainable development,nine critical scientific issues should be focused on climate change impact and adaptation,petroleum and mineral resources,water cycle and water re-sources,soil and land resources,ecosystems,remote sensing and geographic information science,environmental science and technology,disaster risk,and global and regional sustainable development.Suggestions to enhancing funding systems,improve talent cultivation,develop scientific platforms,and strength international cooperation are provided in this study to support scientific policymaking.The promotion of Resources and Environmental Sci-ences enables a more comprehensive and in-depth understanding of economic development and environmental changes relevant to assure a more sustainable global development.展开更多
The present study examined the diurnal variations of summer precipitation in the Beijing area by using subdaily precipitation and wind observations. A combined effect of topography and urbanization on the characterist...The present study examined the diurnal variations of summer precipitation in the Beijing area by using subdaily precipitation and wind observations. A combined effect of topography and urbanization on the characteristics of diurnal variations was suggested. It was shown that stations located in the plain areaexhibited typical night rain peaks, whereas those in the mountainous area exhibited clear afternoon peaks ofprecipitation diurnal variations. The precipitation peaks were associated with wind fields around the Beijing area, which were found to be highly modulated by mountain-valley circulation and urban-country circulation.The lower-tropospheric wind exhibited a clear diurnal shift in its direction from north at 0800 LST to southat 2000 LST, which reflected mountain-valley circulation. The transitions from valley to mountain windand the opposite generally happened after sunset and sunrise, respectively, and both occurred earlier for thestations located closer to mountains. By comparing the diurnal variations of precipitation at stations in anortheast suburb, an urban area, and a southwest suburb, it was revealed that the northeast suburb grouphad the highest normalized rainfall frequency, but the southwest group had the lowest from late afternoon tolate evening. On the contrary, in the early morning from about 0200 to 1000 LST, the southwest group andurban group had the highest normalized rainfall frequency. This pattern might originate from the combined effects of mountain-valley topography and urbanization.展开更多
Wetland soil quality degradation caused by large-scale agricultural reclamation on the Sanjiang Plain of Northeast China has been widely reported. A relative soil quality evaluation (RSQE) model and a projection pursu...Wetland soil quality degradation caused by large-scale agricultural reclamation on the Sanjiang Plain of Northeast China has been widely reported. A relative soil quality evaluation (RSQE) model and a projection pursuit evaluation (PPE) model based on real-coded accelerating genetic algorithm were introduced to evaluate quality variations in top layers of the main wetland soils on the Sanjiang Plain in 1999 and 2003, respectively. As soil quality degradation boundaries were vague, this study established two fuzzy synthetic evaluation (FSE) models based on the original data and criteria used in the RSQE and PPE models. The outputs of the two FSE models were obtained by choosing two fuzzy composite operators M(∧, ∨) and M(·, ⊕). Statistical analysis showed that the results of the FSE, RSQE, and PPE models were correlated. In particular, outputs of the FSE model using M(·, ⊕) were significantly correlated with those of the RSQE model with r = 0.989 at P < 0.01. Compared with RSQE and PPE models, the FSE model may be more objective in showing soil quality variations and was closer to the natural situation, showing the feasibility and applicability of the FSE model in evaluating soil quality degradation. However, the choice of composite operator was of critical importance. The study of wetland soil quality degradation on the Sanjiang Plain was of scientific and practical significance for protection and management of soils and for sustainable development of agriculture in this area in the future.展开更多
The research on sea ice resources is the academic base of sea ice exploitation in the Bohai Sea. According to the ice-water spectrum differences and the correlation between ice thickness and albedo, this paper comes u...The research on sea ice resources is the academic base of sea ice exploitation in the Bohai Sea. According to the ice-water spectrum differences and the correlation between ice thickness and albedo, this paper comes up with a sea ice thickness inversion model based on the NOAA/AVHRR data. And then a sea ice resources quantity (SIQ) time series of Bohai Sea is established from 1987 to 2009. The results indicate that the average error of inversion sea ice thickness is below 30%. The maximum sea ice resources quantity is about 6 × 10 9 m 3 and the minimum is 1.3 × 10 9 m 3 . And a preliminary analysis has been made on the errors of the estimate of sea ice resources quantity (SIQ).展开更多
