global warming has severe impact on water supplies

This post was written as part of Climate Week NYC and Columbia University’s Year of Water.

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Climate change impacts the world’s water in complex ways. Consider a water cycle diagram, lượt thích the one below; global warming is altering nearly every stage in the diagram. These changes will put pressure on drinking water supplies, food production, property values, and more, in the U.S. and all around the world.

water cycle diagram

Image: UK Met Office

In fact, “most of the climate change impacts come down to tát water,” says Upmanu Lall, director of the Columbia Water Center. When people talk about climate change affecting agricultural output, sea level rise, wildfires and extreme weather — “they’re all essentially a water story,” says Lall.


Warmer air can hold more moisture than thở cool air. As a result, in a warmer world, the air will suck up more water from oceans, lakes, soil and plants. The drier conditions this air leaves behind could negatively affect drinking water supplies and agriculture.

On the flip side, the warmer, wetter air could also endanger human lives. A study out of Columbia University’s Lamont-Doherty Earth Observatory found that higher humidity will make future higher temperatures unbearable in some places, by blocking the cooling effects of our sweat.


When all that extra warm, extra wet air cools down, it drops extra rain or snow to tát the ground. Thus, a warmer world means we get hit with heavier rain and snowstorms. The northeastern U.S. is sánh far seeing the largest increase in the intensity and frequency of heavy precipitation events. And in the Central U.S., clusters of thunderstorms have been becoming more frequent and dropping more precipitation since 1979.

map of precipitation changes in the u.S.

How precipitation is changing in the U.S. The colors on the map show annual total precipitation changes for 1991-2012 compared to tát the 1901-1960 average, and show wetter conditions in most areas. The bars on the graphs show average precipitation differences by decade for 1901-2012 (relative to tát the 1901-1960 average) for each region. The far right bar in each graph is for 2001-2012. Image: Adapted from Peterson et al. 2013, via NCA

By changing air temperatures and circulation patterns, climate change will also change where precipitation falls. Some areas — such as the American West, Southwest, and Southeast — are expected to tát get drier. Meanwhile, the northern parts of the U.S. and the Midwest are expected to tát get wetter. These precipitation projections are already becoming reality.

The Southwest, southern Great Plains, and Southeast are predicted to tát see more intense and prolonged droughts, according to tát the National Climate Assessment. And most of the rest of the country is at risk of experiencing more severe short-term droughts, too. Researchers within the Earth Institute have found that climate change may already have exacerbated past and present droughts, and that drier conditions are making wildfires worse.

“The drought scenario could be mitigated by having more water storage in dams, which nobody’s working on,” Lall pointed out, “or in groundwater, which is being discussed in some places but is not that easy to tát vì thế for large quantities of water.”

Changes in precipitation patterns will challenge many farmers, as well as natural ecosystems. Scientists at Columbia University’s International Research Institute for Climate and Society are creating tools and strategies to tát help farmers adapt to tát these challenges. Natural ecosystems, however, may not be able to tát adapt as quickly.

Surface Runoff and Stream Flow

The heavier bursts of precipitation caused by warmer, wetter air can lead to tát flooding, which can of course endanger human lives, damage homes, kill crops, and hurt the economy.

The America’s Water initiative at the Columbia Water Center has been working to tát identify the specific causes of catastrophic flooding, in order to tát more accurately predict them, to tát save lives and property. The project also made projections about how flooding will change as the world continues to tát warm. “On the action side, we looked at what structures lượt thích dams and levees need to tát be refurbished, and what zoning changes need to tát be done sánh that people are out of harm’s way?” said Lall.

flooded backyard

Climate change will make heavy downpours more frequent and more intense in many parts of the U.S. This means more flooding and more pollution flowing into our waterways. Photo: Andy S/Flickr CC

Heavier rainstorms will also increase surface runoff — the water that flows over the ground after a storm. This moving water may strip nutrients from the soil and pick up pollutants, dirt, and other undesirables, flushing them into nearby bodies of water. Those contaminants may muck up our water supplies and make it more expensive to tát clean the water to tát drinking standards. The National Climate Assessment finds that water quality is already diminishing in many parts of the U.S, “particularly due to tát increasing sediment and contaminant concentrations after heavy downpours.”

In addition, as runoff dumps sediments and other contaminants into lakes and streams, it could harm fish and other wildlife. Fertilizer runoff can cause algae blooms that ultimately over up suffocating aquatic critters and causing a stinky mess. The problem is compounded by warming water, which can’t hold as much of the dissolved oxygen that fish need to tát survive. These conditions could harm fisheries, and make conditions unpleasant for folks who lượt thích to tát use lakes and streams for fishing, swimming, and other recreational activities.

Researchers within the Earth Institute at Columbia University are finding that green infrastructure, such as parks, wetlands, and other green areas, can help to tát absorb runoff and filter out its contaminants. These work on a small scale with everyday storms, although Lall notes they aren’t much help when it comes to tát floods.


Warmer temperatures and increasing acidity are making life difficult for sea creatures. These changes are transforming food chains from the bottom-up. In addition, many fish are moving poleward in tìm kiếm of cooler waters, which has implications for the fishing industry and people who lượt thích to tát eat fish.

