Applicability Analysis of Runoff Downscaling and Baseflow Separation Methods in the Upper Vakhsh River Basin

Abstract

Short-term scales (e.g., daily scale) are of great importance for the development of hydrological models and the effective analysis of hydrological conditions. However, there remain knowledge gaps in the regional applicability and selection of runoff downscaling methods. This study considered the concept of baseflow volume balance and aimed to explore the applicability of runoff downscaling methods and baseflow separation methods in the upper Vakhsh River basin, and quantifies their temporal variation characteristics. The results demonstrate that the Chapman Maxwell filtering method provides optimal performance for comparative evaluation of baseflow separation in the basin. During the period from 1995 to 2017, the BFI showed a significant downward trend. In the upper Vakhsh River basin, the water balance concept based on baseflow is more reliable in the selection of runoff downscaling methods. Runoff duration curves (FDCs) and hydrological evaluation indicators cannot directly determine the advantages and disadvantages of most runoff downscaling methods, while the volume balance of runoff and runoff process lines could highlight the advantages of mean-preserving 3rd-order spline interpolation (MP3S) and mean-preserving 2nd-order spline interpolation (MP2S). MP3S performs best in the test method based on baseflow volume balance for the upper Vakhsh River basin. The results of this study supplement the selection of runoff downscaling methods and provide important support for water resource management and optimization.