Determining soil N mineralization response to soil temperature and moisture changes is challenging in the field due to complicated effects from other factors. In the laboratory, N mineralization is highly dependent on...Determining soil N mineralization response to soil temperature and moisture changes is challenging in the field due to complicated effects from other factors. In the laboratory, N mineralization is highly dependent on temperature, moisture and sample size. In this study, a laboratory incubation experiment was carefully designed and conducted under controlled conditions to examine the effects of soil temperature and moisture on soil N mineralization using soil samples obtained from the Stipa krylovii grassland in Inner Mongolia, China. Five temperature(i.e. 9°C, 14°C, 22°C, 30°C and 40°C) and five moisture levels(i.e. 20%, 40%, 60%, 80% and 100% WHC, where WHC is the soil water holding capacity) were included in a full-factorial design. During the 71-day incubation period, microbial biomass carbon(MBC), ammonium nitrogen(NH4 +-N) and nitrate nitrogen(NO3--N) were measured approximately every 18 days; soil basal respiration for qCO2 index was measured once every 2 days(once a week near the end of the incubation period). The results showed that the mineral N production and net N mineralization rates were positively correlated with temperature; the strongest correlation was observed for temperatures between 30°C and 40°C. The relationships between moisture levels and both the mineral N production and net N mineralization rates were quadratic. The interaction between soil temperature and moisture was significant on N mineralization, i.e. increasing temperatures(moisture) enhanced the sensitivity of N mineralization to moisture(temperature). Our results also showed a positive correlation between the net nitrification rate and temperature, while the correlation between the NH4 +-N content and temperature was insignificant. The net nitrification rate was negatively correlated with high NH4 +-N contents at 80%–100% WHC, suggesting an active denitrification in moist conditions. Moreover, qCO2 index was positively correlated with temperature, especially at 80% WHC. With a low net nitrification rate and high soil basal respiration rate, it was likely that the denitrification concealed the microbial gross mineralization activity; therefore, active soil N mineralization occurred in 60%–80% WHC conditions.展开更多
Historical simulations of annual mean surface air temperature over China with 25 CMIP5 models were assessed.The observational data from CRUT3v and CN05 were used and further compared with historical simulations of CMI...Historical simulations of annual mean surface air temperature over China with 25 CMIP5 models were assessed.The observational data from CRUT3v and CN05 were used and further compared with historical simulations of CMIP3.The results show that CMIP5 models were able to simulate the observed warming over China from 1906 to 2005(0.84 C per 100 years)with a warming rate of 0.77 C per 100 years based on the multi-model ensemble(MME).The simulations of surface air temperature in the late 20th century were much better than those in the early 20th century,when only two models could reproduce the extreme warming in the 1940s.The simulations for the spatial distribution of the 20-yearmean(1986–2005)surface air temperature over China fit relatively well with the observations.However,underestimations in surface air temperature climatology were still found almost all over China,and the largest cold bias and simulation uncertainty were found in western China.On sub-regional scale,northern China experienced stronger warming than southern China during 1961–1999,for which the CMIP5 MME provided better simulations.With CMIP5 the diference of warming trends in northern and southern China was underestimated.In general,the CMIP5 simulations are obviously improved in comparison with the CMIP3 simulations in terms of the variation in regional mean surface air temperature,the spatial distribution of surface air temperature climatology and the linear trends in surface air temperature all over China.展开更多
Based on observations and 12 simulations from Coupled Model Intercomparison Project Phase 5(CMIP5) models, climatic extremes and their changes over China in the past and under the future scenarios of three Representat...Based on observations and 12 simulations from Coupled Model Intercomparison Project Phase 5(CMIP5) models, climatic extremes and their changes over China in the past and under the future scenarios of three Representative Concentration Pathways(RCPs) are analyzed. In observations, frost days(FD) and low-temperature threshold days(TN10P) show a decreasing trend, and summer days(SU), high-temperature threshold days(TX90P), heavy precipitation days(R20), and the contribution of heavy precipitation days(P95T) show an increasing trend. Most models are able to simulate the main characteristics of most extreme indices. In particular, the mean FD and TX90 P are reproduced the best, and the basic trends of FD, TN10 P, SU and TX90 P are represented. For the FD and SU indexes, most models show good ability in capturing the spatial differences between the mean state of the periods 1986–2005 and 1961–80; however, for other indices, the simulation abilities for spatial disparity are less satisfactory and need to be improved. Under the high emissions scenario of RCP8.5,the century-scale linear changes of the multi-model ensemble(MME) for FD, SU, TN10 P, TX90 P, R20 and P95 T are-46.9,46.0,-27.1, 175.4, and 2.9 days, and 9.9%, respectively; and the spatial change scope for each index is consistent with the emissions intensity. Due to the complexities of physical process parameterizations and the limitation of forcing data, great uncertainty still exists with respect to the simulation of climatic extremes.展开更多
