Assessing waterlogging conditions across Ethiopia’s rainfed agricultural landscape

Waterlogging - a phenomenon that leads to poor soil aeration when excess soil water displaces air from the soil - is a critical challenge in heavy clay agricultural soils in humid and sub-humid climates. The resulting air deficit in the root zone inhibits crop growth by impairing root function and reducing transpiration, ultimately affecting crop yields. Agroecological conditions favouring waterlogging, such as the presence of vertisols, intense rainfall and gentle to flat slopes, are prevalent across the main agricultural regions of Ethiopia. In a previous analysis of cropland quality (Wakjira et al., 2024), it was identified that land suitability for cereal crops like wheat is limited especially in the humid parts of the country, highlighting the potential limitations posed by waterlogging. In this study, we conduct a detailed agrohydrological analysis to characterize waterlogging conditions across the rainfed agricultural landscape of Ethiopia. We utilize high-resolution climate, soil and elevation data to simulate root zone water balance components, particularly soil moisture at a daily time step, using a curve number-based hydrological model. We quantify and map waterlogging magnitude and duration at 1x1 km grid scale for the period 1981-2010.

Results indicate that hyper-humid areas experience severe waterlogging with an average air deficit of up to 90%, i.e., the root zone is only 10% aerated. An estimated 9% of the rainfed agricultural region experiences air deficit exceeding 50%, lasting for a total duration of about 65 days per year on average. This suggests that proper remedial measures, for example proper seedbed preparation, field drains, and selection of waterlogging-tolerant variety crops could significantly contribute to bridging the yield gaps in these regions of Ethiopia. In our analysis, we evaluate the potential of improved soil drainage to enhance crop yields across the study area, using empirical relations derived from existing paired yield measurements from well-drained and waterlogged conditions. This research provides critical insights to farmers, planners, policymakers, and decision-makers on the urgent need for agricultural soil drainage in waterlogging-prone areas - a challenge that currently receives insufficient attention.

Reference

Wakjira, M. T., Peleg, N., Six, J., and Molnar, P.: Current and future cropland suitability for cereal production across the rainfed agricultural landscapes of Ethiopia, Agric. For. Meteorol., 358, 110262,  https://doi.org/10.1016/j.agrformet.2024.110262, 2024.