Abstract
Drought is a natural disaster caused by long-term water deficit. Because the growth of crops and vegetation is closely related to soil moisture environment, it is of great significance to study the soil drought and vegetation response. In this paper, the soil moisture availability index (SMAI) was developed for quantifying soil drought conditions. The effectiveness and the ability of SMAI to recognize drought events were analyzed, while the vegetation condition index (VCI) was used to characterize the vegetation status. Temporal and spatial variations of soil drought and vegetation condition as well as the impacts of drought on vegetation in North China during 2001–2015 were comprehensively examined. We firstly concluded that SMAI related well with standardized precipitation evapotranspiration index (SPEI), and drought events can be detected by SMAI. Next, the mean value of SMAI in North China showed a decreasing trend in recent 15 years. Finally, the SMAI positively correlated with VCI in most areas of North China, and the response of four types of vegetation to SMAI differed over time. The results of SMAI on vegetation would assist drought research and application in North China.
Highlights
Drought is a natural phenomenon caused by imbalance in water budget, leading to water shortage, a sharp drop in groundwater reserves, crop reduction, and other issues
Studies have shown that the standardized precipitation evapotranspiration index (SPEI) is in good agreement with the actual drought condition both in China and in North China [21, 22]. erefore, TRMM and MODIS global evapotranspiration product data are used to calculate the SPEI in this study, and the relationship between SPEI and soil moisture availability index (SMAI) will be analyzed for the applicability validation of SMAI in our study area
Vegetation Monitoring Index. e normalized difference vegetation index (NDVI) is the most widely used vegetation index. It has a strong correlation with vegetation coverage, vegetation growth status, leaf area, biomass, chlorophyll, and other physiological parameters [23]. e vegetation condition index (VCI) obtained by normalizing NDVI for many years can be used as an indicator of the degree of environmental stress
Summary
Drought is a natural phenomenon caused by imbalance in water budget, leading to water shortage, a sharp drop in groundwater reserves, crop reduction, and other issues. As the reflection of precipitation and evapotranspiration, soil moisture deficit is a comprehensive feedback of meteorological drought in a certain period of time [13, 14]. E seasonal variation of vegetation is significant and especially susceptible to drought conditions because of the low annual precipitation in North China. Considering the impact of drought on vegetation varied in different regions and vegetation types [16], as well as water demand of vegetation differed over seasons [17], it is necessary to study the response of vegetation conditions to soil drought under different conditions from a more detailed spatial and temporal scale [18]. As an indicator of meteorological drought monitoring, SPEI has multiple timescale features while considering the precipitation and potential evapotranspiration simultaneously. Studies have shown that the SPEI is in good agreement with the actual drought condition both in China and in North China [21, 22]. erefore, TRMM and MODIS global evapotranspiration product data are used to calculate the SPEI in this study, and the relationship between SPEI and SMAI will be analyzed for the applicability validation of SMAI in our study area
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