Category: Drought

Climatologist: Vegetation plays a role in developing flash droughts

By Lisa Sheppard, Prairie Research Institute

Farmland vegetation and grasses can affect both the frequency and extent of flash droughts, say scientists at the Illinois State Water Survey (ISWS), who hope to better understand the phenomenon and improve early warnings.

Flash droughts intensify quickly compared to normal droughts, magnifying the resulting economic and environmental effects. Typical droughts can take many months or years to reach peak intensity, whereas flash droughts can become severe within weeks.

In the past few years, scientists have begun examining flash droughts to learn more about the climatic, atmospheric, and environmental conditions that affect them.

“The flash drought is a new type of rapidly developing drought, and there is still a lack of consensus in its definition,” said ISWS climatologist Liang Chen. “Ever since the drought in the summer of 2012, flash droughts have received more attention from the scientific community, particularly because the impact on crop production is so much greater and stakeholders have much less time to prepare.”

The 2012 drought in the central U.S.—one of the most intense droughts on record—was later categorized as a flash drought because of how swiftly it developed. Soil moisture conditions that were normal in early June declined to what is considered exceptional drought just eight weeks later.

Chen and his colleagues studied the climatology of warm-season flash drought occurrence in the United States using data from 1979 to 2014 and experiments in a climate model. Findings showed that vegetation greening over the spring and summer months can significantly increase flash drought occurrence, particularly in the Great Plains and in the western U.S. The extent of flash droughts is also affected, but the duration is not.

A primary reason for the drought sensitivity to vegetation is the enhanced evapotranspiration that can deplete soil moisture with little effect on the health of vegetation until the soil moisture approaches the wilting point of plants. With evapotranspiration, water is transferred from the land to the atmosphere through evaporation from the soil and transpiration from plants.

Variable rainfall, leading to changes in soil moisture, also can potentially cause more flash drought events.

In the Midwest and in the eastern U.S., adequate rainfall and humidity typically provide enough moisture for vegetation and can offset reductions in soil moisture, so flash droughts are more sensitive to vegetation phenology in semi-arid and arid areas than in humid regions.

Climate projections show increasing drought conditions in large parts of the country, so there will likely be an increased risk of flash droughts in a warming climate, Chen said. Although irrigation is a potential option to decrease the risk of flash droughts, groundwater depletion in some areas of the country will likely pose challenges for meeting irrigation water demand.

The results of early studies such as this one can be influenced by the climate model used and the way that flash drought is defined. Chen and his colleagues plan to conduct more experiments to find more answers on how flash droughts develop in their future work.

This study was published in the Journal of Hydrometeorology. State Climatologist Trent Ford, also an author on this study, was interviewed for a previous story about flash drought.

Media contacts: Liang Chen,

This post originally appeared on the Prairie Research Institute blog. Read the original post.

Climate change is hitting the Colorado River ‘incredibly fast and incredibly hard’

Read the full story at AzCentral.

The warming climate is intensifying drought, contributing to fires and drying out the river’s headwaters, sending consequences cascading downstream.

Two-thirds of Earth’s land is on pace to lose water as the climate warms – that’s a problem for people, crops and forests

Cape Town residents queued up for water as the taps nearly ran dry in 2018. Morgana Wingard/Getty Images

by Yadu Pokhrel (Michigan State University)

The world watched with a sense of dread in 2018 as Cape Town, South Africa, counted down the days until the city would run out of water. The region’s surface reservoirs were going dry amid its worst drought on record, and the public countdown was a plea for help.

By drastically cutting their water use, Cape Town residents and farmers were able to push back “Day Zero” until the rain came, but the close call showed just how precarious water security can be. California also faced severe water restrictions during its recent multiyear drought. And Mexico City is now facing water restrictions after a year with little rain.

There are growing concerns that many regions of the world will face water crises like these in the coming decades as rising temperatures exacerbate drought conditions.

Understanding the risks ahead requires looking at the entire landscape of terrestrial water storage – not just the rivers, but also the water stored in soils, groundwater, snowpack, forest canopies, wetlands, lakes and reservoirs.

We study changes in the terrestrial water cycle as engineers and hydrologists. In a new study published Jan. 11, we and a team of colleagues from universities and institutes around the world showed for the first time how climate change will likely affect water availability on land from all water storage sources over the course of this century.

We found that the sum of this terrestrial water storage is on pace to decline across two-thirds of the land on the planet. The worst impacts will be in areas of the Southern Hemisphere where water scarcity is already threatening food security and leading to human migration and conflict. Globally, one in 12 people could face extreme drought related to water storage every year by the end of this century, compared to an average of about one in 33 at the end of the 20th century.

These findings have implications for water availability, not only for human needs, but also for trees, plants and the sustainability of agriculture.

Where the risks are highest

The water that keeps land healthy, crops growing and human needs met comes from a variety of sources. Mountain snow and rainfall feed streams that affect community water supplies. Soil water content directly affects plant growth. Groundwater resources are crucial for both drinking water supplies and crop productivity in irrigated regions.

