Spatio-temporal Variability of Climatic Parameters in the Logone River Basin (Africa)

The Logone river basin spans across three African countries (western Central African Republic, northern Cameroon, and southern Chad) over an area of 78,000 km². The Waza-Logone floodplain covers approximately 8,000 km² downstream of Lake Maga in northern Cameroon. This floodplain is very important ecologically due to its high biodiversity, and economically as its highly productive; providing breeding grounds for fish, dry season pastures that support cattle and, fertile land for agriculture and forest. The basin has two types of climates according to Köppen’s climatic zones; viz. Tropical wet and dry or savanna (Aw; A and w indicate tropical moist and savannah climate, respectively) and semi-arid hot (BSh; B, S and h represent Arid, Steppe and Hot climate, respectively). The purpose of this study was to understand the spatial and temporal climatic variations in the basin using long-term historical data. Grid-based climatic data- temperature and PET during 1921-2013, and rainfall, number of rainy days, during 1901-2013 were obtained from the Climate Research Unit (CRU), a collaborative program by WMO and NOAA. The temporal variations of climatic parameters were analysed using non-parametric Mann-Kendall test at 10% significant level. The magnitudes of trend slopes were estimated by Theil and Sen’s slope estimator test. The spatio-temporal changes in these parameters were analysed within the Aw and BSh zones. Overall, decreasing trends were observed in the annual rainfall and number of rainy days in most of the grids of the basin, regardless of the climatic zone. In general, most grids in both climatic zones showed negative changes ranging from ­‑0.1 to -12.4% for annual rainfall, and -0.8 to -6.0% for number of rainy days during 1901-2013. Temperature trend analysis during 1921-2013 suggests some warming in northern grids, while south-western grids show either lesser warming or cooling in some cases. The magnitude of change in BSh zone ranged from +0.3 to +0.8°C for maximum temperatures and from +0.3 to +0.7°C for minimum temperatures. The average annual PET changed by about +2.3mm in Aw and by about +10.3 mm in the BSh zone. An understanding of the spatio-temporal changes in rainfall and temperatures is a basic and important requirement for the planning and management of water resources. The findings of this study will complement the MORSL (Modeling Regime Shifts in the Logone floodplain), a cross-disciplinary international research project, funded by the NSF Dynamics of Coupled Natural and Human Systems (CNH) program. Extending recent trends forward, it also provides a current and near-future context for understanding the impact of climate change on water resources of the basin.