Aridity and Drought

Drought is a prolonged period of abnormally low precipitation that can lead to water shortages, impacting ecosystems, agriculture, water supply, and various human activities. It is a complex natural hazard with significant environmental, social, and economic consequences. Here are key aspects of drought:

Types of drought

Depending on the variables used to characterize it and the systems or sectors being impacted, drought may be classified in different types, such as

• Meteorological drought: Lack of rainfall or below-average precipitation for an extended period characterizes meteorological drought. This is the most common form of drought.

• Hydrological drought: Hydrological drought refers to water shortage in streams or storages such as reservoirs, lakes, lagoons, and groundwater which usually occurs due to prolonged dry conditions.

• Agricultural and ecological drought: Agricultural drought relates to soil moisture deficits that affect crop growth. It occurs when there's not enough water in the soil to meet the needs of crops.

Impacts of Drought

Drought has extensive impacts across multiple sectors, affecting ecosystems, agriculture, water resources, energy production, commerce, public health, and infrastructure stability.

• Ecosystems and Biodiversity: Changes in soil moisture and surface water can alter the rate of carbon uptake by ecosystems, affecting the carbon cycle and overall ecosystem health. They also alter suitable climate zones for wild species, potentially leading to habitat loss and changes in species distributions. The altered conditions can increase can increase the prevalence of pests and pathogen-carrying vectors. Prolonged dry conditions increase the risk of wildfires, as vegetation becomes more susceptible to ignition.
• Agriculture: Reduction in water availability challenges the water supplies needed for irrigation, affecting crop yields. Insufficient water can stress crops and forests, affecting crop quality. Severe water stress can lead to crop failure, especially during key developmental stages or extended drought periods.
• Power and Energy: Production of all types of energy, including electricity, requires water. Because the energy sector is dependent on water availability, drought can severely impact energy systems. Reduced water availability challenges water supplies. For example, lower water levels affect hydropower generation capacity; higher stream temperatures and reduced water availability can impair the cooling processes of thermal power plants.
  • Thermoelectric electricity generation. Thermoelectric power plants use steam turbines to generate electricity using a variety of fuel sources. Large amounts of water are needed to generate steam and for cooling. Drought conditions can result in reduced plant efficiency and generation capacity and can also impact the supply chain for coal, natural gas, biofuel, and nuclear fuel.  
  • Hydroelectric power generation. Hydroelectric power is generated by funneling water through power plants contained in dam structures. When water levels in reservoirs become low, the force of water pressure required to turn hydro turbine blades is reduced, which affects productivity.
  • Hydraulic fracturing and refining. Reduced water availability affects the production and refining of petroleum and natural gas. During droughts, hydraulic fracturing (or fracking) and fuel refining operations can require alternative water supplies or may be forced to temporarily shut down. Shutdowns can increase costs, which in turn can raise consumer prices.
  • Biofuels. Reduced water availability and decreased soil moisture during drought can reduce the cultivation of biofuel feedstocks.
• Manufacturing: Manufacturers use water for many processes, including fabrication, washing, cooling, and transporting goods. Water is also often incorporated into products themselves. Reductions in the amount of available water can reduce manufacturing productivity or even lead to temporary closures of key manufacturing facilities.
• Navigation and Transportation Drought impacts port and waterway transportation and supply chains, resulting in increased transportation costs. Higher temperatures that often coexist with drought can impact roads, airport runways, and rail lines.
• Recreation and Tourism Low water levels can restrict navigation for commerce and recreational activities.

• Public health: Drought increases disease infection rates, such as for West Nile virus. Low flow volume can lead to reduced dissolved oxygen, more concentrated pollutants, and higher stream temperatures, impacting water quality.
  • Compromised quantity and quality of drinking water
  • Effects on air quality
  • Diminished living conditions related to energy, air quality, and sanitation and hygiene
  • Compromised food and nutrition
  • Increased incidence of illness and disease, including anxiety, depression, or other adverse mental health outcomes
  • Increased recreational risks.
• Water Utilities

7. Infrastructure

• Building and Soil Stability: Changes in soil moisture can lead to swelling and shrinkage of clay soils, causing structural damage to buildings.

