Here is a look at how climate change has affected the planet’s water cycle, and the findings of the report.

But first, what is the water cycle?

The water cycle is the constant movement of water in all its phases — solid, liquid and gas — on the ground, inside the ground and in the atmosphere. Most water cycles through the planet because of the energy from the Sun and changes in temperatures. For instance, water on the ground or in bodies of water escapes into the atmosphere as water vapour through a process called evaporation. Some water is taken up by plants from the soil and released as water vapour, a process known as transpiration.

Water vapour eventually condenses into clouds, and later falls as precipitation in the form of rain or snow. Precipitation enters the ice caps, oceans, lakes, rivers, or glaciers, and can be absorbed by plants, or seep into soil or deeper into the ground. After this, the water cycle starts again.

The water cycle is crucial as it not only enables the availability of water for all living organisms but also regulates weather patterns on the Earth. For example, the rate and distribution of water cycling through the planets affect the frequency, intensity, and distribution of precipitation.

How is climate change impacting the water cycle?

As mentioned before, the water cycle involves water evaporating from the ground and sea, and eventually returning to the Earth as rain snow. Climate change has intensified this cycle as air temperatures soar, more water evaporates into the air. Warmer air can hold more water vapour — for every 1 degree Celsius rise in average temperature, the atmosphere can hold about 7% more moisture. This makes storms more dangerous as it leads to an increase in precipitation intensity, duration and/or frequency, which ultimately causes severe flooding across the world.

While some regions are witnessing more frequent and intense storms, others are experiencing more dry air and drought. As the rise in temperatures causes more evaporation, soils are drying out. And when the rain does arrive, most of the water runs off the hard ground into rivers and streams, and the soil remains dry. As a result, more evaporation takes place from the soil and the risk of drought increases.

With the planet on track for a temperature increase of 2.6-3.1 degree Celsius over the course of this century (if countries do not dramatically slash their greenhouse gas emissions), the water cycle is expected to become more erratic.

A 2022 study, ‘Observed poleward freshwater transport since 1970’, published in the journal Nature found that climate change had intensified the global water cycle by up to 7.4% — compared with previous modelling estimates of 2% to 4%.

The Intergovernmental Panel on Climate Change (IPCC), the United Nations body that advances scientific knowledge about climate change, in its sixth assessment report in 2021 said climate change will cause long-term changes to the water cycle. This would lead to more frequent and intense droughts and extreme rainfall events, the report added.

What are the findings of the latest report?

The new report laid out key aspects of the water cycle in 2024, which was the hottest year on record with the average global temperature reaching 1.5 degree Celsius above pre-industrial levels. The report found that:

• In 2024, water-related disasters caused more than 8,700 fatalities, displaced 40 million people, and resulted in economic losses exceeding $550 billion globally.
• There were 38% more record-dry months in 2024 than for the baseline period (1995-2005). This is not a surprise as scientists have observed that extremely dry months have increased in recent decades.
• Rainfall records are being broken with increasing regularity. For instance, record highs for monthly rainfall were set 27% more often in 2024 than in the year 2000, and daily rainfall records were set 52% more frequently.
• Last year, most of the world’s dry regions experienced ongoing low values of the terrestrial water storage (TWS) — the sum of all water on the continents, including soil water, groundwater and surface water, as well as snow and ice. However, the values increased in western, Central and Eastern Africa.
• In 2025, droughts could worsen in northern South America, southern Africa, and parts of Asia. Wetter regions such as the Sahel and Europe may witness increased flood risks.

© The Indian Express Pvt Ltd

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