Rural land cover management reverses urban humid heat effects across climates

While urban humid heat is a major concern, adaptation strategies often overlook the surrounding rural land management. How rural land cover changes modulate urban humid heat by altering regional thermal-humidity dynamics, and whether these effects differ across climates, remains unclear. Here, we conduct regional‑scale simulations of summer heatwaves under three rural land cover scenarios—bare land, grassland, and forest—for three Chinese cities (humid Guangzhou, semi‑humid Beijing, and arid Lanzhou). We analyze changes in near-surface wet-bulb temperature (T_W) and decompose them into temperature- and humidity-driven components. We find that the impact of rural land cover on urban humid heat shifts with background hydroclimate. Counterintuitively, expanding rural bare land amplifies urban T_W in humid climates (+0.19 ℃) but reduces it in semi-humid and arid climates (-0.36 ℃ and -0.43 ℃). This contrast is driven by water availability: moisture-abundant humid climates can satisfy the increased evaporative demand from enhanced rural sensible heating, adding humidity and reinforcing T_W; whereas water-limited climates cannot, generating a strong drying effect that outweighs warming. Rural greening yields divergent outcomes. Conversion of rural land to high‑evapotranspiration grassland intensifies humid heat stress, particularly in arid climates, where the cooling effect is largely outweighed by pronounced humidification. In contrast, rural afforestation mitigates humid‑heat stress in the humid and semi‑humid climates through a drying effect driven by physiological water retention that suppresses evapotranspiration, while offering little benefit and slightly increasing T_W in the arid city. Our results establish rural hydroclimate as a critical factor in urban humid heat adaptation, demanding climate-specific strategies that account for the trade-off between thermal cooling and humidity accumulation.