The Relationship between Atmospheric Aerosols and Rainfall over the Three Cities in Kenya

Abstract

This study investigates the characteristics of absorbing and non-absorbing aerosols over Nairobi, Kenya and how they relate to the rainfall over the three cities in the Republic of Kenya. The data set used in the study was a daily Aerosol Index (A.I.) for Nairobi city, Kenya obtained from satellite based Total Ozone Mapping Spectrometer (TOMS) observations. Therefore, one aerosol index station was used over Kenya to represent the entire country. Rainfall data ranging from 1979-2005 for three stations which included Dagoretti Corner in Nairobi, Kisumu and Mombasa were used. Monthly averaged rainfall data and aerosol indices from each station were correlated from 1979-2003. The time series analysis showed to a greater extend that there was seasonal variations with the peak of absorbing aerosols corresponding to dry months while that of non-absorbing aerosols mainly occurring during the wet months of the year. This can be linked to the averaged seasonal wind patterns and the prevailing air masses. The correlated results between aerosol indices showed a significant relationship in most of the months except for Mombasa in the month of April where the relationship between absorbing and rainfall was insignificant. In the same station the relationship between non-absorbing and rainfall was weak. During the month of April the winds blowing into our country are south easterlies and hence a station west of Nairobi, for example Kisumu, would show a significant relationship. While this does not demonstrate that one is a cause of the other and vice versa, the relationship suggest a contributing factor hence it may be useful in enhancing predictability of rainfall over the areas of study to compliment the already existing tools of weather forecasting.