Variation of Surface Air Temperature Induced by Enhanced Land-Atmosphere Coupling During 1981-2020 in Xinjiang, Northwest China

Land-atmosphere coupling (LAC) is a critical process in the climate system, and has great effects on surface air temperature over the humid-dry transition zones. Using ERA5/ERA5-land reanalysis datasets, we show that the summer temperature anomalies over Northwest China (NWC), known as one of the most important LAC hotpots in China, are significantly correlated with the LAC strength during 1981-2020. The stronger the coupling strength between air temperature and land surface, the more pronounced decrease in air temperature and extreme hot days over NWC. Among the four pathways of land-air temperature coupling, including soil moisture (SM)/soil temperature-latent heat flux/sensible heat flux-air temperature coupling, SM-sensible heat flux-air temperature pathway corresponds most closely with the temperature changes in summer. By analyzing the possible local and non-local physical links in this relationship, we show that the wave trains composed of the intensification of Ural ridge and Central-Asia trough stimulate a meridional fluctuation of westerly airflow over the mid-high latitudes of Eurasia. Large moisture, therefore, converges into NWC, leading to excessive precipitation and deficient incident solar radiation reaching the land surface. In such case, wetter and cooler soil states accelerate the cooling of the environment through feedbacks between the lands, land-atmosphere exchanging fluxes and air temperature locally, accompanied by a significant enhancement in LAC strength. Our study provides insight into the physical processes causing variations in summer temperature over a typical LAC hotspot and suggests that the role of land surface-atmosphere interactions needs to be considered when studying temperature extremes under climate change.

Automated summary

Land-atmosphere coupling is a critical process that influences surface air temperature over humid-dry transition zones. Through analyzing ERA5/ERA5-land reanalysis datasets, we find a significant correlation between summer temperature anomalies in Northwest China and land-atmosphere coupling strength from 1981 to 2020. Among the four pathways of land-air temperature coupling, the SM-sensible heat flux-air temperature pathway is most closely related to summer temperature changes. By analyzing physical links, we show that wave trains intensify westerly airflow over Eurasia, leading to convergence of moisture in Northwest China and causing excessive precipitation and deficient solar radiation, resulting in enhanced land-atmosphere coupling strength.