Takayuki Kawai

Spatial distribution and temporal trends of rainfall and erosivity in the Eastern Africa region

Soil erosion by water is one of the main environmental concerns in the drought-prone Eastern Africa region. Understanding factors such as rainfall and erosivity is therefore of utmost importance for soil erosion risk assessment and soil and water conservation planning. In this study, we evaluated the spatial distribution and temporal trends of rainfall and erosivity for the Eastern Africa region during the period 1981–2016. The Precipitation Concentration Index (PCI), Seasonality Index (SI) and Modified Fournier Index (MFI) have been analysed using 5×5 km resolution multi-source rainfall product (Climate Hazards Group InfraRed Precipitation with Stations, CHIRPS). The mean annual rainfall of the region was 810 mm ranging from less than 300 mm in the lowland areas to over 1200 mm in the highlands being influenced by orography of the Eastern Africa region. The PCI and SI revealed a spatial pattern of rainfall seasonality dependent on latitude, with a more pronounced seasonality as we go far from the equator. The MFI showed high spatial variability with about 55% of the region subject to high to very high rainfall erosivity. The mean annual R-factor in the study region was calculated at 3246 ±1895 MJ mm ha-1 h-1 yr-1, implying a potentially high water erosion risk in the region. Moreover, increasing and decreasing trends of annual rainfall and erosivity were observed, but with substantial spatial variability for both. This study offers useful information for better soil erosion prediction as well as can support policy development to achieve sustainable regional environmental planning and management of soil and water resources.

Diurnal fluctuation of groundwater levels caused by the invasive alien mesquite plant.

Invasive alien plants such as mesquite (Prosopis juliflora) alter patterns of groundwater uptake. We measured the groundwater level beneath a mesquite stand in an arid area in Sudan. The changes in groundwater level closely followed plant water uptake. The groundwater level started to decline a few hours before sunrise, recovered around noon, and then continued to decline until a few hours after sunset, before recovering again during the night. Thus, groundwater level showed two peaks: just before sunrise and around midday. The midday recovery was due to the depression of photosynthesis by heat and light.