Assessing the role of evapotranspiration in reducing surface temperatures in Harare using the SEBAL algorithm

Abstract

Within urban areas, buildings, roads, and paved surfaces, absorb and re-emit the sun's heat more than natural landscapes. Urban areas, where these structures are highly concentrated and vegetation is limited, become ‘heat islands’ contributing to a range of environmental, economic, and human health problems. Despite this, limited research, has, to date, been carried out to assess the influence of evapotranspiration (ET) on urban surface temperatures for Harare, Zimbabwe. In this study, the uSEBAL algorithm was used to estimate evapotranspiration (ET) and land surface temperature (LST) using Landsat images in Hazare, Zimbabwe. The influence of ET on LST was also examined during the hot and post rain seasons. Results showed significant negative relationships (p < 0.05) between ET and LST. High ET rates were recorded over water bodies and green spaces as compared to built-up areas. High ET rates resulted in correspondingly low LST. This is the first time such results are reported for Harare. The conclusion drawn from these results is that as ET increases, temperature decreases, thus there was a negative relationship between ET and LST during the hot season. Additionally, low ET coincided with high LST in low vegetation and densely built-up areas. From these findings we can deduce ways of mitigating effects of thermal discomfort in urban areas i.e., inclusion of green spaces and water bodies within the cities. It is recommended that more green spaces be created within residential zones and encourage construction of green buildings and cooling technologies.