What Causes Droughts?

Question: What Causes Droughts?

Answer:
Droughts are caused by a depletion of precipitation over time. Unlike a dry spell, prolonged lack of rain will cause regions around the world to slowly dry out. Because of the slow onset of droughts, their cost is often only estimated. Frequently, droughts are billion dollar weather events and are one of the top three threats to population in the world (along with famine and flooding).

Sometimes a drought takes decades to develop fully and predicting droughts is difficult. The frequency of droughts in the United States is literally every year. In other words, somewhere in the US in any given year, a drought is occurring. Droughts are completely natural, but their devastation can be far-reaching and severe. Atmospheric conditions such as climate change, ocean temperatures, changes in the jet stream, and changes in the local landscape are all culprits in the long story of the causes of droughts.

The Impacts of Drought

While droughts do not often cause deaths in the United States, the Dust Bowl in the US Midwest is one example of the devastation that can occur. This site has a great list of other famous droughts.

1. There are three main ways droughts impact lives and communities. First, the economic impacts of drought include losses in the timber, agricultural, and fisheries communities. Many of these losses are then passed on to consumers in the form of higher commodity pricing.
2. Next social impacts include increased chance of conflict over commodities, fertile land, and water resources. Other social impacts include abandonment of cultural traditions, loss of homelands, changes in lifestyle, and increased chance of health risks due to poverty and hygiene issues.
3. Finally, the environmental impacts of drought include loss in species biodiversity, migration changes, reduced air quality, and increased soil erosion.

Other parts of the world experience long periods without rains as well. Even during monsoon season, areas that depend on the seasonal rains will often experience drought if the monsoon rains fail. Once crops fail, famine can become a major problem. In some African countries, rain rituals are often used to try and thwart the dry seasons and bring on the rain. While it is no cure, modern technology has developed ways to help see potential famine situations as satellites see famine conditions from space.

Types of Droughts

While droughts can be defined in many ways, three main drought types are commonly discussed. Also available is a chart of the types of droughts.

1. Hydrological Drought

Many watersheds experience depleted amounts of available water. Lack of water in river systems and reservoirs can impact hydroelectric power companies, farmers, wildlife, and communities.
2. Meteorological Drought

A lack of precipitation is the most common definition of drought and is usually the type of drought referred to in news reports and the media. Most locations around the world have their own meteorological definition of drought based on the climate normals in the area. A normally rainy area that gets less rain than usual can be considered in a drought.
3. Agricultural Drought

When soil moisture becomes a problem, the agricultural industry is in trouble with drought. Shortages in precipitation, changes in evapo-transpiration, and reduced ground water levels can create stress and problems for crops.

Preventing, Predicting, and Preparing for Droughts

Several resources are available to help scientists and forecasters to predict droughts.

• Drought Index Charts Use this brief article to determine how to use 8 different drought indices.
• The US Drought PortalSee how drought impacts your community.
• The National Drought Mitigation Center Great details on the difficulties and successes of predicting droughts are available at the NDMC.
• 10 Steps to Drought Preparation A great article for communities, businesses, and families.
• US Seasonal Drought Outlooks The National Weather Service provides predictions of the chances of drought across the United States.

Definition of Drought

Defining a drought is difficult because of the word normal. In many areas, normal conditions generally mean conditions that do not deviate from long-term averages. However, these averages themselves can change over time.

Sources:
NDMC The flow chart and details on the types of droughts are derived from detailed data available from the NDMC.