Urbanization-induced compression effect accelerates and amplifies dry-wet abrupt alternations in Chinese cities

Abstract Rapid urbanization substantially alters hydrometeorological extremes, yet its effects on compound dry-wet abrupt alternation (DWAA) remain poorly understood. Here we present the first multi-scale analysis of urbanization effects on DWAA across Chinese cities by integrating high-resolution observations, model simulations, and future projections. We reveal a pronounced urbanization-induced “squeeze” effect in approximately 35% of cities, whereby urbanization simultaneously accelerates transitions and amplifies severity of both dry-to-wet and wet-to-dry alternations. Pixel-scale analysis demonstrates that 50-95% of intra-urban areas experience this “squeeze” effect, with strongest impacts at rapidly expanding fringes. Weather Research and Forecasting simulations further attribute these changes to coupled atmospheric-surface modifications, including enhanced urban heat/dry island and boundary layer dynamics. Under future scenarios, exposed urban populations increase nearly twofold, with DWAA transitions compressed by 14.11% and severity intensified by 48.94% by 2100. These findings demand fundamental reconceptualization of targeted urban water management strategies for compressed hydroclimatic timescales and amplified compound extremes.