Urban heat islands and environmental impact

The rapid urbanization and industrialization have brought about microclimatic changes particularly with regard to its thermal structure. The well documented climatic modification of the city is urban heat island. The present paper discusses the nature and intensity of heat islands at Visakhapatnam, the tropical coastal city of South India. A detailed study was carried out with regard to urban heat islands for the last ten years. The study reveals that the intensity of heat island varies from 2°C to 4°C and intensity is high during winter season compared to summer and monsoon seasons. At Visakhapatnam the formation of heat island is controlled by topography and urban morphology. The land and sea breeze circulation also interacts with the heat island. It has been found that cooling at night time is less inside the builtup area than the suburban. Urban cooling rates are compared with the sub-urban and rural environment. The urban heat island helps in setting up of the recirculation of pollutants thus making the pollution problems more serious. Heat island coupled with heat wave conditions during summer season causes human discomfort and higher death rates. At Visakhapatnam, summer months of April, May and June with maximum temperatures of 35°C to 40°C are uncomfortable with oppressive heat. There is a record of 94 heat waves during 1951-2000. Prevalence of heat wave conditions and heat island deteriorate the situation further and residents experience thermal stress and heat deaths. Thermal comfort can be improved by developing green belts which control temperature and reduce heat island effect. Cities must be planned with climate input to make the environments more pleasant and healthier places and to reduce undesirable effects.