While studies often focus just on river flow as an indicator of water availability and drought, our study instead provides a holistic picture of the changes in total water available on land. That allows us to capture nuances, such as the ability of forests to draw water from deep groundwater sources during years when the upper soil levels are drier.

The declines we found in land water storage are especially alarming in the Amazon River basin, Australia, southern Africa, the Mediterranean region and parts of the United States. In these regions, precipitation is expected to decline sharply with climate change, and rising temperatures will increase evaporation. At the same time, some other regions will become wetter, a process already seen today.

Map of water storage loss
The map shows the projected change in terrestrial water storage by the end of the 21st century, compared to the 1975-2005 average, under a mid-range scenario for global warming. A continuum of yellow to orange to dark red reflects increasing severity of loss of stored water; teal to blue to dark blue reflects increasing gains in stored water. Yadu Pokhrel, et al, Nature Climate Change, 2021, CC BY-ND

Our findings for the Amazon basin add to the longstanding debate over the fate of the rainforest in a warmer world. Many studies using climate model projections have warned of widespread forest die-off in the future as less rainfall and warmer temperatures lead to higher heat and moisture stress combined with forest fires.

In an earlier study, we found that the deep-rooted rainforests may be more resilient to short-term drought than they appear because they can tap water stored in soils deeper in the ground that aren’t considered in typical climate model projections. However, our new findings, using multiple models, indicate that the declines in total water storage, including deep groundwater stores, may lead to more water shortages during dry seasons when trees need stored water the most and exacerbate future droughts. All weaken the resilience of the rainforests.

A new way of looking at drought

Our study also provides a new perspective on future droughts.

There are different kinds of droughts. Meteorological droughts are caused by lack of precipitation. Agricultural droughts are caused by lack of water in soils. Hydrological droughts involve lack of water in rivers and groundwater. We provided a new perspective on droughts by looking at the total water storage.

Diagram of water cycle
Water in the environment. U.K. Met Office

We found that moderate to severe droughts involving water storage would increase until the middle of the 21st century and then remain stable under future scenarios in which countries cut their emissions, but extreme to exceptional water storage droughts could continue to increase until the end of the century.

That would further threaten water availability in regions where water storage is projected to decline.

Changes driven by global warming

These declines in water storage and increases in future droughts are primarily driven by climate change, not land-water management activities such as irrigation and groundwater pumping. This became clear when we examined simulations of what the future would look like if climate conditions were unchanged from preindustrial times. Without the increase in greenhouse gas emissions, terrestrial water storage would remain generally stable in most regions.

If future increases in groundwater use for irrigation and other needs are also considered, the projected reduction in water storage and increase in drought could be even more severe.

Yadu Pokhrel, Associate Professor of Civil and Environmental Engineering, Michigan State University

This article is republished from The Conversation under a Creative Commons license. Read the original article.

Error Correction Means California’s Future Wetter Winters May Never Come

Read the full story from the Pacific Northwest National Laboratory.

California and other areas of the U.S. Southwest may see less future winter precipitation than previously projected by climate models. After probing a persistent error in widely used models, researchers at the Department of Energy’s Pacific Northwest National Laboratory estimate that California will likely experience drier winters in the future than projected by some climate models, meaning residents may see less spring runoff, higher spring temperatures, and an increased risk of wildfire in coming years.

Earth scientist Lu Dong, who led the study alongside atmospheric scientist Ruby Leung, presented her findings at the American Geophysical Union’s fall meeting on Tuesday, Dec. 1, and will answer questions virtually on Wednesday, Dec. 16.

Nearly Half of the U.S. Is in Drought. It May Get Worse.

Read the full story in the New York Times.

The most widespread drought in the continental United States since 2013 covers more than 45 percent of the Lower 48 states, federal scientists said.

The effects of repeated droughts on different kinds of forests

Read the full story from the University of California – Santa Barbara.

Drought is endemic to the American West along with heatwaves and intense wildfires. But scientists are only beginning to understand how the effects of multiple droughts can compound to affect forests differently than a single drought alone.

Associated journal article: William R. L. Anderegg, Anna T. Trugman, Grayson Badgley, Alexandra G. Konings, John Shaw. Divergent forest sensitivity to repeated extreme droughtsNature Climate Change, 2020; DOI: 10.1038/s41558-020-00919-1

Atmospheric dust levels are rising in the Great Plains

Read the full story from the University of Utah.

A study finds that atmospheric dust levels are rising across the Great Plains at a rate of up to 5% per year. The trend of rising dust parallels expansion of cropland and even seasonal crop cycles. And if the Great Plains becomes drier, a possibility under climate change scenarios, then all the pieces are in place for a repeat of the Dust Bowl that devastated the Midwest in the 1930s.

