The ice phenology of alpine lakes on the Tibetan Plateau(TP)is a rapid and direct responder to climate changes,and the variations in lake ice exhibit high temporal frequency characteristics.MODIS and passive microwave...The ice phenology of alpine lakes on the Tibetan Plateau(TP)is a rapid and direct responder to climate changes,and the variations in lake ice exhibit high temporal frequency characteristics.MODIS and passive microwave data are widely used to monitor lake ice changes with high temporal resolution.However,the low spatial resolutions make it difficult to effectively quantify the freeze-melt dynamics of lakes.This work used Sentinel-1 synthetic aperture radar(SAR)data to derive high-resolution ice maps(about 6 days),then with the aid of Sentinel-2 optical images to quantify freeze-melt processes in three typical lakes on the TP(e.g.Selin Co,Ayakekumu Lake,and Nam Co).The results showed that three lakes had an average annual ice period of 125-157 days and a complete ice cover period of 72-115 days,from 2018 to 2022.They exhibit different ice phenology patterns.Nam Co is characterized by repeated episodes of freezing,melting,and refreezing,resulting in a prolonged freeze-up period.Meanwhile,the break-up period of Nam Co lasts for a longer duration(about 19 days),and the break-up exhibits a smooth process.Similarly,Ayakekumu Lake showed more significant inter-annual fluctuations in the freeze-up period,with deviations of up to 28 days observed among different years.Compared to the other two lakes,Selin Co experienced a relatively short freeze-up and break-up period.In short,Sentinel-1 SAR data can effectively monitor the weekly and seasonal variations in lake ice on the TP.Particularly,this data facilitates quantification of the freeze-melt dynamics.展开更多
冰湖接触型冰川的“湖-冰”相互作用显著,且共同作用于高山区水循环过程,在山区涵养水源、调节径流、维护生态多样性等方面发挥重要作用。本文基于Landsat遥感影像和ERA5-Land再分析资料,对东昆仑木孜塔格峰冰川区冰湖演变、冰川物质平...冰湖接触型冰川的“湖-冰”相互作用显著,且共同作用于高山区水循环过程,在山区涵养水源、调节径流、维护生态多样性等方面发挥重要作用。本文基于Landsat遥感影像和ERA5-Land再分析资料,对东昆仑木孜塔格峰冰川区冰湖演变、冰川物质平衡进行了探讨。结果表明,木孜塔格峰冰川区冰湖主要分布于海拔5275~5400 m,多为冰川阻塞湖。1990—2020年分布有冰湖16个,其中,冰川5Y624E0022和5Y624F0020阻塞形成的两个冰湖分别发生3次和2次冰湖溃决事件。两湖均为周期性溃决冰湖,前者于1999年和2001年发生较大规模冰湖溃决,溃决前面积分别为(0.250±0.044)km^(2)、(0.500±0.097)km^(2),溃决水量分别为(0.014±0.003)km^(3)、(0.026±0.006)km3;后者为2000年形成的冰川阻塞湖,溃决前面积为(0.110±0.030)km^(2),同年溃决,水量为(0.006±0.002)km^(3)。期间,冰湖数量有所增加,面积和储量均有减少趋势。然而,2000—2010年冰川累积物质平衡呈增加趋势,2010—2020年呈减少趋势,且有冰湖接触型冰川年均物质平衡呈显著的减小趋势(-0.024 m w.e.·a^(-1)),略大于无冰湖接触型冰川的减小趋势(-0.022 m w.e.·a^(-1))。此外,冰川热融侵蚀和冰崩作用使得冰鳞川和木孜塔格冰湖与冰川相连位置分别加速退缩了0.65 km、0.28 km。总之,该地区冰湖正处于数量增加、冰湖空间扩张阶段,其加速了母冰川的物质亏损。展开更多
基金supported financially by the National Nature Science Foundation of China(No.41901129)the University Natural Sciences Research Project of Anhui Educational committee(KJ2020JD06)DUAN Zheng acknowledges the support from the Joint China-Sweden Mobility Grant funded by NSFC and STINT(CH2019-8250).
