According to Statistical Yearbook of Jiangxi Province(2001～2006),We analyze the time-space variation of population distribution of Poyang Lake region from the two points of view.The former is quality of population,wh...According to Statistical Yearbook of Jiangxi Province(2001～2006),We analyze the time-space variation of population distribution of Poyang Lake region from the two points of view.The former is quality of population,which involves culture structure,occupational structure,age structure and sex structure of population.The latter is quantity of population,which only involves the amount of population.Furthermore,we can reveal the internal relations and action mechanism of variation of population distribution by analyzing the regional economic development,population urbanization,land use and ecological landscape of Poyang Lake region.It is important to provide help for region planning,ecological landscape planning and environmental protection by correct understanding the man-land relationship of natural-human ecosystem in Poyang Lake region.展开更多
The karst landform is a typical ecologically vulnerable region,and the problem of karst rocky desertification in southtern and western China has led to impoverishment and a degraded local ecological environment,which ...The karst landform is a typical ecologically vulnerable region,and the problem of karst rocky desertification in southtern and western China has led to impoverishment and a degraded local ecological environment,which severely limits local socioeconomic development.An effective and appropriate control of karst rocky desertification in southtern and western China requires knowledge about its characteristics of variation and driving mechanisms.In this study,we chose eight regions in the southtern and western China as research areas and analysed the characteristics of the changes in karst ecosystem patterns and rocky desertification from 2000 to 2015.Based on these characteristics,we present the mechanisms that drive karst rocky desertification in the southtern and western China by utilizing the redundancy analysis(RDA)ordination method.The results show that the total area of rocky desertification in southtern and western China had been continuously decreasing from 2000 to 2015,revealing a positive development trend in rocky desertification.Rocky desertification variations were mainly affected by human activities.The reduction in farmland area improved farmland management and increased regional gross industrial product,which together with continuously rising gross domestic product of the tertiary industry caused a positive rocky desertification development.However,the local karst tourism has a certain effect on inducing slight rocky desertification.展开更多
[Objective] The aim was to analyze the changes characteristics of sunshine hours of Dalian City. [Method] Based on the data of sunshine hours of Dalian City during 1951 to 2009 and by dint of linear estimation and acc...[Objective] The aim was to analyze the changes characteristics of sunshine hours of Dalian City. [Method] Based on the data of sunshine hours of Dalian City during 1951 to 2009 and by dint of linear estimation and accumulation anomaly, the change characteristics of decade, annual, seasonal, monthly sunshine hours in Dalian City were analyzed. [Result] The change characteristics of decade, annual, seasonal, monthly sunshine hours in Dalian City were in a decrease trend since recent 59 years. The average sunshine hour in 1950s was the maximum one. Since 21st century, the annual sunshine hour was the lowest one. Annual average sunshine hours were the highest in 1978, and lowest in 2003. There were more sunshine hours before 1989 and later less. Among the four seasons, the sunshine hours in autumn decreased fastest and slowest in spring. The monthly average sunshine hours were the most in May and least in December; the sunshine hours in each month decreased fastest in July. It showed increasing tendency only in March. [Conclusion] The study supplied scientific reference for the reasonable utilization of light energy, agricultural production structure and sustainable development of agricultural economy.展开更多
[Objective] The aim was to analyze the change characteristics of haze in Dezhou City. [Method] Based on the data of haze and sunshine duration from 11 counties or cities in Dezhou City from 1970 to 2009, the daily, mo...[Objective] The aim was to analyze the change characteristics of haze in Dezhou City. [Method] Based on the data of haze and sunshine duration from 11 counties or cities in Dezhou City from 1970 to 2009, the daily, monthly, seasonal and annual variation of haze and their variation reasons were studied, meanwhile, the effects of haze on sunshine duration were discussed. [Result] Haze occurred most frequently from 09:00 to 14:00 and daily variation was different in various seasons; haze days were the most in December (200 d), and next came January (161 d), while hazes days were the fewest in August (20 d). From seasonal variation, haze appeared most frequently in winter, accounting for 40% of that in total year, autumn (23%) and summer (20%) the second, and haze days were the fewest in spring (18%). For annual variation, haze days were the fewest from 1970 to 1979 (110 d) and most from 2000 to 2009 (724 d), with the tendency rate of 2.27 and 16.35 d/a, respectively. From regional distribution, haze days were the most in Decheng District, and next came Xiajin, while Yucheng had the fewest haze days. In addition, the annual variation of haze days was related to pollutant concentration in atmosphere, while monthly variation and seasonal variation were controlled by weather situation and meteorological condition. [Conclusion] The study could provide scientific reference for the prevention and impact assessment of haze.展开更多
