A fixed amount
The origin of Earth’s water is now understood to be a hybrid process, with the majority coming from asteroids and a significant portion generated internally during the planet’s formation, rather than primarily from comets as once thought. In the period after earth’s creation, no ‘new’ water has been produced.
So, the total amount of water on earth is a fixed amount, it doesn’t increase or decrease but is trapped in a closed loop system using outflow, evaporation and rain. However, importantly water on Earth is not fixed in location, but in total quantity; droughts occur because climate change and human activity are redistributing water from land to the atmosphere and oceans, creating regional imbalances. Higher global temperatures increase evaporation rates, pulling moisture from soil and vegetation into the air faster than it can return as rain, while shifting jet streams divert storm systems away from traditionally arid regions.
Additionally, land use changes such as deforestation disrupt natural moisture recycling, where trees normally release water vapor to generate local rainfall. When forests are removed, the land becomes drier and less able to sustain precipitation, creating a feedback loop where drought conditions become more frequent and severe even though the global water volume remains constant.
From land storage to oceans
Climate change and human activity are shifting significant volumes of water from land storage into the oceans, causing sea levels to rise while simultaneously drying out terrestrial regions.
1. Melting Land Ice
The primary driver of this redistribution is the melting of glaciers and ice sheets (specifically in Greenland and Antarctica). Unlike sea ice, which is already floating, ice stored on land flows into the ocean as it melts. Since 1960, melting mountain glaciers have accounted for 27% of sea-level rise, while the Greenland and Antarctic ice sheets contribute 15% and 12% respectively. This process physically moves water that was locked on land for millennia into the ocean basin.
2. Groundwater Depletion
Human activity accelerates this transfer through groundwater extraction. When humans pump underground water for agriculture or industry, much of it eventually evaporates or runs off into rivers, ultimately reaching the ocean. This depletion of land water storage contributes approximately 10% to current sea-level rise. Essentially, we are mining ancient aquifers and dumping that water into the sea.
3. Atmospheric Redistribution
While the total amount of water is constant, rising temperatures increase the atmosphere’s capacity to hold moisture by about 7% for every 1°C of warming. This intensifies the water cycle: the atmosphere pulls more moisture from land surfaces (causing droughts) and dumps it in intense bursts over oceans or specific regions. Combined with shifting wind patterns, this creates a “wet gets wetter, dry gets drier” scenario, where land loses moisture to the warming air and oceans faster than it is replenished by rain.
Case study: Colorado river in the US
Complicating matters, the seven states that count on the river disagree on a long-term plan to deal with the shifting climate.
A 26-year drought is sucking the once mighty Colorado river dry, and unprecedented heat is rapidly evaporating this year’s record-low snowpack. These two conditions are leading to low water levels at Lake Powell and Lake Mead, the nation’s two largest reservoirs. That, in turn, jeopardizes critical water infrastructure for a large swath of the West.
In 2026, the Colorado River faces a critical operational transition as the 2007 Interim Guidelines and 2019 Drought Contingency Plans expire at the end of the year, leaving a regulatory void that must be filled by new federal or state-agreed rules. Lake Powell is projected to drop significantly, with forecasts suggesting it could fall below 3,490 feet (minimum power pool) as early as August 2026 under pessimistic scenarios, threatening hydropower generation at Glen Canyon Dam and forcing emergency reductions in water releases.
To mitigate these risks, the Bureau of Reclamation has implemented emergency measures for water year 2026, including reducing releases from Lake Powell to 6 million acre-feet (down from ~7.5 million) and releasing up to 1 million acre-feet from the upstream Flaming Gorge Reservoir to stabilize Powell’s levels. Lake Mead remains in a Level 1 Shortage Condition, necessitating significant water cuts for Arizona, Nevada, and Mexico, while the federal government continues to develop a Draft Environmental Impact Statement to establish long-term post-2026 operating guidelines.
If water levels fall below 3,500 feet in Lake Powell, water releases, which help create hydropower and serve as the primary water source for millions of Americans, could be halted. To stave off such a catastrophe, dam managers with the Bureau of Reclamation (BOR) are impounding water in Lake Powell and unleashing trillions of gallons of water from Flaming Gorge, an upstream reservoir.
Complicating matters, the seven states that count on the river disagree on a long-term plan to deal with the shifting climate. And recently, Interior Secretary Doug Burgum, whose agency oversees the BOR, announced an imminent federal intervention that he said, “nobody will be happy” with. It’s an untenable situation that water managers, experts, and even state leaders say puts the river and those who rely on it on a disastrous collision course.