What is the global water cycle and how is it amplifying climate disasters?

Floods, droughts and heatwaves continue to dominate headlines around the world and in Australia.

In the past few days, hundreds of bushfires have ignited in south-east Australia during an extreme heatwave. And communities in north Queensland have been lashed by heavy rain and flash flooding from ex-tropical Cyclone Koji. This is the seventh cyclone so far this season.

Behind these disasters is a deeper and less visible influence: ongoing shifts in the global water cycle. This is the process by which water evaporates, falls as rain and snow, and ultimately evaporates again. Our latest report shows how changes in rainfall, air temperature and humidity combined to amplify water-related disasters across the world in 2025.

These floods and fires are not simply isolated weather extremes, but signs of a water cycle that is being increasingly destabilised by global warming.

Why the water cycle is changing

The global water cycle connects the atmosphere, land, oceans and ice. Water evaporates from the land and seas, falling as rain and snow. This feeds glaciers, rivers, lakes and groundwater and finally either evaporates again or flows to the ocean. This cycle is driven by the energy from the sun. And as the planet warms, it is becoming more powerful and more erratic.

Global temperatures over land in 2025 were only slightly lower than a record-breaking year in 2024. This makes the last three years the hottest on record, in line with rapid global warming.

Higher temperatures accelerate evaporation from soil, vegetation and inland waters, producing dry conditions more quickly than before. At the same time, warmer air can hold more moisture, which increases the potential for intense rainfall. Together, these processes intensify both floods and droughts, sometimes in rapid succession.

Rainfall followed by heat

In 2025, many regions of the globe experienced this pattern: extreme rainfall followed closely by heat and drying. Scientists describe these abrupt swings between dry and wet extremes as “climate whiplash”.

Climate whiplash occurs when wet and dry extremes follow one another so quickly that ecosystems, infrastructure and communities struggle to cope. One example in 2025 was the severe wildfires in Spain and Portugal.

A wetter-than-average spring promoted strong vegetation growth across parts of the Iberian Peninsula. Then a sudden heatwave was followed by rapid loss of soil moisture. The rapidly-dried vegetation fuelled severe wildfires later in the season.

Queensland floods

Australia has also weathered shifts in the water cycle in the past year. In February 2025, Cyclone Alfred landed in southeast Queensland. It is not unprecedented to have cyclones so far south, but it was the first time in 50 years. In the following months, the rest of Queensland was hit hard by torrential rains and severe flooding.

Also in early 2025, tropical low-pressure systems near north Queensland produced rainfall totals comparable to those in a cyclone. More than 1,000 millimetres of rain fell within days in some areas, and Townsville recording its wettest month on record.

The event caused widespread damage to homes, transport and essential services, with economic losses exceeding $A1.2 billion.

The wet conditions, combined with high temperatures, also triggered an unprecedented outbreak of melioidosis. This is a disease caused by bacteria that occur naturally in soil and freshwater but can become dangerous when rainfall and flooding bring them to the surface. By May, Queensland Health had recorded 221 cases and 31 deaths, making it the largest outbreak in the state’s history.

The shows how water cycle extremes affect natural and human systems. Torrential rains and flooding has become a regular occurrence in Queensland and northern New South Wales.

Global instability

Several other events in 2025 revealed how different parts of the water cycle are becoming more unstable. In the Himalayas a series of unprecedented glacial lake floods occurred within just a few months following warm conditions.

Meanwhile, a rare cyclone close to the equator took Indonesian and Malaysian communities by surprise.

The increasing frequency of tropical cyclones in historically uncommon locations reflects how warming oceans and shifting atmospheric conditions are expanding the reach of water-related hazards.

The human and economic toll

Globally, our report shows that water-related disasters in 2025 were associated with nearly 5,000 deaths, displaced around 8 million people, and caused economic losses exceeding US$360 billion (A$536 billion).

In Europe, prolonged heatwaves were linked to many thousands of heat-related deaths. And in South and Southeast Asia, flooding displaced millions in countries such as the Philippines, Thailand, Malaysia, and Bangladesh.

This show how different parts of the water cycle — from the atmosphere to soil conditions, river flows and surface water — can influence ongoing global warming.

Being prepared helps

Our report finds that preparedness really matters. Early-warning systems and evacuation planning saved many lives in several major floods, such as those on the west coast of the US in December 2025. However, severe disruption and economic damage still occurred where infrastructure had been designed for stable, historical conditions.

Conditions in the global water cycle at the end of 2025 point to greater drought risk in parts of the Mediterranean, the Horn of Africa, Brazil and Central Asia in 2026. On the other hand, wet conditions mean flood and landslide risks remain high in the Sahel, south of the Sahara Desert, southern Africa, northern Australia and much of Asia.

As climate instability continues, the global water cycle is likely to become even more variable. Understanding how water moves through the climate system — and how quickly it can shift from one extreme to another — will help us reduce the impacts of future disasters. Managing both heat and water extremes will be key to adapting to a rapidly warming world.

Albert Van Dijk, Professor, Water and Landscape Dynamics, Fenner School of Environment & Society, Australian National University

This article is republished from The Conversation under a Creative Commons license. Read the original article.