A new approach to quantify propagation time from meteorological to hydrological drought

Abstract

Of particular importance in a world of increasing water scarcity is the temporal and spatial relationship between a shortage in rainfall—meteorological drought—and a shortage in available water, or hydrological drought. Propagation time from meteorological to hydrological drought should be calculated at a higher (sub-monthly) temporal resolution with considerations for spatial expansion. A new framework for propagation time calculation from one index to another is established that uses the run theory, high-resolution remote sensing data on a daily time step. The framework is demonstrated using standardized drought indices representing precipitation, runoff, evapotranspiration, and soil moisture in the Central Asian subcontinent to measure the temporal shift (propagation time) in affected drought area, bringing a new perspective to contemporary drought analysis. Several variables from the water cycle are chosen to provide hydrological context for different propagation times. Correlation analyses for propagation time are shown to be ambiguous in interpretation and precision when compared to the temporal shift, which is clearly defined and calculated on a daily time step. Moreover, the results of temporal shift analyses indicate that deficits in evapotranspiration and runoff can precede deficits in precipitation, while soil moisture deficit almost always follows, highlighting the effects of additional influencing factors aside from precipitation on types of hydrological drought. While it is limited by current understanding of drought definition techniques, availability and quality of remote sensing products, and selection of characteristics for observation, use of the temporal shift over the correlation analysis provides a sub-monthly estimate of drought propagation time that may prove useful for detailed analyses, particularly in rapidly developing flash drought events.