An investigation of the effects of urbanization on the climate of Maseru, Lesotho

Abstract

The influence of urbanization on the local climate has been identified in various parts of the world by a careful study of trends in meteorological parameters over a period of time. Although these effects may not be immediately discernible, it is necessary to start investigating what is happening in our cities. The study examines the long-term urban modification of mean annual conditions of surface temperature and rainfall in the city of Maseru, Lesotho. This is realized through studying trends in the minimum and maximum temperatures, rainfall and number of rain days time series. Data from one urban station (Mejametalana) and three rural stations (Mafeteng, Moshoeshoe I and Teyateyaneng) was used. The data comprised minimum and maximum temperatures for the period 1970-2005 and daily rainfall figures for the period 1922-2005. The data were tested for homogeneity . using the Short-Cut Bartlett Test, A Variant of the Standard Normal Homogeneity Test and the Cumulative Mass Curve. Major parts of the rainfall and temperature time series at both the urban and rural stations were found to be homogeneous. Some inhomogeneities were observed in the rainfall series between the late 1920s and early 1930s at both stations, and late 1940s to 1960s at the rural station. The sequential version of the Mann-Kendall test was used to investigate any abrupt changes in the temperature, rainfall and rainy days time series for the urban and rural stations. Regression analysis was used to delineate the magnitude of trends in the temperature, rainfall and rainy days time series for the two stations. This was useful in comparing the trends between the rural stations and the urban station In order to investigate the urban induced trend. Results showed that abrupt climatic change in temperatures towards warming occurred at the urban station than at the rural station. This was observed to be larger in the minimum temperature series and this began in the early 1990s. No significant changes in rainfall for the period 1922-2005 were found, except for short time periods within the series; decreasing trends in rainfall observed during the period between the mid 1920s and the late 1930s at both the urban and the rural stations. Similarly, no significant changes in the number of rainy days were observed during the period 1922-2005. The established significant warming trends in minimum temperature, pose serious challenges on climate and urban planning of city. In particular the effect of increased minimum temperature on human physiological comfort, building and urban design, wind circulation and air pollution. Therefore the findings must be incorporated in the future planning of the city.