Urban form dynamics in three sahelian cities: consequences on climate change vulnerability and sustainable measures

Climate change is induced by urban form as well as by global and regional changes. Scattered housing and sparse nuclei increase the impact of very heavy rains, high temperatures and drought. This article has three aims: (i) ascertain the recent changes of urban form in three cities of the Sahel; (ii) understand the consequences of scattered housing and sparse nuclei on the vulnerability to climate change; (iii) identify the measures to contrast the discontinuity of the urban form. The cases of Kébémer (estimated 27,200 inhabitants/2013) and Louga (est. 96,000 inhabitants/2013) in Senegal and Niamey (1 million inhabitants/2012) in Niger are analysed. The changes of urban form are observed by comparing two high spatial resolution satellite images taken in correspondence of the 2002 and 2012/13 censuses of the population. The nature of change is ascertained by overlapping the built-up area with the mosaic of the subdivision plans and infrastructural networks. Vulnerability is analysed in its three components: exposure, sensitivity, coping capacity. All three cities lose compactness in the densest part due to the persistence of vacant land. In Niamey, scattered development in the suburban wards is the visible result of an incessant production of formal subdivision plans that are much higher than the need for the entire next decade. Improving local taxation could reduce the over-supply of building plots as the second source of council income. The taxation/requisition of vacant lands and the increase of planning fees could increase compactness of the urban form.