An all-star cast for this important CRS report 16 September 2021): Charles V. Stern and Eva Lipiec, Coordinators; Lisa S. Benson, Nicole T. Carter, Elena H. Humphreys, Pervaze A. Sheikh, and Megan Stubbs: 'Drought in the United States: Science, Policy, and Selected Federal Authorities'.
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Summary
Drought―a deficiency of moisture that results in adverse effects―occurs to some extent almost every year in areas of the United States. Droughts can simultaneously reduce available water supplies and increase demands for water. Drought has the potential to affect economic and environmental conditions on local, regional, and national scales, as well as to cause disruptions in water supplies for households and communities.Droughts are a component of climate variability and may be seasonal, multiyear, or multi-decadal in duration. According to an August 2021 Intergovernmental Panel on Climate Change (IPCC) report on the physical science of climate change, variable precipitation and rising temperatures are intensifying droughts in some U.S. regions. According to the report, certain types of droughts, such as those causing agricultural impacts, are expected to be more likely in the western and central regions of the United States in the future.
The federal government generally defers to state primacy in surface and groundwater allocation, and states and local entities typically lead efforts to prepare for drought. Multiple federal agencies contribute to these efforts to predict, plan for, and respond to drought. The federal government, and in particular the National Oceanic and Atmospheric Administration (NOAA), plays a key role in researching and monitoring drought through the National Integrated Drought Information System (NIDIS) and the U.S. Drought Monitor. Other federal agencies, such as the U.S. Department of Agriculture (USDA) and the U.S. Geological Survey (USGS), also research and monitor drought factors and conditions. The USDA provides the primary federal financial aid to lessen the impacts of drought and compensate for agricultural production loss after drought onset.
Congress has authorized federal assistance for other aspects of drought, but these programs generally are limited in scope. In localities or watersheds with major projects managed by the U.S. Bureau of Reclamation (Reclamation, which operates exclusively in the 17 arid western states) and the U.S. Army Corps of Engineers (USACE, which operates nationwide), the federal role in water management is more direct and can be especially controversial during times of drought, when multiple users compete for water. Congress has directed both Reclamation and USACE to plan for future droughts at federally authorized projects. Other federal programs, such as those supporting nonfederal efforts to develop water conservation, water reuse and recycling, rural water supplies, or other municipal and industrial water supplies, may prioritize projects that lessen the impacts of drought even when these programs do not focus exclusively on drought.
Severe drought in California from 2012 to 2016, as well as widespread drought in the western United States in 2021 and other recent events, has raised the profile of drought and led to increasing congressional and administrative proposals to prepare for and respond to its impacts. Congressional interest in drought may include new and amended authorities for drought planning and response; emergency appropriations to alleviate drought impacts and enhance related activities; and oversight of ongoing federal drought science, preparedness, and management efforts.
Introduction
Drought―a deficiency of moisture that results in adverse impacts―occurs to some extent almost every year in areas of the United States. Drought has the potential to create economic and environmental impacts on local, regional, and national scales, as well as disruptions in water supplies for households and communities. For example, the National Oceanic and Atmospheric Administration (NOAA) estimates the United States has experienced 29 billion-dollar drought events since 1980, at an estimated total cost of over $267.9 billion. Although droughts are a component of climate variability and may be seasonal, multiyear, or multi-decadal in duration, variable precipitation and rising temperatures are intensifying droughts in some regions. Severe droughts in California from 2012 to 2016, as well as widespread drought in the western United States in 2021, have raised the profile of drought and led to increasing congressional and administrative proposals to prepare for and respond to its impacts.
Multiple federal agencies contribute to efforts to predict, plan for, and respond to drought. NOAA plays a key role in monitoring drought through the National Integrated Drought Information System (NIDIS) and the U.S. Drought Monitor (through a partnership with the University of Nebraska–Lincoln and the U.S. Department of Agriculture [USDA]). USDA provides the primary federal financial aid to lessen drought’s impacts and compensate for agricultural production loss after its onset. Federal water resource agencies such as the U.S. Bureau of Reclamation (Reclamation) and the U.S. Army Corps of Engineers (USACE) face difficult tradeoffs in operating federal water projects during drought; both agencies also have authorities and conduct activities to mitigate drought impacts. Various other federal agencies and emergency authorities also play a role in drought response and mitigation, including the U.S. Environmental Protection Agency (EPA).
This report provides an overview of drought in the United States, including information on drought science, monitoring, and forecasts and on drought types and intensity classifications. It also discusses federal authorities related to drought planning and response, with a focus on selected water-related agricultural, environmental, and natural resource-related authorities with explicit ties to drought. It does not discuss broader disaster-related authorities and their potential nexus to drought, such as the programs and authorities of the Federal Emergency Management Agency (FEMA) and interactions between drought and other hazards and concerns (e.g., wildfire, dust, and public health).
What Is Drought?
Droughts are a component of climate variability and may be seasonal, multiyear, or multi-decadal (sometimes called megadroughts) in duration. Drought may be defined in various ways; NOAA, for instance, defines it as “a deficiency of moisture that results in adverse impacts on people, animals, or vegetation over a sizeable area.” Although a lack of precipitation is often central to drought, high temperatures, high winds, lack of clouds, and low humidity also can contribute. Experts categorize definitions into four basic approaches to measuring drought: meteorological, hydrological, agricultural, and socioeconomic. However, no one definition applies to all circumstances. Meteorological drought typically is defined based on the degree of dryness in comparison to some “normal” or average amount and the duration of a dry period. Meteorological drought is region-specific, because atmospheric conditions creating precipitation deficiencies vary from region to region.
Hydrological drought is defined by the effects that periods of shortfalls in precipitation (including snowfall) have on surface and subsurface water supply, such as streamflows, reservoir and lake levels, and groundwater. The frequency and severity of this type of drought are measured on a watershed or river basin scale.
Agricultural drought links characteristics of meteorological or hydrological drought to agricultural impacts, with a focus on precipitation shortfalls, evapotranspiration differences, soil moisture deficits, reduced groundwater or reservoir levels, and other effects. The timing and severity of drought conditions and the types of plants involved may yield different agricultural impacts. Some experts use the term agricultural and ecological drought to capture not only the agricultural effects but also the ecological effects of drought, such as plant water stress that contributes to tree mortality.
Socioeconomic drought associates the “supply and demand of some economic goods with elements of meteorological, hydrological, and agricultural drought.” A socioeconomic drought may occur when the demand for an economic good, such as water, food grains, fish, or hydroelectric power, exceeds supply due to a shortfall in water supply.
Scientists also have been studying a phenomenon referred to as hot drought. In contrast to precipitation-driven droughts, hot droughts are a result of high air temperatures, as warmer air absorbs more water than cooler air.
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