Modelling the impacts of water harvesting and climate change on rainfed maize yields in Senegal

The agricultural sector of Senegal is prone to drought and climate change impacts. Despite this, the country counts less than 5% of irrigated lands, suggesting that its national agriculture is still strictly dependent on the rainy season. Moreover, rainfall is characterized by the presence of great variability, both on interannual and interdecadal timescales. In this framework, a research gap is represented by the lack of analyses on how much the current agricultural practices can be resilient, and on what water management strategies can be effective against climate change.

Using FAO’s AquaCrop crop-growth model, made up of a set of four sub-model components (climate, crop, soil, and management) to simulate a crop cycle, we simulated plausible climate change scenarios at different fertility levels, testing the efficiency of tied ridges water harvesting for the maize crop in the Fatick region, Senegal. Non-conservative parameters were adjusted with crop data collected within the project "Rain, Forest and People" of the International Rainwater Harvesting Alliance (IRHA, https://www.irha-h2o.org/en/projects/la-pluie-la-foret-et-les-hommes) while calibration and validation were performed with regional yield data.

Considering the current climatic scenario and soil fertility, tied ridges did not significantly impact the maize yields. Rainfall amount was enough for maize production and to avoid high water stresses along the cropping season. Under climate change scenarios, high reductions in yield were registered up to 70% in optimally fertilized soil and 50% in conditions of fertility stress.  Tied ridges only slightly increased yields up to 3.8% when a high reduction of rainfall occurred. When also considering the occurrence of dry spells in addition to climate change, maximum yield reductions do not exceed the values found without dry spells. However, in such context, tied ridges water harvesting performed better against climate change, especially under full fertilization management.

Our results highlighted how the current maize production in the Fatick region of Senegal is sustainable in the current climate scenario, while it could be potentially impacted by climate change in the near future. In a pessimistic climate change scenario with dry spells occurring in the rainy season, in-situ water harvesting has the potentiality to avoid excessive crop losses.