The local climate impact of an African city during clear‐sky conditions—Implications of the recent urbanization in Kampala (Uganda)

• Published in: International journal of climatology Vol. 40; no. 10; pp. 4586 - 4608
• Main Authors: Brousse, Oscar, Wouters, Hendrik, Demuzere, Matthias, Thiery, Wim, Van de Walle, Jonas, Lipzig, Nicole P. M.
• Format: Journal Article
• Language: English
• Published: Chichester, UK John Wiley & Sons, Ltd 01.08.2020; Wiley Subscription Services, Inc
• Subjects: Air circulation; Air temperature; Breeze circulation; Clear sky; Climate; Climate effects; Climate models; Convection; COSMO‐CLM TERRA_URB; Future climates; Lakes; Land breezes; Land surface temperature; local climate zones; Local climates; Night; Parameter identification; Parameterization; Regional climates; Relative humidity; Remote sensing; Sky; Specific humidity; Surface temperature; Temperature; Tropical climate; Urban areas; urban boundary layer dynamics; urban climate modelling; Urban climates; Urban heat islands; urban tropical climate; Urbanization; Weather stations; WUDAPT; Uganda; Kampala Uganda
• ISSN: 0899-8418; 1097-0088
• DOI: 10.1002/joc.6477

This study aims at assessing and understanding the impact of recent urbanization on the (surface) urban heat island ((S)UHI) under clear‐sky conditions in a tropical African city using different sources of remotely sensed data sets together with an urban climate model (UCM). The observed SUHI during clear sky conditions is found to be about 4°C on average over the capital city of Kampala, Uganda. The UCM, consisting of TERRA_URB embedded in COSMO‐CLM, represents the SUHI well during night but overestimates it by about 3°C in the mean during day. Moreover, a systematic warm land surface temperature bias of about 4°C is identified by night. Improved urban input parameters—derived from Local Climate Zones following the World Urban Database and Access Portal Tool (WUDAPT) framework—lead to a more realistic representation of spatial land surface temperatures patterns. In addition, this parameterization of the UCM can properly represent atmospheric variables such as air temperature, specific and relative humidity, as observed by the automated weather stations. A model sensitivity study furthermore demonstrates that the stronger urban heat island induced by the recent urbanization of Kampala over the past 15 years strongly interacts with the lake–land breeze circulation. Stronger daytime convection over the hotter city leads to areas of convergence that amplify the afternoon lake breeze in the Southern parts of the metropolis. Overall, this study demonstrates that the city of Kampala has a tangible effect on the regional climate that needs to be considered when studying present and future climate impacts. Urbanization is known to impact the local climate but developing cities' climate is poorly studied because of data scarcity. Using a variety of techniques to cope with this scarcity, an urban canopy model is applied over the city of Kampala in Uganda, located on the Northern shores of Lake Victoria. After validating model outputs, results show that recent urbanization over the past 15 years in Kampala have had a tangible effect on the lake coastal climate and dynamics.