The simulated impact of deforestation on the changes in the East African climate: a GCM study

Abstract

This study investigates the possible impact of deforestation on the climate of Eastern Africa. The study area is located between approximately longitudes 25 °E to 50 °E and latitudes 20 "N to 10 "S. The data used in the study comprised monthly rainfall data for the period 1931 - 2000 obtained from the Kenya Meteorological Department, Nairobi, Kenya and deforestation scenarios developed by the Integrated Model to Assess the Global Environment (IMAGE) of the National Institute of Public Health and the Environment, the Netherlands. Climate variability over the study region was analyzed using the rainfall data. The quality and homogeneity of the data was assessed to detect any errors and inconsistencies. Mass curve analyses were used to test for the homogeneity of the data and the data sets that satisfied the quality criteria used in the subsequent analyses. Time series analysis was used to examine the possibility of climate change over the study region through the trend . and cyclic variations of the seasonal and annual rainfall. Binomial coefficient method was used to smooth the series and the student t-statistic used to evaluate the statistical significance of the trends. In order to examine the impact of deforestation on the climate over the East African region, the ECHAM5 climate model developed at the Max Planck Institute of Meteorology, Hamburg, was used. The suitability of the climate model for use over the region was evaluated by examining how well it simulates the regional climatology. Using scenarios developed by the IMAGE model, two 1O.5-year experiments were run and the results analyzed differentially; the initial six months for each experiment were regarded as spin up time and neglected. The first experiment, which constitutes the reference experiment, used 1995 deforestation scenarios while the second, referred to as the future simulation, was run using the future (2050) scenarios as obtained from IMAGE. The boundary conditions were the same for both the experiments. Significant trends were observed over most of the regions over East Africa. The major cycles revealed from spectral analysis were 2 - 2.5 years, 3.6 - 4.4 years, 5 years and 10 - 12 years. These results from temporal and spectral analysis suggest a climatic variation and quasi-periodic variability within the data over the region. The results from the III reference experiment of the ECHAM5 climate model showed a fairly good comparison between the observed and simulated rainfall climatology. The results from IMAGE vegetation scenarios indicated an increase in the net solar radiation over the western parts of the study region as a result of the decrease in vegetation, and hence exposure of the surface to the incoming radiation. Projected evapotranspiration decreased over most of the western and northern parts of East Africa due to the decreased amount of leaf area index. Rainfall and cloud cover increased for the future case over the western parts of the study area which was attributed to increased moisture convergence into those regions. However, the study projected a decline in rainfall and cloud cover to the east, which was associated with the decrease in moisture convergence. The increase in rainfall over the western parts of the study region led to increased runoff over these regions, whereas the converse was evident towards the eastern parts where declines in rainfall and cloud cover were evident. The results from this study show that deforestation will have a considerable effect on the climatic regime of the study region. Since nearly every sector of the economies of the nations over the study region is affected by weather/climate in one way or the other, including the water, energy, transport and agriculture sectors, climate alterations will disrupt the smooth running of the various socio-economic activities in these sectors. The negative impacts are most likely to affect the agricultural production on which the economies of the countries in Eastern Africa rely. This study provides relevant information that may be useful in the planning and management of sectoral activities to mitigate against the adverse effects resulting from climate alterations due to deforestation over Eastern Africa.