Flash Droughts Identification Based on an Improved Framework and Their Contrasting Impacts on Vegetation Over the Loess Plateau, China

Abstract

Abstract Flash drought occurs in a short timescale and has more adverse impacts on society and ecosystems than regular drought. Considering flash drought as a special type of regular drought and identifying it by the rate of the first intensification period might ignore posterior intensification periods. To this end, we introduced the combinatorial decomposable flash drought identification framework (CDFDI) to identify flash drought from the perspective of regarding it as the subphase of drought and explore the characteristics and vegetation response of flash drought in the Loess Plateau (LP), China, where is prone to drought and its ecological environment is very fragile. The neffectiveness of the framework is evaluated through the comparison analysis with a preexisting identification method proposed by Li et al. (2020, https://doi.org/10.5194/essd-12-1217-2020 ). Results indicate that: (a) the CDFDI framework can better capture flash drought events than the Liu’s method in terms of time series and spatial patterns, its rationality was further demonstrated by the obvious latitudinal pattern of correlation between flash drought and normalized difference vegetation index (NDVI); (b) the correlation shows an southeast (positive) and northwest (negative) contrasting pattern in the LP; (c) such contrasting pattern was also found in the response time of GPP, which suggests a more rapid impact on vegetation of flash drought in the arid northwestern LP; and (d) flash drought shows an exacerbating trend across the LP under the background of climate warming and mainly concentrated in the southern part. In general, this study provides new insights on flash drought connotations in a changing environment. , Plain Language Summary Flash drought is an extreme disaster in which drought condition develops rapidly. Identification method considering flash drought as a special type of regular drought and regarding it as an entire drought event has potential limitations. In this study, we develop a new flash drought identification framework that considers it as the subphase of regular drought to fill this gap, and use it to explore the flash drought characteristics and vegetation response in the Loess Plateau (LP). The framework showed a better performance in capturing flash drought compared with the method proposed by Li et al. (2020, https://doi.org/10.5194/essd-12-1217-2020 ). It can be found that the southern LP is the hotspot of flash drought and large areas of the LP are dominated by summer. Larger exacerbating trend was also observed in the southeastern part which could be related to the warming climate. The correlation between flash drought and normalized difference vegetation index (NDVI) is positive in the southeastern LP and negative in the northwestern LP, and such contrasting pattern was also found in the response time of GPP, where the value is much shorter in the arid northwestern LP. It suggests a more rapid impact on vegetation of flash drought in the area that needs to be alerted. , Key Points An improved framework to identify flash drought considering it as the subphase of drought is proposed and verified in the Loess Plateau The contrasting pattern was observed in the response of normalized difference vegetation index and gross primary production to flash drought across the Loess Plateau The southern Loess Plateau is the hotspot of frequent and severe flash drought with an increasing trend