oa Modeling Risks of Urban Heat Island (UHIs) and Microclimate Change in Doha City Using Geoinformatics

The economic boom that has taken place in Qatar in the last few decades has resulted in rapid population growth, urban expansion and change in life-style. Qatar Gross Domestic Product (GDP) has increased from 5.05 billion USD in 1986 to 211.8 billion USD in 2014. At the same time population has increased from 0.4 million in 1986 to 2.17 million in 2014. Urban expansion was and the accompanied modern urban life-style was necessary to accommodate this rapid population increase. Doha City has had the biggest share of urban expansion in the country.

Recently, Doha faced a huge urban development and urban expansion in a short period of time. The modern urban designs in the city and the material used in the construction have changed the land surface albedo and the Land Surface Temperature (LST) in city. With this urban expansion, the Urban Heat Island phenomenon has become more noticeable between the urban center and the suburbs. Changing of landscape in the city due to the construction of roads and buildings has increased the surface temperature, as paving and building material replaces the Earth's natural surface causing surface compactness. Surfaces that were once pervious moist have become impermeable and dry. Open land and vegetation are replaced by buildings, roads, and other infrastructures and surfaces with high heat capacity, which impacted and created microclimates. This impact is due to the fact that many surfaces and asphalt absorb heat during the day and releases it during the night.

Anthropogenic heat is one of the main causes of UHI in cities. The main sources of this heat include cooling and heating buildings, industrial processes, and transportation (highways, airports,..etc). Other causes of UHI are: air pollution; surface waterproofing; thermal properties of fabrics; and surface geometry.

Urban heat island and temperature increase have a negative impact on the environment and on human health. Increased temperature also increases energy demand, air pollution and water shortages.

This study uses remotely sensed data (high resolution satellite images) to highlight the urban expansion in Doha and the expansion of the UHI phenomenon as the city expands. Multi-date images from Enhanced Thematic Mapper (ETM) sensor on board Landsat Satellite were classified using supervised and un-supervised classification techniques to accurately identify and map the urban expansion in Doha. The classification results were verified and tested. Support Vector Machine supervised classification provided the most accurate classification of urban areas.

In addition to the classification of the images, Thermal Bands of the same Landsat ETM images were modeled to calculate LST images for Qatar using Planck's function:

T = K_2/In([K1^*ϵ]/[CV]_R1+1)

Where: T is degrees Kelvin

K1 & K2 are satellite sensor constants obtained from the image metadata

CVR1 is cell value as radiance

ϵ_is emissivity (typically 0.95)

The LST images show higher LST in the urban areas than in the desert suburbs by considerable margins especially in compacted areas, such as asphaltic roads and airports.

This study also looked at the changes of urban fabrics over time and their land surface temperature Varian's in Doha. These variations in LST within the city and between the city and the desert suburbs create microclimates. These LST images could be used for the identification of different micro-climates within Doha. This micro-climates identification is very important to town planners, The results could also be used for air quality, solar energy and land-use planning studies.

This study made some recommendations on how to reduce the UHI and increase in temperature phenomena by introducing Green Building technologies and green positive road network, and the interlocution of more green spaces in the cities.