Dynamic assessment of ecological risk owing to drought in alpine meadows based on SPEI index and GIS technology

The study of drought risk is a hot topic in environmental research. We selected Gannan Prefecture as the study area and combining GIS spatial analysis and statistical methods, we calculated the standardized precipitation evapotranspiration index (SPEI) from the years 1955 to 2014 in the study area; the SPEI was selected as the optimum time scale for monitoring drought in the alpine meadows of Gannan Prefecture. In addition, based on the SPEI index and drought risk probability model, ecological risk assessment due to drought was conducted. Four major results were observed. 1) SPEI6 is the optimal value for monitoring alpine meadows based on the SPEI index. 2) The results of Morlet continuous wavelet analysis showed that there was a significant " dry–wet” change in the alpine meadow of the study area within a short period of 3–6 years. 3) In terms of spatial distribution, the occurrence of drought in the growing season of the alpine meadows was mainly in the eastern part of Gannan Prefecture in the past 15 years, while the frequency of drought in the western part has been relatively low. Overall, the frequency of drought in the entire study area has gradually reduced over the past 15 years. 4) The areas with a high risk of drought in the future were located in the south of Luqu county and the south of Maqu county, especially around the Maqu wetland. The results of this study can provide a useful reference for related research on the ecological safety of meadow resources.