Relative humidity and solar radiation exacerbate snow drought risk in the headstreams of the Tarim River

Abstract

Snow drought is commonly defined as the phenomenon of abnormally low snow snowpack caused by below-normal precipitation and/or above-normal temperatures for a period of time. This poses a critical knowledge gap, requiring a deeper understanding of its multivariate risk under various scenarios, dynamics, and driving mechanisms in a changing environment. In this study, we constructed a density kernel estimation for the Nonparametric Standardized SWE Index (NSWEI) to gain new insights into the implications of snow drought. We further demonstrated its ability, specifically the ability Equitable Threat Score (ETS), to anticipate warm-season hydrological droughts using a Random Forest (RF) model. In addition, we applied the concept of multivariable return periods under different scenarios for snow drought risk assessment in combination with Copula theory and its dynamics under a changing environment. This exploration was followed by a preliminary attribution analysis. Our results indicate that: (1) the NSWEI is more reasonable in characterizing snow drought than previous snowpack metrics; (2) the most probable droughts (occurring with less than a 50-year return period) belong to the moderate drought scenario; (3) the interaction between vapor pressure deficit and solar radiation significantly influences static risk, while the Digital Elevation Model (DEM) also plays undeniable roles in affecting snow drought risk; (4) a contrasting pattern is found in spatial distribution of snow drought risk dynamics, with an exacerbating snow drought risk observed in the southern part; and (5) the increasing snow drought risks in the south are generally triggered by reducing relative humidity and increasing solar radiation. Overall, this study provides new insights into snow drought risk and its dynamics, which are important for developing robust and effective management practices.