Latitudinal characteristics of aridity spatiotemporal evolution in Lancang River Basin

The Lancang River Basin in China spans about 13° of latitude and has significant altitude gradients.Quantifying how aridity varies with latitude helps interpret hydrological responses and supports differentiated water-resources management.Using the United Nations Environment Programme (UNEP) aridity index and publicly available high-resolution datasets, we divided the basin into 26 latitudinal bands at 0.5°N intervals.We examined interannual and seasonal aridity-index variability from 1940 to 2022.We estimated trends and tested their latitudinal dependence.The research results show that the spring aridity index increased significantly (slope = 0.001 677, Z=2.38), indicating an overall wetting tendency across the basin.The aridity-latitude relationship shows clear spatial and seasonal contrasts.It is negative south of 24.75°N and positive north of 30.5°N.The central basin shows a seasonal transition and a clear latitudinal differentiation with a boundary at 27.25°N.The long term trend of aridity index north of 27.25°N are significantly higher than those in the southern basin (p < 0.001).These results reveal a robust latitudinal pattern of aridity change and provide evidence for adaptive water-allocation strategies under climate change.