Effects of land use changes on climate in the Greater Horn of Africa

The relationships between historical land use transformations and spatio-temporal patterns of precipitation and temperature over the Greater Horn of Africa (GHA) were examined based on Landsat satellite observations for the years 1986, 1995, and 2000 and regional climate model simulations in the period 1991-2000. The satellite-derived land use/cover classification shows increased conversion of large portions of forests over the GHA to agriculture, particularly in Kenya, with land (acreage) under crops increasing from 6.55% in 1986 to almost 18% by the year 2000. Sensitivity experiments performed with regional climate model, Version 4 (RegCM4), indicate that expanding agriculture into forested areas led to a modest reduction in monthly rainfall totals and also may be contributing to notable shifts in moisture convergence zones and centers of rainfall maxima. Student's t-test at a 0.1 significant level showed a decrease in precipitation and an increase in surface temperature around the lake region when surface vegetation cover is converted to agricultural land cover type. Conversely, under the assumption that large sections of croplands are converted to forest, the simulations resulted in a modest increase in precipitation and a reduction of surface temperature around the lake region, changes that are significant at the 0.1 confidence level. A substantial trade-off in the components of the surface energy balance between sensible heat flux (SHF) and latent heat flux (LHF) was observed for the different conversion types. Under the assumption of reforestation, both SHF and LHF increased. The increase in SHF was almost twice that of LHF. On the other hand, when land cover types were converted to agricultural types, SHF decreased, while LHF did not show any significant change.