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Heavier Rainfall Will Increase Water Pollution In the Future (nationalgeographic.com)
An anonymous reader shares a report from National Geographic: If climate change continues to progress, increased precipitation could mean detrimental outcomes for water quality in the United States, a major new study warns. An intensifying water cycle can substantially overload waterways with excess nitrogen runoff -- which could near 20 percent by 2100 -- and increase the likelihood of events that severely impair water quality, according to a new study published by Science. When rainfall washes nitrogen and phosphorus from human activities like agriculture and fossil fuel combustion into rivers and lakes, those waterways are overloaded with nutrients, and a phenomenon called "eutrophication" occurs. This can be dangerous for both people and animals. Toxic algal blooms can develop, as well as harmful low-oxygen dead zones known as hypoxia, which can cause negative impacts on human health, aquatic ecosystems, and the economy. In the new study, researchers predict how climate change might increase eutrophication and threats to water resources by using projections from 21 different climate models, each of which was run for three climate scenarios and two different time periods (near future, 2031-2060, and far-future, 2071-2100).
If we were talking about pure rainwater falling directly into bodies of water, it would. But we're talking about runoff. After that initially pure water runs over the land it's not so pure by the time it reaches a natural water body.
Take an empty cup and fill it from a city gutter during a heavy rain. Now drink it. Not an attractive proposition, is it?
In the case of eutrophication, we're worried about fertilizers applied to crops and lawns. This is in the form of various highly soluble nitrogen and phosphorous salts which are highly soluble and readily washed away. People use these highly soluble compounds because they stimulate rapid plant growth. These do the same thing for microorganisms when they reach a marine or fresh water body.
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For those who are merely confused and ignorant, yet not fully deprived of intellectual honesty or interest in learning, here are two excerpts from Wikipedia that may help:
“Assuming high growth in GHG emissions (IPCC scenario RCP8.5), presently dry regions may be affected by an increase in the risk of drought and reductions in soil moisture. Over most of the mid-latitude land masses and wet tropical regions, extreme precipitation events will very likely become more intense and frequent.” (in “Effects of global warming”).
“The warmer atmospheric temperatures observed over the past decades are expected to lead to a more vigorous hydrological cycle, including more extreme rainfall events. Erosion and soil degradation is more likely to occur.” (in “Climate change and agriculture”).