Abstract
The impact of drought on ecosystems has become increasingly prominent. This study used the MODIS remote-sensing vegetation index and the standardized precipitation index to quantify vegetation coverage status and meteorological drought level. Using the copula method, the joint distribution of the drought index and related vegetation cover variables were simulated for the first time. The conditional distribution of vegetation biomass was deduced, and the multidimensional response between the vegetation biomass and drought was explored to understand the possible vegetation loss under different drought severity conditions. The three-river headwaters (TRH) region is the source place of the Yangtze River, Yellow River, and Lancang River, where the ecosystem is characterized by the innate vulnerability. Using this region as a case study, the results show that the spatiotemporal evolution of drought and vegetation in the TRH region has apparent regional heterogeneity. The vegetation cover in the eastern region is significantly better than that in the northwestern region, while the vegetation growth trend in the northwestern region is stronger than that in the southeastern region. It is feasible to build a vegetation-drought multidimensional response model based on the copula method. In 92.5% of the TRH region, vegetation cover was significantly affected by the severity of the drought. The impact on the growth of vegetation caused by persistent drought events was higher than that of short-term but high-intensity drought. The vegetation in the TRH area has a certain degree of drought resistance. This study provides outstanding theoretical support and reference for the protection of the TRH basin ecosystem.
Highlights
D ROUGHT refers to a phenomenon that has a wide range of negative effects on ecosystems, agricultural production, the water environment, and human activities and is defined as a period when the amount of available water is well below the long-term recorded averages
We found that the vegetation cover in the three-river headwaters (TRH) area has increased since 2000, and the vegetation increase area is mainly distributed in the northwest of the Yangtze River
This study found that the change in vegetation index had a higher correlation with the cumulative negative standardized precipitation index (SPI) value than with the quarterly minimum SPI value, indicating that continuous water shortage had a larger impact on the TRH area, and a short duration of intense drought had relatively little impact
Summary
D ROUGHT refers to a phenomenon that has a wide range of negative effects on ecosystems, agricultural production, the water environment, and human activities and is defined as a period when the amount of available water is well below the long-term recorded averages. Among the various natural and human communities affected, the degraded terrestrial ecosystems that have suffered severe drought stress may subsequently trigger a series of surface and atmospheric responses [1], [2]. Continuous meteorological and hydrological droughts will affect vegetation growth in ecosystems. In addition to global warming, drought events frequently occur throughout the world, causing severe ecological and environmental impacts [3]. Vegetation cover is an essential factor that reflects the ecological environmental change. For the long-term vegetation change monitoring, satellite remote-sensing data sources, such as the normalized difference vegetation index (NDVI) and the enhanced vegetation index (EVI), can usually be used [8]. The NDVI is widely used for measuring vegetation cover [9]. The EVI has the advantage of relatively high spatial and large-area near-real-time data resolution [10]
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