How climate change is changing the water cycle

What is the water cycle?

Simply put, the water cycle – also known as the hydrologic cycle – is the process by which water moves through Earth’s lands, seas and atmosphere. Water in its three natural phases, whether gaseous, liquid or solid, is part of the natural cycle that continually renews the supply of water that we, and all other living beings, need to survive.

Of the world’s finite water supply, about 97% is salty. The remaining 3% is fresh water that we use for drinking, bathing or irrigating crops. Most of that, however, is out of reach, locked away in ice or deep in aquifers. Only about 1% of the world’s total water supply is readily available to support all life on Earth.

How does the water cycle work?

The water contained in lakes, rivers, oceans and seas is constantly heated by the sun. As the surface warms, liquid water evaporates and becomes vapor, escaping into the atmosphere. The wind can accelerate this evaporation process. Plants also release water vapor through the pores, or stomata, of their leaves and stems, in what is known as transpiration.

Once in the air, the vapor begins to cool and condense around tiny suspended particles of dust, smoke or other pollutants, forming clouds. These clouds can move around the planet in horizontal bands known as atmospheric rivers – a key feature of the global cycle that powers weather systems.

When enough water vapor accumulates, the droplets suspended in the clouds begin to merge and grow. Eventually, they get too heavy and fall to the ground in the form of rain – or snow and sleet, depending on the air temperature. This precipitation recharges the rivers, lakes and other bodies of water below, and the cycle begins again.

Water also percolates through the ground under the influence of gravity and pressure, where it accumulates in underground reservoirs or aquifers. It keeps moving to lower altitudes, sometimes for thousands of years, in a process called groundwater flow before finally seeing a body of water to go back into the cycle.

How climate change is affecting the water cycle

Recent research shows that in some parts of the world, the water cycle is accelerating in response to human-caused climate change.

Warmer temperatures are warming the lower atmosphere and increasing evaporation, adding more water vapor to the air. More water in the air means a greater chance of precipitation, often in the form of intense and unpredictable thunderstorms. On the other hand, increased evaporation can also intensify drought conditions in drought-prone areas, with water escaping into the atmosphere rather than remaining in the soil where it is needed.

A recent study by researchers at the Institute of Marine Sciences in Barcelona, ​​Spain, illustrated how climate change is accelerating the cycle by looking at ocean surface salinity, which increases as water evaporation intensifies.

“The acceleration of the water cycle has implications both in the ocean and on the continent, where storms can become increasingly intense,” said Estrella Olmedo, lead author of the study, in a press release. “This greater amount of water circulating in the atmosphere could also explain the increased precipitation that is being detected in some polar areas, where the fact that it is raining instead of snowing is accelerating melting.”

what can we do to help?

It has become clear that drastic cuts in fossil fuel emissions will not be easy and any noticeable improvements will not be quick. But some more immediate fixes to stabilize the water cycle are possible.

Restoring wetlands and rethinking agriculture to incorporate agricultural techniques that conserve water and preserve and rebuild the soil can help maintain and restore the soil’s ability to absorb, purify and store water.

Bringing rivers and streams back to a more natural state could also help reverse some of the damage. Projects to remove obsolete dams and weirs in Europe and elsewhere are an important step in restoring floodplains, which absorb water and help replenish groundwater supplies.

Cities can also turn to nature-based solutions to support the water cycle, making urban surfaces more permeable. “Sponge cities” use porous surfaces to allow water to filter through streets, squares and other spaces, rather than being funneled away. This stores water for use in times of drought, while also helping to fight floods.

what is at stake?

Cities and regions in the Hindu Kush watershed and the Himalayan ranges of Central Asia may need to start turning to solutions like these in the coming years. Billions of people there depend on the seasonal accumulation of packed snow and ice stored in mountains and glaciers for their drinking water.

But a third of the region’s major ice fields are set to disappear by the end of this century, according to a 2019 study by the International Center for Integrated Mountain Development in Nepal — and that’s if we can keep global warming to 1.5 degrees Celsius. (2.7 Fahrenheit).

Without a consistent flow of meltwater, water scarcity will increase for billions of people. And while groundwater may make up some of the shortfall, that too is expected to decline in coming decades due to climate change. Farming has already become more difficult in places like the Indian-administered Ladakh region of the Hindu Kush Himalayan range, where scientists have recorded a drop in snowfall and retreat of glaciers in recent decades.

“This is the climate crisis you’ve never heard of,” said Philippus Wester of the International Center for Integrated Mountain Development. “The impacts on people in the region, which is already one of the most fragile and risk-prone mountain regions in the world, range from an increase in extreme weather events, a reduction in agricultural yields and more frequent disasters.”

Edited by: Tamsin Walker