Analysis of the correlation between Land Use Land Cover Changes and Urban Heat Island Effect using Geospatial Techniques; Case Study Kiambaa Sub-County, Kiambu County

Abstract

Most studies on the Urban Heat Island (UHI) phenomenon in Nairobi have proved its presence, however, little is documented about its effect in the urban fringe, areas often characterised by rapid urbanization. Amongst them is Kiambaa sub-county, Kiambu County, which has recorded a significant land use change over the last 25 years. In this light, this study was aimed at analysing the correlation between Urban Heat Island (UHI) effect and Land Use Land Cover (LULC) changes in the sub-county from 1995 to 2018 by use of Landsat imagery. It was achieved by converting the Landsat images to their spectral radiance and calculating the at-satellite temperature as well as the land surface emissivity thereafter. The Land Surface Temperatures (LST), rate of LULC change and Normalised Difference Vegetation Index (NDVI) were then estimated and the correlation between the LULC changes and UHI effect analysed. The study area was classified into three classes namely; agricultural land, built-up area and water bodies. The results indicated reduction of the proportion of vegetation cover and shrinking water bodies from 1995 and 2018 as well as an increase in the built-up area over the said time period. The highest (42.81°C) and lowest (19.57°C) LST was estimated in year 2000 and 1995 respectively. The study revealed that these temperatures had increased over time and that the change was inversely proportional to the loss of vegetation cover. Furthermore, the UHI effect increased from 12.62°C to 21.02°C from 1995 to 2000 and later reduced to 19.46°C and 16.38°C in 2015 and 2018 respectively. The correlation analysis between the variables indicated two different scenarios that occurred between 1995 to 2000 and 2000 to 2018. The first scenario indicated a negative correlation of -1 between the LULC changes (agricultural land and built-up areas) and UHI in the time period 1995 to 2000. In the second time period, the results revealed a positive correlation of 0.946 between the UHI and agricultural land and a negative correlation of -0.947 between UHI and built-up area. It can then be concluded that the rapid urbanization being experienced in Kiambaa sub-county as well as other areas of the larger Nairobi urban fringe has resulted into increase of the surface temperatures and resultant reduction of the UHI effect. It is therefore recommended that proper urban planning policies be formulated and implemented to counter the rapid urban sprawl as well as reduce the LST. This study can be extended to include other areas in the Nairobi urban fringe such as Ruai and Ongata Rongai which are also experiencing a high rate of urbanization and the methodology can also be used in UHI studies in other urban areas in the country.