Abstract
Abstract. Within the Budyko framework, the controlling parameter (ω in the Fu equation) is widely considered to represent landscape conditions in terms of vegetation coverage (M); however, some qualitative studies have concluded that climate seasonality (S) should be incorporated in ω. Here, we discuss the relationship between ω, M, and S, and further develop an empirical equation so that the contributions from M to actual annual evapotranspiration (ET) can be determined more accurately. Taking 13 catchments in the Loess Plateau as examples, ω was found to be well correlated with M and S. The developed empirical formula for ω calculations at the annual scale performed well for estimating ET by the cross-validation approach. By combining the Budyko framework with the semi-empirical formula, the contributions of changes in ω to ET variations were further decomposed as those of M and S. Results showed that the contributions of S to ET changes ranged from 0.1 to 74.8 % (absolute values). Therefore, the impacts of climate seasonality on ET cannot be ignored, otherwise the contribution of M to ET changes will be estimated with a large error. The developed empirical formula between ω, M, and S provides an effective method to separate the contributions of M and S to ET changes.
Highlights
The water cycle has been influenced greatly by human activities and climate change since the 1960s, and considerable variability in hydrological processes has been observed in many basins around the world; this has led to a series of problems concerning essential water resources (Stocker et al, 2014)
The Budyko framework is usually used for analyses of long-term average catchment water balance; in this study, it was employed for the interpretation of the interannual variability of the water balance by using the hydrological year approach described earlier
To validate the feasibility of using Fu’s equation for interannual variability, the evapotranspiration ratio (ET /P ) and dryness index (ET0/P ) on the annual scale for 13 basins are presented in the supporting information (Fig. S1 in the Supplement), and it can be seen that almost all points are focused on Fu’s curves in each basin
Summary
The water cycle has been influenced greatly by human activities and climate change since the 1960s, and considerable variability in hydrological processes has been observed in many basins around the world; this has led to a series of problems concerning essential water resources (Stocker et al, 2014). Analyses of the mechanisms of the interactions among the water balance, climate, and catchment surface conditions are important for understanding these complex processes at different spatio-temporal scales (Zhang et al, 2008), and such work has practical significance in regard to the improvement of water resources and land management (Rodriguez-Iturbe, 2000; Xu et al, 2014). The Budyko framework is considered one of the most abiding frameworks linking climatic conditions to the runoff (R) and actual evapotranspiration (ET) of a catchment (Donohue et al, 2007), and it has been used successfully to investigate interactions between hydrological processes, climate variability, and landscape characteristics The Fu (Fu, 1981; Zhang et al, 2004) and Choudhury–Yang equations (Choudhury, 1999; Yang et al, 2008) have been used widely; the controlling parameters ω (in the Fu equation) and n (in the Choudhury–Yang equation) are related linearly (Yang et al, 2008)
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