[Objective]The research aimed to analyze variation characteristics of the precipitation in Zigong City in recent 50 years.[Method] Based on daily precipitation data at three observation stations in Zigong City from 19...[Objective]The research aimed to analyze variation characteristics of the precipitation in Zigong City in recent 50 years.[Method] Based on daily precipitation data at three observation stations in Zigong City from 1961 to 2010,linear tendency method and accumulative anomaly method were adopted to analyze climatic change characteristics of the annual,seasonal,monthly rainfalls and rain days in Zigong City in recent 50 years.[Result]The annual rainfall overall presented a decreasing trend at the variation tendency rate of-28.0 mm /10 a in Zigong City.The annual rain days obviously declined at the variation tendency rate of-5.6 d /10 a.The decline of rain days was more obvious than that of the rainfall.Decline of the light rain days was especially serious.Not only trends of summer,autumn and winter rainfalls were all negative,but also trends of the four-season rain days were all negative.Reductions of autumn rainfall and rain days were the most remarkable and the largest in magnitude.Monthly rainfall presented single-peak type distribution,and monthly rain days presented double-peak type distribution.Days of each-level precipitation within one year in each area of Zigong City were nearly consistent.Moreover,rain days decreased as magnitude increased.An obvious characteristic of the precipitation variation in Zigong City in recent 50 years was synchronal decrease of the annual rainfall and rain days.[Conclusion]In general,the natural rainfall resource in Zigong City was tending to reduce,and autumn drought was obvious.展开更多
[Objective] The research aimed to analyze change characteristics of the average temperature in Sichuan in 50 years.[Method] By using average temperature data at 156 stations of Sichuan from 1961 to 2010,interannual an...[Objective] The research aimed to analyze change characteristics of the average temperature in Sichuan in 50 years.[Method] By using average temperature data at 156 stations of Sichuan from 1961 to 2010,interannual and interdecadal evolution characteristics,regional and seasonal differences of the average temperature in Sichuan in 50 years were analyzed.[Result] Variations of the average temperatures in the whole province and each climatic region in 50 years all presented rise trends.Rise amplitude of the average temperature was obvious in the prior 10 years of the 21st century.Rise amplitude of the temperature was 0-0.5 ℃ in 48.7% of stations in the whole province,and was 0.5-1.0 ℃ in 32.3% of stations.Rise amplitude of the temperature was the maximum in winter.The second one was in spring,and the minimum was in autumn.The annual average temperature in the whole province in 50 years presented east-high-west-low spatial distribution.The regional difference was from-1.2 to 20.9 ℃,and temperature difference was 22.1 ℃.Interannual variation of the average temperature from 1961 to 1997 in the whole province was relatively stable.After that,it presented obvious fluctuation rise trend.Interdecadal variation of the average temperature from the 1960s to the 1990s was relatively stable,and average temperatures were from 8.56 to 8.86 ℃.The maximum interdecadal average temperatures in the whole province and each climatic region all emerged in the prior 10 years of the 21st century,while emergence decades of the minimums were different.[Conclusion] The research provided reference for analyzing climatic change characteristics in Sichuan.展开更多
[Objective] This study aimed to analyze the change characteristics of sunshine hours in Benxi mountainous area in recent 57 years.[Method] Based on the data of monthly sunshine hours,total cloudiness,vapor pressure a...[Objective] This study aimed to analyze the change characteristics of sunshine hours in Benxi mountainous area in recent 57 years.[Method] Based on the data of monthly sunshine hours,total cloudiness,vapor pressure and ≥0.1 mm precipitation days from Caohekou weather station during 1954-2010,by using linear tendency,Mann-Kendall method and wavelet analysis,the change characteristics of sunshine hours in Benxi mountainous area in recent 57 years were analyzed,as well as the possible climatic factors resulting in the decrease of sunshine hours.[Result] In recent 57 years,except for the slight increase of sunshine hours in winter,annual sunshine hours and sunshine hours in other seasons showed significantly decreasing trend,and annual sunshine hours varied abruptly in 1971.In addition,total cloudiness,vapor pressure and ≥0.1 mm precipitation days affected sunshine hours obviously,but sunshine hours didn't simply increase as the reduction of total cloudiness and ≥0.1 mm precipitation days,which showed that the influencing factors of sunshine hours were complex.[Conclusion] The research could provide scientific references for the reasonable utilization of light energy,adjustment of agricultural industrial structure and sustainable development of agricultural economy in mountainous areas.展开更多