文摘The ice phenology of alpine lakes on the Tibetan Plateau(TP)is a rapid and direct responder to climate changes,and the variations in lake ice exhibit high temporal frequency characteristics.MODIS and passive microwave data are widely used to monitor lake ice changes with high temporal resolution.However,the low spatial resolutions make it difficult to effectively quantify the freeze-melt dynamics of lakes.This work used Sentinel-1 synthetic aperture radar(SAR)data to derive high-resolution ice maps(about 6 days),then with the aid of Sentinel-2 optical images to quantify freeze-melt processes in three typical lakes on the TP(e.g.Selin Co,Ayakekumu Lake,and Nam Co).The results showed that three lakes had an average annual ice period of 125-157 days and a complete ice cover period of 72-115 days,from 2018 to 2022.They exhibit different ice phenology patterns.Nam Co is characterized by repeated episodes of freezing,melting,and refreezing,resulting in a prolonged freeze-up period.Meanwhile,the break-up period of Nam Co lasts for a longer duration(about 19 days),and the break-up exhibits a smooth process.Similarly,Ayakekumu Lake showed more significant inter-annual fluctuations in the freeze-up period,with deviations of up to 28 days observed among different years.Compared to the other two lakes,Selin Co experienced a relatively short freeze-up and break-up period.In short,Sentinel-1 SAR data can effectively monitor the weekly and seasonal variations in lake ice on the TP.Particularly,this data facilitates quantification of the freeze-melt dynamics.
文摘由于气候变化和人类活动等多重影响,流域河湖水系格局与连通程度发生了显著变化,进而引发洪涝灾害等一系列水资源问题。本文以鄱阳湖流域为研究区,基于Google Earth Engine(GEE)提取1989—2020年5期水系数据,采用图论方法构建水系评价体系,定量分析该地区近30年来水系格局和结构连通性的时空演变特征,并结合该时期地形、土地利用和归一化植被指数(NDVI)等数据,利用连通性指数(index of connectivity,IC)评估功能连通性的动态变化,进而探讨水文连通与径流量和输沙量的联系。结果表明,近30年来鄱阳湖流域水系结构趋于复杂化,主要体现在流域北部。除干流外,其他等级河流的数量和长度均有所增加,其中Ⅲ级河流最为明显。河网密度、水面率、河网复杂度和发育系数均呈增加趋势,2000年后的变化率约为2000年前的两倍。水系连通环度、节点连接率和水系连通度总体增加,结构连通性呈好转趋势且变化幅度较小。功能连通分析表明,近30年来大部分流域IC减少,流域下游靠近主河道的平坦地区IC较高,上游远离河道的植被密集区域IC较低。此外,IC与年径流量和输沙量表现为显著的正相关性(相关系数分别为0.6和0.7)。总体而言,随着鄱阳湖流域水利工程建设的增加以及土地利用的变化,水系结构变化显著,结构连通性呈增长趋势,而表示径流泥沙的功能连通性在2000年后逐渐减小。本文基于流域结构和功能连通的视角,开展连通性评价指标的时空变化研究,可显著提升对新时期鄱阳湖流域水系连通演变及水土资源保护的理解与认识。
文摘冰湖接触型冰川的“湖-冰”相互作用显著,且共同作用于高山区水循环过程,在山区涵养水源、调节径流、维护生态多样性等方面发挥重要作用。本文基于Landsat遥感影像和ERA5-Land再分析资料,对东昆仑木孜塔格峰冰川区冰湖演变、冰川物质平衡进行了探讨。结果表明,木孜塔格峰冰川区冰湖主要分布于海拔5275~5400 m,多为冰川阻塞湖。1990—2020年分布有冰湖16个,其中,冰川5Y624E0022和5Y624F0020阻塞形成的两个冰湖分别发生3次和2次冰湖溃决事件。两湖均为周期性溃决冰湖,前者于1999年和2001年发生较大规模冰湖溃决,溃决前面积分别为(0.250±0.044)km^(2)、(0.500±0.097)km^(2),溃决水量分别为(0.014±0.003)km^(3)、(0.026±0.006)km3;后者为2000年形成的冰川阻塞湖,溃决前面积为(0.110±0.030)km^(2),同年溃决,水量为(0.006±0.002)km^(3)。期间,冰湖数量有所增加,面积和储量均有减少趋势。然而,2000—2010年冰川累积物质平衡呈增加趋势,2010—2020年呈减少趋势,且有冰湖接触型冰川年均物质平衡呈显著的减小趋势(-0.024 m w.e.·a^(-1)),略大于无冰湖接触型冰川的减小趋势(-0.022 m w.e.·a^(-1))。此外,冰川热融侵蚀和冰崩作用使得冰鳞川和木孜塔格冰湖与冰川相连位置分别加速退缩了0.65 km、0.28 km。总之,该地区冰湖正处于数量增加、冰湖空间扩张阶段,其加速了母冰川的物质亏损。