Associated journal article: Andrew Lambert, A. Gannet Hallar, Maria Garcia, Courtenay Strong, Elisabeth Andrews, Jenny L. Hand. Dust Impacts of Rapid Agricultural Expansion on the Great PlainsGeophysical Research Letters, 2020; DOI: 10.1029/2020GL090347

New Citizen Science Program Will Use Social Media Posts To Monitor Drought In Utah

Read the full story from Utah Public Radio.

Through a new citizen science initiative, the Utah Climate Center will capture drought data through public observations posted on social media.

Redefining drought in the US Corn Belt

Read the full story from the University of Illinois.

As the climate trends warmer and drier, global food security increasingly hinges on crops’ ability to withstand drought. But are scientists and producers focusing on the right metric when measuring crop-relevant drought? Not exactly, according to new research from University of Illinois scientists, who urge the scientific community to redefine the term.

“Plants have to balance water supply and demand. Both are extremely critical, but people overlook the demand side of the equation, especially in the U.S. Corn Belt,” says Kaiyu Guan, principal investigator on two new studies, Blue Waters professor in the Department of Natural Resources and Environmental Sciences and the National Center for Supercomputing Applications at Illinois.

Associated journal articles
1) Kimm, H., et al (2020). “Redefining droughts for the U.S. Corn Belt: The dominant role of atmospheric vapor pressure deficit over soil moisture in regulating stomatal behavior of Maize and Soybean.” Agricultural and Forest Meteorology 287, 107930.

2) Zhou, W., et al (2020). “Connections between the hydrological cycle and crop yield in the rainfed U.S. Corn Belt.” Journal of Hydrology 590, 125398.

Illinois team contributes to vital weekly drought assessment

by Tricia Barker, Prairie Research Institute

Every week, the U.S. Drought Monitor releases a map showing which parts of the country are experiencing drought. The drought monitor is used to make critical decisions, such as disaster declarations, drought responses, and eligibility for assistance programs. 

While the U.S. Drought Monitor draws on multiple objective data indicators, like rainfall levels, it also relies on experts across the country, to synthesize and interpret this data and provide their local recommendations.Illinois State Climatologist Trent Ford coordinates the Illinois drought advisory team, which includes several scientists from the Illinois State Water Survey, representatives of the five National Weather Service offices covering Illinois, the director of the USDA Midwest Climate Hub, and other drought specialists. 

The drought map is issued each Thursday and provides a snapshot of the past week’s drought conditions. In order for the weekly map’s author—one of several experts across the country who cover this role in shifts—to produce the drought snapshot each Thursday, they need to receive input from the Illinois team no later than Tuesday. That means Ford typically starts on Sunday to compile data and develop a draft recommendation for the Illinois team. 

Sometimes, this is a quick process. For example, in the first quarter of 2020, Illinois was receiving lots of precipitation and had to worry more about flooding—all the data clearly indicated Illinois was not experiencing drought. But starting in late May and early June, the state has had some areas that were receiving little rainfall

According to the U.S. Drought Monitor map released on Aug. 27, a few patches of Northern Illinois are experiencing “moderate drought” (light orange). The larger yellow region is considered abnormally dry, but not (yet) in a state of drought. 

“For most of this summer, we’ve had more involved discussions about what indicators are showing us for Illinois,” Ford said. “When some indicators are pointing to no drought and some are pointing to drought, or when indicators are pointing to different severities of drought, that’s when it’s most important for our Illinois team to make recommendations to the author of the national map.” 

The team draws on a wealth of objective data to make their recommendations. Precipitation data from weather stations, citizen scientists, and radar are key, of course, but rainfall anomalies, temperatures, soil moisturestreamflow, and the condition of crops and native vegetation are also taken into consideration. 

Data and observations from citizen scientists, farmers, and other Illinoisans supplements the long-term data collected by the Water Survey and NWS. For example, more than 20,000 volunteers across the country contribute weather observations to the Community Collaborative Rain, Hail and Snow Network (CoCoRaHS), and Illinois farmers and gardeners often send Ford photos of the condition of their crops, lawns, and other vegetation. He considers all of this information in addition to the satellite remote sensing and his own observations of Illinois conditions.  

Currently, Illinois is not experiencing the type of widespread, severe drought it saw in 2012, but the northern third of the state is dry and hot. 

“We had spotty, heavy rainfall in July and August, so most areas of Northern Illinois have gotten timely enough rain to just skirt drought,” Ford said. On the U.S. Drought Monitor map released on Aug. 27, most of Northern Illinois is categorized as D0—abnormally dry, but not yet in drought. 

When temperatures surged into the 90s, the abnormally high heat evaporated the scant moisture reserves in some areas, pushing them into D1, or moderate drought. 

“That’s what we refer to as a ‘flash drought’, when the longer-term precipitation deficit is compounded by short but acute increases in temperature,” Ford explained. 

This post originally appeared on the Prairie Research Institute blog. View the original post.

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