Rapid increase of potential evapotranspiration weakens the effect of precipitation on aridity in global drylands

Drylands are of great significance on terrestrial ecosystems and economic development, while being sensitive to climate changes and human activities. How global drylands extent and climate changed is not clear, and the dominant factor is the dispute over enhanced air evaporative demand and insufficient precipitation. This study attempted to fill this gap by exploring the trends in dryland areas, aridity index (AI), precipitation (P), and potential evapotranspiration (PET), and quantifying the temporal contributions of P and PET to AI. The results showed that the total dryland area shrunk 0.71 x 10(6) km(2) during 1901-2017 with reversed trend of shrinking to expanding. Precipitation dominates aridity in 88% of drylands, except for some regions in Europe and East Asia. With global warming, the relative contribution of PET to aridity in drylands increased significantly with a rate of 0.07% per year. The effect of PET exceeded that of P in 1966, which was the reason for the trend reversals of average AI.