The majority of West Africa’s rural population are smallholder farmers. They are practicing rainfed agriculture on small farms (less than 1 ha). During the dry season (seven to eight months per year) the farmers are mostly jobless. In Dano, in South-Western Burkina Faso, nearly 60% of people live on less than 0.5 Euro per day (average per capita). Farmers are already experiencing the impact of climate variabilities, which are expected to increase in the future. Due to the limited capacity of the government only a few adaptation measures are in place. One adaptation strategy promoted by governmental and non-governmental organizations consists in shifting agricultural cultivation from the uplands to inland valleys to benefit from better water and soil conditions. However, many such projects have failed because the basic hydrological information needed for effective management is lacking.
Understanding and modeling hydological processes
My research aimed at supporting the management of these landscapes by improving the understanding of hydrological processes. Using a process-based model and investigating the impact of climate change and land use/land cover change on water resources, an intensive instrumentation was carried out.
Technical implementation in four sub-catchments
In four data-sparse sub-catchments (Bankandi-Loffing, Mebar, Moutori, and Fafo), the instrumentation included five rain recorders, seven stream gauges, 64 piezometers in shallow groundwater, and 64 soil moisture point measurements at three different depths, and three deep wells. From 2014 to 2016, meteorological data were recorded at five to ten minute intervals, and piezometer and soil moisture were automatically recorded at 30 minute to six hour and manually recorded at weekly time steps. A hydrological model (Water flow and balance Simulation Model, WaSiM) was applied. The Land Change Modeler was utilized to predict future land use/land cover change, and the Africa dataset of Coordinated Regional Climate Downscaling Experiment (CORDEX) was used to assess the impact of climate change.
Water reservoirs: Simple steps could have huge impact
The results show a runoff coefficient (share of runoff in relation to rainfall) of 14% and suggest that four million m3 per year flow out of Bankandi-Loffing alone. This is ten times the average reservoir size in the area. A runoff harvest equivalent of one or two reservoirs could help farmers cope with water scarcity in the dry season without impeding the needs of ecosystems and the people living downstream. 65% of annual rainfall is lost by evaporation and does not contribute to biomass production. The annual groundwater flow to the stream (approximately two million m3 per year on average) suggests that groundwater could be used for supplementary irrigation.
Preparing for a future with more climate change effects
The gradual conversion of savanna into croplands, which leads to an increase in surface runoff and subsequent soil erosion and soil fertility losses, has to be considered in land use planning and soil conservation strategies. Rainfall intensity is expected to increase in the future, which creates the need for flood preparations in the area that could be combined with water storage reservoirs. With the proper management of water resources, the potential for agroforestry or afforestation for increasing biomass production is huge.
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Source: Center for Development Research (ZEF), 24 September 2020