Human thermal comfort and urban climate of Zambia’s economic and political hub: a RayMan model study

Abstract

One of the most acute environmental effects of urban sprawl in a changing climate is related to human thermal comfort (HTC) especially in developing countries. This necessitates applied urban design and civil engineering works that take HTC into account. Here, we employ the radiation and human-bioclimate model, RayMan to interrogate HTC and urban climate in Zambia’s biggest city—Lusaka. We chose RayMan because of its tried and proven robust ability to compute radiation flux densities and thermo-physiologically important indices using only a few input variables. To assess HTC, we used synoptic data at 3 hourly intervals as observed at Kenneth Kaunda International Airport (KKIA) from 2000 to 2018. We also retrieved high-resolution monthly data for the period 1901–2016 from the Climatic Research Unit and used it to better understand the long-term evolution of urban climate over Lusaka. We observed that during September–November (SON), the highest physiologically equivalent temperature (PET) values are similar to those of the December–February (DJF) season with moderate heat stress at midday. However, with PET values of about 11 °C at dawn, SON is slightly colder than DJF hence making DJF the most thermal stressful season to people in Lusaka. In the evening, the city is generally comfortable to slightly warm from October to March and experiences moderate cold stress to no thermal stress from April to August. The most obvious finding to emerge from these analyses is that the thermal comfort of Lusaka varies between moderate cold stress and slight heat stress. Together, these results provide important insights that can be used in applied urban design for the health of urban dwellers.