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The rate of surface warming in cities exceeds that in rural areas, but urban greening can partly offset enhanced urban warming that is driven by climate change and urban expansion, according to an analysis of satellite land surface temperature data in 2000 city clusters between 2002 and 2021.

Knowledge of the day-to-day dynamics of surface urban heat island (SUHI) as well as their underlying determinants is crucial to a better design of effective heat mitigation. However, there remains a lack of a globally comprehensive investigation of the responsiveness of SUHI variations to meteorological variables. Based on the MODIS land surface temperature and auxiliary data in 2017, here we investigated 10 000+ cities worldwide to reveal day-to-day SUHI intensity (SUHII) variations (termed as SUHII _dv ) in response to meteorological variables using Google Earth Engine. We found that: (a) meteorological variables related to the thermal admittance, e.g. precipitation, specific humidity (SH) and soil moisture (SM) (represented by daily temperature range in rural area, DTR _r ), reveal a larger regulation on SUHII _dv than those related to the air conditions (e.g. wind speed and near-surface air temperature) over a global scale. (b) Meteorological regulations on SUHII _dv can differ greatly by background climates. The control of SH on SUHII _dv is significantly strengthened in arid zones, while that of wind speed is weakened prominently in equatorial zones. SUHII _dv is more sensitive to SM in cities with higher background temperatures. (c) All meteorological variables, except that related to SM (DTR _r ), show larger impact on SUHII _dv with antecedent precipitation over the global scale. Precipitation is observed to mitigate the SUHII _dv globally, and such effects are even more pronounced in equatorial and arid zones. We consider that our findings should be helpful in enriching the knowledge of SUHI dynamics on multiple timescales.

Northwestern China (NWC) is among the major global hotspots undergoing massive terrestrial water storage (TWS) depletion. Yet driver(s) underlying such region-wide depletion remain controversial, i.e. warming-induced glaciermelting versus anthropogenic activities. Reconciling this controversy is the core initial step to guide policymaking to combat the dual challenges in agriculture production and water scarcity in the vastly dry NWC toward sustainable development. Utilizing diverse observations, we found persistent cropland expansion by >1.2 × 10 ^4 km ^2 since 2003, leading to growth of 59.9% in irrigated area and 19.5% in agricultural water use, despite a steady enhancement in irrigation efficiency. Correspondingly, a substantially faster evapotranspiration (ET) increase occurred in crop expansion areas, whereas precipitation exhibited no long-term trend. Counterfactual analyses suggest that the region-wide TWS depletion is unlikely to have occurred without an increase in crop expansion-driven ET even in the presence of glaciermelting. These findings imply that sustainable water management is critically needed to ensure agriculture and water security in NWC.