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Freshwater and Climate Change
We need water to survive. But although water covers almost three-quarters of the Earth’s surface, less than 1% of that water is available for our use—the rest is in the ocean or frozen.1 The water we use for drinking, bathing, cooking, and cleaning comes from rivers and lakes, groundwater, and, to a much lesser extent, rainwater collection, desalinated seawater and recycled water.
Globally, more than two billion people don’t have access to safe, readily available drinking water.2 And due to pollution or populations using more water than their water sources can naturally replenish, we’re damaging our freshwater supplies. For example, 21 of the Earth’s 37 largest aquifers, areas where water collects underground, are shrinking.3 As populations develop and urbanize, they consume more water. High consumption of freshwater for agricultural irrigation, industry, and domestic uses, together with our planet’s population growth, means that demand for water continues to grow.
Climate change, which worsens droughts and floods, threatens our stressed freshwater supplies. Human activity has already warmed our planet by about 1 degree Celsius (1.8 degrees Fahrenheit), and climate scientists say that 2 degrees C (2.7 degrees F) of warming will dramatically increase risks of global water shortages.4
Imperiled global water supplies
Climate change affects both the quantity and quality of the freshwater we depend on. Burning fossil fuels for energy and cutting down forests releases carbon dioxide and other planet-warming greenhouse gases. Our warmer Earth has sent the water cycle into overdrive: warmer temperatures increase the rate of evaporation, and warmer air can hold more water vapor — making storms more intense when it does rain.
At the same time, that increased evaporation, combined with other weather pattern changes, is making droughts more common in other places around the world,5 like parts of western North America and the Mediterranean.6 As the planet continues to warm, climate scientists say that the total amount of rainfall will decrease in parts of the subtropics, which are the regions just north and south of the tropics that include parts of North Africa and the Middle East and southern Australia.7 Meanwhile, disappearing glaciers put the roughly 1.9 billion people who live downstream of the Himalayas and rely on glacier-fed rivers for their water—and hundreds of millions of others around the globe who also depend on glaciers for water—at risk.8
Some parts of the world, however, will get more precipitation. While additional rain might not seem like as big of a problem as drought, more severe storms can lead to floods that overwhelm the infrastructure we depend on to treat and manage our drinking water. Heavier rains also bring with them more pollutants like fertilizers and petrochemicals (for example, oil from the road); when these pollutants enter our lakes, rivers, and aquifers, they harm our water quality and, in turn, our health.
Beyond rainfall changes, climate change impacts our water supplies in other ways. Warmer waters provide better breeding grounds for bacteria and viruses, and droughts concentrate these pathogens in dried-up water supplies — meaning we’ll likely see more water-related diseases like giardia because of climate change.9 And sea level rise brings saltwater further inland, threatening drinking water in coastal areas such as Los Angeles, California,10 and Bangladesh.11
Protecting our freshwater
Because we’re already seeing how a warming world affects our access to freshwater, experts say we need to act now.
Climate scientists say that limiting global warming at 1.5 degrees Celsius or below—the goal of the Paris Agreement—would dramatically reduce the risk of increased droughts and other water-related impacts.12
To manage the impacts we’re already experiencing, regions can both improve their traditional, “gray” infrastructure, like water and wastewater treatment plants and pipes that move water around, while protecting and building up “green” infrastructure, like forests and wetlands, which naturally soak up and filter water. In monsoon-prone areas like India, for example, efforts are underway to revive the millennia-old tradition of capturing excess water from monsoons and storing it underground so that it can be used during the dry season.13
Cities are also looking at using wetlands, rain gardens, porous pavements, and other measures to filter and slow down rain so that it can have more time to drain into the soil and replenish aquifers. Water conservation, watershed protection, water quality testing, and collecting better data about water availability can help us better manage this precious resource even as we face uncertainties from climate change.
1 United States Bureau of Reclamation California-Great Basin. “Water Facts - Worldwide Water Supply.” Central California Area Office, 4 Nov. 2020, https://www.usbr.gov/mp/arwec/water-facts-ww-water-sup.html.
2 WHO/UNICEF Joint Monitoring Programme for Water Supply, Sanitation and Hygiene. Progress on Household Drinking Water, Sanitation and Hygiene 2000‒2020: Five Years into the SDGs. World Health Organization and UNICEF, 2021, https://www.who.int/publications/i/item/9789240030848.
3 Richey, Alexandra S., et al. “Quantifying Renewable Groundwater Stress with GRACE.” Water Resources Research, vol. 51, no. 7, 16 June 2015, pp. 5217–5238., https://doi.org/10.1002/2015wr017349.
4 Liu, Wenbin, et al. “Global Freshwater Availability below Normal Conditions and Population Impact under 1.5 and 2 °C Stabilization Scenarios.” Geophysical Research Letters, vol. 45, no. 18, 19 Aug. 2018, https://doi.org/10.1029/2018gl078789.
5 Marvel, Kate, et al. “Twentieth-Century Hydroclimate Changes Consistent with Human Influence.” Nature, vol. 569, no. 7754, 1 May 2019, pp. 59–65., https://doi.org/10.1038/s41586-019-1149-8.
6 Cook, Benjamin I., et al. “Climate Change and Drought: From Past to Future.” Current Climate Change Reports, vol. 4, no. 2, 2018, pp. 164–179., https://doi.org/10.1007/s40641-018-0093-2.
7 Intergovernmental Panel on Climate Change, Working Group I, 2021, Climate Change 2021: The Physical Science Basis Summary for Policymakers, https://www.ipcc.ch/report/ar6/wg1/downloads/report/IPCC_AR6_WGI_SPM_final.pdf.
8 Wester, Philippus, et al. The Hindu Kush Himalaya Assessment: Mountains, Climate Change, Sustainability and People. Springer, 2019, https://link.springer.com/book/10.1007/978-3-319-92288-1.
9 Levy, Karen, et al. “Climate Change Impacts on Waterborne Diseases: Moving toward Designing Interventions.” Current Environmental Health Reports, vol. 5, no. 2, 2018, pp. 272–282., https://doi.org/10.1007/s40572-018-0199-7.
10 U.S. Geological Survey California Water Science Center. “Seawater Intrusion.” Sustainable Groundwater, https://ca.water.usgs.gov/sustainable-groundwater-management/seawater-intrusion-california.html.
11 Shammi, Mashura, et al. “Impacts of Salinity Intrusion in Community Health: A Review of Experiences on Drinking Water Sodium from Coastal Areas of Bangladesh.” Healthcare, vol. 7, no. 1, 22 Mar. 2019, p. 50., https://doi.org/10.3390/healthcare7010050.
12 Allen, Myles R., et al. Intergovernmental Panel on Climate Change, 2018, Special Report: Global Warming of 1.5°C Summary for Policymakers, https://www.ipcc.ch/sr15/chapter/spm/.
13 Meter, Kimberly J., et al. “Monsoon Harvests: The Living Legacies of Rainwater Harvesting Systems in South India.” Environmental Science & Technology, vol. 48, no. 8, 2014, pp. 4217–4225., https://doi.org/10.1021/es4040182.