As my trip to my parents’ home in western Massachusetts for Thanksgiving drew to a close, a familiar and shocking alert lit up on my phone. Smoke can reduce visibility and air quality in the area. ”In my childhood in rural New England, wildfires were almost unheard of. The main reason for this is that the region receives more than 3 feet of rainfall annually, and fall is usually one of the wettest seasons. But this year, September and October each received less than 2 inches of rain, making it the driest fall in at least 20 years.
The same was true for most parts of the country. On November 5, the U.S. Drought Monitor reported that more than 85% of the continental United States was experiencing “abnormally dry” conditions (or worse). This percentage is the highest since the organization was established as a partner with the University of Nebraska-Lincoln in the United States. The Department of Agriculture and the National Oceanic and Atmospheric Administration began keeping records in 2000.
Remarkably, this included places like Asheville, North Carolina, which was devastated by flooding during Hurricane Helen in late September. After receiving 14 inches of rain in three days, far more than the soil could absorb, the city received just 0.03 inches of rain for the entire month of October. Less than three months after the worst flood in North Carolina’s history, the ground has dried out enough that nearly 90% of the state is in drought.
Closer to home, while water levels in Northern California reservoirs remain healthy after recent atmospheric rivers brought historic rainfall, conditions in the lower Colorado River have worsened in recent months. The region is currently classified as experiencing “extreme drought” by the U.S. Drought Monitor, with Lake Powell and Lake Mead both barely one-third full.
This could be a problem for water managers in Los Angeles and San Diego, especially since those cities have seen less than 10% of normal rainfall since early October. This has led to explosive wildfires like the Franklin Fire in Malibu. Dangerous winter wind patterns are starting to develop at a time when in normal years, heavy rains would have already ended wildfire season.
The boom-and-bust pattern, with periods of severe drought interspersed with unusually heavy rainfall, is a notable effect of climate change. Hot air makes you feel thirsty. Because it can hold more water, it evaporates faster. As a result, climate change causes more groundwater to be lost to the atmosphere, causing droughts to begin earlier during periods of low rainfall. When this extra water vapor is released into the atmosphere, it increases the likelihood of extreme precipitation. But heavier rains do not necessarily lead to groundwater replenishment. Rather, it means more runoff, as the top layer of soil can easily receive more rain than it can absorb.
Although counterintuitive, this is especially true after long periods of drought. In well-hydrated (but not saturated) soils, surface tension can quickly direct water downwards, whereas in dry soils the same process can take up to 100 times longer. there is. Additionally, without proper stormwater management, every gallon of water that runs off as runoff becomes unusable during subsequent droughts. (The American Society of Civil Engineers’ 2021 report gave the country’s stormwater infrastructure a “D” grade.)
As a result of all this, a recent United Nations report found that over the past 30 years (compared to the previous 30 years), 75% of the world’s land has % or more means that the degree of dryness has increased. inches for the same period.
Another problem comes from vegetation. Not only do land plants depend on rain to survive, but they also play an important role by returning moisture to the atmosphere to produce more rain. In fact, the main mode of groundwater loss on land is a process called “transpiration.” This occurs when water is drawn from the soil by the plant’s roots and evaporated from the leaves during photosynthesis.
When the air gets hot, plants are more likely to lose water through transpiration, especially since photosynthesis occurs during the day when temperatures are highest. If a plant cannot get enough water from its roots to meet this demand, air bubbles form in its vascular system and it dies.
This can lead to dangerous feedback cycles in regions of the world where transpiration is the main source of water vapor that becomes precipitation, such as the Amazon rainforest. As drought conditions become more common, parts of the rainforest will wither and die (or be burned in the case of wildfires), leading to reduced transpiration, less rain, more trees dying, etc. A phenomenon occurs. Recent studies suggest that between 10% and 47% of the Amazon could transition from lush rainforest to arid savannah over the next 25 years if deforestation and climate change continue unabated.
There is one factor that works in the opposite direction. It’s carbon fertilization. The main reason plants lose large amounts of water through their leaves is because they need to open microscopic pores called stomata to absorb carbon dioxide. Carbon dioxide (along with water and sunlight) is an important component of photosynthesis. As atmospheric carbon dioxide levels rise, plants open their stomata less frequently, which reduces transpiration and potentially retains more groundwater.
The question of how climate change will affect plant health and groundwater availability across different biomes is a matter of disagreement within the scientific community, with competing models and approaches providing different answers. I’m doing it.
Ultimately, this uncertainty should strengthen preparedness, rather than weaken it. This means implementing measures to reduce catastrophic flooding, such as managing floodplains and replacing pavement with living “green” infrastructure, as well as more efficient irrigation systems and replacing dry lawns with xeriscape. This means implementing improvements that conserve water during droughts. Otherwise, communities will only see more deaths and economic disruption as drought and flood cycles continue to intensify.
Ned Kleiner is a scientist and catastrophe modeler at Verisk. He holds a PhD in atmospheric science from Harvard University.
