Ensuring groundwater sustainability in the face of climate change and a growing population
October 18, 2021
October 18, 2021
Tapping into underground reservoirs can potentially improve resiliency to endure droughts and climatic shocks. However, there are some limits.
Niger is one of the poorest and least developed countries in the world. The country also has the world’s highest growth rate and could see its population triple by 2050. More than 80% of the nation is reliant on rain-fed agriculture and livestock for its food and income. Frequent droughts and increasingly limited and erratic rainfall pose a growing threat to the livelihood and food security of the people of this landlocked African country. Climate change is expected to make these conditions worse. For example, the already extreme temperatures in Niger are expected to increase by 3 to 5 degrees Celsius by 2050—1.5 times faster than the global rate.
Tapping into Niger’s vast underground aquifers has the potential to improve resiliency to withstand droughts and climatic shocks. This includes the improvement of food security by enabling increased crop yields throughout the year. However, it’s critical to assess the sustainability of such investments to ensure they yield water for years to come and avoid impacting nearby water users.
Much of Niger is situated on large quantities of groundwater found in two types of aquifers—deep sedimentary and shallow. Deep sedimentary—or “fossil”—aquifers are ancient reserves of water formed thousands of years ago. Such aquifers are considered a nonrenewable resource as they receive little recharge. In contrast, shallow aquifers are more easily accessible and are recharged from seasonal rainfall.
Extraction greater than the annual recharge results in a lowered water table. This could mean that a well fails soon after installation. It could also negatively impact nearby water users by drying out wells or reducing their productivity. Both issues are a cause for concern in arid climates, like Niger and the surrounding Sahel region, which receive only minimal rainfall throughout the year.
Sustainable groundwater is a key focus of the Niger Compact. The compact is run by the Millennium Challenge Corporation (MCC)—an independent US Government agency working to reduce global poverty through economic growth. Our team is supporting the MCC and the Compact’s Climate Resilient Communities (CRC) Project. The project focuses on making sound investments to support small-scale communities that rely on agriculture and livestock. The CRC Project intends to help these communities become more resilient to the effects of climate change. The goal is to increase farmer incomes in rural Niger by improving crop and livestock productivity and sustainably managing the natural resources. This will help increase the growth of farming enterprises and increase sales in the target markets.
Proposed investments under the CRC Project are based on communities’ needs. These needs can include small-scale irrigation programs, pond development, livestock markets, and rehabilitation of livestock corridors and water points. We’re helping the MCC assess community investments in small-scale infrastructure while prioritizing projects for a diverse portfolio.
A key factor is the projected water demand over the lifetime of a proposed investment. It is important to understand the capacity of local groundwater resources to sustain demand while avoiding impacts of nearby water users. Various methods exist to estimate water recharge. However, they require extensive data specific to a particular site. Given the limited data on geology or groundwater flows in Niger, these methods are not applicable. To overcome this scarcity of data, we developed a simplified tool to assess localized groundwater sustainability.
It is important to understand the capacity of local groundwater resources to sustain demand while avoiding impacts of nearby water users.
The first step is to determine whether the aquifer at a proposed investment site is a deep sedimentary or shallow aquifer.
For deep aquifers, we run a static reserve assessment. This involves estimating local, nonrenewable groundwater available and calculating the lifetime water demand. Next, a qualitative policy plan along with a planning decision are needed. These determine whether this depletion level is acceptable. For example, say an investment is estimated to deplete 5% of groundwater within a 1-kilometre distance over its lifetime. This would mean 19 similar investments in the nearby area would use up this portion of the aquifer.
For shallow aquifers, we conduct a dynamic reserve assessment. This involves a simple mass balance to compare projected water demand versus the estimated annual recharge of the aquifer. First, recharge traits are defined based on location, site-specific estimates of annual rainfall, soil type, and infiltration characteristics. The area required to recharge the proposed amount of withdrawn groundwater is then estimated based on the projected water demand of the investment and the recharge figure.
We then compare the recharge radius of the catchment area to the distance to nearby existing wells or boreholes. Also, annual water use, recharge areas of any existing wells, and boreholes located within the estimated recharge radius are assessed. An assessment of the potential impact of the proposed investment on current water users is required where estimated areas overlap. Finally, the annual volume of groundwater that can be sustainably withdrawn is estimated.
Our team is supporting MCC as they oversee the MCA and local consultants employing this method. The goal is to assess the feasibility of 18 proposed livestock markets in 4 regions of Niger. Additionally, the tool will be used to assess groundwater sustainability for up to 530 hectares of small-scale irrigation in 66 sites. Given the high demand for irrigation water, the proximity to villages, and already scarce water resources, it is important to assess the potential impacts irrigation investments may have on nearby water users.
The population in the Sahel region of Africa is projected to continue growing rapidly over the coming years. It is estimated to grow from 135 million people today to 330 million by 2050. This growth, along with the impacts of climate change—including rising temperatures and decreasing rainfall—threatens food security. Investments to tap into vast underground reservoirs of water in Niger and the Sahel as well as parts of Eastern and Southern Africa have the potential to positively impact these areas. It would boost agricultural productivity, increase climate resilience, and foster economic growth.
However, it’s critical that the local capacity of aquifers yields over the investment’s lifetime. It also should avoid impacts to nearby water users. With limited data available on geology and groundwater flows, this simplified groundwater sustainability tool provides useful information. It can be used to determine the feasibility of investments given competing water uses and provide decision makers with a sound basis on which to make groundwater investment decisions.
About the authors
Jeannette is a civil engineer with a career focused on all aspects of the sanitation service chain.
Joe is a hydrogeologist with 30 years of experience in a wide range of subdisciplines.