To make a living in the West African Sahel, farmers and herders must look for ways to stretch what little rain they receive.
In this vast, unforgiving landscape where tropical savannah gives way to the Sahara Desert, climate change and desertification are very real threats, contributing to reduced rainfall and increasingly poor soil health. In a region where many rely on subsistence agriculture or herding livestock, desertification threatens to destabilize communities’ livelihoods. An initiative funded by USAID's Bureau for Humanitarian Assistance and implemented by the World Food Programme is working to address these threats and improve regional water resilience through sustainable landscape restoration techniques.
In Niger, “half-moons” are an increasingly popular strategy for rainwater retention. These small, semicircular ponds help dry and degraded soils hold rainwater longer and are much less expensive for aid agencies to build and maintain. Excavated soil is deposited on each pond’s downhill edges, forming systems of terraces that keep the immediate area well-supplied with water to support surrounding vegetation.
The World Food Programme has used half-moons as a land restoration approach in West Africa for several years, but now it wants to know–is the plan working? Satellite imagery pre- and post-intervention may hold the answer.
“Geo-spatial analysis is an important tool in our monitoring and evaluation tool box,” said Dr. Arid Rashid, Acting Chief of the Design, Monitoring and Evaluation, and Applied Learning Division at the Bureau of Humanitarian Assistance. “USAID is increasingly using remotely sensed data to monitor and evaluate USAID's emergency response and development investments.”
SERVIR—a joint initiative of USAID, NASA, and partner organizations across Asia, Africa, and the Americas—used images captured by Landsat 7 to measure normalized differentiated vegetation indices (NDVI) surrounding the half-moons over time. A common measurement of vegetation health, NDVI reflects the amount of “greenness” observed by a satellite’s sensors.
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“These are exciting times – satellite-based vegetation condition information is increasingly being used to assess the impact of land rehabilitation efforts,” said Dr. Vikalp Mishra, a SERVIR research scientist involved in the project. “The additional perspective that satellite observations provide has the potential to monitor the ground conditions in an efficient and unbiased way for a much longer time period that would otherwise require substantial resources using traditional methods.”
At over 18 half-moon sites constructed in southern Niger, average NDVI increased 50 percent from pre-intervention baselines. Before the addition of half-moon ponds, NDVI values did not significantly differ between study sites and nearby control sites, but a year after the intervention, the peak season NDVI for the sites with half-moons was 25 percent higher than the corresponding control sites.
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“Satellite observations have their share of limitations,” said Mishra, “but our analysis clearly shows a significant improvement in vegetation conditions post-intervention, underlining both the impact of these interventions on the ground and the efficacy of satellite observations in measuring these impacts.”
SERVIR’s findings strongly suggest that half-moons are an effective response to deteriorating growing conditions in the Sahel. Before and after satellite images show stark visual differences in the amount of vegetation present. Inexpensive and simple to construct, they represent an accessible and sustainable approach to water resource management. USAID is currently interested in supporting similar land restoration projects in other countries, such as Zimbabwe.
Combined with other resilience measures, such as climate financing, half-moons are a promising option for supporting a more resilient future for the Sahel.
Jake Ramthun
Jake Ramthun is the Science Communications Lead for NASA SERVIR’s Science Coordination Office in Huntsville, Alabama. He holds Bachelor’s and Master’s degrees in Geography from Macalester College in St. Paul, Minnesota and the University of South Carolina. His work has focused on the geography of environmental hazards, as well as the role of maps in publicly communicating disaster risk and resilience.
Dr. Vikalp Mishra
Dr. Vikalp Mishra is a scientist with NASA SERVIR's Science Coordination Office, Huntsville, Alabama. He holds a Doctorate and Master's degree in Civil and Environmental Engineering from the University of Alabama in Huntsville. His research work is focused on the application of latest remote sensing technologies in solving environmental challenges particularly dealing with hydrology, agricultural food security, and resilience.
