In this paper, we analyze warming data on Urban Heat Islands in dry versus humid environments to estimate their feedback. We find UHI local warming second difference estimate of about 3 W/m2/K and an estimate maximum related difference feedback of 4 W/m2/K for UHI in humid versus dry environments. Relative to global warming water-vapor climate feedback estimates of about 2 W/m2/K, this is a factor of 1.5 to 2 times more feedback for UHIs in humid environments likely due to lapse rate effects. This result is for daytime hours. Water-vapor feedback is known to be one of the most important in our climate system. It is thought that it can double the direct known forcing. In this case we find a much higher UHI water-vapor feedback effect. We suspect that dome heat from urban heat islands and loss of latent heat cooling are key contributor, as warm air holds more water vapor amplifying urban heat especially in humid atmospheres. The only way to mitigate such surfaces is by increasing their reflectivity at least equal to and optimally higher than the average reflectivity of the Earth (≈0.25).