Surveying of Heat waves Impact on the Urban Heat Islands: Case study, the Karaj City in Iran

From July 6th to August 5th of 2014, a severe heatwave happened in Iran. This study analysis the formation and relative effect of this heatwave event on the environmental situation in the Karaj city (west of Iran capital). This city has experienced warm summers and high amounts of heat-related mortality. This research is accomplished according to the statistical-synoptic-approach and mobile survey data. Two main data sets are collected during this event from 20 stations in the urban and rural areas. The results of data are derived from hierarchical cluster analysis by using Ward's method. Analysis of mid-level synoptic charts demonstrate a low pressure at ground level in North West of India (Gange's thermal low pressure) which covers the case study area together with a high-pressure system that dominates in the middle levels. This phenomenon affects the thickness of the atmosphere and causes warm air subsidence, abnormal air heating and a stable urban heat island (UHI) in the region. Compared to the rural areas, the temperature of the city is about 1 °C warmer within the day times and up to 2.5 °C warmer at nights. Furthermore in comparison with the rural areas, in urban environment the temperature value combination of surrounding humidity stations, determined systematically warmer status. This intensity of UHI is the simplest and most quantitative indicator of the thermal modification imposed by the Karaj city upon its territory, and shows its relative warming compared to the surrounding rural environment at night times.