基金supported by the National Natural Science Foundation of China (Grant no. 42122047)the National Key Research and Development Program of China (Grant no. 2018YFC1406103)the Basic Fund of the Chinese Academy of Meteorological Science (Grant no. 2021Z006)。
文摘Satellite-borne microwave radiometers provide essential measurements to study the surface melt state of ice sheets. Therefore, selecting suitable microwave radiometer data is critical to characterize the spatial distribution of surface melt. In this study, we investigated the Greenland Ice Sheet and evaluated the usefulness, as climate indicators, of data acquired by microwave radiometers onboard the F17 satellite of the United States of America Defense Meteorological Satellite Program(DMSP) and the Soil Moisture and Ocean Salinity(SMOS) satellite of the European Space Agency. First, surface melt was simulated using the DMSP dataset as input for a brightness temperature threshold algorithm, the Microwave Emission Model of Layered Snowpacks(MEMLS2), and the SMOS dataset as input for the L-band Specific MEMLS(LS-MEMLS). For accuracy evaluation, the simulation results were then compared with surface melt estimates derived from air temperature measurements at Automatic Weather Stations and from ice surface temperature measurements from the Moderate Resolution Imaging Spectroradiometer(MODIS) satellite-borne instrument. Our results show that global(over Greenland) MEMLS2 simulation performance(overall accuracy 83%) was higher than that of LS-MEMLS(overall accuracy 78%). However, in southeastern Greenland, MEMLS2 omission error was markedly higher than that of LS-MEMLS, whereas LS-MEMLS could detect longer-lasting surface melt than MEMLS2. This analysis showed that DMSP-based surface melt simulations are more accurate than SMOS-based simulations, thereby providing a data selection reference for surface melt studies of the Greenland Ice Sheet.
文摘As the world’s top two economies,the United States(U.S.)and China face a number of similar water resources problems.Yet,few studies have been done to systematically compare policies and approaches on water resources management between China and the U.S.This study compares water resources policies of China and the U.S.in the areas of national authority,water supply,water quality,and ecosystem use of the water to draw lessons learned and shed light on water resources management in China,the U.S.,and the rest of the world.The lessons learned from the comparison include six aspects.1)New paradigms of people-water harmony and a water-saving society are urgently needed to address the pressing water crisis and achieve the United Nations Sustainable Development Goals(UN SDGs).2)A comprehensive,consistent,forward-looking national policy is necessary to achieve sustainable use of water resources.3)Empowerment of river basin commissions with comprehensive authority over the integrative management of air,land,water,and biological resources in the river basin could significantly enhance the benefits and effectiveness of economic development and environmental protection.4)Expansion of water exchange through market mechanisms among water users promotes efficient and beneficial water uses.5)Use of water for ecosystem services should be an integral part of water resources management.China has set up a national blueprint for achieving ecological civilization;maintaining appropriate amounts of flow in rivers and lakes for maintenance of wildlife and fisheries and ecosystems should be institutionalized as part of this national strategy as well.6)By sharing their rich experiences and lessons in water resources management,economic development,and ecological protection with other countries,China and the U.S.can help the world to achieve global human-water harmony and the UN SDGs.
基金Under the auspices of Opening Funding of State Key Laboratory for Remote Sensing ScienceNational High-tech Research and Development Program (863 Program) (No. 2007AA120205, 2007AA120306)
文摘The thermal infrared channel (IRS4) of HJ-1B satellite obtains view zenith angles (VZA) up to ±33°. The view angle should be taken into account when retrieving land surface temperature (LST) from IRS4 data. This study aims at improving the mono-window algorithm for retrieving LST from IRS4 data. Based on atmospheric radiative transfer simulations,a model for correcting the VZA effects on atmospheric transmittance is proposed. In addition,a generalized model for calculating the effective mean atmospheric temperature is developed. Validation with the simulated dataset based on standard atmospheric profiles reveals that the improved mono-window algorithm for IRS4 obtains high accuracy for LST retrieval,with the mean absolute error (MAE) and root mean square error (RMSE) being 1.0 K and 1.1 K,respectively. Numerical experiment with the radiosonde profile acquired in Beijing in winter demonstrates that the improved mono-window algorithm exhibits excellent ability for LST retrieval,with MAE and RMSE being 0.6 K and 0.6 K,respectively. Further application in Qinghai Lake and comparison with the Moderate-Resolution Imaging Spectroradiometer (MODIS) LST product suggest that the improved mono-window algorithm is applicable and feasible in actual conditions.
