Runoff Generation Signaled by Deviations from the Budyko Framework

Abstract

Water‒energy dynamics, often characterized via the Budyko framework, drives various hydrological processes. However, the influence of short-term deviations from the long-term Budyko curve on runoff is rarely discussed. This study utilized the SWAT model to simulate different runoffs in an Ethiopian watershed with scarce datasets; which addressed the linkage between short-term evaporation deviation and runoff generations. The results revealed that the SWAT model effectively simulates the discharge satisfactorily with a Nash–Sutcliffe efficiency (NSE) of 0.78; curve number (CN), available water capacity (SOL_AWC), and groundwater delay (GW_DELAY) are the predominant parameters for runoff generations. Furthermore, 86% of the Budyko governing factor (n) variance can be attributed to fractional vegetation cover and catchment slope. The sub-catchments with relatively high n-values are characterized by dense vegetation and permeable soils. Most importantly, the deviations between the long-term Budyko curve and annual evaporative values were negatively correlated with surface runoff and return flow. The positive deviations, indicating the lower actual evaporation than the Budyko expected, frequently get accompanied by the shrunk surface runoff and return flow in dry years (limited rainfall) in this study. These findings suggest that the short-term deviations within the Budyko framework can serve as valuable proxies for runoff estimations and can be used for drought assessment in regions with complex climatic and catchment conditions.