[Objective] The aim was to study the characteristics of high temperature in Xi'an City over the last 59 years. [Method] By dint of daily highest temperature in the Xi'an observatory, the climate characteristic...[Objective] The aim was to study the characteristics of high temperature in Xi'an City over the last 59 years. [Method] By dint of daily highest temperature in the Xi'an observatory, the climate characteristics of high temperature at different intensities and the high attitude circulation were studied by statistical method. [Result] Over the last 59 years, there were 22.95 high temperature days each year on average in Xi'an City, which occurred from the last ten days of April to the first ten days of September. Most high temperature days occurred in the last ten days of July, followed by that in the last ten days of June. There were two peak values in the last ten days of June and last ten days of July when temperature ≥38.0 ℃. For the hottest day, it occurred most in the last twenty days of June, followed by July, and rarely in August. The interannual changes in the high temperature day, hot day and hottest day showed one-little and one-much trend. It was much from 1950s to 1960s, from 1970s to 1980s and then grew more after 1990s. The annual extreme highest temperature took place in the last twenty days of June, and then in the last ten days of July. Its interannual changes showed high-low-high trend. The high temperature appeared most often in July and also lasted for the longest duration. The hot day lasted for two days. The hottest days of ≥40.0 ℃ were very rare. The circulation of high temperature generally fell into one of four categories: continental high pressure controlling type, subtropical high controlling type, strip high pressure controlling type and northwest airstream controlling type. [Conclusion] The study provided references for the forecast and pre-warning of high temperature.展开更多
Based on the observation data of temperature from Yibin station and other five surrounding meteorological stations in 1961-2009,temperature variation in Yibin station affected by urbanization was studied.The results s...Based on the observation data of temperature from Yibin station and other five surrounding meteorological stations in 1961-2009,temperature variation in Yibin station affected by urbanization was studied.The results showed that urban heat island effect in Yibin became more and more strong,and it had great influence on minimum temperature and little influence on maximum temperature,with obvious daily variation.In addition,heat island effect was more obvious at night than daytime,while temperature went up most greatly in summer,and next came spring,but it was weakest in winter.Compared with 1960s,the average warming rate of temperature at 02:00,08:00,14:00 and 20:00,daily average temperature,maximum temperature and minimum temperature reached 0.483 2,0.168 0,0.001 4,0.209 8,0.215 4,-0.013 4 and 0.333 2 ℃ in 40 years,respectively.Moreover,regional background had certain effect on urban climate,and the influence of urban heat island effect on various meteorological stations was distinct in different stages of urbanization process.展开更多
Based on the tortuous capillary network model,the relationship between anisotropic permeability and rock normal strain,namely the anisotropic dynamic permeability model(ADPM),was derived and established.The model was ...Based on the tortuous capillary network model,the relationship between anisotropic permeability and rock normal strain,namely the anisotropic dynamic permeability model(ADPM),was derived and established.The model was verified using pore-scale flow simulation.The uniaxial strain process was calculated and the main factors affecting permeability changes in different directions in the deformation process were analyzed.In the process of uniaxial strain during the exploitation of layered oil and gas reservoirs,the effect of effective surface porosity on the permeability in all directions is consistent.With the decrease of effective surface porosity,the sensitivity of permeability to strain increases.The sensitivity of the permeability perpendicular to the direction of compression to the strain decreases with the increase of the tortuosity,while the sensitivity of the permeability in the direction of compression to the strain increases with the increase of the tortuosity.For layered reservoirs with the same initial tortuosity in all directions,the tortuosity plays a decisive role in the relative relationship between the variations of permeability in all directions during pressure drop.When the tortuosity is less than 1.6,the decrease rate of horizontal permeability is higher than that of vertical permeability,while the opposite is true when the tortuosity is greater than 1.6.This phenomenon cannot be represented by traditional dynamic permeability model.After the verification by experimental data of pore-scale simulation,the new model has high fitting accuracy and can effectively characterize the effects of deformation in different directions on the permeability in all directions.展开更多
