Peril as warming alters planet water cycle

Tracey Ferrier | January 12, 2023

Global warming is changing the planetary water cycle which heightens the risk of disasters like bushfires and drought, a new report says.

The report led by the Australian National University is another stark warning of climate change perils amid faltering efforts to address the crisis.

Using ground measurements and satellite observations, the report details water movements via rainfall, air temperature and humidity, soil moisture, river flows, and water stores in natural and artificial lakes.

“We found there are some very clear signs that the global water cycle is changing,” the report’s lead author Albert van Dijk said.

“In practice, that means that natural disasters, or hazards that relate to water, are also changing in severity and frequency. Increasing temperatures are really starting to have an effect on things like droughts, fire, and water scarcity.”

Air temperature over land in 2022 followed the long-term warming trend, while air humidity declined.

“This means that nature, crops and people will need more water to stay healthy, which compounds the problem,” Professor Van Dijk said.

“It is a safe prediction that we will see more and more heatwaves and flash droughts. 

“We also see evidence of the impact of global warming on glaciers and the water cycle in cold regions, and in fact melting glaciers contributed to the Pakistan floods. That will continue until those glaciers are gone.”

The water cycle was dominated last year by relatively warm ocean waters in the western Pacific and the eastern and northern Indian Ocean.

As a result, a severe heatwave developed in South Asia early in the year, followed by a very wet monsoon that caused massive floods in Pakistan as well as India.

Australia also saw deadly floods after a third consecutive La Nina event delivered the nation’s ninth-wettest year on record, and the second “once-in-a-century” flood in 11 years in parts of Australia.

In Europe and China, extreme heatwaves produced flash droughts that develop within a few months, drying out landscapes that have historically escaped them.

Prof Van Dijk said the third La Nina in a row not only caused flooding in Australia, but also deepened drought conditions in the western United States and parts of South America.

“The jury is still out on whether those three La Nina years were a statistical fluke or the first signs of something more sinister,” he said.

“If La Nina or (drier) El Nino patterns are going to stay around longer in future, that is going to cause a lot of trouble with worse, longer droughts and worse floods alike.”

Prof Van Dijk says it’s difficult to study the water cycle in Australia because its climatic conditions are so strongly tied to La Nina and El Nino cycles.

“And they don’t change very fast. On top of that, Australia hasn’t had records of rainfall and temperature for as long as Europe or China, so it’s much more difficult to see where the trends are at, or the ordinary, in a historical sense.

“But what we do know is that northern Australia has gradually been getting wetter, and that’s a common pattern with other monsoon areas in the world, from India to Indonesia.

“Whereas the south of Australia is definitely getting hotter but is also getting drier, on average.”