Cross-regional impact of land and ocean evaporation on extreme precipitation in North China

Overview

This study examines the changing characteristics and atmospheric mechanisms driving summer extreme precipitation events in North China from 1979 to 2023. The research employs Self-Organizing Map classification and information flow analysis to identify distinct circulation patterns associated with extreme precipitation and to establish quantitative causal linkages between antecedent terrestrial evaporation and precipitation extremes. The investigation reveals that shifts in atmospheric circulation regimes, particularly an increased frequency of high-pressure dominated configurations, correspond with observed trends in extreme precipitation intensity and occurrence.

Methods and approach

The analysis utilizes CN05.1 precipitation data and ERA5 reanalysis fields over a 45-year period. Self-Organizing Map clustering identifies four dominant atmospheric circulation patterns associated with 207 extreme precipitation days. Long-term trend analysis quantifies changes in the frequency and characteristics of these circulation regimes. The Liang-Kleeman Information Flow method provides a directional, causal diagnostic framework to measure the contribution of antecedent terrestrial evaporation fields to subsequent precipitation extremes, enabling temporal lead-lag relationships to be established across geographic regions.

Key Findings

Four distinct circulation patterns characterize extreme precipitation events, with two high-pressure type configurations accounting for 56 percent of identified events. These high-pressure types have demonstrated significant frequency increases over the study period, driven by poleward displacement of the Western Pacific Subtropical High and intensification of mid-high latitude anticyclonic systems. Conversely, trough-type events driven by northern vortices have declined in frequency. Information flow analysis reveals cross-regional terrestrial evaporation as a critical precursor: evaporation from the Middle-Lower Yangtze River Basin exhibits causal influence on high-pressure type events with a 1-2 day lead time, while trough-type events derive their terrestrial moisture primarily from South China with a 3-4 day transport lag. These findings establish antecedent southern Chinese terrestrial moisture as a measurable precursor signal for North China extreme precipitation.

Implications

The identification of distinct atmospheric circulation regimes and their varying frequencies provides a mechanistic framework for understanding long-term trends in North China extreme precipitation. The dominance of eastside high-pressure patterns and associated frequency increases illuminate how atmospheric circulation changes contribute to regional precipitation extremes. Cross-regional terrestrial evaporation emerges as a quantifiable precursor variable, suggesting that moisture initialization from southern Chinese source regions substantially modulates extreme precipitation development in North China.