Amadou Tahirou Diaw

Rainfall Variability in Sine Saloum River Basin in a Context of Climate Change and Variability

Drought is one of the most worrying manifestations of variability and change of climate in many West African countries. Due to its threats on human life, socio-economic activities, agricultural productivities, shortage of water, natural resources and environments, the problems related to drought have caught the attention of scientists, researchers and policy makers in recent decades. Original Research Article Doumouya et al.; AIR, 6(6): 1-12, 2016; Article no.AIR.25349 2 The aim of this paper is to characterize and analyze climatic events and their impact on water resources, environmental ecosystems and population. For this, we have selected rainfall time series of Sine Saloum river basin at Foundioune’s rain gauge. We have first conducted an exploratory analysis based on the graphic study. So, histograms relating to annual rainfall, monthly rainfall decadal, interannual monthly rainfall and interannual monthly averages, were analyzed separately compared to the corresponding average; this has highlighted the spatial and temporal distribution of intra and inter annual rainfall compared to the average and allowing viewing wet and dry years and months. We have secondly calculated the drought indices such as standardized precipitation index and normal precipitation index to evaluate climate fluctuations, characterize the progression of drought and its degree of intensity. This has also highlighted the deficit years and surplus years. In total, over the 43 years of the study period, we have counted 13 wet years and 20 dry years. We have also noted that 1971 was the wettest year and 2007 the least wet year. Characterization of these 30 deficit years has highlighted 3 categories of drought: mild drought, moderate drought and great drought. It appears from this study that the impacts of drought can be attributed in part to a deficit or erratic rainfall. Analysis of the results has showed the high vulnerability of the watershed to drought. Examination of drought years revealed a higher frequency in space and in the time of light drought. These results are very useful for drought monitoring, evaluation and mitigation.

Modélisation spatiale de la mobilité dans la région de Dakar (Sénégal)

La population urbaine connait une croissance acceleree en Afrique, avec une augmentation encore plus importante du nombre de deplacements journaliers. D’une bonne connaissance de la mobilite dependra la planification et la mise en oeuvre d’infrastructures urbaines et de systemes de transport durables. Traditionnellement, les etudes sur la mobilite reposent sur l’exploitation de bases de donnees et de modeles complexes sur la demande et l’offre de transport. Cet article presente une methode qui permet d’obtenir a peu de frais et de maniere semi automatisee des estimations spatialisees de l’intensite de deplacements et des zones de mobilite autour de poles d’activites. A partir d’une carte de l’occupation du sol associee a des fonctions urbaines et a une estimation du nombre de deplacements journaliers, nous obtenons une representation spatiale de l’attractivite des lieux et du volume de mobilite par unite de surface. Puis, par analogie entre cette representation et un modele numerique de terrain, nous localisons les poles d’activites et delimitons les bassins de population qu’ils drainent (zones de mobilite) en faisant appel a differentes fonctions hydrologiques de ArcGIS. Nous analysons les resultats obtenus pour la ville de Dakar et leur pertinence pour une meilleur. In Africa the rapid increase of urban population is followed by an even more rapid increase in daily mobility. Better knowledge of mobility is critical to sustainable planning and implementation of urban infrastructures and transport systems. Typically, mobility studies rely on extensive and complex databases and models of transport supply and demand. This paper presents a method to produce, at low cost and in a semi-automated way, spatial estimates of mobility densities and zones around activities poles. We start from a land use map to which we associate urban functions and estimates of related daily mobility, to obtain a spatial representation of the attractivity of places and of mobility rates per unit surface. Then, by analogy of this representation with a digital terrain model, we locate poles of activities and delineate the population basins that they drain (mobility zones) by using various ArcGIS hydrological tools. We analyse the results obtained for Dakar and their relevance for urban planning in a data-poor environment.