Earth's Continents Are Drying Up - Climate Adaptation Center

San Joaquin Valley, California Credit: M. Patrick/Flickr CC BY-NC-ND 2.0

…While Sea Level Rises

The Earth is experiencing an unprecedented loss of freshwater at continental scales. In the last two decades, continents have lost so much water to the oceans that they now contribute more to global sea level rise than the melting ice caps.

At the same time, extremes of rainfall and drought are becoming common in our warming world. The Global Water Monitor reports that in 2024, the hottest year on record, months with record-low precipitation were 38% more common than during the report’s 1995-2005 reference period, while the number of record-high daily rainfall extremes was 52% higher. The “Flash Flood Summer” of 2025 is clear evidence that the trend is continuing unabated in the U.S.

The World Meteorological Organization (WMO), in its latest State of Global Water Resources report, warns that the global water cycle has become “increasingly erratic and extreme, swinging between deluge and drought,” leading to cascading impacts of too much or too little water. The Global Water Monitor analysis of water disasters in 2024, found they had killed at least 8,700 people, driven 40 million from their homes and caused economic damage of more than $550 billion.

The Global Water Cycle

Earth’s water resides in the hydrosphere—representing the total quantity of water found on, under and above the Earth’s surface. The total mass of the hydrosphere is relatively constant at 1.4 × 10¹⁸ metric tons, which is about 0.023% of Earth’s total mass. The water cycle (also called the hydrologic cycle) describes the continuous exchange of water molecules between the oceans, the atmosphere and the land. A simple example of the cycle would begin with ocean evaporation, then wind transporting the water to land, condensation and precipitation on the land, and runoff and the flow of water in rivers back to the ocean.

Figure 1: The Water Cycle Credit: NASA Earth Observatory

Within the water cycle, about 96.5% of Earth’s water is held in the global oceans. As for the rest, approximately 1.7% is stored in the polar icecaps, glaciers, and permanent snowpacks, and another 1.7% is stored in groundwater, lakes, rivers, streams, and soil.

Just 0.001% of the water on Earth exists as water vapor in the atmosphere, but that small percentage has an enormous impact on global climate and local weather. As the most abundant greenhouse gas, water vapor is responsible for much of the natural greenhouse effect that makes Earth livable.

Unlike CO2 and other greenhouse gases, the amount of water vapor that the atmosphere can hold is determined by temperature. As the atmosphere becomes hotter, the amount of water vapor it can hold increases exponentially–leading to further warming and fueling extreme rainfall events. Conversely, a hotter atmosphere becomes a powerful engine for evapotranspiration–extracting water from the land to the atmosphere by evaporation from the soil and surface water, and by transpiration from vegetation, as shown in Figure 1.

Freshwater–A Critical Resource

Freshwater is liquid (or frozen) water containing no more than a low concentration of salt and other dissolved solids. Less than three percent of the water found on Earth is classified as freshwater, and the remaining 97 percent is salt water (e.g., seawater). Freshwater is a continental or land-based resource, used for drinking water, agriculture, irrigation, industry and hydroelectric power generation. In addition, 10% of the world’s animal species live exclusively in freshwater environments.

Most of the world’s freshwater is not readily usable. Approximately 69 percent is locked away in the form of ice in glaciers and polar ice caps, and another 30 percent is beneath the surface in the form of groundwater. Only about one percent of Earth’s freshwater is readily available for human use, so monitoring and managing the amount of freshwater available across the continents is of vital importance.

The total amount of water stored on land, in ice caps, glaciers, snowpacks, soil moisture, groundwater, surface water (lakes and rivers), and vegetation, is referred to as Terrestrial Water Storage, or TWS. Encompassing all the water on, in, and beneath the land surface, TWS is essentially a measurement of freshwater. At a given location, TWS varies seasonally and over longer periods as a result of climate change and human water usage.

Comprehensive, long-term, global monitoring of TWS has only been possible since 2002, with the launch of the GRACE (Gravity Recovery and Climate Experiment) and GRACE-FO (Follow-On) satellites. By measuring subtle changes in local gravity due to fluctuations in water mass, analysis of over two decades of GRACE data have revealed significant TWS loss across the continents.

