With a growing global population that's becoming increasingly urban and aspiring to middle class lifestyles, the demands on our food, water, and energy systems is expected to grow considerably in coming decades. Add climate change into the mix, and this creates a very precarious nexus of demands for basic needs like food and water.
Food insecurity linked to climate change impacts will be one of the most pressing consequences of a changing climate. Many areas of the globe –– particularly in Africa –– lack basic food security. Droughts and floods aggravate already bad situations, reducing yields and sometimes causing crop failure, further weakening already vulnerable populations.
This week, we'll explore just a few examples of the impacts of climate change on our global food security, recognizing that the impacts are complex, intertwined, and far-reaching. These examples include:
Sometimes, climate change impacts create winners and losers. It's important to understand that climate change leading to food insecurity is more nuanced than it's hotter here and we can't grow food. Climate shifts happen regionally and it's important to understand what that looks like at a smaller scale. Take a look at this map of anticipated agricultural yields in the US by the end of the 21st century. What do you notice?
The issue is more complicated than deciding to follow the climatic conditions with our farming. What does this mean for land use planning, both in the places which stand to lose productivity and those which stand to gain?
In a changing climate with predominant warming trends, we're seeing the lengthening of our growing seasons (as defined by the period of time with frost-free days). Given what we understand about the increased pressures to feed a growing global population, a longer growing season sounds like it might be the silver lining of climate change impacts we've been searching for, doesn't it? Let's take a closer look.
A longer growing season does mean that some crops and forests are growing for longer periods of time each year; sequestering more carbon dioxide from the atmosphere - good news! But, longer growing seasons for good plants also mean longer growing seasons for less desirable plants. Remember when we looked at the lengthening of seasonal allergy seasons when we talked about human health? Plants like ragweed will enjoy these longer growing seasons, too (EPA, 2016 [12]).
Climate change is creating major consequences for water resources through its impacts on the planet’s hydrology.
To put it another way, our impacts on water are a bit of a double whammy. Because anthropogenic climate change is altering water’s distribution, movement, and quality, climate change is also causing humans to adjust the ways we use water.
We'll spend a fair bit of time exploring the impacts of climate change on water resources and understanding how these impacts vary from place to place. But first, it takes a look at the physical impacts of climate change on hydrology so we approach that exploration with a solid foundation of its root causes.
Alterations in hydrology caused by climate change are complex. A simple increase in average temperature results in greater evaporation from soils, drying them out and providing less water to plants and diminished input to groundwater. Less soil water and groundwater lead to lower stream and lake levels and reduced wetland areas. Increased temperatures also mean greater evaporation from lakes and wetlands. Greater evaporation from land surfaces and water bodies, including the oceans, produces more water vapor, which translates into global precipitation increases. (Oh, good news! A few sentences ago it was looking like we were having less water enter the groundwater. Not so fast...)
Those increases, however, are not evenly distributed in time and space (geography matters!). Those places getting much more precipitation find that the increased precipitation offsets the greater evaporation from land and water surfaces; these places are wetter. Those places seeing only a modest increase in precipitation or no increase at all find that increased evaporation rates overshadow precipitation and total available water decreases. Finally, in combination with increased evaporation, those places receiving less precipitation are much drier than before climate change.
These combinations of factors become even more complex if the seasonality of precipitation changes. Some places are becoming wetter in some seasons and drier in others, and the impact of those changes on hydrology is a function of which season is becoming wetter and which one is becoming drier, of the timing of those changes in the annual water cycle, and of the type of precipitation that falls. For example, some mountainous regions are finding that the first snowfall in autumn is coming later and the last snowfall in spring is coming earlier. This change means that the snowfall season is much shorter and snowpacks are much thinner on average. Not only does that change result in less water in the snowpack, but also it causes the release of that water with spring melt to come earlier and to have a significantly smaller peak flow in streams. Regions that rely on mountain snowpacks for their water supply watch these changes with growing alarm. This feels a bit confusing; let's walk through this more carefully with The Importance of Mountain Snowpack to Water Resources [17]. I like this brief write-up because it talks about a few specific regions in the US and what this means for each of them.
More water vapor in the atmosphere from increased evaporation causes some areas to get more rainfall. When the greater latent heat stored in the evaporation process is released by condensation–that is, the formation of clouds–this energy produces stronger updrafts with more liquid water and, ultimately, heavier precipitation. Indeed, like most other areas on Earth, observed precipitation over the United States shows that precipitation totals have been going up for the last century. Moreover, precipitation events are getting more intense and these stronger events are becoming more numerous over most of the country.
