Abstract Ample evidence shows that cities can enhance precipitation in the downwind region due to the urban heat island (UHI) effect and the high momentum roughness of urban land. Surprisingly, global observational results show that the downwind enhancement of precipitation caused by large metropolitan areas is weaker under conditions of stronger surface UHIs. This is because stronger UHIs tend to be associated with lower background wind speeds, while the downwind enhancement of precipitation is stronger with higher background wind speeds. These results suggest a competition between thermodynamic and dynamic factors in regulating the downwind enhancement of precipitation, with the background wind speed playing a more important role than the UHI effect. By considering the urban‐rural difference in momentum roughness length, a simple model is utilized to qualitatively explain the link between the downwind enhancement of precipitation and background wind speed.
Observations from the Little Bunker
Last updated: August 18, 2025 04:13 PM
Atmospheric CO₂
425.4 ppm
+18.4
ppm/year
Atmospheric CH₄
1934.91 ppb
+9.11
ppb/year
Global Temperature
+1.48 °C
Peak: +1.73°C
World Population
8.1 billion
+67
million/year