The latest estimates from the United Nations suggest that the total population of sub-Saharan Africa could grow to approximately 3.5 billion by the end of the century. Improving crop yields is widely recognised as a critical priority for the region, especially as its food system—which is largely dependent on rain-fed and flood-recessed agriculture—struggles in a hotter, drier climate.
A tertiary canal intake provides irrigation to agricultural lands in Podor, Senegal. Photo by Jean-Yves Jamin
Past studies suggested that adopting irrigated agriculture could help the region’s farmers meet demand, but the lack of reliable land-use and agricultural data has made it difficult to empirically assess the impact of building dams, canals, and other irrigation infrastructure.
To help fill that knowledge gap, a team of economists from UC Berkeley, the World Bank, the University of Wisconsin, and Senegal’s Gaston Berger University examined the long-term effects following the 1980s damming of the Senegal River. Their findings, which were published in the February issue of the Journal of Development Economics, indicate that the ongoing development of irrigation infrastructure led to significant and sustained increases in agricultural cultivation and reduced sensitivity to temperature shocks across the Senegal River Valley.
“It was important for us to evaluate how these large-scale projects perform on the ground in Africa, and we were pleasantly surprised by the persistence and improvement in land-use rates over time,” said co-author Marco Gonzalez-Navarro, George Pardee Jr. Professor of International Sustainable Development at UC Berkeley’s Department of Agricultural & Resource Economics (ARE). Additional ARE co-authors include Alain de Janvry and the late Elisabeth Sadoulet, both professors of the Graduate School; Joel Ferguson, PhD ’23; and Abdoulaye Cisse, PhD ’25.
The researchers based their analysis on more than 3,000 publicly available Landsat satellite images captured from 1985 to 2019. Pixels in each image correspond to areas of roughly 30 square meters and can be easily classified as either cultivated or uncultivated using the normalized difference vegetation index (NDVI), a widely used measure of vegetation greenness. The co-authors combined this newly developed dataset with Senegalese government data covering 871 distinct irrigation infrastructure projects completed between 1988 and 2019.
Merging the two datasets made it easy to trace the effects of irrigation infrastructure, both over time and by year of completion. Cultivation rates increase substantially following the completion of an irrigation project, the study showed, and remain nearly seven times higher for the first 20 years. Benefits of infrastructure projects persist even after 20 years, particularly during the dry season, when cultivation rates exceed pre-irrigation levels by more than 50 percentage points. Similar beneficial effects were observed in vegetation greenness, with the region showing consistently higher NDVI values in both wet and dry seasons following completion of irrigation projects.
Despite large average increases in cultivation rates, the study found that a majority of the region’s more than 1,300 farms and agricultural operations use irrigated land only intermittently or at below-average rates. Additionally, the authors report that, as of 2019, roughly a quarter of the region's irrigated land remained unused. Farmers surveyed by the researchers routinely cited a lack of water availability—either due to their distance from a canal or maintenance issues that render the canal inoperable—as the main reason their land remained uncultivated. Farmers who only intermittently used their land cited financial constraints, namely an inability to afford a pump needed to draw water from nearby canals.
Gonzalez-Navarro said the study’s findings highlight the importance of maintaining (not just expanding) irrigation infrastructure to address water access problems. They also underscore the need to expand access to financial services—like lines of credit—as a strategy to improve land utilization.
Read the full study online in the Journal of Development Economics.