The payoff from these changes in hydrology is easy to understand and to document. Despite overall increases in precipitation, drought is becoming more frequent because in those areas where precipitation has not been increasing strongly, greater evaporation results in drier soils and less available water. Even in areas that are becoming wetter on average, a period of decreased rainfall––say, a few weeks––coupled with higher temperatures results in quick drying and rapid conversion to drought. Ironically, the more frequent, more intense downpours lead to more flash floods. Prolonged, stronger wet periods also generate more floods. Thus, climate change results in greater hydrologic variability over time and space, producing more droughts and floods overall and in any one place. Streamflow and groundwater is, therefore, more variable than ever and much harder to predict and manage.
It is worth noting that sea-level rise resulting from climate change also affects hydrology. Saltwater intrusion into coastal aquifers is increasing partly from greater extraction by growing human populations, and partly from the greater osmotic pressures produced by rising sea levels. Simply, when people install wells, they draw down the water table, causing pressure that can pull saltwater into the aquifer. Concurrently, as sea levels rise, the pressure of all that water can force saltwater into the groundwater system. Saltwater is also increasingly working its way upstream in estuaries and coastal rivers, degrading and replacing freshwater.
The impacts presented above are an important subset of the total changes to hydrology produced by climate change. The following section explores how these hydrologic impacts translate into challenges for water resource and other managers.
Drought is especially tough on agricultural production. Nearly all crops require moisture as they germinate, grow, mature, flower, and fruit. Yields of water-intensive crops especially depend on how much water is available during crucial life stages. For instance, corn yields are strongly associated with temperatures and precipitation totals in July: if conditions are cool and wet in that month, then yields will be high; if it is dry and hot in July, then yields will be low. Livestock operations also depend on water. For example, because feedlot cattle require significant quantities of water per cow per day, when drought strikes, feedlots must cut back on the number of cattle they process. It is easy to see that those areas experiencing increased frequencies and intensities of drought because of climate change will feel substantial impacts on agriculture output.
Drought influences many aspects of society beyond municipalities and agriculture. For instance, drought even has a big impact on transportation. A large proportion of U.S. commercial transport occurs on barges along the Ohio, Missouri, and Mississippi Rivers and their tributaries. Over 40 percent of all US grain exports travels on the Mississippi River alone. The devastating drought of 1988 stopped all barge traffic on the Mississippi for weeks and affected billions of dollars in exports. The less severe, but prolonged drought affecting the Missouri River drainage from 2003-2010 diverted products totaling many billions of dollars away from barges and onto less cost-effective trains and trucks. If climate change were to cause more droughts in the Midwest or generally dry out the area, then transportation costs and, subsequently, food costs would rise.
Wet and dry periods have major impacts on the water quantity and water quality of both surface water and groundwater systems. Water quantities go up during wet spells and down during dry spells. Dams and reservoirs help solve surface water quantity problems by helping to control floods during wet periods, holding back floodwaters and allowing them to release gradually, thereby reducing the impact of the flood wave generated by nature. At the same time, dams and reservoirs help maintain adequate water supplies during dry periods by impounding water -- perhaps generated during earlier wet periods -- and releasing it as needed. Climate change could therefore necessitate more dams and reservoirs, with the large economic and environmental costs associated with them, such as the impacts on communities submerged by reservoirs or the impacts on ecosystems caused by changes in the quantities and timings of streamflows.
Groundwater quantities are also greatly influenced by wet and dry periods, with water tables rising when climate is wetter and falling when climate dries. One effect of rising and falling water tables is rising and falling streams. Many people do not realize that most water in streams comes not from storm water, but instead from groundwater. Streams occur at low points where the land surface intersects the water table, so when groundwater rises, stream levels rise. Conversely, when the water table falls below the streambed, the stream dries up, running only when a storm temporarily washes water into the channel. Climate change impacts on groundwater therefore will result in changing streams. Another, more purely human, technology associated with groundwater levels is wells. Wells experience few problems when water tables are high, but when they fall it becomes more difficult for wells to pump water, requiring well owners to purchase bigger pumps or -- in those cases when the water table falls below the well depth--dig deeper wells. Deeper wells and stronger pumps result in overpumping and a further drawdown in the regional water table. Consequently, those areas dependent on groundwater where climate change lowers the water table should expect less and more expensive water.
