Hydro-thermal heterogeneity contributes to the asymmetry of vegetation sensitivity to precipitation across northern mid-latitudes

A notable ecological phenomenon in northern terrestrial ecosystems, known as "the asymmetric response of vegetation to precipitation", has emerged over the past 20-plus years. However, it remains uncertain whether the response of northern terrestrial ecosystems to driving factors are temporally synchronous or has exhibit heterogeneity, and whether these impacts have been quantitatively evaluated. Here, we analyze the spatio-temporal patterns of vegetation sensitivity to precipitation (S_ppt) across the NTML from 2001 to 2023, using two independent proxies of vegetation productivity–gross primary productivity (GPP) and solar-induced chlorophyll fluorescence (SIF). We confirm a pronounced asymmetry in S_ppt trends between Eurasia and North America. S_ppt increased significantly across Eurasia (GPP: +3.2×10^-3 g·C·m^-2·mm^-1·yr^-1) but decreased in North America (GPP: -3.8×10^-3 g·C·m^-2·mm^-1·yr^-1). Moisture budget diagnostics reveal asymmetric roles of zonal moisture transport in shaping precipitation trends over the two regions. This asymmetry is primarily driven by changes in hydro-thermal heterogeneity, which collectively modulate moisture availability and plant physiological processes. Crucially, further results from machine learning attribution analysis indicate that diurnal temperature range dominates S_ppt changes across more than 23.5% of Eurasia, while precipitation is the key driver over 22.5% of North America. Our findings highlight the critical role of hydro-thermal heterogeneity in regulating vegetation–climate feedback and underscore the necessity of incorporate regional asymmetries into future Earth system models.