## 1 Introduction  
Evapotranspiration (ET) is the total flux of water vapor transferred from surface soil and vegetation to the atmosphere, mainly includes evaporation of soil moisture and transpiration of water in vegetation, and is an essential component of the land-atmosphere hydrological cycle and the surface water and heat balance [1, 2]. In the context of global warming and surface environmental changes, investigating the spatiotemporal distribution of ET and its response to climatic factors is pivotal for climate change research [3, 4, 5], drought monitoring [6, 7, 8], water resource management [9, 10], crop yield estimation [11, 12], and environmental protection [13, 14]. The Yangtze River Basin (YRB) is the largest basin in China, its water and hydropower resources are the richest in China [15], and its ecological security in the basin is receiving increasing attention as the region with the most rapid economic and social development in China in recent years. It is facing the new impact of the transformation from large-scale development to large-scale protection in the future [16]. Its hydroelectric resources are vulnerable and sensitive to environmental changes [17, 18]. Therefore, it is very challenging and significant to accurately study the spatiotemporal distribution of ET in the YRB and its response to the influencing factors. In recent decades, many efforts have been devoted to investigating the trend of evapotranspiration in the YRB, mainly involving two kinds of evapotranspiration, namely actual evapotranspiration and reference evapotranspiration (ET\({}_{0}\)) [19; 20; 21; 22]. ET\({}_{0}\) is defined as \"the evapotranspiration of a hypothetical crop with a plant height of 12 cm, at a ground resistance of 70 s/m and an albedo of 0.23\" [23], which is a good indicator of the variability of evapotranspiration and its causes. Based on the ET\({}_{0}\) measurement in meteorological stations in the YRB, many studies had found that the annual ET\({}_{0}\) in this region had an obvious downward trend during 1961-2000 [20; 24]. [PERSON] et al. studied the annual ET\({}_{0}\) over 46 stations located in the Yangtze River Delta in stages and found that within 1957-1989, nearly 85% of the stations showed a decreasing trend, while within 1990-2014, more than half of the stations showed a significant increasing trend, except for February and September. However, overall, 73.91% of the stations showed an increasing annual trend from 1957 to 2014 and were mainly distributed in the southeast [25]. [PERSON] et al. studied the ET\({}_{0}\) in the Jialing River Basin (located in the upper reaches of the YRB) from 1964 to 2014 and found that the annual ET\({}_{0}\) showed a slight downward trend [26]. [PERSON] et al. found that the ET\({}_{0}\) of the whole Upper Yangtze River Basin (UYRB) increased significantly by 3.3 mm/year from 1951 to 2020, and the stations with significant increases in annual ET\({}_{0}\) were concentrated in the central part of the UYRB [19]. Based on the above findings, it could be inferred that the ET\({}_{0}\) in the YRB during 1951-2020 showed a trend of first decreasing and then increasing in a fluctuating pattern, and the variation pattern was different in different regions. Compared with the ET\({}_{0}\), actual ET has a better representation of the true amount of water evaporated from a watershed [27]. A few studies have been conducted to analyze the trend of actual ET in YRB. [PERSON] et al. simulated the actual ET of the YRB from 1961 to 2000 by using the advection\(-\)aridity (AA) model and found that the annual actual ET of the upper and mid-lower reaches of the YRB showed a downward trend [21]. [PERSON] et al. studied actual ET from 1960 to 2007 based on 72 meteorological stations in the UYRB and found that the annual average actual ET in the region increased slightly in the first decade, then decreased, followed by fluctuations and low growth, and then showed a sharp decline in the latest ten years, but overall showed a slight downward trend [28]. [PERSON] et al.