Temperature changes also have the potential to tát alter major ocean currents. Because ocean temperatures drive atmospheric circulation patterns, this could change weather patterns all over the world. Climate scientist Richard Seager from Columbia’s Lamont-Doherty Earth Observatory has found that higher ocean surface temperatures could make rainfall more variable, and thus less predictable, from year to tát year.

And of course, as ice sheets and mountaintop glaciers melt, they’re dumping extra water into the oceans; the resulting sea level rise jeopardizes coastal properties around the world.

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Ordinarily, as winter snowpack melts in the springtime, it slowly adds fresh water to tát rivers and streams and helps to tát replenish drinking water supplies.

However, as the air warms, many areas are receiving more of their precipitation as rain rather than thở snow. This means less water is being stored for later as snowpack. In addition, the rain actually accelerates the melting of snow that’s already on the ground.

The lack of snowpack can lead to tát drier conditions later in the year, which can be bad news for regions that rely on snowmelt to tát refill their drinking water supplies. In California, for example, declines in snowpack have contributed to tát long-term drought and water shortages. At the same time, as the rains come faster rather than thở slowly melting from snow, California’s ability to tát control floods is decreasing.

Changes in snowpack can also negatively impact wildlife and income from skiing and winter tourism.


A study last year out of Lamont-Doherty Earth Observatory found that increasing summer heat is driving off California’s morning clouds. This lack of clouds allows more sunlight to tát strike the ground, raising temperatures further, exacerbating drying and the risk of wildfires.

Changes in Water Demand

In addition to tát changing the water cycle, climate change could change how we use water and how much we need. Higher temperatures and evaporation rates could increase the demand for water in many areas.

map of future water withdrawals in the us

Maps show percent change from 2005 to tát 2060 in projected demand for water assuming (a) change in population and socioeconomic conditions, and (b) combined changes in population, socioeconomic conditions, and climate (assuming gradual reductions from current emission trends beginning around mid-century). Source: Brown et al. 2013, via NCA

Water Stress

These changes in water supply, demand, and quality will “exacerbate our current problem,” says Lall, “which is that we have aging water infrastructure across the country that is failing, and we simply vì thế not have the capacity to tát giảm giá with even historical variation, let alone what people are projecting for the future.”

Climate change will make water shortages more likely in parts of the U.S., particularly the southern U.S. and the Caribbean and Pacific islands.

An estimated 1.6 million Americans already don’t have regular access to tát safe drinking water. A study out of Michigan State University found that, because of climate change, aging infrastructure and other factors, up to tát 40.9 million American households may not be able to tát afford water and wastewater services in 2022.

map of current water stress in the U.S.

Caption: There is already widespread water stress in much of the Southwest, western Great Plains, and parts of the Northwest, and climate change could exacerbate the problem in the future. In this index, watersheds are considered stressed when water demand from power plants, agriculture, and municipalities exceeds 40 percent (water supply stress index of 0.4) of available supply. Source: Averyt et al. 2011, via NCA

A recent study from Harvard projects that by 2071, nearly half of the 204 fresh water basins in the United States may not be able to tát meet their monthly water demand. This is due in part to tát growing populations, but also because of the effects of climate change. Around 50 years from now, the study found, many U.S. regions may see their water supplies reduced by a third of their current size, while demand continues to tát increase. The authors warn this could pose serious challenges for agriculture.

What Can Be Done

Work from the Columbia Water Center could help municipalities to tát meet the challenges of the future; the America’s Water project has been examining how water can be allocated to tát prevent shortages, and where more water storage is needed to tát withstand future droughts.

To make these calculations, the Columbia Water Center teamed up with folks from Lamont-Doherty, using tree ring data to tát reconstruct droughts and floods from the last 700 years in all the major river basins in the U.S. In the process, they learned that in the 1300s and 1400s, the U.S. experienced droughts far more severe and widespread than thở anything we’ve seen in modern times.

“The reason for going back 700 years is that, whether or not people believe in future climate change projections, this is something that has happened, and sánh we should prepare for it in case it happens again,” Lall explained.

Whereas climate models always have some degree of uncertainty, he continued, with historical data, “it’s easier to tát convince people that, for example, if you remove some of the dams on the Colorado River, there’s really just no ability to tát meet even the more modest older droughts.”

Lall’s team built an open-source optimization model which allows anyone to tát investigate and explore different scenarios for water supply and demand in their own watershed. This tool can help to tát identify which crops would grow best under certain water regimes, or how adding renewable energy will affect the water supply.

Increasing water storage, making irrigation systems more efficient, and making sure crops are appropriate for the local climate are a few ways municipalities can help to tát stave off water stress. Wind and solar power projects can help, too, because they use less water than thở traditional power plants.

There are also things that the rest of us can vì thế to tát help conserve water, lượt thích fixing leaky plumbing, taking shorter showers, watering the lawn less often, and avoiding foods that require a lot of water. For example, it requires 1,800 gallons of water to tát produce one pound of beef.

Lall also suggests that people learn more about how climate change is going to tát affect the water in their own region, and start taking action locally.

“In the process, you discover that your water system is inadequate to tát meet the challenges of climate change,” said Lall. “You will discover that the rivers that you go fishing in and jetskiing and things lượt thích that, they’re likely to tát become stinky swamps. Once you go through this discovery process, then it becomes much more tangible to tát get action at a local level, and start changing things from the bottom-up.”

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