青海湖两季水体范围时空变化遥感监测

Spatial and Temporal Variation of Qinghai Lake in Two Seasons Monitored by Remote Sensing

青海湖是维系青藏高原东北部生态完整性的重要水体,也是控制西部荒漠化向东蔓延的天然屏障,研究青海湖的水体变化对区域生态安全与经济发展有重要意义。以探讨青海湖1990~2020年水体变化趋势与原因为目的,在Google Earth Engine(GEE)平台的支持下,利用Landsat数据实现30 a青海湖冬春和夏秋两季水体面积的动态变化监测,并结合气象与径流量数据分析其变化的原因。结果表明:①1990~2020年,青海湖的水体面积以2004年为拐点,整体上呈现出先减少后增加的趋势,以近几年的增加最为明显。在1990~2004年,青海湖面积在冬春季减少了140.36 km^(2),约为1990年的3.19%,夏秋季减少了157.55 km^(2),约为1990年的3.56%。在2004~2020年期间,青海湖面积在冬春季增加了336.59 km^(2),约为2004年的7.89%,夏秋季增加了349.38 km^(2),约为2004年的8.18%。②年内变化方面,在1990~2000年,冬春季到夏秋季面积变化量较大,年平均变化量为26.09 km^(2),在2000年后年内变化量则逐渐减小,其中2004~2020年,平均年内变化量为5.87 km^(2),说明青海湖季节性的总补给量与流失量差异在减弱。③在1990~2004年期间,青海湖地区降水和径流的不稳定与高稳定的蒸发量是影响青海湖面积的重要原因,高蒸发与低降水、低径流三重因素导致青海湖面积减小。在2004~2020年,降水量与径流量的同步增加,同时在蒸散发微弱的降低趋势助攻下,使得青海湖面积显著增加。④青海湖岸线形态在不断变化,其中东岸的沙岛,西岸的鸟岛、铁布卡湾与北岸沙柳河入口区域变化最为明显,可能是流域流失土壤的沉积和湖水动力机制的变化引起的,但具体原因有待进一步探讨。本研究对湖泊水文以及湖泊在不同尺度气候变化下的响应研究具有一定的参考价值。

Qinghai Lake is an important water body that maintains the ecological integrity of the northeastern Qinghai-Tibet Plateau and is also a natural barrier to control the spread of the western desertification to the east.And the study of the changes Qinghai Lake area is of great significance to regional ecological security and economic development.Therefore,this study aims to investigate the trends and causes of the changes of Qinghai Lake area from 1990 to 2020.With the support of Google Earth Engine(GEE)platform,Landsat data were used to monitor the dynamic changes of Qinghai Lake for winter-spring and summer-autumn in the past 30a,and the reasons for the changes were analyzed in combination with meteorological and hydrologic data.The results show that:(1)With 2004 as the inflection point,the area of Qinghai Lake showed a trend of decreasing first and then increasing during 1990 to 2020.In recent years,the area increase is most obvious.During 1990~2004,the area of Qinghai Lake decreased by 140.36 km^(2)in winter-spring,about 3.19%of the area in 1990;and decreased by 157.547 km^(2)in summer-autumn,about 3.56%of the area in 1990.During the period 2004~2020,the area of Qinghai Lake increased by 336.59 km^(2)in winter-spring,about 7.89%of the area in 2004;and increased by 349.3814 km^(2)in summer-autumn,about 8.18%of the area in 2004.(2)In terms of intra-annual variation,the change in area from winter-spring to summer-autumn was large from 1990 to 2000,with an average change value of 26.09 km^(2)/a,and the intra-annual variation was small after 2000,with an average change value of 5.87 km^(2)/a.(3)From 1990 to 2004,the instability of precipitation and runoff and high steady evaporation in Qinghai Lake area were the important reasons affecting the area of Qinghai Lake.High evaporation,low precipitation and low runoff together led to the decline of the area of Qinghai Lake.From 2004 to 2020,the simultaneous increase of precipitation and runoff makes the area of Qinghai Lake increase significantly,assisted by the weak decreasing trend of evapotranspiration.(4)The shoreline morphology of Qinghai Lake is constantly changing,and the most obvious changes are in Shadao Island on the east bank,Niaodao Island and Tiebuka Bay on the west bank,and the entrance of Shaliu River on the north bank.It may be caused by the sediment of runoff soil and the dynamic mechanism of lake water.The specific reasons need to be further discussed.This study has certain value for the study of lake hydrology and the response of lakes to climate change at different scales.