Continental Drying

Recent research by H. Chandanpurkar and colleagues (Science Advances, July 2025) shows that the continents (excluding Greenland and Antarctica) have experienced “unprecedented” TWS loss since 2002. The areas experiencing drying expanded on average by twice the size of the State of California every year. The rapid expansion of dry areas created large “mega-drying” regions across the Northern Hemisphere, as previous drying “hot spots” for TWS loss grew and merged together.

Figure 2 shows the four continental-scale mega-drying regions (outlined in black), all located in the Northern Hemisphere: Regions 1 (northern Canada) and 2 (northern Russia), where the previously wet high latitudes have transitioned to drying; Region 3 which combines southwestern North America and Central America, where aridification and groundwater depletion are prevalent and increasing; and Region 4, ranging from North Africa, to Europe, across the Middle East and Central Asia, to northern China and Southeast Asia.

Figure 2: Long-term global trends in TWS (cm per year). Red/orange areas are drying, blue areas are getting wetter.

Credit: Chandanpurkar et al,, Science Advances, July 2025

A major factor driving TWS loss is groundwater depletion, accounting for 68% of TWS loss in non-glaciated regions. As temperatures rise, dry areas become even drier, and the availability of water in rivers and lakes declines, the go-to solution is groundwater extraction. Groundwater is a renewable resource, naturally replenished by precipitation. However the rate of groundwater extraction is often greater than the rate of replenishment. Deep aquifers can take centuries to recover after they are depleted.

The far northern Regions 1 and 2 in Figure 2 were originally gaining water. However, climate change is causing the northern latitudes to warm four times faster than the global rate, and large areas in Canada and northern Russia are now drying.

We first discussed the megadrought in the southwestern U.S. in 2002, and conditions have only worsened since then. Mega-drying Region 3 includes the southwestern U.S. and adds rapidly declining TWS in Mexico and Central America.

Region 4 highlights mid-latitude areas becoming dryer, with the notable addition of Great Britain and Western Europe. Throughout the Middle East and Central Asia, groundwater depletion is contributing to the decline in TWS.

Sea Level Rise

Climate warming affects the global average sea level in two ways. The ocean absorbs over 90% of the excess heat from climate warming due to its large size and high heat capacity. As the water heats up it expands, and sea level rises. The mass of water in the oceans is unchanged, but its volume increases.

The warming climate also causes melting of land-based glaciers and ice sheets, and the meltwater raises sea level by increasing the mass of the ocean.

Drying trends in TWS also contribute to sea level rise by causing a transfer of water mass from the land to the ocean. In fact, the research of Chandanpurkar et al show that within the global water budget, the drying continents are now the leading contributor of freshwater to the ocean causing 44% of mass-driven sea level rise, while the Greenland and Antarctic melting ice caps contribute about 37% and 19% respectively. Nearly 70% of the freshwater lost to the oceans is due to groundwater extraction, which removes water from deep aquifers and ultimately transfers it to the ocean.

Impacts

Continental drying is affecting most of the population and countries in the world. Nearly 6 billion people, about 75% of the global population in 2020, live in the 101 countries that have been losing freshwater since 2002. The expanding drying regions, declining Terrestrial Water Storage, and diminishing freshwater resources are driven by a combination of increasingly severe droughts, decreasing surface water availability, and groundwater depletion.

It will get worse:

Based on global climate warming of 2.7°C, 68% of the remaining glaciers are projected to melt out by 2100.
The last five years (2020-2024) have seen increasingly severe droughts around the world, including in regions like the Southwestern U.S. and Europe. The U.S. saw drought coverage reach a record 87% in late 2024.
Surface water storage in rivers, lakes and reservoirs is declining
Groundwater is declining in 71% of the world’s aquifers, with the rate of decline accelerating since 2000

In the closing discussion of their research article, Chandanpurkar and colleagues offer this warning:

“The robustness of the trends reported here, along with a critical shift in the behaviour of TWS and continental drying following the major El Niño beginning in 2014, may well mean that reversing these trends is unlikely. Combined, they send perhaps the direst message on the impact of climate change to date. The continents are drying, freshwater availability is shrinking, and sea level rise is accelerating.”

Earth’s Continents Are Drying Up