Many people are familiar with flash floods — torrents that develop quickly after heavy rainfall. But there’s also such a thing as a flash drought, and these sudden, extreme dry spells are becoming a big concern for farmers and water utilities.
Flash droughts start and intensify quickly, over periods of weeks to months, compared to years or decades for conventional droughts. Still, they can cause substantial economic damage, since communities have less time to prepare for the impacts of a rapidly evolving drought. In 2017, a flash drought in Montana and the Dakotas damaged crops and grasses that served as forage for cattle, causing US$2.6 billion in agricultural losses.
Flash droughts also can increase wildfire risks, cause public water supply shortages and reduce stream flow, which harms fish and other aquatic life.
These satellite images show the development of a flash drought in the U.S. Southeast in early September 2019. The event began when a stubborn ridge of high-pressure air hung over the region for several weeks, bringing record-breaking temperatures, dry air and very little rain. Evaporative stress is a measure of how ‘thirsty’ the atmosphere is. Move the slider to see the change in moisture. NASA Earth Observatory
Less rain, warmer air
Flash droughts typically result from a combination of lower-then-normal precipitation and higher temperatures. Together, these factors reduce overall land surface moisture.
Water constantly cycles between land and the atmosphere. Under normal conditions, moisture from rainfall or snowfall accumulates in the soil during wet seasons. Plants draw water up through their roots and release water vapor into the air through their leaves, a process called transpiration. Some moisture also evaporates directly from the soil into the air.
Scientists refer to the amount of water that could be transferred from the land to the atmosphere as evaporative demand — a measure of how “thirsty” the atmosphere is. Higher temperatures increase evaporative demand, which makes water evaporate faster. When soil contains enough moisture, it can meet this demand.
But if soil moisture is depleted — for example, if precipitation drops below normal levels for months — then evaporation from the land surface can’t provide all the moisture that a thirsty atmosphere demands. Reduced moisture at the surface increases surface air temperatures, drying out the soil further. These processes amplify each other, making the area increasingly hot and dry.
Moist regions can have flash droughts
Flash droughts started receiving more attention in the U.S. after notable events in 2012, 2016 and 2017 that reduced crop yields and increased wildfire risks. In 2012, areas in the Midwest that had had near-normal precipitation conditions through May fell into severe drought conditions in June and July, causing more than $30 billion in damages.
New England, typically one of the wetter U.S. regions, experienced a flash drought in the summer of 2022, with areas including Boston and Rhode Island receiving only a fraction of their normal rainfall. Across Massachusetts, critically low water levels forced towns to issue mandatory water restrictions for residents.
Planning for flash droughts in a changing climate
Conventional droughts, like the Dust Bowl of the 1930s or the current 22-year drought across the southwestern U.S., develop over periods of years. Scientists rely on monitoring and prediction tools, such as measurements of temperature and rainfall, as well as models, to forecast their evolution.
Predicting flash drought events that occur on monthly to weekly time scales is much harder with current data and tools, largely due to the chaotic nature of weather and limitations in weather models. That’s why weather forecasters don’t typically make projections beyond 10 days — there is a lot of variation in what can happen over longer time spans.
And climate patterns can shift from year to year, adding to the challenge. For example, Boston had a very wet summer in 2021 before its very dry summer in 2022.
Scientists expect climate change to make precipitation even more variable, especially in wetter regions like the U.S. Northeast. This will make it more difficult to forecast and prepare for flash droughts well in advance.
But new monitoring tools that measure evaporative demand can provide early warnings for regions experiencing abnormal conditions. Information from these systems can give farmers and utilities sufficient lead time to adjust their operations and minimize their risks.
Antonia Hadjimichael receives funding from the U.S. Department of Energy.
This article is republished from The Conversation under a Creative Commons license.
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The United States, specifically the Southwest, has not experienced a drought as severe as the one it is presently withstanding in roughly 1,200 years. Any drought lasting longer than 20 years is considered a megadrought. The American West is entering year 23 of devastating dryness, and by most measures, the situation is worsening. Experts say these conditions could last through 2030.