A reduction in water availability challenges water supplies needed for for municipal, industrial, agriculture and hydropower use.

Low flow volume and intermittency thresholds can indicate reductions in dissolved oxygen, more concentrated pollutants, and higher stream temperatures relevant for ecosystems, water resource quality and thermal power plant cooling . Low water levels may also restrict waterway navigation for commerce and recreation (Forzieri et al., 2018).

Agricultural and ecological drought indices relate to the ability of plants to meet growth and transpiration needs and the timing and duration of droughts can lead to substantially different impacts (Peña-Gallardo et al., 2019). Drought stress for agriculture and ecosystems is difficult to directly observe, and therefore scientists use a variety of drought indices (Table 11.3), proxy information about changes in precipitation supply and reference evapotranspiration demand, the ratio of actual/potential evapotranspiration or a deficit in available soil water content, particularly at rooting level . Drought also raises disease infection rates for West Nile virus (Paull et al., 2017), and the alternation of dry and wet spells induces swelling and shrinkage of clay soils that can lead to sinkholes and destabilize buildings (Hadji et al., 2014).

• Water Scarcity: Reduced precipitation and water availability lead to water scarcity, affecting both surface water and groundwater resources.
• Water Supply Challenges: Municipal water supplies may face shortages, impacting communities, industries, and essential services.
• Wildfires:
• Livestock and Wildlife: Drought affects the availability of water and forage for livestock, leading to challenges in animal husbandry. Wildlife may face similar challenges.

Observed and Projected changes in Drought (TBA)

or called "How does CO2 increase impact drought"

Error creating thumbnail: File missing

Drought related risk analysis

Droughts are often analyzed using indices that are measures of drought severity, duration and frequency . There are many drought indices published in the scientific literature. Below are some metrics and indices used in regional assessments on droughts. They are subdivided into the three drought categories listed above.

Indices for Agricultural and Ecological Drought

Palmer drought severity index (PDSI)

PDSI is a regional drought index commonly used for measuring the severity of drought conditions. It is a standardized index that ranges from -10 (dry) to +10 (wet), with >4 indicating extreme wet conditions and <-4 indicating extreme dry conditions.

Data Access

• Monthly PDSI over global land area on a 2.5 degree grid from Aiguo Dai (ensemble mean monthly data from 1900-2100 using CMIP 6 data is also provided)
• Historical monthly (from 1850/01 to 2014/12) PDSI gridded data
• Current weekly PDSI Indices, maps and info at NOAA CPC
• NCDC Climate Division Data (text); see 'pdsi' key

Methodology

Self-calculating PDSI is not easy as a multitude of computation is involved. Some open-source code is available though. Here is one from Jacobi et al. (2013)(see "Supporting Information" for code).

Other resources

The US Drought monitor

The US Drought Monitor (USDM) is a comprehensive and collaborative effort by several federal agencies, including the National Drought Mitigation Center (NDMC), the United States Department of Agriculture (USDA), and the National Oceanic and Atmospheric Administration (NOAA), among others. It provides up-to-date information and assessment of drought conditions across the United States.

Link for the US Drought Monitor Map (November 2023): https://droughtmonitor.unl.edu/Maps/MapArchive.aspx

Dataset can be accessed here: https://docs.google.com/spreadsheets/d/1k1YhIULXMt4URSIpeJfgfRbiee_YA7oXfl2_s6xfnpk/edit?usp=drive_link

National Integrated Drought Information System

The National Oceanic and Atmospheric Administration’s (NOAA's) National Integrated Drought Information System (NIDIS) program is an integrated information system that coordinates drought monitoring, forecasting, planning, and information at federal, tribal, state, and local levels across the country.

Notes

(Notes from Xiaojuan: List the sectors impacted by drought and create separate page for each sector; the webpage should be information on what and how climate hazards impact the sector

Reference

1. https://climatedata.imf.org/

2. https://yaleclimateconnections.org/2021/06/california-americas-garden-is-drying-out/