Dynamic evolution and frequency analysis of hydrological drought from a three‐dimensional perspective

Abstract

Drought events show a continuous spatiotemporal structure. The evolution of drought and its probabilistic modeling from a three-dimensional perspective are important for drought mitigation and risk management. This study therefore aimed to extract hydrological drought variables using a three-dimensional identification method in the Upstream of Heihe River Basin (UHHRB) in Northwest China during 1961–2014. Then, the spatiotemporal dynamic evolution of hydrological drought event was quantified, and drought frequency was evaluated using copula functions. Results showed that the spatiotemporal structure of drought can be satisfactorily reflected using the three-dimensional framework. The most severe drought originated in the middle part of the basin, and propagated towards the eastern part with variable migration velocity. The Gumbel copula was the most suitable model for determining the joint distribution of drought duration, severity, and area. The conditional probability of drought variables with a given conditional factors decreases as the values of factor increase, and the increasing trend had no significant effect on reducing the probability of drought occurrence for a relatively higher value of drought variable. Drought risks would be underestimated (or overestimated) if simply the ‘and’ (or ‘or’) case return periods were considered. Drought frequency analysis considering the spatiotemporal drought features can be regarded as a reliable method. This study could help to better understand the spatiotemporal dynamic evolution of drought and to facilitate water resources allocation and drought mitigation.