"Dawadawa Tree in Clean and Beautiful Environment," Ghana © Tahiru Rajab, CC BY-SA 4.0
Roots of resilience
Across Sub-Saharan Africa’s drylands, farmers face one of the toughest limits in agriculture: water. Rainy periods are shorter, more unpredictable, and increasingly unreliable due to climate change. Rainwater harvesting (RWH) offers a practical path forward. By capturing and storing rainfall, farmers can extend growing seasons, reduce erosion, and stabilize yields.
A new study — Investment trends and evaluation gaps in rainwater harvesting in Sub-Saharan African drylands — takes stock of two decades of RWH investments and their evaluation record. Led by researchers from AidData, the Centre for Remote Sensing and Geographic Information Services, University of Ghana, IITA, Worcester State University, and others, the paper maps hundreds of projects across the region and asks a critical question: Are we measuring the right indicators to determine whether rainwater harvesting delivers lasting resilience?
Investment distribution and existing gaps
The review found that governments and donors have steadily invested in diverse rainwater harvesting (RWH) approaches—from contour bunds and Zai pits to small reservoirs and rooftop catchments. Yet, despite this sustained funding, the evidence to evaluate their long-term impact remains limited. Most evaluations focus narrowly on short-term crop yields or incomes, often over a single season. Very few track whether structures last, whether households see sustained improvements, or how water availability shifts over time. This leaves policymakers with a blind spot: they know RWH is popular, but they aren’t certain where it works best or why.
“Policymakers are encouraged to design climate change adaptation programs that integrate RWH as an essential tool for community-based water management,” said Foster Mensah of the Centre for Remote Sensing and Geographic Information Services, University of Ghana. “But this must be matched with evidence to show how these systems affect food security and resilience in African drylands.”
Gaps that matter for farmers
The authors highlight three areas where evidence is especially thin. First, few studies measure how RWH affects local hydrology, groundwater recharge, soil moisture, or runoff. Second, evaluations rarely move beyond yield to capture broader outcomes like nutrition, household labor, or ecosystem benefits. Third, most projects are not tracked long enough to see whether adoption continues once external support ends.
“The knowledge gap is in how rainwater harvesting affects the local water budget for improved crop yield over time,” said Mensah. “Remote sensing provides an efficient Earth Observation platform for monitoring these patterns.”
A Systems View
For Julius Adewopo of IITA, what stands out from the study is that RWH cannot be treated as a technical fix alone. “Rainwater harvesting is not just a technical solution; it’s a systems solution,” he explained. “Our review shows that interventions work best when they link water management with land tenure security, community-led design, and plans for long-term maintenance.”
Scaling remains difficult because projects face financial, institutional, and social barriers. Large structures demand high investment and time before returns appear, while smaller ones require intensive labor and upkeep. Weak land tenure and limited market access further discourage farmers from investing in long-term maintenance.
Why Earth observation matters
The study calls for new approaches to evaluation. Traditional field monitoring alone is costly and often patchy. By combining household surveys with hydrological monitoring and Earth observation, researchers can track adoption and outcomes at scale and over time. Remote sensing can detect vegetation growth, soil moisture, and water body formation, even in areas where field data are scarce or hard to collect.
As Adewopo put it, “Earth Observation technologies open the door for scalable, cost-effective monitoring, including in fragile or data-sparse regions. That is what will allow funders and governments to understand not just where RWH is being built, but whether it is working.”
Looking to 2030
What would success look like by the end of this decade? The authors envision programs that go beyond counting structures to generate evidence for scale. That means measurable yield and income gains over multiple seasons, improvements in soil and erosion indicators, better groundwater recharge, reduced time spent collecting water for women and children, and durable systems that communities maintain long after projects close.
“Avoiding the build–neglect–rebuild cycle is key to achieving lasting resilience and impact,” Adewopo noted.
Why this matters for GeoField
For the GeoField Community of Practice, this paper underscores why evaluation cannot be an afterthought in climate adaptation. Rainwater harvesting holds enormous promise, but without robust and long-term evidence, investments risk being scattershot. By weaving Earth observation into evaluation frameworks, we capture not just water but resilience and ensure that every dollar invested moves us closer to food security and climate stability in African drylands.
As this important work moves forward, GeoField will continue convening researchers, policymakers, and implementers to refine evaluation methods, share critical lessons, and develop a shared standard for assessing water management interventions at scale. By fostering collaboration and building consensus, we aim to drive more effective, evidence-based solutions to today’s most pressing water challenges.