Food security is the primary prerequisite for achieving other Millennium Development Goals(MDGs).Given that the MDG of“halving the proportion of hungers by 2015”was not realized as scheduled,it will be more pressing...Food security is the primary prerequisite for achieving other Millennium Development Goals(MDGs).Given that the MDG of“halving the proportion of hungers by 2015”was not realized as scheduled,it will be more pressing and challenging to reach the goal of zero hunger by 2030.So there is high urgency to find the pattern and mechanism of global food security from the perspective of spatio-temporal evolution.In this paper,based on the analysis of database by using a multi-index evaluation method and radar map area model,the global food security level for 172 countries from 2000 to 2014 were assessed;and then spatial autocorrelation analysis was conducted to depict the spatial patterns and changing characteristics of global food security;then,multi-nonlinear regression methods were employed to identify the factors affecting the food security patterns.The results show:1)The global food security pattern can be summarized as“high-high aggregation,low-low aggregation”.The most secure countries are mainly distributed in Western Europe,North America,Oceania and parts of East Asia.The least secure countries are mainly distributed in sub-Saharan Africa,South Asia and West Asia,and parts of Southeast Asia.2)Europe and sub-Saharan Africa are hot and cold spots of the global food security pattern respectively,while in non-aggregation areas,Haiti,North Korea,Tajikistan and Afghanistan have long-historical food insecurity problems.3)The pattern of global food security is generally stable,but the internal fluctuations in the extremely insecure groups were significant.The countries with the highest food insecurity are also the countries with the most fluctuated levels of food security.4)The annual average temperature,per capita GDP,proportion of people accessible to clean water,political stability and non-violence levels are the main factors influencing the global food security pattern.Research shows that the status of global food security has improved since the year 2000,yet there are still many challenges such as unstable global food security and acute regional food security issues.It will be difficult to understand these differences from a single factor,especially the annual average temperature and annual precipitation.The abnormal performance of the above factors indicates that appropriate natural conditions alone do not absolutely guarantee food security,while the levels of agricultural development,the purchasing power of residents,regional accessibility,as well as political and economic stability have more direct influence.展开更多
文摘According to Statistical Yearbook of Jiangxi Province(2001～2006),We analyze the time-space variation of population distribution of Poyang Lake region from the two points of view.The former is quality of population,which involves culture structure,occupational structure,age structure and sex structure of population.The latter is quantity of population,which only involves the amount of population.Furthermore,we can reveal the internal relations and action mechanism of variation of population distribution by analyzing the regional economic development,population urbanization,land use and ecological landscape of Poyang Lake region.It is important to provide help for region planning,ecological landscape planning and environmental protection by correct understanding the man-land relationship of natural-human ecosystem in Poyang Lake region.
基金Under the auspices of National Key Research and Development Program of China(No.2016YFC0503402)。
文摘The karst landform is a typical ecologically vulnerable region,and the problem of karst rocky desertification in southtern and western China has led to impoverishment and a degraded local ecological environment,which severely limits local socioeconomic development.An effective and appropriate control of karst rocky desertification in southtern and western China requires knowledge about its characteristics of variation and driving mechanisms.In this study,we chose eight regions in the southtern and western China as research areas and analysed the characteristics of the changes in karst ecosystem patterns and rocky desertification from 2000 to 2015.Based on these characteristics,we present the mechanisms that drive karst rocky desertification in the southtern and western China by utilizing the redundancy analysis(RDA)ordination method.The results show that the total area of rocky desertification in southtern and western China had been continuously decreasing from 2000 to 2015,revealing a positive development trend in rocky desertification.Rocky desertification variations were mainly affected by human activities.The reduction in farmland area improved farmland management and increased regional gross industrial product,which together with continuously rising gross domestic product of the tertiary industry caused a positive rocky desertification development.However,the local karst tourism has a certain effect on inducing slight rocky desertification.
