Controlling Factors of Evapotranspiration Predictability Under Diverse Climates With the Effects of Water Storage Change in the Budyko Framework

Abstract

Abstract The Budyko models (BM) have been extended in previous studies by incorporating water storage change (Δ S ) (subtracting Δ S from precipitation) to estimate evapotranspiration (ET) under non‐steady state conditions at scales finer than the climatological mean scale. However, a systematic assessment of the interannual ET predictability of the extended BM is still lacking, hence its validity and controlling factors of improvement (over the original BM) under globally diverse climates is not yet well understood. Based on a long‐term (1984–2008) gridded water budget data set, we present a comparative analysis of annual ET predictability between the original BM (ET 1 ) and the extended BM considering Δ S (ET 2 ) in 32 global river basins to explore the sensitivity of climate factors and catchment hydrologic responses in determining ET predictability. Results show that the difference between ET 1 and ET 2 increases linearly with Δ S , with ET 2 < ET 1 (ET 2 > ET 1 ) when Δ S > 0 (Δ S < 0). When both ET 1 and ET 2 overestimate (underestimate) observed ET, the error in ET 2 is smaller than ET 1 when Δ S > 0 (Δ S < 0) for all 32 basins considered. When the error signs of ET 2 and ET 1 differ, however, the difference in the absolute magnitude of ET 2 and ET 1 errors (RE diff ) under extremely humid climates is determined by the difference between potential ET and ET, leading to comparable accuracy between ET 2 and ET 1 . In contrast, under extremely arid climates, RE diff is controlled by the combined influences of Δ S and R , resulting in more accurate ET 2 than ET 1 under the condition of the in‐phase, positive‐correlated relationship between Δ S and R .