Drought characteristics and its elevation dependence in the Qinghai-Tibet plateau during the last half-century.

Associated with global warming, drought has destructive influences on agriculture and ecosystems, especially in the fragile Qinghai-Tibet Plateau (QTP). This study investigated spatial-temporal patterns of meteorological drought in the QTP and its surrounding areas and made an attempt to explore the relationship between drought conditions and elevation. Robust monitoring data from 274 meteorological stations during 1970-2017 were analyzed using the Sen's slope method, Mann-Kendall trend test and rescaled range analysis. Results revealed that under the wetting trend in the QTP, Standardized Precipitation Evapotranspiration Index (SPEI) increased of maximum 0.012/year in spring. Moreover, severe drought frequency in winter and future drought risk in summer also showed an increasing trend. Wetter trends were positively correlated with elevation, with a key point being 4,000 m where the change trend above 4,000 m was about 6.3 times of that below 4,000 m in study area. The difference of drought severities between SPEI in the QTP and its surrounding areas has increased from - 0.19 in 1970 to 0.38 in 2017 and kept growing in future.