Quantifying changes in the vulnerability of vegetation to various drought stresses in different seasons is important for rational and effective ecological conservation and restoration. However, the vulnerability of vegetation and its dynamics in a changing environment are still unknown, and quantitative attribution analysis of vulnerability changes has been rarely studied. To this end, this study explored the changes of vegetation vulnerability characteristics under various drought stresses in Xinjiang and conducted quantitative attribution analysis using the random forest method. In addition, the effects of ecological water transport and increased irrigation areas on vegetation vulnerability dynamics were examined. The standardized precipitation index (SPI), standardized precipitation-evapotranspiration index (SPEI), and standardized soil moisture index (SSMI) represent atmospheric water supply stress, water and heat supply stress, and soil water supply stress, respectively. The results showed that: (1) different vegetation types responded differently to water stress, with grasslands being more sensitive than forests and croplands in summer; (2) increased vegetation vulnerability under drought stresses dominated in Xinjiang after 2003, with vegetation growth and near-surface temperature being the main drivers, while increased soil moisture in the root zone was the main driver of decreased vegetation vulnerability; (3) vulnerability of cropland to SPI/SPEI/SSMI-related water stress increased due to the rapid expansion of irrigation areas, which led to increasing water demand in autumn that was difficult to meet; and (4) after ecological water transport of the Tarim River Basin, the vulnerability of its downstream vegetation to drought was reduced.
Under the background of global warming, increased heating has changed the spatiotemporal distribution of hydrometeorological variables and altered the characteristics of extreme events (Samaniego et al., 2018). The report from Trenberth et al. (2013) indicated that the warming climate has characterized drought with more rapid development. The rapid development in dry spell reduces the time available for mitigating measures, potentially lead-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 warmi...
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