Understanding the Spatiotemporal Links Between Meteorological and Hydrological Droughts From a Three-Dimensional Perspective

Investigating the spatiotemporal link among different drought types is of great significance for understanding the causative mechanism of droughts. In this study, we propose a new approach for connecting meteorological and hydrological drought events by considering their overlaps in drought persistence time and spatial coverage in three dimensions (i.e., latitude, longitude, and time). The variable infiltration capacity model with daily hydrometeorological observations in and around the Yellow River basin for the period of 1961-2012 is used to derive the standardized precipitation evapotranspiration index and standardized runoff index. Results show that minor meteorological drought events with short durations and small areas generally are not prone to cause a hydrological drought, especially in winter for the source region, leading to failure matches between the two drought types. By contrast, meteorological droughts of large magnitudes are more likely to influence a hydrological drought in different ways. In three dimensions, the transformation from meteorological to hydrological droughts is characterized by lengthened duration, lagged response time, and attenuated drought severity, which is in accordance with previous studies. Moreover, the drought area also decreases during this process. The increase in potential evapotranspiration from February to April after 1998 is the reason for the attenuation of drought area. The enlarged evaporative demand from potential evapotranspiration aggravates the atmospheric dry condition and promotes the development of meteorological drought but does not necessarily cause a hydrological drought.