基金funded by the National Key Program for Global Change Research of China(Grant No.2010CB950504)the National Basic Research Program of China(973 Program)(Grant No. 2012CB95570001)the nationallevel major cultivation project of Guangdong Province entitled:"The construction and application of coupled earth system and social economic models"(Grant No.2014GKXM058)
文摘Integrated assessment models and coupled earth system models both have their limitations in understanding the interactions between human activity and the physical earth system. In this paper,a new human–earth system model,BNUHESM1.0,constructed by combining the economic and climate damage components of the Dynamic Integrated Model of Climate Change and Economy to the BNU-ESM model,is introduced. The ability of BNU-HESM1.0 in simulating the global CO2 concentration and surface temperature is also evaluated. We find that,compared to observation,BNU-HESM1.0underestimates the global CO2 concentration and its rising trend during 1965–2005,due to the uncertainty in the economic components. However,the surface temperature simulated by BNU-HESM1.0 is much closer to observation,resulting from the overestimates of surface temperature by the original BNU-ESM model. The uncertainty of BNU-ESM falls within the range of present earth system uncertainty,so it is the economic and climate damage component of BNU-HESM1.0 that needs to be improved through further study. However,the main purpose of this paper is to introduce a new approach to investigate the complex relationship between human activity and the earth system. It is hoped that it will inspire further ideas that prove valuable in guiding human activities appropriate for a sustainable future climate.
基金The National High Technology Research and Development Program of China under contract No.2011AA100505the National Key Technology R&D Program of China under contract No.2006BAB03A03the State Key Laboratory of Earth Surface Processes and Resource Ecology,Beijing Normal University of China under contract Nos 2010-TD-02 and 2011-TDZD-050
文摘The surface roughness characteristics(e.g., height and slope) of sea ice are critical for determining the parameters of an electromagnetic scattering, a surface emission and a surface drag coefficients. It is also important in identifying various ice types, retrieval ice thickness, surface temperature and drag coefficients from remote sensing data. The point clouds(a set of points which are usually defined by X, Y, and Z coordinates that represents the external surface of an object on earth) of land fast ice in five in situ sites in the eastern coast Bohai Sea were measured using a laser scanner-Trimble GX during 2011–2012 winter season. Two hundred and fifty profiles selected from the point clouds of different samples have been used to calculate the height root mean square, height skewness, height kurtosis, slope root mean square, slope skewness and slope kurtosis of them. The root mean square of the height, the root mean square of the slope and the correlation length are about 0.090, 0.075 and 11.74 m, respectively. The heights of 150 profiles in three sites manifest the Gaussian distribution and the slopes of total 250 profiles distributed exponentially. In addition, the fractal dimension and power spectral density profiles were calculated. The results show that the fractal dimension of land fast ice in the Bohai Sea is about 1.132. The power spectral densities of 250 profiles can be expressed through an exponential autocorrelation function.
基金supported in part by grants from the National Natural Science Foundation of China(Grant Nos.42001187 and 41701629)。
文摘Slope farmland is an important component of farmland resources in China.The utilization and change of slope farmland have significant effects on ecosystems,and understanding the impact of slope farmland change on ecosystem services(ESs)is critical for effective land utilization and ecosystem protection.This study aims to analyze slope farmland changes in China between 2000 and 2020 and quantify the impact of these changes on ESs by the use of a land use dynamic attitude study,and an ecosystem services value(ESV)equivalent.Results show that the area of slope farmland in China was mainly concentrated on slopes of 2°-6°,and exhibited a downward trend between 2000 and 2020.There were significant differences in the spatial distribution of the farmland,which was mainly located in the Taihang,Qinling,Wushan,and Xuefeng mountains.ESV increased by$179.235 million due to the conversion between slope farmland and forest,grassland,and construction land from 2000-2010.Conversely,from 2010 to 2020,ESV decreased by$2613.919 million due to the conversion of forest and grassland to slope farmland as well as the conversion of slope farmland to construction land.
基金supported by the National Natural Science Foundation of China(NSFC)Project(Grant No.41790474)Shandong Natural Science Foundation Project(Grant No.ZR2019ZD12)Fundamental Research Funds for the Central Universities(Grant No.201962009).
文摘In this paper,we investigate the influence of the winter NAO on the multidecadal variability of winter East Asian surface air temperature(EASAT)and EASAT decadal prediction.The observational analysis shows that the winter EASAT and East Asian minimum SAT(EAmSAT)display strong in-phase fluctuations and a significant 60-80-year multidecadal variability,apart from a long-term warming trend.The winter EASAT experienced a decreasing trend in the last two decades,which is consistent with the occurrence of extremely cold events in East Asia winters in recent years.The winter NAO leads the detrended winter EASAT by 12-18 years with the greatest significant positive correlation at the lead time of 15 years.Further analysis shows that ENSO may affect winter EASAT interannual variability,but does not affect the robust lead relationship between the winter NAO and EASAT.We present the coupled oceanic-atmospheric bridge(COAB)mechanism of the NAO influences on winter EASAT multidecadal variability through its accumulated delayed effect of~15 years on the Atlantic Multidecadal Oscillation(AMO)and Africa-Asia multidecadal teleconnection(AAMT)pattern.An NAO-based linear model for predicting winter decadal EASAT is constructed on the principle of the COAB mechanism,with good hindcast performance.The winter EASAT for 2020-34 is predicted to keep on fluctuating downward until~2025,implying a high probability of occurrence of extremely cold events in coming winters in East Asia,followed by a sudden turn towards sharp warming.The predicted 2020/21 winter EASAT is almost the same as the 2019/20 winter.
