Water–Heat Synergy Shapes Evapotranspiration–Precipitation Coupling Patterns across Northern China
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Graphical Abstract
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Abstract
Northern China is a prominent “hotspot” for land–atmosphere interactions, with substantial gradients in both moisture and thermal conditions. Previous studies have identified a link between land–atmosphere coupling and the individual roles of each factor, but the synergistic effect of the two factors remains unclear. This study considers the covariation of evapotranspiration and precipitation to assess evapotranspiration–precipitation (ET–P) coupling across northern China, exploring its spatial variations and their linkage to water and heat factors. Our findings reveal a transition from strongly positive coupling in the northwest to weakly negative coupling in the southeast, peaking in spring. These spatial variations are attributable to water (soil moisture) and heat (air temperature), which explain 39% and 25% of the variability, respectively. The aridity index (AI), a water–heat synergy factor, is the dominant factor, explaining 66% of the spatial variation in ET–P coupling. As the AI increases, ET–P coupling shifts from strongly positive to weakly negative, with an AI around 0.7. This shift is determined by a shift in the evapotranspiration–lifting condensation level (LCL) coupling under an AI change. Regions with an AI below 0.7 experience water-limited evapotranspiration, where increased soil moisture enhances evapotranspiration, reduces sensible heat (H), and lowers the LCL, resulting in a negative ET–LCL coupling. Conversely, regions with an AI above 0.7 experience energy-limited evapotranspiration, where the positive ET–LCL coupling reflects a positive H–LCL coupling or a positive impact of the LCL on evapotranspiration. This analysis advances our understanding of the intricate influences of multifactor surface interactions on the spatial variations of land–atmosphere coupling.
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