Urban Heat Island High Local Water-Vapor Feedback Estimates Requiring Albedo Management

Abstract In this paper, we analyze warming data on Urban Heat Islands (UHI) in dry versus humid environments to estimate local water-vapor feedback from city growth. We find looking at such data and comparing rural to urban areas, UHI local water-vapor feedback is about 3 W/m2/oK to a maximum of 4 W/m2/oK. Relative to global climate feedback estimates of about 2 W/m2/o K, this is a factor of 1.5 to 2 times higher. This UHI effect is observed during daytime hours. Water-vapor feedback is known to be one of the most important in our climate system and thought that it can double the direct known forcing and is found here to be an even stronger UHI local effect. We suspect with city growth there is a loss of natural convection cooling and an increase in dome heat/humidity from UHI impermeable surfaces since warm air holds more water-vapor creating a local greenhouse gas (GHG). These are key contributors to local water-vapor feedback raising local temperatures in humid cities. An optimum way to mitigate this effect is with UHI albedo management. We suggest that this warming effect can be an important factor in UHI global warming contributions and should be mitigated.