A comparative analysis of pre- and post-industrial spatiotemporal drought trends and patterns of Tibet Plateau using Sen slope estimator and steady-state probabilities of Markov Chain

Abstract

Drought poses a significant risk to human life, agriculture, energy, ecosystem, wildlife, and other aspects of the terrestrial system. Climate warming may increase drought hazards around the globe. This study compares the pre- and post-industrial impact of climate change on the spatiotemporal evolution of drought over the Tibet Plateau region. Two standardized drought indices (SDIs), namely Standardized Precipitation Index (SPI) and Standardized Precipitation Evapotranspiration Index (SPEI), are utilized to characterize drought by averaging the time-series data of precipitation and temperature from 23 climate models of Coupled Model Intercomparison Project 6 database. Sen slope estimates and steady-state probabilities of the Markov Chain are used to assess drought characteristics. This study shows that an increasing trend in temperature has led to increased evaporation. Increasing evaporation had caused expansion in water deficiency; the decreasing trend of SPEI index on almost the entire Tibet Plateau reveals the persistence of future drought. A slight increase has been observed in extreme wet classes in higher timescales. However, the long-term probabilities of extreme drought and extreme wet episodes at the one-month timescale of SPI are equivalent and stable in both periods. The chance of occurrences of severe drought episodes has decreased. Comparatively, a significant increase in the likelihood of severe drought has been observed under the SPEI. Furthermore, the spatiotemporal quantitative comparison reveals that the SPI index is consistent in both periods. However, a significant decline ratio of SPEI values has been observed in the post-industrial period. It is because increasing temperature causes more evaporation. Consequently, the increase in water deficiency is the main reason for increasing drought episodes under SPEI.