UHI in Fortaleza and trends on screen-level air temperature and precipitation

There is a consensus that Urban Heat Island phenomenon - UHI occurs in every large city. This effect is characterized by higher air temperatures in cities than in the neighboring countryside at night. However, to date, there has been no systematic study on the Fortaleza case, the Brazil's 5th largest city. By the comparison between screen-level air temperature measured by two automatic weather stations, one located in the city and the other in the neighboring region, this work shows the occurrence of the UHI in Fortaleza, even during the rainy season. In an attempt to find some effect of the UHI on precipitation (and vice-versa), historical series of air temperature and precipitation were analyzed from 1966 to 2020. Besides the considerable increase in air temperature over the years, a slight downward trend was observed in UHI and even more in accumulated precipitation between the hours of 15:00 and 21:00 (local time). However, one believes that these trends may be related to climate change at large scale rather than an urban scale.