综合干旱指数构建及其在不同草原类型中的应用

干旱指数是评估旱情等级、制定防旱减灾对策的重要指标。该研究从干旱发生的物理机制出发,基于CRITIC(Criteria Importance Through Inter-criteria Correlation)客观赋权法,综合考虑气象标准化降水蒸散指数(Standard Precipitation Evapotranspiration Index,SPEI)、植被供水指数(Vegetation Supply Water Index,VSWI)和日光诱导叶绿素荧光指数(Solar-induced Chlorophyll Fluorescence,SIF)在干旱发展过程中的作用机制,构建融合多源信息的综合干旱指数,探究其在不同草原类型干旱中的适用性和敏感性,进而分析干旱的时空分布及演化特征。结果表明:综合干旱指数既能敏锐捕捉气象干旱的早期开始,亦能从水文和牧业干旱角度综合反映旱情的持续过程和时间,相比单一干旱指数,具有综合表征多尺度干旱演化特征的优势;2007—2018年,内蒙古锡林郭勒草原干旱频率呈波动中下降趋势,干旱强度主要以轻中旱为主,重旱及以上干旱集中在春秋两季;空间分布上从西北向东南逐渐降低,呈现荒漠草原典型草原草甸草原,典型草原中北部旱情严重的特征。该研究对蒙古高原不同草原类型干旱事件精准监测及旱灾防御具有重要意义。

Construction and application of comprehensive drought index in different steppe types

Abstract: The drought index is important to the drought grade evaluation, drought prevention, and mitigation measures formulating. Based on the physical mechanism of drought, the objective weighting method of Criteria Importance Through Inter-criteria Correlation (CRITIC) was used to construct a comprehensive drought index with multi-source information. The mechanism of Standardized Precipitation Evapotranspiration Index (SPEI), Vegetation Supply Water Index (VSWI), and Solar-induced Chlorophyll Fluorescence index (SIF) were comprehensively considered in the drought development process. The vegetation types, coverage, and their sensitivity to precipitation and temperature of different steppes were also been considered in the comprehensive drought index construction. Taking Xinlingol steppe in Inner Mongolia as an example, the applicability and sensitivity of comprehensive drought index in different steppe types were explored compared with the precipitation anomaly percentage index of meteorological drought and the Relative Soil Moisture Index (RSM) of agricultural drought. The temporal and spatial distribution and evolution characteristics of drought were further analyzed in desert, typical and meadow steppes during 2007-2018. The results showed that: 1) The comprehensive drought index can not only sensitively capture the early stage of drought but also comprehensively reflect the duration and time of drought from the perspective of hydrology and pastoral area drought. The comprehensive drought index makes up for the limitation of drought information revealed by a single drought index to a certain extent, which can effectively identify the temporal and spatial distribution characteristics of drought, and improve the pertinence and accuracy of drought monitoring. 2) The temporal and spatial distribution characteristics of drought in Xinlingol steppe evaluated by the comprehensive drought index were more consistent with the actual drought condition compared with precipitation anomaly percentage index and RSM, and the correlation between 0-20 cm RSM and comprehensive drought index was the most significant. The drought frequency of the Xilingol steppe during 2007-2018 showed a fluctuating downward trend, which had a significant positive correlation with the drought crop area, affected population, and direct economic loss. 3) The drought intensity of the Xinlingol steppe was mainly light and moderate drought, in which the severe and extreme drought mainly happened in spring and autumn. For different steppe types of Xilingol, the drought frequency of desert steppe was significantly higher than that of typical steppe and meadow steppe, and the spatial distribution of drought shows a gradually decreasing trend from northwest to southeast and serious drought in the middle and north part of the typical steppe. This study carried out an optimal combination of drought information, in which the input information is easy to obtain and calculate, and the application of solar-induced chlorophyll fluorescence index effectively revealed the response of vegetation to drought stress. The application intensity of the comprehensive drought index in the desert steppe is relatively weak compared with meadow and typical steppe because the soil and biodiversity situation of the desert steppe is poor, the vegetation is sensitive to a precipitation process, and the cumulative effect is significant. This study is of great significance to the drought events monitoring and prevention in different steppe types on the Mongolian Plateau.