Abstract: Estimation of reference evapotranspiration (ET₀) could contribute to revealing water-heat balance and water cycle process and consequently provide reference for the sustainable utilization and exploration of regional water resources. Here, we re-fitted the net shortwave emissivity and calculated ET₀ in Guangxi Xijiang River Basin from 1965 to 2018, using improved Penman-Monteith model. The trend analysis and mutation point detection of ET₀ were performed by Mann-Kendall method. The spatialtemporal variations of ET₀ were analyzed by interpolation with inverse distance weighting method. Factors influencing ET₀ were determined based on the contribution rate of meteorological factors. At spatial scale, ET₀ presented an increasing tendency with decreasing altitude. The highest ET₀ values were mainly distributed in the central part of thebasin, while the lowest values occurred in the edge and slope zone of the YunnanGuizhou Plateau, which lies in the northwest part of the basin. ET₀ in spring varied with the longitude, while summer ET₀ showed a similar spatial pattern to that of the inter-annual ET₀. The mean annual ET₀ of the basin was 637.2 mm, with a declining rate of -0.018 mm·a^-1. The ET₀in spring, summer, winter and autumn were 0.053, -0.053, -0.007 and -0.011 mm·a^-1, respectively. ET₀ in all the seasons except spring showed an downward trend. The largest increase in ET₀ occurred in winter. The importance of dominant factors influencing ET₀ of the basin followed an order of relative humidity (with a contribution rate of 39.0%) > average wind speed (27.2%) > sunshine duration > average temperature. Relative humidity negatively affected ET₀, with a correlation coefficient of -0.673. Sunshine duration, average wind speed, and average temperature positively affected ET₀. The dominant driving factors of ET₀ and their contribution rates varied across different parts of the basin.

Key words: Larix olgensis plantation, mortality model, effects of thinning, Logistic regression, generalized estimating equation.