An Evaluation of the effects of land use changes on the urban climate of the Colombo metropolitan region

Abstract

The first ever systematic study of city-induced climate change was carried out Howard in London in 1833 (Landsberg, 1981). Since then studies on urban climate modifications has progressed from mere descriptive studies (up to about the 1930s) to complex spatial and temporal variability and linkage of climate effects to weather and urban structure (up to 1965) (cf. Oke, 1991). More recently, the emphasis has shifted to seek the physical basis of urban climate modifications and to construct models to simulate them with a view to devising strategies to mitigate the negative impact of urban climate modifications. The modifications to a city’s climate in contrast to its rural surroundings, known as the Urban Heat Island (UHI) phenomenon, is sparsely studied in the tropical areas. Early work in these areas occurred only in the late 1960s (Nieuwolt, 1966, for example). Nevertheless, considerable progress in developing the knowledge base on tropical UHIs and their causes has occurred within a short span of approximately 40 years. However, the study of the UHI phenomenon in Sri Lanka lags far behind that of other countries. Lack of easily accessible climate data could be one of the reason for the low research output in this field. The first ever comprehensive historical survey of the UHI phenomenon in the Colombo Metropolitan Region (CMR) was completed only in 1999 (Emmanuel, 1999). Thus, a lot of ground work needs to be covered before UHI studies on Sri Lankan cities become comparable in scientific depth and maturity to that of other cities. Such an advanced knowledge is essential, particularly for the CMR, for two reasons. On the one hand, an unprecedented acceleration of urbanization is currently underway in Sri Lanka. From a steady rate of approximately 22% urbanization in the decades leading up to the 1980s, Sri Lanka has now entered a rapid phase of urbanization whereby the year 2010 urban levels are expected to top the 50% mark (<f. CMRSP, 1998). Most of this rapid urbanization is centered around the CMR. The second reason is that the environmental changes and associated quality of life issues that arise from the changing urban climate has hitherto received little or no attention from the Sri Lankan urban policy makers and designers. A sound understanding of the phenomenon and the associated causes is necessary before policy initiatives could be formulated to arrest die negative impact of die UHI phenomenon in Sri Lanka.