基金supported by the key research and development and transformation project of Qinghai Province,China(2022-SF-173)the Second Tibetan Plateau Scientific Expedition and Research Program,China(2019QZKK0606)the National Natural Science Foundation of China(42101027).
文摘Soil erosion is one of the most serious environmental issues constraining the sustainable development of human society and economies.Soil compound erosion is the result of the alternation or interaction between two or more erosion forces.In recent years,fluctuations and extreme changes in climatic factors(air temperature,precipitation,wind speed,etc.)have led to an increase in the intensity and extent of compound erosion,which is increasingly considered in soil erosion research.First,depending on the involvement of gravity,compound erosion process can be divided into compound erosion with and without gravity.We systematically summarized the research on the mechanisms and processes of alternating or interacting soil erosion forces(wind,water,and freeze-thaw)considering different combinations,combed the characteristics of compound erosion in three typical regions,namely,high-elevation areas,high-latitude areas,and dry and wet transition regions,and reviewed soil compound erosion research methods,such as station observations,simulation experiments,prediction models,and artificial neural networks.The soil erosion model of wind,water,and freeze-thaw interaction is the most significant method for quantifying and predicting compound erosion.Furthermore,it is proposed that there are several issues such as unclear internal mechanisms,lack of comprehensive prediction models,and insufficient scale conversion methods in soil compound erosion research.It is also suggested that future soil compound erosion mechanism research should prioritize the coupling of compound erosion forces and climate change.
文摘This special edition of the Journal of Geodesy and Geoinformation Science(JGGS)presents a curated selection of papers that offer novel techniques in the realm of intelligent interpretation of remote sensing images.In recent years,tremendous efforts have been made across a wide spectrum including theory,models,algorithms,applications and datasets,etc.Such advancements have demonstrated their stunning performance in a variety of remote sensing topics spanning from general challenges like remote image classification and object detection,to highly specialized tasks such as autonomous situation awareness and disaster response.Moreover,such achievements have redefined disciplinary boundaries and also reshaped our education.
基金supported by the National Key Research&Development Program of China (Grant no.2018YFC1406104)conducted by Geological Survey of Denmark and Greenland (GEUS)under support from the Danish Ministry of Climate,Energy and Utilities via The Programme for Monitoring of the Greenland Ice Sheet (PROMICE)the INTAROS project under the European Union's Horizon 2020 Research and Innovation Program under grant agreement no.727890。
文摘Rainfall was witnessed for the first time at the highest area of the Greenland Ice Sheet on 14 August,2021.The thermodynamic mechanisms supporting the rainfall are revealed by ERA5 reanalysis,in-situ and satellite data.We find that a strong southward intrusion of the polar vortex favored the maintenance of a deep cyclone over Baffin Island and an amplification of anticyclonic circulation over the southeastern ice sheet,which pumped warm and moist air toward Greenland from anomalously warm waters south of Greenland.Across a wide swath of the ice sheet,atmospheric uplift maintained above-melting and rainfall conditions via condensation and enhanced downward infrared irradiance.Without the low-level liquid clouds,the spatial extent and duration of the rainfall would have been smaller.Over the ice sheet topographic summit,the air temperature from the ground to 250 hPa level was~2℃higher than the previous record set on 12 July,2012.Such events may occur more frequently with the decreased temperature contrast between the Arctic and the mid-latitude regions that drives highly amplified jet streams.Thus,this extreme event serves as a harbinger of a more likely wet surface condition across all elevations of the ice sheet.
