Study shows groundwater declining at high rate due to climate change

Milliam Murigi

March 22, 2024

As World  Water Day is marked today, a recently published study shows a rapid groundwater depletion around the world and that rates of decline have accelerated in recent decades, with levels falling by 20 inches or more yearly in some locations.

Groundwater is the primary water source for many homes, farms, industries, and cities worldwide. According to the World Bank, it provides about half of the world’s population with drinking water and nearly half of all water used to irrigate crops. It also sustains rivers, lakes, and wetlands during droughts.

According to the study, though many factors determine groundwater levels, such as geology, climate, and land use, groundwater levels dropping deeper and deeper in a particular location often signal that people are pumping it out faster than nature can replenish it.

World Water Day article

“In Kenya, the surge in urban population has significantly exacerbated the decline in groundwater levels over time because the failure of the city infrastructure to meet the per capita demand for water supply fully has resulted in a paradigm shift and interest in groundwater sources,” says JN Gosho, a Kenya-based water resource engineer.

Research by Samson Oiro from Kenya’s Water Resources Authority shows that since the mid-1970s, groundwater abstraction has increased 10-fold in Nairobi alone, the country’s capital,  at a rate similar to urban population growth. Groundwater levels have also declined at a median rate of six meters per decade underneath Nairobi since 1950, while built-up areas have increased by 70 percent since 2000.

Groundwater levels have declined four meters on average across the entire aquifer area. However, the decline is more severe beneath Nairobi, reaching 46 meters. This reduction has resulted in a net loss of groundwater storage totaling 1.5 billion cubic meters and a nine percent reduction in river base flow since 1950.

These figures are projected to increase six-fold by 2120 based on current practices and trends.

“Because of this depletion, nominal borehole depth has shifted in most of the country. For example, between 1990 and 1996, boreholes were nominally drilled to 200 to 250 meters. But from 1999 to date, the depth datum has shifted this nominal depth to 380 to 480 meters,” says Gosho.

According to Gosho, some of the worst-affected areas in Kenya are the Nairobi suburbs of Karen and Parklands and Timau, an agricultural town in Meru County.

Lack of interest in sharing resources

Karen has nearly depleted its entire reservoir, with depths shifting to 350-450 meters for a limited yield of 5.0 cubic meters per hour (M3/hr). The higher per capita and improved investment options, accompanied by the wealthy living and lack of interest in sharing resources, have resulted in each homestead developing its water source.

In Parklands, depths have moved from 300 meters to 380 meters. This rise in depth can be attributed to the construction of multiple high-rise apartments, leading to a surge in population density within the area. For Timau, unlike in 2002-2007, when available flows were more than 60.0m3/hr, the current flows have dropped to 15.0m3/hr.

“People are forced to dig deeper in search of deeper aquifers and more reliable and sustainable supply sources. This is becoming a misplaced practice with adverse climatic trends, where erratic rainfall patterns highly constrain recharge,” says Gosho, who is also the Technical Director at Insta-Pumps Group PLC.

Farmers turning to boreholes

Apart from the surging population, farming also contributes to the decline in groundwater levels, says Gosho. He adds that most farmers are turning to boreholes to irrigate their fields because many rivers have dried up, and the widespread reliance on boreholes is exacerbating the depletion of aquifers around the globe.

A 2022 study by the World Bank shows that boreholes now provide 43 percent of the world’s irrigation water. Irrigation is responsible for around 70 percent of the global underground water withdrawals, estimated at more than 200 cubic miles per year. This exceeds recharge from rainfall by nearly 70 cubic miles per year.

But what are the effects of groundwater depletion? Gosho says that the consequences are multifaceted. They include increased energy costs for pumping and well infrastructure adjustments. Other effects are water quality deterioration, water reduction in streams and lakes, and land subsidence.

“Groundwater pumping can alter how water moves between an aquifer and a stream, lake, or wetland by intercepting groundwater flow that discharges into the surface-water body under natural conditions or by increasing the rate of water movement from the surface-water body into an aquifer. In either case, the net result is a reduction of flow to surface water, though the full effect may take many years to develop,” Gosho says.

Climate change-induced shifts in rainfall patterns

Is anything being done to conserve our groundwater? Gosho says there has been very little or no effort to safeguard groundwater sources in Kenya. If nothing is done urgently, groundwater source availability and sustainability will be bleak. The situation requires serious redress on water resources policy, legislation, and feasible management options.

Victor Ndiege, CEO of Kenya Climate Ventures, says that if Kenya wants to solve this problem, it must acknowledge the complex interplay of elements leading to underground water depletion. These include climate change-induced shifts in precipitation patterns and recharge of underground water sources, over-extraction for agricultural irrigation, rapid urbanization, and inefficient water management practices. Understanding this complexity is crucial for formulating effective and sustainable solutions.

“Effective water management practices stand as our crucial shield against the looming threats of water depletion. KCV’s engagement in collaborative endeavors underscores the shared responsibility in financing sustainable water extraction and utilization towards a water-secure future,” says Ndiege.

This year’s World Water Day theme is Leveraging Water for Peace. _______________________________________________________________________________________________

Milliam Murigi is a Kenyan science journalist who writes for the People Daily newspaper, Sayansi Magazine, and the Bird news agency on health, the environment, agriculture, and technology.