3.3 Impacts of climate change on water quality
Climate change affects water quality indirectly, by affecting precipitation frequency and intensity, by increasing the variety and growth of invasive species, and by causing sea-level rise.
Under climate change, the variability, timing and intensity of precipitation are changing. Wetter periods are becoming wetter, and dry spells are becoming drier. When storms occur, they are more severe, with higher winds, and higher rainfall in shorter periods of time. Precipitation in temperate and boreal regions is becoming more concentrated in the non-growing season, when plants are not active in water uptake. Throughout the world, droughts may occur at unexpected times of the year, and, in general, may occur earlier in the growing season.
Both drought and flooding can affect water quality. During droughts, water levels drop, concentrating pollutants. Increased levels of toxins and, often, decreased oxygen levels lead to deaths of aquatic organisms, which further increase pollution levels.
Floods increase erosion and sedimentation, overcome water-pollution control structures, and result in dead organisms in the water, which can increase pathogen levels. Settling ponds used to trap water to reduce erosion may overflow, releasing sediment into flood waters. Ponds used to trap animal wastes at large-scale livestock operations known as confined-animal feeding operations (CAFOs) similarly overflow, releasing animal wastes and associated pollutants, including pathogens. Many older cities combine their industrial waste, sewage, and stormwater systems, with the same pipes carrying all three kinds of water to treatment plants. Combined sewer overflows (CSOs) occur when stormwater volumes overwhelm the capacity of water treatment plants to accept inflows. The treatment plants are forced to dump the overflow, including industrial waste and raw sewage, into the receiving waters that usually receive treated water. As flooding increases under climate change, CSOs are also increasing. Projects that separate stormwater pipes from waste/sewage pipes can eliminate CSOs but are expensive and time-consuming.
During severe floods, contaminated water from the all the kinds of overflows described above combine with flood waters to cover the entire landscape, flooding and contaminating fields used to grow food crops, contaminating and damaging homes and businesses, and contaminating wells and bodies of water used for recreation and drinking water. Water treatment plants may be inactive for some period of time due to damage, so that residents must boil water or use bottled water. This further increases the risk of human health impacts.
We have seen in the previous section that warming water can also increase numbers and population sizes of invasive species and can trigger harmful algal blooms. More tropical species continue to move into more polar regions as a result of warming, giving management agencies, industries, and private citizens an increasing number of problem species to address. In addition, global warming can exacerbate existing thermal pollution.
Knowledge Check
Take a moment to complete the short quiz below to assess your understanding of this section. Read each question carefully and refer to the section content as needed. This quiz is not graded – it’s simply an opportunity for you to reflect on what you’ve learned and reinforce key concepts.