基金supported by the project "Investigation of Climate Change Mechanisms by Observation and Simulation of the Polar Climate Past and Present" (PE14010) of the Korea Polar Research Institutethe National Natural Science Foundation of China (Grant No.41375003)the Beijing High Education Young Elite Teacher Project and the Chinese Academy of Sciences (Grant No.XDA05110303)
文摘Two parallel sets of numerical experiments(an ozone-hole simulation and a non-ozone-hole simulation) were performed to investigate the effect of ozone depletion on surface temperature change using the second spectral version of the Flexible Global Ocean–Atmosphere–Land System model(FGOALS-s2), focusing on the eastern Antarctica(EA) continent in austral summer. First, we evaluated the ability of the model to simulate the EA surface cooling, and found the model can successfully reproduce the cooling trend of the EA surface, as well as the circulation change circling the South Pole in the past 30 years.Second, we compared the two experiments and discovered that the ozone depletion causes the cooling trend and strengthens the circumpolar westerly flow. We further investigated the causes of the EA surface cooling associated with the ozone hole and found two major contributors. The first is the ozone-hole direct radiation effect(DRE) upon the surface that happens because the decrease of the downward longwave(LW) radiation overcomes the increase of the downward shortwave(SW)radiation under clear sky. The second is the cloud radiation effect(CRE) induced by ozone depletion, which happens because the decreased downward SW radiation overcomes the increased downward LW radiation in the case of increased cloud.Although the CRE is theoretically opposite to the DRE, their final net effect makes comparable contributions to the EA surface cooling. Compared with the surface radiation budget, the surface heat flux budgets have a much smaller contribution.We additionally note that the CRE is basically ascribed to the circulation change.
基金the auspices of National Natural Science Foundation of China(No.41531174)National Basic Research Program of China(No.2015CB953702)。
文摘Land surface hydrothermal conditions(LSHCs) reflect land surface moisture and heat conditions, and play an important role in energy and water cycles in soil-plant-atmosphere continuum. Based on comparison of four evaluation methods(namely, the classic statistical method, geostatistical method, information theory method, and fractal method), this study proposed a new scheme for evaluating the spatial heterogeneity of LSHCs. This scheme incorporates diverse remotely sensed surface parameters, e.g., leaf area index-LAI, the normalized difference vegetation index-NDVI, net radiation-Rn, and land surface temperature-LST. The LSHCs can be classified into three categories, namely homogeneous, moderately heterogeneous and highly heterogeneous based on the remotely sensed LAI data with a 30 m spatial resolution and the combination of normalized information entropy(S’) and coefficient of variation(CV). Based on the evaluation scheme, the spatial heterogeneity of land surface hydrothermal conditions at six typical flux observation stations in the Heihe River Basin during the vegetation growing season were evaluated. The evaluation results were consistent with the land surface type characteristics exhibited by Google Earth imagery and spatial heterogeneity assessed by high resolution remote sensing evapotranspiration data. Impact factors such as precipitation and irrigation events, spatial resolutions of remote sensing data, heterogeneity in the vertical direction, topography and sparse vegetation could also affect the evaluation results. For instance, short-term changes(precipitation and irrigation events) in the spatial heterogeneity of LSHCs can be diagnosed by energy factors, while long-term changes can be indicated by vegetation factors. The spatial heterogeneity of LSHCs decreases when decreasing the spatial resolution of remote sensing data. The proposed evaluation scheme would be useful for the quantification of spatial heterogeneity of LSHCs over flux observation stations toward the global scale, and also contribute to the improvement of the accuracy of estimation and validation for remotely sensed(or model simulated) evapotranspiration.
基金This work was supported by the National Key R&D Program on the Monitoring,Early Warning and Prevention of Major Natural Disasters[grant number 2017YFC1502103]the Key Special Project for the Introducing Talents Team of the Southern Marine Science and Engineering Guangdong Laboratory(Guangzhou)[grant number GML2019ZD0601]the National Natural Science Foundation of China[grant numbers 41875136,41305099,and 41801019].
基金This work was supported by the National Natural Science Foundation of China(Grant No.L1924041)Research Project on the Discipline De-velopment Strategy of Academic Divisions of the Chinese Academy of Sciences(Grant No.XK2019DXC006),and the Fundamental Research Funds for the Central Universities in China.
文摘The great challenges of sustainable development highlight an urgent need to systematically understand the mech-anisms linking humans and nature.Resources and Environmental Sciences are a broad and practical discipline focused on coupled human and natural systems.They aim to study the formation and evolution of resources in the earth system,the drivers of various environmental problems,processes and relationships between resources and the environment,particularly under the combined impacts of natural conditions and human activities.The major resources and environmental problems drive the discipline development;international science programmes guide the direction of the discipline;interdisciplinary and transdisciplinary integration promotes new branches of the discipline;and technological progress results in a research paradigm shift.Facing the critical research re-quirements of strengthening trans-and interdisciplinarity,breaking through the key technology,targeting major environmental and disaster issues,and supporting sustainable development,nine critical scientific issues should be focused on climate change impact and adaptation,petroleum and mineral resources,water cycle and water re-sources,soil and land resources,ecosystems,remote sensing and geographic information science,environmental science and technology,disaster risk,and global and regional sustainable development.Suggestions to enhancing funding systems,improve talent cultivation,develop scientific platforms,and strength international cooperation are provided in this study to support scientific policymaking.The promotion of Resources and Environmental Sci-ences enables a more comprehensive and in-depth understanding of economic development and environmental changes relevant to assure a more sustainable global development.
