Impacts of climate and land coverage changes on potential evapotranspiration and its sensitivity on drought phenomena over South Asia

Abstract

AbstractUnderstanding the spatiotemporal historical drought pattern and their sensitivity effect on potential evapotranspiration (PET) and vegetation coverage changes is essential for efficient drought mitigation policies under climate change. In this study, we used the standardized precipitation evapotranspiration index (SPEI) at multiple timescales, such as SPEI‐01, SPEI‐03, SPEI‐06, SPEI‐09 and SPEI‐12; we explored their regional‐scale dry and wet annual changes across seven sub‐regions of South Asia from 1902 to 2018. Results suggest that from 1981 to 2018, the extreme drought of SPEI has increased in South Asia, which mostly affects the summer and winter growing seasons, that is, SPEI‐06 to SPEI‐12 across seven sub‐regions of South Asia. The frequency of drought events during dry and wet annual changes of SPEI had an extremely dry year starting from 1998 to 2018, which mostly affected the South Asia region. Data from the past 18 years showed that the land changing detection has increased in the forests, cultivated land, arid land, savanna and farmland; by contrast, there has been significantly reduced permanent ice and snow, mixed forests, open shrub, grasslands, permanent wetlands, water bodies and evergreen broadleaf forests. Seasonal SPEI presented diverse characteristics such as showing a dry trend in Afghanistan, India, Pakistan and Sri Lanka during autumn and winter. Afghanistan and Bhutan are wet during the summer compared with other sub‐regions of South Asia, with drought frequency occurring at 45.3% and 44.4%. Sri Lanka, Pakistan and India are the driest regions in South Asia due to their high drought frequency, duration and intensity. The correlation between PET and crop water stress index (CWSI), PET and regional ETp reduction (Er) indicated a considerably negative correlation, while a significantly positive correlation was found between CWSI and Er, NDVI and Er. This study provides a comprehensive assessment of climate and vegetation coverage changes on PET, ET and SPEI, and can help in formulating long‐term adaptive strategies to reduce the cumulative impacts of droughts.