No abstract

High Mountain Asia (HMA) has the world's largest ice and snow reserves outside the polar regions and is an important source of water for the major river systems in Asia, providing water for a population of more than a billion people, which is increasing rapidly (Immerzeel, 2010;Immerzeel et al., 2020;Stocker et al., 2013). The HMA region is characterized by contrasting atmospheric circulation patterns (Bookhagen & Burbank, 2006;Cannon et al., 2016). Midlatitude westerlies and Asian monsoon systems supply most moisture as snow or rain in the western and eastern parts of HMA, respectively.

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. Drought is one of the most widespread and costly natural disasters 1 , which can endanger the production of agriculture and animal husbandry, worsen the ecological environment, and even expose human to the risk of disease 2,3. Previous studies have suggested that under global warming, the percentage of dry areas in the world has increased by approximately 1.74% per decade during 1950-2008 4,5. With an average elevation above 4,000 m and an area of 200,000 square kilometers, the Qinghai-Tibet Plateau (QTP) is the source of major rivers in Asia 6-8. It is extremely vulnerable to global change, and easily suffers from drought. The drought herein will have profound impacts on the neighboring regions. Therefore, a comprehensive understanding of drought characteristics in the QTP is of great importance. Many studies on spatiotemporal characteristics of drought in the QTP and its surrounding areas have been conducted, mainly concluded that the QTP has become warmer and wetter in the past decades, especially in the vast northwestern QTP 5-7,9-13. Additionally, Gao et al. 8 analyzed the aridity changes using P/PET ratio in recent 30 years based on 83 stations, and found that the eastern QTP was becoming drier and the aridity change pattern was significantly correlated with precipitation, sunshine duration and diurnal temperature range. Liang et al. 14 investigated 74 stations in the QTP during 1980-2014 and found that the drought pattern exhibited obvious inter-decadal variation and severe drought mainly occurred before the 1990s. Yang et al. 15 forecasted an increasing drought trend in southwest China (including Yunnan Province) but an increasing wetting trend for the QTP based on simulation of Global Climate Models (GCM) taken from the Coupled Model Intercomparison Project Phase 5 (CMIP5) framework. Other studies have addressed the seasonal drought evolution in the QTP. Some concluded that the dro...