Responses of meteorological drought-hydrological drought propagation to watershed scales in the upper Huaihe River basin, China.

Spatial scale is a crucial factor in drought propagation and characterization. To investigate the response behavior of the meteorological drought-hydrological drought propagation to different watershed scales, three nested subbasins in the upper Huaihe River basin were selected as case study sites. The Standardized Precipitation Index and the Standardized Streamflow Index were adopted to characterize the meteorological drought and hydrological drought respectively. The relationship between meteorological drought and hydrological drought was then examined by wavelet coherency analysis and linear/nonlinear regression models. Results showed that (1) linear regression model captured drought propagation best in all subbasins, and the correlation strengthened as the watershed area increased with drought duration being highest correlated among the five drought characteristics; (2) with the watershed area growth, the coherence between hydrological and meteorological drought reduced, the lagging effect of hydrological drought attenuated, and the hydrological one tended to be more synchronized with meteorological one over the long period; and (3) the larger the watershed scale, the later (earlier) occurrence of the hydrological drought onset (termination), while the longer drought duration and larger magnitude for triggering hydrological drought.