Estimation of intra-urban thermal variability in Ahmedabad city using moving vehicle transects

Abstract: Temperature differences within a city are called Intra-Urban Heat Islands (IUHI) and are important to estimate as they directly affect human health conditions. Monitoring the air temperature (T_air) throughout the city helps identify the places prone to extreme heat conditions, and such places require immediate warnings to mitigate extreme weather conditions like heat waves. The present study attempts to investigate intra-urban thermal variability within Ahmedabad city, India, by measuring near-surface T_airof different places representing diverse types of roads, vegetation, build-up areas like commercial or residential, water bodies like small ponds, lakes and rivers at different time of the day. T_airdata is collected using HOBO thermo-hygrometer coupled with an automatic data logger mounted on a mobile vehicle (for every 1 second) and at stationary sites (for every 2 minutes). The Indian regional navigation satellite system (IRNSS), with the operational name of NAVIC (acronym for Navigation with Indian constellation) and global positioning system (GPS) receiver, is used to record vehicle location, speed and altitude for every second. The results show that there are significant differences in temperature responses at different places in urban areas. Surface properties and surroundings significantly influence spatial and temporal variability in T_airwithin a city. The temperature in residential areas is found to be lower than the nearest market places. Transect data analysis suggests that IUHI are more intense during night (ΔT= 6°C) than in day (ΔT= 0.5°C), which is mainly due to differences in cooling rate of the surfaces. Research highlights: <list list-type="bullet"> <list-item> <p id="Par3">The diurnal variability in the air temperature at different places of Ahmedabad city during summer months has been studied using mobile vehicle transects experiments. </list-item> <list-item> <p id="Par4">It is found that this form of mobile transect methodology is a quick and relatively economical approach in comparison to stationary automatic weather stations to investigate intra-urban thermal variability in Ahmedabad city. </list-item> <list-item> <p id="Par5">The inter-comparison of air temperature observed by transect, rural and urban reference sites shows high thermal variabilities within a 1 km distance in the city. The sharp temperature gradients (4–6°C) ensure a significant intra-urban heat island. </list-item> <list-item> <p id="Par6">The study is able to identify locations in the city where temperature is found higher during day and night hours, and this will provide some guidance to the concerned government authorities responsible for taking adequate mitigation measures. </list-item> </list>