Assessing the variations of evapotranspiration and its environmental controls over a subalpine wetland valley in China

•We examined the environmental control of evapotranspiration (ET) over a wetland.•Available energy (net radiation, Rn) mainly controlled ET at a daily scale.•Seasonally, Rn, air temperature (Ta) and vapor pressure deficit (VPD) controlled ET.•Interannual variation in ET was mainly controlled by Ta and precipitation (P).•ET used most of P leads to decreasing runoff and streams drying up in Jiuzhaigou valley.