A framework for identifying propagation from meteorological to ecological drought events

Drought severely affects vegetation growth owing to its multidimensional characteristics (e.g. duration and severity). However, current studies regarding the propagation of meteorological to ecological drought are not investigated well from an event-scale perspective. Therefore, a framework for identifying the propagation relationship between meteorological and ecological drought at an event scale is proposed. The gross primary productivity (GPP) and standardized precipitation evapotranspiration index are used to characterize ecological and meteorological drought, respectively. The pooling of ecological drought events (GPP anomalous events, GAs) and the exclusion of meteorological drought events (MDs) are considered in the framework. Matching events between these two types of droughts are identified, and their propagation characteristics are analyzed. The framework is tested in the Yangtze River Basin (YRB). The main results are as follows: (1) The propagation time from meteorological to ecological drought in the YRB varied from 1 to 48 months, with significant spatiotemporal heterogeneity; (2) Four propagation types from meteorological to ecological drought are identified: multiple MDs trigger a GA (MTO), an MD triggers multiple GAs (OTM), an MD triggers a GA (OTO), and multiple MDs trigger multiple GAs (MTM), which constituted 16.17%, 11.32%, 55.57%, and 16.94% of the total matching events, respectively. Most of these events occur in semiarid and subhumid regions. In addition, OTO typically occurs throughout the YRB. (3) For the four matching types, the average duration (or severity) of MDs (or GAs) is in the order of MTM > OTM > MTO > OTO. For MTM and OTM, the duration of MD is longer (more severe) than that of the GA caused by it, and a more significant linear relationship is indicated (R2>0.7), whereas the opposite is observed for OTM and OTO.