文摘[Objective] The aim was to analyze the changes characteristics of sunshine hours of Dalian City. [Method] Based on the data of sunshine hours of Dalian City during 1951 to 2009 and by dint of linear estimation and accumulation anomaly, the change characteristics of decade, annual, seasonal, monthly sunshine hours in Dalian City were analyzed. [Result] The change characteristics of decade, annual, seasonal, monthly sunshine hours in Dalian City were in a decrease trend since recent 59 years. The average sunshine hour in 1950s was the maximum one. Since 21st century, the annual sunshine hour was the lowest one. Annual average sunshine hours were the highest in 1978, and lowest in 2003. There were more sunshine hours before 1989 and later less. Among the four seasons, the sunshine hours in autumn decreased fastest and slowest in spring. The monthly average sunshine hours were the most in May and least in December; the sunshine hours in each month decreased fastest in July. It showed increasing tendency only in March. [Conclusion] The study supplied scientific reference for the reasonable utilization of light energy, agricultural production structure and sustainable development of agricultural economy.
文摘[Objective] The aim was to analyze the change characteristics of haze in Dezhou City. [Method] Based on the data of haze and sunshine duration from 11 counties or cities in Dezhou City from 1970 to 2009, the daily, monthly, seasonal and annual variation of haze and their variation reasons were studied, meanwhile, the effects of haze on sunshine duration were discussed. [Result] Haze occurred most frequently from 09:00 to 14:00 and daily variation was different in various seasons; haze days were the most in December (200 d), and next came January (161 d), while hazes days were the fewest in August (20 d). From seasonal variation, haze appeared most frequently in winter, accounting for 40% of that in total year, autumn (23%) and summer (20%) the second, and haze days were the fewest in spring (18%). For annual variation, haze days were the fewest from 1970 to 1979 (110 d) and most from 2000 to 2009 (724 d), with the tendency rate of 2.27 and 16.35 d/a, respectively. From regional distribution, haze days were the most in Decheng District, and next came Xiajin, while Yucheng had the fewest haze days. In addition, the annual variation of haze days was related to pollutant concentration in atmosphere, while monthly variation and seasonal variation were controlled by weather situation and meteorological condition. [Conclusion] The study could provide scientific reference for the prevention and impact assessment of haze.
文摘[Objective]The research aimed to analyze variation characteristics of the precipitation in Zigong City in recent 50 years.[Method] Based on daily precipitation data at three observation stations in Zigong City from 1961 to 2010,linear tendency method and accumulative anomaly method were adopted to analyze climatic change characteristics of the annual,seasonal,monthly rainfalls and rain days in Zigong City in recent 50 years.[Result]The annual rainfall overall presented a decreasing trend at the variation tendency rate of-28.0 mm /10 a in Zigong City.The annual rain days obviously declined at the variation tendency rate of-5.6 d /10 a.The decline of rain days was more obvious than that of the rainfall.Decline of the light rain days was especially serious.Not only trends of summer,autumn and winter rainfalls were all negative,but also trends of the four-season rain days were all negative.Reductions of autumn rainfall and rain days were the most remarkable and the largest in magnitude.Monthly rainfall presented single-peak type distribution,and monthly rain days presented double-peak type distribution.Days of each-level precipitation within one year in each area of Zigong City were nearly consistent.Moreover,rain days decreased as magnitude increased.An obvious characteristic of the precipitation variation in Zigong City in recent 50 years was synchronal decrease of the annual rainfall and rain days.[Conclusion]In general,the natural rainfall resource in Zigong City was tending to reduce,and autumn drought was obvious.
