Climatic Control on Mean Annual Groundwater Evapotranspiration in a Three‐Stage Precipitation Partitioning Framework

Abstract

Groundwater evapotranspiration (GWET) is the principal component of groundwater budgets of arid basins with shallow aquifers (Loheide, 2008;Nichols, 2000), and plays an important role in the watershed-scale water balance when water table depth is comparable with the rooting depth of plants (Yeh & Famiglietti, 2009). Capillary forces move groundwater upward from the water table. Groundwater contributes to evapotranspiration (ET) through direct evaporation when the capillary zone intersects the land surface and through transpiration by root water uptake from plants (Lam et al., 2011). With the combined impacts of climate change (Mukherjee & Mishra, 2021) and increased anthropogenic groundwater withdrawal (Wada et al., 2014), the quantification of GWET becomes more crucial for sustainable groundwater management.GWET is usually estimated based on observed hydrologic variables such as streamflow and water table elevation since there is no direct measurement of GWET (Orellana et al., 2012). Daily GWET has been estimated based on base flow recession from observed streamflow (Daniel, 1976) and diurnal water table fluctuations (WTF) from observed groundwater level in unconfined aquifer (White, 1932). Particularly, the WTF method has been applied for estimating groundwater consumption by phreatophytic vegetation with shallow water table in the riparian zone of arid and semi-arid regions (e.g., Carlson Mazur et al., 2014;Diouf et al., 2020;Gribovszki et al., 2008). Besides the observed groundwater level, the WTF method requires specific yield of unconfined aquifer which depends on soil properties and water table depth, and therefore varies spatially and temporally (Orellana et al., 2012;Parajuli et al., 2019Parajuli et al., , 2020Sophocleous, 1985). The WTF method has been improved by capturing robust, diurnal WTF (Soylu et al., 2012) and by accounting for the dependence of specific yield on depth to water table (DWT;Nachabe, 2002). The estimated GWET from the WTF method is at the point or local scale, requiring a high density of observation wells to capture the spatial variability of GWET (Lautz, 2008).The estimated GWET from the WTF method provides insights into the controlling factors of GWET. These factors include meteorological variables (Kray et al., 2012), vegetation type (Butler et al., 2007

Spatiotemporal Variations in Actual Evapotranspiration Based on LPJ Model and Its Driving Mechanism in the Three Gorges Reservoir Area

“…The acquisition of AET has always been an important and difficult point in ecohydrological research [11][12][13]. The AET, which is composed of canopy transpiration (EP), vegetation interception (EI), and bare soil evaporation (ES), is not only influenced by climate change but also closely related to vegetation, and it is greatly influenced by the underlying surface and vegetation dynamics [14]. Therefore, it is necessary to consider the growth process of vegetation in AET simulation [7,15].…”