Gero Steup

Use and constraints on the use of inland valley ecosystems in central Benin: Results from an inland valley survey

This paper assesses the current use and constraints on the use of inland valleys in central Benin are assessed to analyse their agro-potential. The methodology applied in this study is comprised of a survey of local authorities and inland valley users conducted with standardised questionnaires and the mapping of inland valley surfaces with GPS. The questionnaire contains questions to socio-economic aspects such as access to an inland valley, land tenure, current use, use constraints as well as questions to physical properties such as soil quality. In addition to the assessment of the inland valley surface area, this approach enabled a detailed socio-economic and rough physical characterization of all detected inland valleys. In total, 817 inland valleys were surveyed in this study. The local population currently uses sixty-seven percent of the valleys, primarily for crop cultivation. In most cases, only a small part of each surveyed inland valley is used. The intensity of exploitation varies across communes and across seasons. Especially in the more densely populated communes of Djougou and Parakou, where the upland soils are often degraded and arable land has become scarce in recent years, the use of inland valleys is greater than in less populated communes. This exploitation occurs primarily during the rainy season, and only a few farmers cultivate crops during the dry season. This study revealed high unused agro-potential in the inland valleys of central Benin. The main reason why inland valleys in the study area currently remain unexploited is a lack of experience in cultivating wetland. In fact, for more than 60% of the unused inland valleys, the local farmers claim to have no knowledge of which crops are adapted to seasonally waterlogged and swampy land or how to cultivate such crops. Due to climate change and population growth, the agricultural use of inland valleys in this region could become more important in the future. To ensure effective use, farmers should be supported by the regional agricultural organisation CeRPA (Centres Régionaux pour la Promotion Agricol) or development organisations to improve the knowledge of cultivation methods and inland valley management.

Modeling the effect of land use and climate change on water resources and soil erosion in a tropical West African catch-ment (Dano, Burkina Faso) using SHETRAN

This study investigates the effect of land use and land cover (LULC) and climate change on catchment hydrology and soil erosion in the Dano catchment in south-western Burkina Faso based on hydrological and soil erosion modeling. The past LULC change is studied using land use maps of the years 1990, 2000, 2007 and 2013. Based on these maps future LULC scenarios were developed for the years 2019, 2025 and 2030. The observed past and modeled future LULC are used to feed SHETRAN, a hydrological and soil erosion model. Observed and modeled climate data cover the period 1990-2030. The isolated influence of LULC change assuming a constant climate is simulated by applying the seven LULC maps under observed climate data of the period 1990-2015. The isolated effect of climate scenarios (RCP4.5 and 8.5 of CCLM4-8) is studied by applying the LULC map of 1990 to the period 1990-2032. Additionally, we combined past modeled climate data and past observed LULC maps. Two chronological and continuous simulations were used to estimate the impact of LULC in the past and in the future by gradually applying the LULC maps. These simulations consider the combined impact of LULC and climate change. The simulations that assumed a constant climate and a changing LULC show increasing water yield (3.6%-46.5%) and mainly increasing specific sediment yield (-3.3%-52.6%). The simulations that assume constant LULC and climate as changing factor indicate increases in water yield of 24.5% to 46.7% and in sediment yield of 31.1% to 54.7% between the periods 1990-2005 and 2006-2032. The continuous simulations signal a clear increase in water yield (20.3%-73.4%) and specific sediment yield (24.7% to 90.1%). Actual evapotranspiration is estimated to change by between -7.3% (only LUCC) to +3.3% (only climate change). When comparing observed LULC and climate change alone, climate change has a larger impact on discharge and sediment yield, but LULC amplifies climate change impacts strongly. However, future LULC (2019-2030) will have a stronger impact as currently observed.