文摘[Objective] The research aimed to analyze change characteristics of the average temperature in Sichuan in 50 years.[Method] By using average temperature data at 156 stations of Sichuan from 1961 to 2010,interannual and interdecadal evolution characteristics,regional and seasonal differences of the average temperature in Sichuan in 50 years were analyzed.[Result] Variations of the average temperatures in the whole province and each climatic region in 50 years all presented rise trends.Rise amplitude of the average temperature was obvious in the prior 10 years of the 21st century.Rise amplitude of the temperature was 0-0.5 ℃ in 48.7% of stations in the whole province,and was 0.5-1.0 ℃ in 32.3% of stations.Rise amplitude of the temperature was the maximum in winter.The second one was in spring,and the minimum was in autumn.The annual average temperature in the whole province in 50 years presented east-high-west-low spatial distribution.The regional difference was from-1.2 to 20.9 ℃,and temperature difference was 22.1 ℃.Interannual variation of the average temperature from 1961 to 1997 in the whole province was relatively stable.After that,it presented obvious fluctuation rise trend.Interdecadal variation of the average temperature from the 1960s to the 1990s was relatively stable,and average temperatures were from 8.56 to 8.86 ℃.The maximum interdecadal average temperatures in the whole province and each climatic region all emerged in the prior 10 years of the 21st century,while emergence decades of the minimums were different.[Conclusion] The research provided reference for analyzing climatic change characteristics in Sichuan.
文摘[Objective] This study aimed to analyze the change characteristics of sunshine hours in Benxi mountainous area in recent 57 years.[Method] Based on the data of monthly sunshine hours,total cloudiness,vapor pressure and ≥0.1 mm precipitation days from Caohekou weather station during 1954-2010,by using linear tendency,Mann-Kendall method and wavelet analysis,the change characteristics of sunshine hours in Benxi mountainous area in recent 57 years were analyzed,as well as the possible climatic factors resulting in the decrease of sunshine hours.[Result] In recent 57 years,except for the slight increase of sunshine hours in winter,annual sunshine hours and sunshine hours in other seasons showed significantly decreasing trend,and annual sunshine hours varied abruptly in 1971.In addition,total cloudiness,vapor pressure and ≥0.1 mm precipitation days affected sunshine hours obviously,but sunshine hours didn't simply increase as the reduction of total cloudiness and ≥0.1 mm precipitation days,which showed that the influencing factors of sunshine hours were complex.[Conclusion] The research could provide scientific references for the reasonable utilization of light energy,adjustment of agricultural industrial structure and sustainable development of agricultural economy in mountainous areas.
文摘[Objective] The aim was to study the characteristics of high temperature in Xi'an City over the last 59 years. [Method] By dint of daily highest temperature in the Xi'an observatory, the climate characteristics of high temperature at different intensities and the high attitude circulation were studied by statistical method. [Result] Over the last 59 years, there were 22.95 high temperature days each year on average in Xi'an City, which occurred from the last ten days of April to the first ten days of September. Most high temperature days occurred in the last ten days of July, followed by that in the last ten days of June. There were two peak values in the last ten days of June and last ten days of July when temperature ≥38.0 ℃. For the hottest day, it occurred most in the last twenty days of June, followed by July, and rarely in August. The interannual changes in the high temperature day, hot day and hottest day showed one-little and one-much trend. It was much from 1950s to 1960s, from 1970s to 1980s and then grew more after 1990s. The annual extreme highest temperature took place in the last twenty days of June, and then in the last ten days of July. Its interannual changes showed high-low-high trend. The high temperature appeared most often in July and also lasted for the longest duration. The hot day lasted for two days. The hottest days of ≥40.0 ℃ were very rare. The circulation of high temperature generally fell into one of four categories: continental high pressure controlling type, subtropical high controlling type, strip high pressure controlling type and northwest airstream controlling type. [Conclusion] The study provided references for the forecast and pre-warning of high temperature.
