Spatiotemporal Variability of China's 800 mm Precipitation Isohyet (1961–2022): Multi-scale Analysis of its Migration and Impact on Hydroclimatic Extremes

Abstract

Under global climate change, precipitation variability and extreme events pose significant challenges to regional ecological security and water resource management. This study proposes the Dynamic Line Scanning Method (DLSM) to quantitatively assess the migration of China's 800 mm precipitation isohyet during 1961–2022. Using long-term precipitation data, we systematically examined its spatial and temporal variation, explored links with drought–flood regimes and extreme precipitation, and identified the main drivers. Results indicate that the isohyet experienced a two-phase shift: an initial southward retreat followed by accelerated northward movement after 2001, with the latter trend markedly intensifying. These shifts have directly influenced regional drought–flood patterns and altered the frequency and intensity of extreme precipitation events. Analysis further reveals that the East Asian Summer Monsoon Index (EASMI) is the dominant factor driving the isohyet's movement. Overall, this study provides novel methodological insights and robust empirical evidence regarding the dynamics of precipitation isohyets in China in the context of climate change. The findings enhance understanding of hydroclimatic variability and offer a scientific foundation for developing region-specific adaptation and water management strategies.