基金supported by grants from the National Basic Key Research Program (973) under Grant No. 2006CB403606the National Key Technology R&D Program under Grant No. 2007BAC29B04the National Science Foundation Project for Post-doctoral Scientists of China under Grant No. 20080440343
文摘The present study examined the diurnal variations of summer precipitation in the Beijing area by using subdaily precipitation and wind observations. A combined effect of topography and urbanization on the characteristics of diurnal variations was suggested. It was shown that stations located in the plain areaexhibited typical night rain peaks, whereas those in the mountainous area exhibited clear afternoon peaks ofprecipitation diurnal variations. The precipitation peaks were associated with wind fields around the Beijing area, which were found to be highly modulated by mountain-valley circulation and urban-country circulation.The lower-tropospheric wind exhibited a clear diurnal shift in its direction from north at 0800 LST to southat 2000 LST, which reflected mountain-valley circulation. The transitions from valley to mountain windand the opposite generally happened after sunset and sunrise, respectively, and both occurred earlier for thestations located closer to mountains. By comparing the diurnal variations of precipitation at stations in anortheast suburb, an urban area, and a southwest suburb, it was revealed that the northeast suburb grouphad the highest normalized rainfall frequency, but the southwest group had the lowest from late afternoon tolate evening. On the contrary, in the early morning from about 0200 to 1000 LST, the southwest group andurban group had the highest normalized rainfall frequency. This pattern might originate from the combined effects of mountain-valley topography and urbanization.
基金Project supported by the National Natural Science Foundation of China (No. 40830535)the National Key Technology R&D Program of China (No. 2007BAC30B02)the Scientific Program of Department of Education, Hebei Province,China (No. Z2008102)
文摘Wetland soil quality degradation caused by large-scale agricultural reclamation on the Sanjiang Plain of Northeast China has been widely reported. A relative soil quality evaluation (RSQE) model and a projection pursuit evaluation (PPE) model based on real-coded accelerating genetic algorithm were introduced to evaluate quality variations in top layers of the main wetland soils on the Sanjiang Plain in 1999 and 2003, respectively. As soil quality degradation boundaries were vague, this study established two fuzzy synthetic evaluation (FSE) models based on the original data and criteria used in the RSQE and PPE models. The outputs of the two FSE models were obtained by choosing two fuzzy composite operators M(∧, ∨) and M(·, ⊕). Statistical analysis showed that the results of the FSE, RSQE, and PPE models were correlated. In particular, outputs of the FSE model using M(·, ⊕) were significantly correlated with those of the RSQE model with r = 0.989 at P < 0.01. Compared with RSQE and PPE models, the FSE model may be more objective in showing soil quality variations and was closer to the natural situation, showing the feasibility and applicability of the FSE model in evaluating soil quality degradation. However, the choice of composite operator was of critical importance. The study of wetland soil quality degradation on the Sanjiang Plain was of scientific and practical significance for protection and management of soils and for sustainable development of agriculture in this area in the future.
基金State Key Laboratory of Earth Surface Processes and Resource Ecology Beijing Normal University of China under contract No.2009-KF-08the Key Project of the National Natural Science Foundation of China under contract No.ID:40335048+1 种基金the National Science and Technology Plans to Support Major Projects Subject under contract No.ID: 2006BAB03A03the National ‘863’ Key Project of China under contract No.ID: 2006AA100206
文摘The research on sea ice resources is the academic base of sea ice exploitation in the Bohai Sea. According to the ice-water spectrum differences and the correlation between ice thickness and albedo, this paper comes up with a sea ice thickness inversion model based on the NOAA/AVHRR data. And then a sea ice resources quantity (SIQ) time series of Bohai Sea is established from 1987 to 2009. The results indicate that the average error of inversion sea ice thickness is below 30%. The maximum sea ice resources quantity is about 6 × 10 9 m 3 and the minimum is 1.3 × 10 9 m 3 . And a preliminary analysis has been made on the errors of the estimate of sea ice resources quantity (SIQ).