基金Supported by Sichuan Meteorology Project of Sichuan Meteorological Bureau(2010-Focus-04)~~
文摘Based on the observation data of temperature from Yibin station and other five surrounding meteorological stations in 1961-2009,temperature variation in Yibin station affected by urbanization was studied.The results showed that urban heat island effect in Yibin became more and more strong,and it had great influence on minimum temperature and little influence on maximum temperature,with obvious daily variation.In addition,heat island effect was more obvious at night than daytime,while temperature went up most greatly in summer,and next came spring,but it was weakest in winter.Compared with 1960s,the average warming rate of temperature at 02:00,08:00,14:00 and 20:00,daily average temperature,maximum temperature and minimum temperature reached 0.483 2,0.168 0,0.001 4,0.209 8,0.215 4,-0.013 4 and 0.333 2 ℃ in 40 years,respectively.Moreover,regional background had certain effect on urban climate,and the influence of urban heat island effect on various meteorological stations was distinct in different stages of urbanization process.
基金Supported by the National Natural Science Foundation of China(52274048)Beijing Natural Science Foundation Project of China(3222037)Shaanxi Provincial Technical Innovation Project of China(2023-YD-CGZH-02).
文摘Based on the tortuous capillary network model,the relationship between anisotropic permeability and rock normal strain,namely the anisotropic dynamic permeability model(ADPM),was derived and established.The model was verified using pore-scale flow simulation.The uniaxial strain process was calculated and the main factors affecting permeability changes in different directions in the deformation process were analyzed.In the process of uniaxial strain during the exploitation of layered oil and gas reservoirs,the effect of effective surface porosity on the permeability in all directions is consistent.With the decrease of effective surface porosity,the sensitivity of permeability to strain increases.The sensitivity of the permeability perpendicular to the direction of compression to the strain decreases with the increase of the tortuosity,while the sensitivity of the permeability in the direction of compression to the strain increases with the increase of the tortuosity.For layered reservoirs with the same initial tortuosity in all directions,the tortuosity plays a decisive role in the relative relationship between the variations of permeability in all directions during pressure drop.When the tortuosity is less than 1.6,the decrease rate of horizontal permeability is higher than that of vertical permeability,while the opposite is true when the tortuosity is greater than 1.6.This phenomenon cannot be represented by traditional dynamic permeability model.After the verification by experimental data of pore-scale simulation,the new model has high fitting accuracy and can effectively characterize the effects of deformation in different directions on the permeability in all directions.
基金National Natural Science Foundation of China,No.71734001。
文摘Food security is the primary prerequisite for achieving other Millennium Development Goals(MDGs).Given that the MDG of“halving the proportion of hungers by 2015”was not realized as scheduled,it will be more pressing and challenging to reach the goal of zero hunger by 2030.So there is high urgency to find the pattern and mechanism of global food security from the perspective of spatio-temporal evolution.In this paper,based on the analysis of database by using a multi-index evaluation method and radar map area model,the global food security level for 172 countries from 2000 to 2014 were assessed;and then spatial autocorrelation analysis was conducted to depict the spatial patterns and changing characteristics of global food security;then,multi-nonlinear regression methods were employed to identify the factors affecting the food security patterns.The results show:1)The global food security pattern can be summarized as“high-high aggregation,low-low aggregation”.The most secure countries are mainly distributed in Western Europe,North America,Oceania and parts of East Asia.The least secure countries are mainly distributed in sub-Saharan Africa,South Asia and West Asia,and parts of Southeast Asia.2)Europe and sub-Saharan Africa are hot and cold spots of the global food security pattern respectively,while in non-aggregation areas,Haiti,North Korea,Tajikistan and Afghanistan have long-historical food insecurity problems.3)The pattern of global food security is generally stable,but the internal fluctuations in the extremely insecure groups were significant.The countries with the highest food insecurity are also the countries with the most fluctuated levels of food security.4)The annual average temperature,per capita GDP,proportion of people accessible to clean water,political stability and non-violence levels are the main factors influencing the global food security pattern.Research shows that the status of global food security has improved since the year 2000,yet there are still many challenges such as unstable global food security and acute regional food security issues.It will be difficult to understand these differences from a single factor,especially the annual average temperature and annual precipitation.The abnormal performance of the above factors indicates that appropriate natural conditions alone do not absolutely guarantee food security,while the levels of agricultural development,the purchasing power of residents,regional accessibility,as well as political and economic stability have more direct influence.
