Abstract: Evapotranspiration is of great significance for understanding climate change and regional ecological protection. We analyzed the variation and driving factors of potential evapotranspiration (PET) of Yuanjiang savanna ecosystem research station in China through principal component analysis and Pearson’s twosided correlation test. The process of evapotranspiration was interpreted according to the analysis results on forest interior and open land. Results from the analyses on daily PET data from 2015 to 2018 showed that thePET in forest interior was 0.86 mm·d^-1 lower than that in open land. The PET in forest interior and open land showed a periodic decrease, with a greater decrease trend in the open land. The drought index of the forest interior and open land in the dry and rainy seasons during 2015-2018 and corresponding years was calculated. Results showed that the drought degree of Yuanjiang savanna ecosystem was alleviated in the study period, with the drought index in forest interior being lower than that in open land. The driving factors of PET in forest interior were air temperature (T_a), surface net radiation (R_n), and soil heat flux at 5 cm below the surface. The driving factors of PET in open land were T_a, soil temperature at 5 cm below the surface, and R_n. The layers of evapotranspiration in forest interior could be clearly divided according to its intensity. The intense layer lay in the middle-upper layer of the shrub forest type and the intensity of evapotranspiration decreased from the middle-upper layer to the lower layer. The layers of evapotranspiration in the open land were relatively mixed, and the layer with the highest intensity of evapotranspiration located in the interface of air and soil.

Key words: savanna ecosystem, forest interior and open land, potential evapotranspiration.