Groundwater for Agriculture and Drinking Water
In 2017, the World Bank estimated that, globally 70% the percentage of freshwater is used for agricultural activity that feeds the human population of Earth. In 2019, The Global Agriculture Organization estimated the percentage of freshwater used for agricultural in major regions of the world as shown in Figure 67, also estimating that globally 70% of freshwater use is for agriculture. Groundwater provides drinking water entirely or in part for as much as 50% of the global population and accounts for 43% of all of water used for irrigation (UNWWAP, 2015). Worldwide, 2.5 billion people depend solely on groundwater resources to satisfy their basic daily water needs (UNWWAP, 2015).
The groundwater is critical to production of food needed to support Earth’s current population, and has served humanity reasonably well for centuries, but is now under great stress. At present, as much as 10% of the world’s food is produced by depleting groundwater systems and the number of people to feed is rising rapidly. Irrigated agriculture is generally twice as productive as dry land farming, however, there is only a limited amount of accessible water that is not already allocated.
The world population of nearly 8 billion in 2020 is projected to be near 11 billion at the end of the 21st century. The food supply of many countries is threatened. The advances made by the Green Revolution are fading and, in some regions, there is a decrease in the amount of food production due to soil erosion and salinization. China, with 19% of the world’s population (1.4 billion people) but only 7% of the arable land, is soon to complete the largest water diversion project in the world in order to end decades of groundwater depletion in the North China Plain. Water from the Yahtzee River is being diverted 1,000 kilometers northward where much of the water will be used to replenish the vast aquifers. In contrast, India, with a population projected to exceed that of China in 2024, has an even greater need for more water, but the prospects for a solution are much less. India uses twice as much groundwater as China, with 89% of the water used to irrigate crops. Much of the current groundwater use in India is depleting aquifers, thus the use is not sustainable. Large areas of India have substantial rainfall, but much of the rainfall quickly makes its way to the oceans without being used to produce food. Climate change is projected to bring even more challenges to many of the countries already in a state of water stress and water insecurity.
As this book elucidated, surface water bodies in all types of terrains are sustained by the steady release of groundwater (Figure 68). This is the primary reason that our streams do not run dry despite days to months without rain. Also, groundwater does not heat or cool quickly, despite the fluctuating air temperature, thus its inflow to streams provides a stable habitat for aquatic plants and animals. Along the edges of streams and lakes, as well as in lowlands and on coastal plains, unique environments called wetlands (which include marshes, bogs, swamps and peatlands) occur as the transition zone between the lowland aquatic and the upland terrestrial environments. They exhibit unique dynamics of water and air availability; hence, they support life specialized in “making a living” in wet places with minimal oxygen.
Wetlands are dispersed throughout the globe and cover over 12 million km2, an area almost as large as Greenland. Natural wetlands are in long‑term decline around the world, having decreased in area by 35% between 1970 and 2015, which is about three times the rate of forest loss. Wetlands exist not because more rain fell on their locations, but because they are located in an area with a shallow water table within the reach of plant roots. In other words, it is shallow groundwater that creates and maintains wetland habitats. Further upland, where the water table is deeper and plant roots can respire, but where the water table is shallow enough to be within reach of large plants with deep roots, groundwater provides much needed water during dry seasons when the shallow subsurface dries out.
Groundwater provides multiple services by: regulating surface water flow, supporting ecosystems, and providing water for humankind. In short, groundwater is the Earth’s life support system. In 2019, van der Gun grouped groundwater service according to the Millennium Ecosystem Assessment classification of ecosystem services as shown in Figure 69.
In summary, groundwater provides vital water supplies for human societies, directly for drinking water, and indirectly through large‑scale irrigation for food and fiber production. Like natural ecosystems, humans require sustainable sources of water. Long‑distance groundwater convergence toward, and discharge to springs has provided life support for our species for millions of years. The difference today is that humans have the unprecedented power to withdraw large volumes of groundwater and have the power to transport that water over long distances, in many places surpassing the capabilities of the natural hydrologic cycle. Therefore, modern humans are using much more groundwater and withdrawing it much faster than nature can replenish, while also introducing anthropogenic chemicals faster than nature can assimilate them. There is no question that our lives depend on groundwater, and as the human population grows, more demand will be placed on this vast, but finite, resource. The need for understanding our groundwater systems and for managing them in a thoughtful manner within the constraints of the hydrologic cycle, is greater than ever.