Flood risk assessment at municipal level in the Tillabéri region, Niger

The Tillabéri region (population 2.7 million, 97,250 km2) is the hinterland of the Niger’s capital city and the second most susceptible region to flooding of the country, with 416 settlements hit from 2008 to 2013. This chapter aims to present the potential benefits of flood risk assessment at municipal scale: a tool that can help local authorities in disaster risk reduction. Risk (R) is considered here a function of Hazard (H), Exposure (E) and Damages (D) according the equation R = H * E * D. Risk is measured using six indicators. The probability in each year to have e rain causing settlement flooding is measured for each municipality using daily rainfall from meteorological stations (1981-2010) and three-hourly Tropical Rainfall Measuring Mission (TRMM) datasets by NOAA (1998-2011). Settlements flooded (E), people affected, homes destroyed, fields flooded and livestock killed (D) are sourced from Niger’s early warning system and disaster prevention unit (EWS DP), all errors corrected and units of measurement standardised. From the results, it emerged that 765 settlements have been flooded between 1998 and 2013. Contrary to what one might expect, the floods caused by the swelling of the River Niger hit few settlements. Most of the areas susceptible to flooding are located in the vast Bosso and Maouri dallols, two fossil rivers that run from Mali towards Niger for over 300 km. The right-bank tributaries of the Niger and along the minor hydrographic network are the next most affected areas. 95 settlements were hit more than once and 19 flooded in two or more consecutive years. Seven municipalities out of 41 are at very high or high risk of being flooded. These are crossed by the River Niger or by its main tributaries on the right bank, by the Ouallam intermittent creek or the Bosso dallol. Seven municipalities show damage in three areas (people, dwellings, fields).