A drought is a prolonged period of below-normal precipitation that depletes water supplies and dries out soil, crops, and ecosystems. Unlike a flood or a hurricane, a drought has no single dramatic start. It builds gradually, sometimes over weeks, sometimes over months or years, and its effects ripple outward from dry soil to empty reservoirs to rising food prices. Droughts occur on every continent and rank among the most costly natural disasters worldwide.
How Drought Is Defined
There is no single universal threshold that triggers a “drought.” Instead, scientists classify droughts by what they affect. The National Drought Mitigation Center recognizes several distinct types, each measured differently.
Meteorological drought is the most straightforward: it means a region is getting significantly less rain or snow than normal for an extended period. Some definitions count the number of consecutive days below a precipitation threshold; others compare monthly or seasonal rainfall to historical averages. This is the type most people picture when they hear the word “drought.”
Agricultural drought focuses on what that missing rain does to farms. It tracks soil moisture deficits, how much water crops are losing through evaporation compared to what they’re taking in, and whether groundwater levels can still support irrigation. Because different crops need water at different growth stages, agricultural drought can hit one crop hard while barely affecting another in the same county.
Hydrological drought shows up in rivers, lakes, reservoirs, and underground aquifers. It typically lags behind the other types because surface and groundwater systems take time to respond to reduced rainfall. A region can experience a meteorological drought in winter and not see its reservoirs drop until the following summer.
What Causes a Drought
At the most basic level, drought happens when high-pressure weather systems park over a region and refuse to move. These systems push air downward, which suppresses cloud formation and blocks incoming storms. The longer a high-pressure system persists, the drier conditions become.
Shifts in the jet stream, the river of fast-moving air high in the atmosphere that steers weather systems, play a major role. When the jet stream redirects storm tracks away from a region, that area can go weeks or months without meaningful rain. Large-scale climate patterns like El Niño and La Niña also rearrange global precipitation, pushing wet conditions to some areas and pulling them away from others.
Temperature matters too. Higher temperatures increase evapotranspiration, the process by which water evaporates from soil and is released by plants. Even if rainfall stays near normal, a stretch of extreme heat can dry out the landscape fast enough to trigger drought conditions. A January 2026 NOAA global drought report documented this pattern on nearly every continent: excessive warmth was intensifying and expanding drought in Europe, Asia, Africa, Australia, and large parts of North and South America, all by accelerating moisture loss from the land surface.
Flash Drought: When It Happens Fast
Not all droughts creep in slowly. Flash droughts intensify rapidly, driven by a combination of low rainfall, abnormally high temperatures, strong winds, and increased solar radiation. Together, these factors pull moisture out of the soil at an unusual rate. A landscape that looks healthy can deteriorate into drought conditions in just a few weeks, leaving farmers and water managers with little time to respond. Flash droughts are particularly dangerous for agriculture because crops can be stressed beyond recovery before anyone recognizes the severity.
How Drought Severity Is Measured
In the United States, the U.S. Drought Monitor publishes a weekly map that classifies conditions on a five-level scale:
- D0 (Abnormally Dry): conditions are drier than usual but not yet causing serious problems
- D1 (Moderate Drought): some crop damage, water shortages developing
- D2 (Severe Drought): significant crop and pasture losses, water restrictions likely
- D3 (Extreme Drought): widespread crop failure, major water shortages
- D4 (Exceptional Drought): the worst category, with exceptional and widespread losses
These ratings draw on multiple data streams. One widely used tool is the Palmer Drought Severity Index, which measures cumulative departure from a location’s normal moisture balance on a scale that typically runs from negative 4 (extreme drought) to positive 4 (extremely wet), though more extreme values are possible. A score below negative 3 signals severe to extreme drought.
Effects on Crops and Food Supply
Drought hits agriculture in stages. First, topsoil dries out, stressing shallow-rooted crops and young seedlings. As conditions persist, deeper soil layers lose moisture too, and even established plants begin to wilt, drop leaves, and reduce the energy they put toward producing grain or fruit.
Interestingly, plants exposed to mild water stress early in the growing season sometimes adapt. Research published in a 2022 study found that young crops subjected to early-season dryness invested more resources into deeper root systems. When a second drought hit later in the season, those “primed” plants lost up to 4% less yield for maize and 7% less for soybeans compared to crops that experienced only the late drought. That’s a meaningful buffer, but it only partly offsets losses in a severe drought year.
When crop yields fall broadly, food prices rise. Drought can also shorten growing seasons and create conditions that invite pest infestations and plant disease, compounding the damage beyond what dry soil alone would cause. Livestock suffer too: reduced pasture growth and scarce water lead to malnourished and diseased animals.
Economic Costs
Drought ranks among the most expensive weather-related disasters precisely because it affects so many sectors at once: agriculture, energy production, shipping, tourism, and municipal water systems. An analysis of weather and economic data from the University of Florida found that a surge in extreme heat and severe drought shaves roughly 0.2% off a country’s GDP. That may sound small, but for a large economy it translates to billions of dollars in a single year.
Health Risks During Drought
Drought affects human health in ways that go well beyond thirst. The CDC identifies several pathways.
Air quality deteriorates as dry soil and vegetation generate more airborne dust and particulates. Wildfire risk climbs, filling the air with smoke. Pollen concentrations rise. For people with asthma or other chronic respiratory conditions, these changes can trigger flare-ups, bronchitis, and even bacterial pneumonia. Freshwater algal blooms, which thrive in warm, stagnant water, can release airborne toxins that irritate the lungs.
Water quality drops as rivers and reservoirs shrink, concentrating pollutants, bacteria, and heavy metals. Pathogens like E. coli and Salmonella thrive in the warm, shallow water that remains. When contaminated water is used for irrigation, those pathogens can end up on crops. And when rain finally does arrive, it often runs off the hardened, compacted soil rather than soaking in, washing surface contaminants into water supplies.
Nutrition suffers when low crop yields drive up food prices or cause outright shortages. In lower-income regions, prolonged drought can push vulnerable populations toward malnutrition, particularly children and the elderly.
Why Droughts Are Getting Worse
Rising global temperatures are intensifying droughts even in places where total rainfall hasn’t changed much. The mechanism is straightforward: warmer air pulls more moisture out of soil, plants, rivers, and lakes. NOAA’s January 2026 global drought summary documented this pattern across six continents simultaneously. In Europe, regional warmth increased evaporative demand enough to worsen drought in areas that were only marginally dry. In Africa, persistent heat expanded drought coverage well beyond what precipitation deficits alone would explain. The same story played out in Australia, South America, and parts of North America.
This means that a region receiving the same amount of rain it got 50 years ago can still experience more frequent and more intense droughts, simply because higher temperatures are pulling water out of the landscape faster than precipitation can replace it.