Abstract
During periods of global warming (GW), expected increases in urban temperatures can have adverse impacts on city climate and thermal discomfort due to combined urban and global warming effects. The different climates in four cities in Israel are studied for the purpose of differentiating global vs. urban warming. Trends in urban and nearby rural areas were compared in order to estimate the urbanization effect on the local climate zones. Daily 06:00 and 15:00 Local Time (LT) temperatures for July 1980-2014 were investigated. The linear relationship between the urban warming and population growth observed in present climate data is assumed to continue into the near future. The Regional Climate Model (RegCM) temperature trends into the 21st century are assumed to represent primarily the GW because of the relatively coarse grid interval of 25 km. Hence, this study first differentiates between global and local warming past trends, and then uses this past result to make future projections that consider both factors. A unique feature of this study is the large climatic variety over Israel—a small country that encompasses no less than 5 different K?ppen climatic zones. The urban minus rural temperature (1980-2014) changes, ΔTu-r, show more intense warming in the afternoon in all 4 cities. For instance, in Jerusalem and Eilat, the ΔTu-r has increased by ~1.2°C. Following the RegCM predictions, by 2060 with “No population growth”, this temperature increase is expected to continue, by 1.114°C and 1.119°C, respectively. If, however, these cities grow rapidly, air temperature will increase by 2.937°C - 4.129°C and 2.778°C - 3.939°C, respectively.
Highlights
Cities, towns and settlements contain more than 50% of the Earth’s population [1]
Future urban air temperatures are expected to increase as a result of land use modifications, changes in the characteristics of urban structures as well as urban sprawl [4] [5]
Fujibe [11] has claimed that global and regional warming can aggravate urban warming during summer months, and increase the frequency and duration of air temperature extremes in urban areas, events that are more pronounced in arid regions [47]
Summary
Towns and settlements contain more than 50% of the Earth’s population [1]. From an environmental standpoint, cities are viewed as an efficient way to concentrate intensive human impacts on the one hand; while on the other, they embody a plethora of negative environmental impacts that cross scale and municipal boundaries [2]. Given the main urbanization characteristics such as land use change, street geometry and albedo effects, the urban climate (as compared to rural area nearby) is often characterized by amplified air temperature, lower humidity and moderated wind velocities [5] [7]. Urban populations are exposed to both urban climate modifications on a local scale, and to the effect of regional and global climate changes on a larger scale. This combination of local and global warming tends to be exacerbated during summer months [11]. Because our method compensates for some of these limitations, the air temperature changes
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