Between 2000 and 2021, temperatures in the West were, on average, 1.6 degrees Fahrenheit warmer than during the previous 50 years. As a result, about 75% of all land in the nine westernmost states in the continental U.S. are facing drought conditions; 35% of the land in those states is baking under drought conditions classified as extreme or exceptional. And while the situation is worst in the West, more than 80% of the U.S. is facing abnormally dry conditions, according to the U.S. Drought Monitor.
Major systems pivotal to daily life and economic stability in the West are under threat. The flow of the Colorado River, a lifeline for 40 million people in the upper and lower river basins, has declined by 20% since the start of the megadrought. Reservoirs along the river, like Lake Mead and Lake Powell, are central to agricultural and utility operations, and they are drying up at certain times of the year at a rate of 1 foot per week.
A 2022 UCLA study found that human-caused climate change has led to a 42% reduction in soil moisture, which is among the most serious consequences of drought. As temperatures rise, moisture is sapped from the soil, leaving behind poor-quality or unworkable farmland. Seasonal snowmelts, which help to quench dry lands, are happening earlier and faster and cannot adequately replenish moisture. Moisture reductions in the vegetation also lead to an increased risk of wildfires, turning entire landscapes into tinderboxes.
Droughts are likely to be a regular occurrence in the future. To better understand what our future might look like, and how we could be better prepared, Stacker cited data from the U.S. Drought Monitor, USDA Natural Resources Conservation Service, and the California Department of Water Resources to visualize the current megadrought in the West and its impact on the region.
You may also like: What summer weather was like the year you were born
https://s3.amazonaws.com/stacker-images/10180X3A.png
The United States, specifically the Southwest, has not experienced a drought as severe as the one it is presently withstanding in roughly 1,200 years. Any drought lasting longer than 20 years is considered a megadrought. The American West is entering year 23 of devastating dryness, and by most measures, the situation is worsening. Experts say these conditions could last through 2030.
Between 2000 and 2021, temperatures in the West were, on average, 1.6 degrees Fahrenheit warmer than during the previous 50 years. As a result, about 75% of all land in the nine westernmost states in the continental U.S. are facing drought conditions; 35% of the land in those states is baking under drought conditions classified as extreme or exceptional. And while the situation is worst in the West, more than 80% of the U.S. is facing abnormally dry conditions, according to the U.S. Drought Monitor.
Major systems pivotal to daily life and economic stability in the West are under threat. The flow of the Colorado River, a lifeline for 40 million people in the upper and lower river basins, has declined by 20% since the start of the megadrought. Reservoirs along the river, like Lake Mead and Lake Powell, are central to agricultural and utility operations, and they are drying up at certain times of the year at a rate of 1 foot per week.
A 2022 UCLA study found that human-caused climate change has led to a 42% reduction in soil moisture, which is among the most serious consequences of drought. As temperatures rise, moisture is sapped from the soil, leaving behind poor-quality or unworkable farmland. Seasonal snowmelts, which help to quench dry lands, are happening earlier and faster and cannot adequately replenish moisture. Moisture reductions in the vegetation also lead to an increased risk of wildfires, turning entire landscapes into tinderboxes.
Droughts are likely to be a regular occurrence in the future. To better understand what our future might look like, and how we could be better prepared, Stacker cited data from the U.S. Drought Monitor, USDA Natural Resources Conservation Service, and the California Department of Water Resources to visualize the current megadrought in the West and its impact on the region.
You may also like: What summer weather was like the year you were born
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Emma Rubin // Stacker
Over a quarter of all land in the West experienced exceptional drought conditions during the summer of 2021. This designation is defined primarily by widespread and exceptional loss of agricultural lands like crops and pastures and water emergencies due to extensive reservoir, river, stream, and well depletion, according to the U.S. Drought Monitor. The central valley region of California, home to more than 5 million acres of farmland, is among the hardest hit by exceptional drought.
