Spatio-temporal evolution of drought events in Huaihe River Basin: a non-stationary standardized precipitation evapotranspiration index study

Drought is an extreme climatic event normally develops slowly but lasts quite long．With meteorological drought represented by non-stationary normalized precipitation evapotranspiration index, we identified evolution law with run theory and Copula function, analyzed combined frequency of drought duration and intensity, and examined effects of drought on vegetation cover．NSPEI in the middle of Huaihe River Basin was found to be low, 68% of the sites in the region were with an index on the rise, drought degree along the Huaihe River and in southern area was enhanced．Drought events with long duration and high intensity were found concentrated mainly near the southern Dabie Mountains and Bengbu, drought events with high intensity were concentrated near Dingtao in the central north．Drought events were concentrated within 0.5-1.5 months, with intensities of < 3, and strength of mostly within 10-30．The low value (1.6 a) of combined duration and intensity recurrence period of drought events was concentrated in Xinyang, Bengbu and Heze, the low value (1.7 a) of combined duration and intensity recurrence period was concentrated in Xinyang and Bengbu stations．Area of cultivated land in the Huaihe River Basin decreased by 2.01% fom 1990 to 2015, but construction land increased by 2.07%．Change of land use type was concentrated in the northern region．NDVI change trend in the region was 0.89%．Change trend of vegetation coverage was not obvious, effect of drought was low．