Spatiotemporal Evolution of the Aridity Index and Its Latitudinal Patterns in the Lancang River Basin, China

Under the context of global climate change, aridity responses exhibit significant differences across various latitudinal zones, and quantifying the dependency relationship between aridity and latitudinal zones is of great importance for differentiated water resource management. The Lancang River Basin in China spans 13 latitudinal zones with distinct altitudinal gradients, making it crucial to analyze the relationship between long-term aridity variation patterns and latitude for understanding basin hydrological response mechanisms. This study adopted the United Nations Environment Programme (UNEP) aridity index definition and utilized publicly available high-resolution datasets to divide the Chinese Lancang River Basin into 26 regions at 0.5° N intervals. The spatiotemporal evolution characteristics of the aridity index at interannual and seasonal scales from 1940 to 2022 were analyzed, and the trends of aridity index changes and their relationship with latitude were quantified. Results indicate: (1) The spring aridity index increased significantly (trend rate of 0.015/10a, Z = 2.39), driving an overall basin-wide humidification trend. (2) The aridity index exhibited significant spatial and seasonal differences with latitude: southern regions (south of 24.75° N) showed negative correlations, northern regions (north of 30.5° N) showed positive correlations, while central regions displayed distinct seasonal transitions and spatial differentiation characteristics bounded by 27.25° N. (3) The rate of aridity index change in regions north of 27.25° N was significantly higher than in southern regions (p < 0.001). This study reveals the latitudinal patterns of AI changes in the Lancang River Basin, providing guidance for developing adaptive water resource allocation strategies under climate change scenarios.