Evolution of urban heat island in Khartoum

摘要

A comparison is made between mean maximum and minimum temperatures, Tx and Tn, respectively, taken at Khartoum International Airport (urban) and Shambat Agrometeorological Station (rural) in the capital of Sudan. The objective was mainly to examine the influence of urbanization on the monthly, seasonal and annual temperature observations for the time period 1941-2005. Strong evidence exists for a decrease in the diurnal temperature range (DTR) in all seasons on the urban site due to different combinations of trends in Tn and Tx. A reverse tendency is notable on the rural site. The effect in Khartoum appears to be greatest in the hot season and least in the wet season, and is because of more warmth in Tn than in Tx. Significant increasing rates of Tn are apparent at both stations in the series of the hot and wet seasons as well as for the year, but the urban site (Khartoum) is warming at a faster rate than the rural one, except in the wet season because of excess rainfall in the urban site. Higher intra-annual variability in temperature is pronounced for Shambat than for Khartoum, while mixed results are obtained with regard to inter-annual variability. The night-time temperature (Tn) experiences stronger urban effect than the daytime temperature (Tx). An urban heat island intensity (UHII) of up to 6.4 °C occurred at night in May (hot season) compared to a maximum UHII of 4.1 °C during the daytime in November (dry season). Significant trends of urban warming are conspicuous in Tn during the dry and hot seasons. On the other hand, significant trends towards urban cooling are observed in Tx in all the seasons. The results of the present study suggest that the estimated UHII in the temperature series for Khartoum must be removed before an assessment of climatic change is made.