Investigation of urban heat island intensity and developing mitigation strategies for istanbul

Urbanization and climate change may be the two most significant socio-ecological issues of the 21st century. The intersection between these trends is intensified by increasing population. Thus, the quality of life is influenced negatively. Cities are the defining ecological phenomenon in the decades ahead and the majority of the population of world now lives in them (While and Whitehead, 2013). Significant urbanization has occurred in Istanbul due to incerase of the population. Urban growth and associated landscape transformation might be a major driver of local and regional environmental change in this city. Istanbul is the largest city of Turkey with the population over 14 million inhabitants and the urbanization is drastically expanded since 1965 due to the population increase from 2 million to 14 million. As long as cities proceed to grow and develop with climate change, in order to mitigate urban temperatures by identifying and assessing practical strategies, is critical to provide socio-ecological urban sustainability and thermal comfort (Coutts et al. 2013). Using green and cool (high-albedo material) roofs are commonly reported to provide urban heat mitigation potential; however, their performance is highly dependent upon their design, sunshine duration, and location of the built-up area. This study compares the role of land use and wind field modifications to alter the urban climate in Istanbul by modeling spatial distribution of the urban heat island given 33 mitigation strategies (including white, green and hybrid scenarios) and 10 sensitivity analyses (with wind speed and wind direction scenarios). In this study, the impacts of urban expansion on meteorological variables in relation to the urban heat island (UHI) effect in Istanbul is investigated. To estimate the strength of UHI, the temperature differences between urban and suburban stations are calculated by using temperature observations from 6 stations for 1960-2014 years, and 34 stations for 2007–2012. In order to examine what type of changes in the urban landscape elevate the intensity of UHI in Istanbul, by using the dry days which were determined with the meteorological station data, the effects of change in land use on daytime and nighttime urban heat island (UHI) of Istanbul is examined using the micro-scale climate model MUKLIMO 3. The model simulation for mitigation strategies takes place for 07.08.2012, which was the hottest day in a heat wave that lasted five days and exceeded 30.5°C (threshold value) from the 90th percentile of all six station's data. A Case domain (Maslak) for date (07.08.2012) is selected and the implementation of green roofs and high-albedo materials are considered in order to lower the temperature. Due to the fact that MULIMO_3 provides the opportunity to implement green roofs as well as high-albedo materials in built-up areas easily, several mitigation strategies are applied. The implementation of cool (high-albedo) materials for urban structures and green roofs as mitigation strategies in general show lower temperatures throughout the whole day, while the effects of white and hybrid scenarios are much higher than green roofs. For the roof treatments explored here, results suggest that cool roofs (white scenarios), provide the greatest overall benefit in terms of urban heat mitigation and energy transfer into buildings. The high albedo of the cool roof substantially reduced net radiation, leaving less energy available at the surface for sensible heating during the day. Under warm and sunny conditions, when soil moisture was limited, evapotranspiration from the green roof was low, leading to high sensible heat fluxes during the day. Irrigation improved the performance of the green roof by increasing evapotranspiration. Consequently, the thermodynamic version of MUKLIMO_3 has decent skills to capture general pattern of urban climate parameters such as temperature, relative humidity and wind velocity. In order to evaluate the utilizability of mitigation strategies to reduce potential of heat stress, the results demonstrate suitable promise as a valuable tool for national stakeholders and urban climatologists. On the other hand, the rooftops of mega city Istanbul must be designed accordingly to target specific performance objectives, such as heat mitigation rather than receiver system or brick located roofs.