Emma Rubin // Stacker
Over a quarter of all land in the West experienced exceptional drought conditions during the summer of 2021. This designation is defined primarily by widespread and exceptional loss of agricultural lands like crops and pastures and water emergencies due to extensive reservoir, river, stream, and well depletion, according to the U.S. Drought Monitor. The central valley region of California, home to more than 5 million acres of farmland, is among the hardest hit by exceptional drought.
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Emma Rubin // Stacker
Prolonged drought exacerbated by human-driven climate change is depleting reservoirs throughout the West. In California alone, nearly every major reservoir is below—often significantly below—historical averages, according to data collected by the California Department of Water Resources. Due to drought conditions, hydroelectric power in California was down by nearly 50% in 2021.
Lake Mead and Lake Powell, the two largest reservoirs in the U.S., recorded unprecedented low water levels in 2021. Over the last two decades, Lake Mead has been depleted from roughly 1,200 feet to 1,041 ft. If the reservoir falls below 895 feet, reaching what experts call "dead pool" status, water will not be able to flow downstream from the Hoover Dam, impacting hydroelectric capacity, drinking water access, and irrigation for more than 25 million people who rely on the lake for daily life. Experts believe this possible outcome is still years away.
To preserve the Colorado River system, the U.S. Bureau of Reclamation announced the first-ever tier 2a shortage for Lake Mead in August 2022, instituting water usage restrictions for millions throughout lower basin states, including a one-fifth reduction in Arizona.
Emma Rubin // Stacker
Prolonged drought exacerbated by human-driven climate change is depleting reservoirs throughout the West. In California alone, nearly every major reservoir is below—often significantly below—historical averages, according to data collected by the California Department of Water Resources. Due to drought conditions, hydroelectric power in California was down by nearly 50% in 2021.
Lake Mead and Lake Powell, the two largest reservoirs in the U.S., recorded unprecedented low water levels in 2021. Over the last two decades, Lake Mead has been depleted from roughly 1,200 feet to 1,041 ft. If the reservoir falls below 895 feet, reaching what experts call "dead pool" status, water will not be able to flow downstream from the Hoover Dam, impacting hydroelectric capacity, drinking water access, and irrigation for more than 25 million people who rely on the lake for daily life. Experts believe this possible outcome is still years away.
To preserve the Colorado River system, the U.S. Bureau of Reclamation announced the first-ever tier 2a shortage for Lake Mead in August 2022, instituting water usage restrictions for millions throughout lower basin states, including a one-fifth reduction in Arizona.
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PATRICK T. FALLON/AFP via Getty Images
As extreme drought dries out and kills plant life, this natural waste acts as vegetative fuel, or tinder, for wildfires. The buildup of this fuel, when ignited, can lead to hotter, larger fires that spread faster and burn longer. Carefully planned controlled burns executed by fire professionals are essential to maintaining a healthy ecosystem by clearing vegetative fuel, unhealthy flora, and overgrowth. The U.S. Forest Service has acknowledged the agency's fire mitigation efforts have not matched the worsening conditions on the ground and, as a result, is committed to treating 50 million acres of government-owned, tribal, and private lands against wildfires. These intentional burns are not without risk, however. The largest wildfire in New Mexico's history, which took place in May 2022, resulted from a controlled burn that escaped its confines.
Another factor that makes dry landscapes so dangerous and prone to wildfires is humans. People ignite about 85% of all wildfires in the U.S., often in regions called the wildland-urban interface where human development meets wild, often drought-ridden land. Highly desirable real estate regions in the West and Southwest, including the Sierra Nevada foothills, San Francisco Bay, San Diego, and San Antonio, have some of the largest swaths of land covered in this type of low-moisture vegetative fuel. In recent years, they have also experienced significant population increases, creating a volatile mixture of tinder and spark.
