Droughts happen when several climate forces align at once: rising temperatures pull more moisture from soil, stubborn high-pressure systems block rain from arriving, and ocean cycles shift precipitation patterns away from vulnerable regions. No single cause explains every drought, but the combination of warming temperatures, natural climate cycles, and decades of groundwater overuse is making droughts more frequent, more intense, and harder to recover from.
Warmer Air Pulls More Water From the Ground
The most fundamental driver is straightforward physics. As global temperatures rise, warmer air increases the rate of evaporation from soil, lakes, rivers, and vegetation. Water turns to vapor faster than precipitation can replace it, and the ground dries out even in places that still receive some rain. This is why many regions experience drought conditions not because rain has completely stopped, but because the moisture that does fall evaporates before it can soak in and do any good.
This effect compounds over time. Once soil dries out, it triggers a feedback loop that makes things worse. Dry ground heats up more than moist ground because the energy that would normally go into evaporating water instead raises surface temperatures directly. That extra heat pushes cloud bases higher in the atmosphere, and those higher clouds let more solar energy pass through to the surface below. Research modeling the full water cycle from groundwater to cloud tops found that drought conditions increase incoming solar radiation by roughly 2.5 watts per square meter on average, which further dries the land. In short, drought breeds more drought.
High-Pressure Systems That Refuse to Move
Under normal conditions, weather systems travel west to east across the mid-latitudes, delivering regular rounds of rain. Sometimes, though, a large mass of high pressure parks itself over a region and refuses to budge. Meteorologists call this atmospheric blocking, and it can stall weather patterns for days, weeks, or even months.
When a blocking ridge sets up, it acts like a boulder in a stream. Storm systems carrying moisture get diverted around the block instead of passing through it. The region underneath the high-pressure dome gets stuck with clear skies, no rain, and scorching temperatures. The longer the block persists, the deeper the drought becomes. These events are a natural part of atmospheric variability, but research suggests that changes in temperature gradients between the Arctic and the tropics may be making blocking patterns more frequent or longer-lasting in some regions.
Ocean Cycles Steer Rain Toward or Away From Land
Vast ocean temperature patterns exert enormous influence over where rain falls on land. Two cycles matter most for drought in the Americas.
The El Niño-Southern Oscillation (ENSO) swings between El Niño, which warms the central Pacific and shifts rainfall patterns in one direction, and La Niña, which cools those same waters and shifts them back. As of early 2025, the Pacific was in a La Niña phase, with below-average sea surface temperatures across the east-central equatorial Pacific. La Niña typically suppresses rainfall in parts of the southern and western United States while boosting it in the Pacific Northwest and parts of the Ohio Valley. For much of the Southwest, La Niña means drier winters and reduced snowpack, which translates directly into less water during the warm months when demand peaks.
The Pacific Decadal Oscillation (PDO) operates on a longer timescale, cycling every 20 to 30 years. It naturally brings alternating decades of wetter and drier conditions to the western U.S. Recent research combining paleoclimate reconstructions with climate model simulations found that moderate warming in the Northern Hemisphere can lock North Pacific sea surface temperatures into a pattern that dramatically reduces winter precipitation in the Southwest. If global temperatures continue to rise, models suggest the Southwest could remain in a drought-dominated regime through at least 2100, essentially disrupting the natural rhythm that historically brought relief.
Decades of Groundwater Overuse
Even when rain eventually returns, the damage from prolonged drought doesn’t simply wash away. Agriculture alone accounts for 47 percent of total freshwater withdrawals in the United States, and much of that water comes from underground aquifers that took centuries or millennia to fill. During droughts, farmers and cities pump even harder from these reserves, drawing down water tables that are already strained.
A Stanford study of the Los Angeles basin illustrates how slow recovery can be. After an extreme 2023 storm season dumped record rainfall across Southern California, shallow aquifers bounced back. But deeper aquifers, those 50 meters or more below the surface, regained only about 25 percent of the groundwater they had lost since 2006. A single epic storm season was not enough to restore what decades of drought and overuse had depleted. Researchers noted that after prolonged droughts and historic overuse, porous aquifers can physically collapse, permanently losing their ability to hold as much water as they once did. That kind of storage loss is irreversible.
This means that even in a year with good rainfall, a region can still be in a functional drought because its underground reserves remain critically low. The water people depend on for drinking, farming, and industry isn’t just what falls from the sky this season. It’s what’s been stored underground over generations.
How Drought Severity Gets Measured
In the United States, the Drought Monitor classifies conditions on a scale from D1 (moderate drought) to D4 (exceptional drought). These categories are based on where current conditions fall in the historical record. D1 means conditions are drier than roughly 80 to 90 percent of historical observations. D2, severe drought, means you’re in the driest 5 to 10 percent. D3 (extreme) falls in the driest 3 to 5 percent, and D4, exceptional drought, means conditions are worse than all but the driest 2 percent of anything on record.
These classifications matter because they trigger water restrictions, emergency declarations, and agricultural disaster designations. When your area shows up in the deep red or maroon on the Drought Monitor map, it means the combination of rainfall deficits, soil moisture loss, reservoir levels, and streamflow has pushed conditions into genuinely rare territory.
Why This Drought Era Feels Different
Previous generations experienced droughts too, including the Dust Bowl of the 1930s and severe dry spells in the 1950s. What makes the current era distinct is that human-caused warming is loading the dice. Natural variability still drives the timing, determining which year is wet and which is dry, but the baseline has shifted. Soils start drier, snowpack melts earlier, and heatwaves arrive hotter. Every drought now unfolds on top of that warmer baseline, which means even a moderate rainfall deficit can produce conditions that would have been considered severe a few decades ago.
The compounding nature of these forces is the real concern. Rising temperatures increase evaporation. Increased evaporation dries soil. Dry soil heats the surface further. Hotter surfaces change cloud behavior. Changed clouds let in more sunlight. More sunlight dries the soil even more. Layer ocean cycles that steer rain away from already-dry regions, add decades of groundwater pumping that has left underground reserves depleted, and the result is a system where droughts start faster, hit harder, and take far longer to recover from than they used to.