Water quantity is not the only aspect of water resources affected by climate; climate change will also affect water quality. Where net water quantities increase by moderate amounts, surface water quality will generally improve as streams and lakes fill and dilute their pollutants; where available surface water decreases, pollutants will concentrate and water quality will go down. In those areas where water quantities go up dramatically, or where intense precipitation events become more common, water quality will deteriorate substantially as more pollutants are washed into water supplies. Moreover, overloaded storm and sewage systems will spill effluent into streams and water supplies, producing important health hazards. Exceeded capacities will lead to damages, not only causing health hazards but also costing taxpayers large sums to repair, modify, or replace inadequate and damaged systems. Groundwater quality is declining, too, with climate change. Increasing heavy downpours are washing pollutants into wells more frequently, compromising local drinking water supplies after each heavy precipitation event. Sea level rise is causing more frequent cases of saltwater intrusion into groundwater supplies, making coastal drinking water unpleasant in many instances and undrinkable in others.
Climate change is also increasing competition for water resources. Competition for water already exists in drier areas. The U.S. and Mexico compete over Colorado River water, and Northern and Southern California compete for meltwater from the Sierra Nevada Mountains, for example. Such rivalries will increase as climate continues to dry in the Southwest, snowpacks continue to shrink in California, and other regions experience decreases in water resources. There will be competition not only within regions, but also between regions as water-poor regions fight for survival and water-rich regions seek to maintain competitive economic advantage.
In addition, climate change is bringing growing competition between and within market sectors. For example, in many regions of the nation, competition already exists as agricultural interests, municipalities, and energy production companies vie for shrinking water resources; that struggle is growing more combative over time, even resulting in calls for changes in longstanding water laws. Within sectors, such as agriculture, economically and politically entrenched water-intense activities are competing for water with less powerful, more environmentally sensitive, and less water-intense practices. Such competition will continue to intensify as the distribution of water over time and space changes with the climate.
North America is not the only continent facing this problem. The Murray River in Australia, for instance, is drying up and not reaching the population centers near its mouth. The cause of this drying is a combination of long-term drought and overuse by upstream farmers growing such water-intensive crops as rice. Severe competition therefore exists between agricultural and urban interests.
Links
[1] https://www.cna.org/cna_files/pdf/MAB_5-8-14.pdf
[2] https://documents.wfp.org/stellent/groups/public/documents/newsroom/wfp229182.pdf?_ga=2.178975460.1755706057.1571594290-948000668.1571594290
[3] https://nca2018.globalchange.gov/chapter/10/
[4] https://www.ipcc-data.org/guidelines/pages/glossary/glossary_r.html
[5] https://www.ucsusa.org/resources/climate-change-and-agriculture
[6] https://nca2018.globalchange.gov/downloads/NCA4_Ch07_Ecosystems_Full.pdf
[7] https://www.climate.gov/news-features/climate-and/climate-chocolate
[8] https://www.bloomberg.com/news/articles/2018-08-06/is-climate-change-coming-for-your-champagne
[9] https://www.yaleclimateconnections.org/2018/09/climate-change-could-harm-your-hoppy-brews/
[10] https://www.theguardian.com/environment/2018/may/30/avocado-california-climate-change-affecting-crops-2050
[11] https://www.npr.org/sections/thesalt/2018/10/25/658588158/5-major-crops-in-the-crosshairs-of-climate-change
[12] https://www.epa.gov/climate-indicators/climate-change-indicators-ragweed-pollen-season
[13] https://www.epa.gov/climate-indicators/climate-change-indicators-length-growing-season
[14] https://nca2014.globalchange.gov/report/our-changing-climate/frost-free-season
[15] https://www.waterboards.ca.gov/centralvalley/water_issues/climate_change/1703_r5climate_pres.pdf
[16] http://www.physicalgeography.net/fundamentals/8b.html
[17] https://www.watercalculator.org/water-use/importance-mountain-snowpack-water/
[18] http://climatechangenationalforum.org/
[19] https://www.epa.gov/sites/production/files/2015-12/documents/interagency-climate-change-adaptation-progress-report.pdf
[20] https://www.ipcc.ch/report/ar4/wg1/
[21] http://www.flickr.com/photos/nile_red/5729190970/in/photostream/
[22] http://www.flickr.com/photos/nile_red/
[23] http://creativecommons.org/licenses/by/2.0/
[24] http://www.flickr.com/photos/mundoo/2666984188/in/set-72157613424646919/
[25] http://www.flickr.com/photos/mundoo/
[26] http://creativecommons.org/licenses/by-nc-nd/2.0/
[27] https://pixabay.com/users/stux-12364/
[28] https://pixabay.com/
[29] http://www.flickr.com/photos/mundoo/3256374546/in/set-72157613424646919