• Energy Research

Abstract The study investigates how the rising global temperature will affect the spatial pattern of rainfall and consequently drought in West Africa. The precipitation and potential evapotranspiration variables that are obtained from the Rossby Centre regional atmospheric model (RCA4) and driven by ten (10) global climate models under the RCP8.5 scenario were used. The model data were obtained from the Coordinated Regional Climate Downscaling Experiment (CORDEX) and analyzed at four specific global warming levels (GWLs) (i.e., 1.5 °C, 2.0 °C, 2.5 °C, and 3.0 °C) above the pre-industrial level. This study utilized four (4) indices: the standardized precipitation index, the precipitation concentration index, the precipitation concentration degree, and the precipitation concentration period over West Africa to explore the spatiotemporal variations in the characteristics of precipitation concentrations. Additionally, studying the impact of the four GWLs on consecutive dry days, consecutive wet days, and frequency of the intense rainfall events led to a better understanding of the spatiotemporal pattern of extreme precipitation. The results show that, at each GWL studied, the onset of rainfall comes 1 month earlier in the Gulf of Guinea compared to the historical period (1971–2000) with increasing rainfall intensity in the whole study domain, and the northeastern part of the study area becomes wetter. The rainfall concentration is uniformly distributed over the Gulf of Guinea and the Savanna zone for both the historical period and RCP8.5 scenario, while the Sahel zone which has shown an irregular concentration of rainfall for the historical period shows a uniform concentration of rainfall under all four GWLs.

Gravity waves generated by the Vestfjella Mountains (in western Droning Maud Land, Antarctica, southwest of the Finnish/Swedish Aboa/Wasa station) have been observed with the Moveable atmospheric radar for Antarctica (MARA) during the SWEDish Antarctic Research Programme (SWEDARP) in December 2007/ January 2008. These radar observations are compared with a 2-month Weather Research Forecast (WRF) model experiment operated at 2 km horizontal resolution. A control simulation without orography is also operated in order to separate unambiguously the contribution of the mountain waves on the simulated atmospheric flow. This contribution is then quantified with a kinetic energy budget analysis computed in the two simulations. The results of this study confirm that mountain waves reaching lower-stratospheric heights break through convective overturning and generate inertia gravity waves with a smaller vertical wavelength, in association with a brief depletion of kinetic energy through frictional dissipation and negative vertical advection. The kinetic energy budget also shows that gravity waves have a strong influence on the other terms of the budget, i.e. horizontal advection and horizontal work of pressure forces, so evaluating the influence of gravity waves on the mean-flow with the vertical advection term alone is not sufficient, at least in this case. We finally obtain that gravity waves generated by the Vestfjella Mountains reaching lower stratospheric heights generally deplete (create) kinetic energy in the lower troposphere (upper troposphere-lower stratosphere), in contradiction with the usual decelerating effect attributed to gravity waves on the zonal circulation in the upper troposphere-lower stratosphere.Keywords: gravity wave; radar observation; numerical modelling; kinetic energy; budgetCitation: Tellus A 2012, 64, 17261, DOI: 10.3402/tellusa.v64i0.17261

Abstract The relationship between climate and land use land cover change over West Africa has often been assessed with climate simulations, although the model-based approach suffers from the limitations of climate models specifically for West Africa. In this paper, an alternative approach based on physical analysis of historical land cover data and standardized climatic indices is used to investigate climate-land interactions to establish the climatic thresholds and their corresponding land use impacts. Annualized land change intensities and the climatic indices are first estimated separately and then linked at various spatiotemporal scales. The result shows that climate-induced land cover change results from abrupt changes in climatic conditions. A regional change of (-1.0–1.0)\(℃\), (0–1.5)\(℃\),(-0.5–0.5)\(℃\), and up to \(\pm\)50 mm changes in precipitation and climatic water balance leads to (45039–52133) km2, (20935–22127) km2 and approximately 32000 km2 changes respectively, while a \(\pm\)0.5\(℃\) and \(\pm\)20 mm change represents normal climate conditions with changes below 20000 km2. Conversely, the plausible pathways through which West African land surface impacts the climate is the conversion of cropland, forest, grassland, and shrubland. The average climatic risk ranges from − 0.025 to 0.025 yr−1 while the probability of occurrence ranged variably from 0 to 0.833. The results offer the basis to re-evaluate land and climatic information necessary for improving the reliability of climate models over West Africa. For sustainable development, this work reveals the need for policy-driven interventions for efficient resource management and the prevention of degradation and deforestation in the region.