Influence of Urbanisation on Minimum and Maximum Temperature characteristics over Nairobi City

Abstract

Urban Heat Island being the most investigated aspect of urban climate is not prominently investigated in tropical African urban areas. This paper seeks to address the influence of urbanization on outdoor temperature characteristics in the city of Nairobi. Monthly minimum and maximum temperature data from four ground-based weather stations namely, Dagoretti Corner (DC), Wilson Airport (WA), Jomo Kenyatta International Airport (JKIA) and Moi Air Base (MAB) stations over a 47-year period from 1961 to 2007 were used. The data were subjected to time series analysis. Station to station correlation analysis was performed as an indicator of the linear association of station records and also to understand spatial variability. Spatial analysis of temperature across the city pointed out that the most representative station in studying the urban canopy characteristics of the city of Nairobi is MAB. The minimum temperature across the city shows a significant positive trend. This may be attributed to urbanization effect. Among all the four stations, only DC exhibited a significant positive trend of maximum temperature. Trend analysis revealed that there was significant minimum temperature increase of 0.430C with a significant maximum temperature increase of 0.110C per decade during the 47-year period. This is a strong evidence of temperature modification due to urbanization. Comparative analysis of temperatures across the city of Nairobi depict heterogeneity among the four weather stations, with MAB being the hottest while DC is the coldest. Therefore, the microclimate of Nairobi is not homogeneous and implications of urbanization on planning of climate sensitive structures and services should be area specific. Further analysis to establish Urban Heat Island (UHI) characteristics of the city in future is recommended especially with availability of more weather stations around the city of Nairobi and adjacent rural areas.