Hydrological effects of climate variability and vegetation dynamics on annual fluvial water balance at global large river basins
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Abstract. The partitioning of water and energy, governed by the controlling parameter in the Budyko framework (i.e., n parameter in the Choudhury and Yang equation), is critical to assess the water balance at global scale. It is widely acknowledged that the spatial variation of this controlling parameter is affected by landscape characteristics, but characterizing its temporal variation remains yet to be done. Considering effective precipitation (Pe), the Budyko framework was extended to the annual water balance analysis. To reflect the mismatch between water supply (precipitation, P) and energy (potential evapotranspiration, E0), a climate seasonality and asynchrony index (SAI) were proposed in terms of both phase and amplitude mismatch between P and E0. Considering streamflow changes in 26 large river basins as a case study, SAI was found to the key factor explaining 46% of the annual variance of parameter n. Furthermore, the vegetation dynamics (M) remarkably impacted the temporal variation of n, explaining 67% of the variance. With SAI and M, a semi-empirical formula for parameter n was developed at the annual scale to describe annual runoff (R) and evapotranspiration (E). The impacts of climate variability (Pe, E0 and SAI) and M on R and E changes were then quantified. Results showed that R and E changes were controlled mainly by the Pe variations in most river basins over the globe, while SAI acted as the controlling factor modifying R and E changes in the East Asian subtropical monsoon zone, E0 in the temperate maritime climate of Europe, and M in the temperate grassland zone of South America.
