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Greater Groundwater Loss Due to Rising Seal Levels
28 Nov, 2007 11:29 am
People who live near the coast could lose their fresh water supplies due to sea-level rise caused by global climate change. Our study indicates that they could lose up to 45 percent more of the water supply than previously thought.
We illustrate that there is another way that climate change can potentially reduce available drinking water in coastal areas. Almost 40 percent of the world's population lives in coastal areas less than 60 kilometers from the shoreline, and many cities rely on groundwater as a drinking water source. Most people are probably aware of the damage that rising sea levels can do above ground, but are not aware of the damage underground, where it affects the freshwater aquifers.
Our research group has conducted numerical simulations to understand how saltwater will intrude into fresh water coastal aquifers. We use the rate of the sea level rise predicted by the Intergovernmental Panel on Climate Change (IPCC). The 2007 IPCC report has concluded that sea level could rise as much as 58 cm within the next 100 years and flood coasts worldwide.
Saltwater intruding from the ocean into the aquifer due to sea-level rise mixes with inland freshwater and creates a zone of brackish water. Previous studies have shown that saltwater would penetrate underground only as far as it did above ground in aquifers consisting of coarse sands and create a relatively sharp boundary between saltwater and freshwater. Our research, however, shows that when saltwater intrudes into a fresh water aquifer they mix intensively. The size of this mixing zone greatly depends on the stratigraphic structures of the sand layers in the coastal aquifer.
In general, coastal aquifers are made of different sandy and silty layers that have formed over time. Some layers may contain coarse sand, and others may contain fine sand and silt. Fine sand and silt tend to permit less water flow, while coarse sand allows more water flow. We simulated coastal aquifers consisting of realistic layers containing sands and silt. The simulation results showed that more mixing occurs between the saltwater and freshwater as the complexity of the aquifer's stratigraphy increases. This is because different water velocities in layers create complex flow paths in the aquifer.
Brackish water in the aquifer can extend 10 to 45 percent further inland in a stratigraphically complex aquifer than a sharp boundary between saltwater and freshwater which has been shown in many other studies. Brackish water is not safe to drink and creates salt accumulation on the ground if it is used for irrigation resulting in damage to crops.
In order to sustain our life, we need clean fresh water for everybody. Most of the freshwater on the earth exists as glaciers which are melting due to climate change. The second largest reservoir of freshwater is groundwater, but major aquifers are depleting at a rapid pace in many countries. These include the High plains aquifer in the USA, which provides irrigation water to the largest agricultural area in the country, and northern parts of China and India, which provide water for agriculture and cities.
One approach to solve this freshwater shortage problem is desalination of saltwater. This is energy intensive, and our water problem could become an energy problem in the future. Another approach is to transfer water from regions which have abundant water to regions that face water shortage. This approach could lead to political and cultural conflicts and security issues among countries and regions. In the worst scenario, people or countries who cannot afford energy or are politically or financially weak would have difficulty obtaining clean fresh water.
Smith, Josiah and Motomu Ibakari. "Data mining and spatiotemporal analysis of extreme precipitation and Northern Great Plains drought". Presented at the 2007 Geological Society of America meeting in Denver, Colorado, October 28-31, 2007.