基金funded by the National Natural Science Foundation of China (31270500, 31240002)the Strategic Priority Research Program of Chinese Academy of Sciences (XDA05 050602)+1 种基金the Open Research Fund of the Key Laboratory of Vegetation Restoration and Management of Degraded Ecosystems, Chinese Academy of Sciencesthe support of the Duolun Restoration Ecology Research Station, which is part of the Institute of Botany, Chinese Academy of Sciences, for providing access to the sampling site
文摘Determining soil N mineralization response to soil temperature and moisture changes is challenging in the field due to complicated effects from other factors. In the laboratory, N mineralization is highly dependent on temperature, moisture and sample size. In this study, a laboratory incubation experiment was carefully designed and conducted under controlled conditions to examine the effects of soil temperature and moisture on soil N mineralization using soil samples obtained from the Stipa krylovii grassland in Inner Mongolia, China. Five temperature(i.e. 9°C, 14°C, 22°C, 30°C and 40°C) and five moisture levels(i.e. 20%, 40%, 60%, 80% and 100% WHC, where WHC is the soil water holding capacity) were included in a full-factorial design. During the 71-day incubation period, microbial biomass carbon(MBC), ammonium nitrogen(NH4 +-N) and nitrate nitrogen(NO3--N) were measured approximately every 18 days; soil basal respiration for qCO2 index was measured once every 2 days(once a week near the end of the incubation period). The results showed that the mineral N production and net N mineralization rates were positively correlated with temperature; the strongest correlation was observed for temperatures between 30°C and 40°C. The relationships between moisture levels and both the mineral N production and net N mineralization rates were quadratic. The interaction between soil temperature and moisture was significant on N mineralization, i.e. increasing temperatures(moisture) enhanced the sensitivity of N mineralization to moisture(temperature). Our results also showed a positive correlation between the net nitrification rate and temperature, while the correlation between the NH4 +-N content and temperature was insignificant. The net nitrification rate was negatively correlated with high NH4 +-N contents at 80%–100% WHC, suggesting an active denitrification in moist conditions. Moreover, qCO2 index was positively correlated with temperature, especially at 80% WHC. With a low net nitrification rate and high soil basal respiration rate, it was likely that the denitrification concealed the microbial gross mineralization activity; therefore, active soil N mineralization occurred in 60%–80% WHC conditions.
文摘Historical simulations of annual mean surface air temperature over China with 25 CMIP5 models were assessed.The observational data from CRUT3v and CN05 were used and further compared with historical simulations of CMIP3.The results show that CMIP5 models were able to simulate the observed warming over China from 1906 to 2005(0.84 C per 100 years)with a warming rate of 0.77 C per 100 years based on the multi-model ensemble(MME).The simulations of surface air temperature in the late 20th century were much better than those in the early 20th century,when only two models could reproduce the extreme warming in the 1940s.The simulations for the spatial distribution of the 20-yearmean(1986–2005)surface air temperature over China fit relatively well with the observations.However,underestimations in surface air temperature climatology were still found almost all over China,and the largest cold bias and simulation uncertainty were found in western China.On sub-regional scale,northern China experienced stronger warming than southern China during 1961–1999,for which the CMIP5 MME provided better simulations.With CMIP5 the diference of warming trends in northern and southern China was underestimated.In general,the CMIP5 simulations are obviously improved in comparison with the CMIP3 simulations in terms of the variation in regional mean surface air temperature,the spatial distribution of surface air temperature climatology and the linear trends in surface air temperature all over China.
基金funded by the National Key Program for Global Change Research of China (Grant No.2010CB950500)the General Project of the National Natural Science Foundation of China (Grant No.41275108)the National High Technology Research and Development Program of China (Grant No.2010AA012305)
文摘Based on observations and 12 simulations from Coupled Model Intercomparison Project Phase 5(CMIP5) models, climatic extremes and their changes over China in the past and under the future scenarios of three Representative Concentration Pathways(RCPs) are analyzed. In observations, frost days(FD) and low-temperature threshold days(TN10P) show a decreasing trend, and summer days(SU), high-temperature threshold days(TX90P), heavy precipitation days(R20), and the contribution of heavy precipitation days(P95T) show an increasing trend. Most models are able to simulate the main characteristics of most extreme indices. In particular, the mean FD and TX90 P are reproduced the best, and the basic trends of FD, TN10 P, SU and TX90 P are represented. For the FD and SU indexes, most models show good ability in capturing the spatial differences between the mean state of the periods 1986–2005 and 1961–80; however, for other indices, the simulation abilities for spatial disparity are less satisfactory and need to be improved. Under the high emissions scenario of RCP8.5,the century-scale linear changes of the multi-model ensemble(MME) for FD, SU, TN10 P, TX90 P, R20 and P95 T are-46.9,46.0,-27.1, 175.4, and 2.9 days, and 9.9%, respectively; and the spatial change scope for each index is consistent with the emissions intensity. Due to the complexities of physical process parameterizations and the limitation of forcing data, great uncertainty still exists with respect to the simulation of climatic extremes.
