Abstract: Yulong Snow Mountain and its surrounding area  a typical monsoon marine-like glacier region, which is the most suitable area for studying glacier change, geo-air energy exchange, vegetation community succession, and ecosystem carbon-water coupling. Water use efficiency (WUE) is an important parameter linking ecosystem water-carbon cycle and its response to climate factors. In this study, MODIS satellite remote sensing products \[gross primary productivity (GPP) and evapotranspiration (ET)\] and self-calibrating Palmer drought severity index (scPDSI) were used to analyze the spatial variation of WUE in Yulong Snow Mountain and its surrounding area from 2000 to 2020. The relationships between GPP, ET, WUE, and scPDSI were investigated, and the adaptation strategies of vegetations in different landforms to water use and stress were discussed. The results showed that during 2000-2020, the average WUE, GPP, and ET was 2.44 g C·m^-2·mm^-1, 1365.0 g C·m^-2, and 559.6 mm in the study area, respectively. The highest average WUE (2.88 g C·m^-2·mm^-1) was mainly distributed in intermediate relief and sub-high altitude mountains, and the lowest average WUE (1.23 g C·m^-2·mm^-1) was distributed in the high relief and extremely high altitude mountains. Due to the undulating terrain of Yulong Snow Mountain and the significant vertical zonal characteristics of vegetation, WUE increased with altitude below 3500 m, while decreased with altitude above 3500 m. During 2000-2020, the monthly WUE presented a trend of increase-decrease-increase. The change rate of WUE was significantly different due to different geomorphological types. The WUE in large undulating mountains of Yulongxue Mountain and its surrounding area showed an increasing trend, while that of the middle elevation plain showed a decreasing trend. In the whole study area, there were seasonal variations for the response of WUE to drought stress. The monthly correlation between WUE and scPDSI showed a trend of negative correlation-positive correlation-negative correlation-positive correlation, respectively. In the Yulong Snow Mountain area, WUE and scPDSI showed a significant positive correlation in July, but a negative correlation in May. There was a negative correlation between WUE and scPDSI from December to June of the following year, and a positive correlation between July and August in the area around Yulong Snow Mountain.

Key words: water use efficiency, spatiotemporal variation, self-calibrating Palmer drought severity index (scPDSI),  correlation