Prolonged Drought

A drought is defined as "a period of abnormally dry weather sufficiently prolonged for the lack of water to cause serious hydrologic imbalance in the affected area" according to the Glossary of Meteorology (1959). The Fifth National Climate Assessment (NCA5) states drought is an exceptional period of water shortage for existing ecosystems and the human population (due to low rainfall, high temperature, and/or wind). NOAA NCEI recorded the US has endured 31 drought events causing at least $1 billion in damages each, together totaling over 352.9 billion, from 1980 to 2023. Twenty of those events have occurred since 2000, which is more than double the amount of the previous two decades.

The difference between flash drought and prolonged drought is that:

• If a weather pattern that results in a precipitation deficit lasts for a few weeks or months, it is considered short-term or flash drought.
• If the pattern and precipitation deficits last for more than six months, it is typically considered long-term or prolonged drought. 

Flash Drought: the rapid onset or intensification of drought set in motion by lower-than-normal rates of precipitation, accompanied by abnormally high temperatures, winds, and radiation. Together, these changes in weather can rapidly alter the local climate. Higher temperature increases evapotranspiration—the process by which water is transferred from the land to the atmosphere by evaporation from the soil and by transpiration from plants—and further lowers soil moisture, which decreases rapidly as drought conditions continue. If not predicted and discovered early enough, changes in soil moisture that accompany flash drought can cause extensive damage to agriculture, economies, and ecosystem goods and services. https://www.drought.gov/what-is-drought/flash-drought#:~:text=Flash%20drought%20is%20simply%20the,rapidly%20alter%20the%20local%20climate.

The climatological community has defined four types of drought:

1. Meteorological Drought happens when dry weather patterns dominate an area which can begin and end rapidly.
2. Hydrological Drought occurs when low water supply becomes evident, especially in streams, reservoirs, and groundwater levels, usually after many months of meteorological drought. This is harder to recover from than meteorological drought.
3. Agricultural Drought happens when crops become affected due to rainfall or from soil water deficits, reduced ground water, or lower reservoir levels needed for irrigation.
4. Socioeconomic Drought relates the supply and demand of various commodities to drought (e.g., fruits, vegetables, grains, meat, etc.)

To determine the beginning of drought, measure the change from the average precipitation, or some other climatic variable, over a period of time. This is usually done by comparing the current situation to the historical average, often based on a 30-year period of record. The threshold identified as the beginning of a drought (e.g., 75% of average precipitation over a specified period) is usually established somewhat arbitrarily, rather than on the basis of its precise relationship to specific impacts. (National Drought Mitigation Center https://drought.unl.edu/Education/DroughtIn-depth/WhatisDrought.aspx )

Impacts to water use may include limited access to water for household use, including drinking, cooking, cleaning, and watering plants, as well as for agriculture, transportation, and power generation. Droughts may lead to higher water costs, rationing, or even the decimation of important water sources like wells, as a drought did in a rural California community in 2021.

CISA’s Role in Increasing Drought Resilience

CISA is a member of The National Drought Resilience Partnership, which leverages technical and financial Federal resources, strengthens communication, and fosters collaboration among its members to productively support State, tribal, and local efforts to build, protect, and sustain drought resilience capacity at regional and basin scales. CISA remains a principal partner within the council for reporting to the Water Subcabinet.

CISA has produced the Drought and Infrastructure Planning Guide provided below. The guide is intended to be used by CISA Regional staff; local, tribal, territorial, and regional governments; communities; infrastructure providers; and other stakeholders to anticipate and reduce the potential consequences of droughts on critical water, transportation, dams, power, and other services.

CISA also maintains the Water and Wastewater Systems Sector Working Group.

Critical Infrastructure Impacts

Droughts can impact critical infrastructure sectors such as transportation, energy and water that millions of Americans depend upon. As droughts persist for longer periods of time and expand into more regions, impacts to various critical infrastructure will increase:

• Water supply: During droughts, communities may have limited access to water for household use, including drinking, cooking, cleaning, and watering plants, as well as for agriculture, transportation, and power generation. Droughts may lead to higher water costs, rationing, or even the decimation of important water sources like wells, as a drought did in a rural California community in 2021. 
• Agriculture: Droughts affect livestock and crops, including corn, soybeans, and wheat. 
• Drought can cause overpulling of aquifers resulting in subsidence (ground sinking, potholes, large surface cracks) which can damage all parts of the transportation sector, building foundations, supporting infrastructure, and structural integrity of poles/towers. For example, water pipe leaks were up 25% during part of 2023 in Houston, Texas due to high temperatures and little precipitation causing shifting underground. (AP News, https://apnews.com/article/summer-heat-wave-fd19c3995992c93121ef4baedcbcf07e) 
• Less surface water availability may result in a decreased availability of cooling capability for electricity-heavy facilities like datacenters, nuclear plants, and other powerplants in the energy sector.  
• A threat to water provisions may cause local resource hording or theft through resource security. Theft from key facilities like fire stations, reservoirs, water towers, hospitals, and farms/natural sources have been reported in previous longer-term droughts. 
• Drought impacts can reduce water provision to defense industrial bases, can degrade water quality to healthcare sector facilities, can reduce operations for government facilities, and can halt critical manufacturing and could impact the chemical sector as water is a key component in many mixtures and dilutions. 
• Drought can lead to low-flowing river systems and warmer surface waters more conducive to algal blooms potentially damaging dams and locks, reducing water transportation with cascading impacts to the supply chain, and reduced hydroelectric capabilities across multiple regions. Electricity generation from fossil fuels can increase up to 65% during drought conditions because of reduced generation from hydropower. (PNAS, Drought impacts on the electricity system, emissions, and air quality in the western United States | PNAS)
• Drought can result in higher costs for feed/hay for livestock, smaller crop yields, and marine loss from overheated waters resulting in higher grocery costs nationally and a direct impact to the workforce and homelife security. 
• Increased demand with minimal capabilities to fulfill supply can result in uneven distribution of wealth across farming communities and could result in financial instability spreading from local to regional and influencing national pricing, policy.
• Transportation Sector:  Hot temperatures resulting in increased evaporation during a time with decreased rainfall can result in draft and tow restrictions as water levels in the river system become too low to safely operate. About 60% of all US grain exports move down the Mississippi River to ports in Louisiana, while fertilizer, metals, crude oil and other products move upriver. Due to low flowing river waters from an overall decrease in rainfall across the region, the barge transport reported a delay of more than 2,250 vessels the second week of October 2022. The US Army Corps of Engineers has dredged to make water levels deeper. This has raised costs and made US cargoes more expensive when food inflation is already at its highest level in four decades due to drought impacts across the agriculture sector. Drought is also often accompanied by extreme heat, which can buckle roadways, render airport runways unsafe, and warp public transit cables. Drought-fueled wildfires also have repercussions for travel by closing roadways and railroads and grounding planes when smoke is thick. 
• Energy Sector: Droughts can raise concerns about the reliability of electricity production from plants that require cooling water to maintain safe operations. Hydroelectric power may also become unavailable during droughts. When heat waves coincide with droughts, electricity demands can grow, compounding stress on the grid. 
• Public Health Sector: Reduced flows in rivers and streams can concentrate pollutants, threatening the quality of water used for drinking and recreation. Also, drought-fueled wildfires can expose nearby communities to smoke and pollutants, which can exacerbate chronic respiratory illnesses.