PATRICK T. FALLON/AFP via Getty Images
As extreme drought dries out and kills plant life, this natural waste acts as vegetative fuel, or tinder, for wildfires. The buildup of this fuel, when ignited, can lead to hotter, larger fires that spread faster and burn longer. Carefully planned controlled burns executed by fire professionals are essential to maintaining a healthy ecosystem by clearing vegetative fuel, unhealthy flora, and overgrowth. The U.S. Forest Service has acknowledged the agency's fire mitigation efforts have not matched the worsening conditions on the ground and, as a result, is committed to treating 50 million acres of government-owned, tribal, and private lands against wildfires. These intentional burns are not without risk, however. The largest wildfire in New Mexico's history, which took place in May 2022, resulted from a controlled burn that escaped its confines.
Another factor that makes dry landscapes so dangerous and prone to wildfires is humans. People ignite about 85% of all wildfires in the U.S., often in regions called the wildland-urban interface where human development meets wild, often drought-ridden land. Highly desirable real estate regions in the West and Southwest, including the Sierra Nevada foothills, San Francisco Bay, San Diego, and San Antonio, have some of the largest swaths of land covered in this type of low-moisture vegetative fuel. In recent years, they have also experienced significant population increases, creating a volatile mixture of tinder and spark.
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ROBYN BECK/AFP via Getty Images
The agricultural industry in the American West is contending with severely low soil moisture, record-low precipitation rates, and severely reduced water allotments to irrigate farmlands. In 2021, drought in California led to economic losses totaling more than $1 billion, as well as the elimination of nearly 9,000 jobs for farmers and thousands more across upstream industries that touch the agricultural sector. According to the California Department of Food and Agriculture, about 400,000 acres of farmland were fallowed due to water scarcity.
In Texas, cotton farmers anticipate half a normal yield in 2022 and a loss of $2 billion. Drought impacts crops like cotton, grains, fruits, and nuts, as well as the pastures livestock farmers rely on to feed their herds. More than two-thirds of livestock farmers in the West have had to reduce the size of their herds and fallow rangelands due to water scarcity, according to a 2022 survey conducted by the American Farm Bureau Federation.
ROBYN BECK/AFP via Getty Images
The agricultural industry in the American West is contending with severely low soil moisture, record-low precipitation rates, and severely reduced water allotments to irrigate farmlands. In 2021, drought in California led to economic losses totaling more than $1 billion, as well as the elimination of nearly 9,000 jobs for farmers and thousands more across upstream industries that touch the agricultural sector. According to the California Department of Food and Agriculture, about 400,000 acres of farmland were fallowed due to water scarcity.
In Texas, cotton farmers anticipate half a normal yield in 2022 and a loss of $2 billion. Drought impacts crops like cotton, grains, fruits, and nuts, as well as the pastures livestock farmers rely on to feed their herds. More than two-thirds of livestock farmers in the West have had to reduce the size of their herds and fallow rangelands due to water scarcity, according to a 2022 survey conducted by the American Farm Bureau Federation.
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David McNew // Getty Images
Food shortages, dehydration, habitat loss, and even biological changes induced by heat are all causes of declining animal populations in the drought-stricken West, with ripple effects echoing throughout the food web. The food supply for foraging species like the mule deer is dwindling and, as a result, so are their populations. Cold-water fish struggle to breathe in warmer, less oxygenated water and must compete for resources with invasive species that thrive in warmer temperatures. Less food availability means certain species cannot reach full maturity, which is critically important for animals like elk who use antlers—a sign of their physical maturity—to joust for territorial or mating rights. These environmental changes also push more species into contact and often conflict with humans as they seek water and food in the communities abutting their natural habitats.
David McNew // Getty Images
Food shortages, dehydration, habitat loss, and even biological changes induced by heat are all causes of declining animal populations in the drought-stricken West, with ripple effects echoing throughout the food web. The food supply for foraging species like the mule deer is dwindling and, as a result, so are their populations. Cold-water fish struggle to breathe in warmer, less oxygenated water and must compete for resources with invasive species that thrive in warmer temperatures. Less food availability means certain species cannot reach full maturity, which is critically important for animals like elk who use antlers—a sign of their physical maturity—to joust for territorial or mating rights. These environmental changes also push more species into contact and often conflict with humans as they seek water and food in the communities abutting their natural habitats.
