Anthropogenic drought in the Yellow River basin: Multifaceted and weakening connections between meteorological and hydrological droughts

Connections between meteorological and hydrological droughts (CMHDs) have changed due to increasingly intensified human activities. Understanding such changes from an anthropogenic perspective is, therefore, of critical importance for drought monitoring, early warning, and adaptation. As the second-longest river system in China, the Yellow River basin (YRB) has been seriously impacted by humans and has a high risk of drought due to its dry climate, dense population and massive water demand. However, the effects of human activities on CMHDs in the YRB are still unclear. We thus used the standardized precipitation evapotranspiration index (SPEI) and the standardized streamflow index (SSI) to indicate meteorological drought (MD) and hydrological drought (HD), respectively, and analysed CMHDs with multiple indicators including trends, correlation, difference, and drought propagation characteristics. Our results highlighted the heterogeneity of CMHDs in terms of subregions and indicators and showed that this heterogeneity was impacted by humans by quantifying the effects of human activities (mainly referring to water abstraction and regulation) on CMHDs in each subregion. We found that 1) human activities aggravated the disconnections between MD and HD by sharpening the downward trend in the SSI and weakening the correlation (amplifying the difference) between the SPEI and SSI, and 2) human activities reduced the drought propagation rate from MD to HD, manifested by a decreased number of HD but a length-ening of the HD duration. In addition to the abovementioned effects that were consistent for most of the YRB, there were also some effects, for example, on HD intensity and drought propagation time, that differed among subregions, and these kinds of diverse responses of CMHDs might be related to the various human activities in terms of intensities, types, and regions. By analysing human effects on CMHDs, this study may be helpful in understanding drought and drought propagation in the Anthropocene, which is beneficial to watershed management.