蒸散发（Evapotranspiration，ET）是植被和地面整体向大气输送的水汽总通量，其作为能量平衡及水循环的重要组成部分，不仅影响植物的生长发育，还可通过影响大气环流从而调节气候。本研究基于MODIS影像数据，结合数字高程模型（DEM）数据和气象数据，采用ArcGIS空间分析和数理统计方法对2000—2019年青海湖沙柳河流域近20 a的蒸散发时空特征进行了研究，并探究了流域蒸散发和气象因子的相关关系及其地形和海拔效应。结果表明：（1） 青海湖沙柳河流域年均蒸散量在379.7~575.4 mm，平均蒸散量为501.9 mm，年均蒸散量呈显著的增加趋势（P<0.01），线性斜率为5.98 mm·a^-1。（2） 青海湖沙柳河流域多年平均蒸散量空间差异显著，其值表现为“中间高，两端低”的分布格局，即河源地区和下游河口三角洲地区低于中游地区。从不同植被类型带的多年平均蒸散量来看，高山草甸带>高山寒漠带>高山草原带。蒸散量较显著增加的区域主要分布在流域下游河口三角洲地区，占流域面积的9.7%，较轻微增加的区域占据流域主体，占流域81.2%。（3） 年均蒸散量与年均气温、年均降水量呈显著正相关关系，与年均相对湿度呈不显著负相关，气候变暖是蒸散量增加的根本动力。（4） 多年平均蒸散量随坡度的增大呈现“增减增”趋势，但坡度间总体差异不明显。多年平均蒸散量在不同坡向除了平面蒸散量最小外，其余坡向的差异较小。多年平均蒸散量随海拔升高，呈先急剧增加后趋于平缓的趋势。以上结果说明，近20 a来青海湖沙柳河流域气候的暖湿化导致了流域蒸散量增加，其增幅主要集中在海拔较低的高山草原带，海拔较高的高山草甸带和高山寒漠带增幅较小。

Evapotranspiration (ET) is the total flux of water vapor transported by vegetation and the ground as a whole to the atmosphere. As an important part of energy balance and water cycle, ET affects the growth and development of plants and regulates climate by influencing atmospheric circulation. Using MODIS image data combined with digital elevation model data and meteorological data, this work applied ArcGIS spatial analysis and mathematical statistics to study the temporal and spatial characteristics of ET in the Shaliu River Basin of Qinghai Lake in the past 20 years from 2000 to 2019. The correlation between ET and meteorological factors such as air temperature, precipitation, and relative humidity and its topographic effect was also explored. Results show that: (1) the annual average ET in the Shaliu River Basin of Qinghai Lake is between 379.7 and 575.4 mm, and the average ET is 501.9 mm. The overall trend of fluctuation increases significantly with the number of years (P<0.05), and the linear slope is 5.9 mm·a^-1. (2) From a spatial perspective, the average ET in the Shaliu River Basin of Qinghai Lake has significant spatial differences and shows a distribution pattern of “high in the middle and low at both ends,” that is, the ET in the source area and the downstream estuary delta area is lower than that in the middle reaches. The order is as follows: alpine meadow belt > alpine cold desert belt > alpine grassland belt. The areas with a relatively significant increase in ET are mainly distributed in the estuary delta area in the lower reaches of the basin, accounting for 9.7% of the basin area. Meanwhile, the areas with a relatively slight increase occupy the main body of the basin, accounting for 81.2%. (3) The annual ET is related to the annual average temperature, and the annual precipitation is significantly positively correlated with the annual average relative humidity. Warming is the fundamental driving force for the increase in ET. (4) The annual ET showed an “increase-decrease-increase” trend with the increase in the slope, but the overall difference between the slopes is not evident. Except for the smallest plane ET in different slope aspects, the differences in annual ET among the other slope aspects are small. The annual ET increases sharply at first and then gradually with the altitude. The above results show that in the past 20 years, the warming and humidification of the climate in the Shaliu River Basin of Qinghai Lake has led to an increase in ET. However, the band increase is small.