Extreme weather: Between deluge and drought, freshwater sources are struggling to replenish | Environment| All topics from climate change to conservation | DW | 22.03.2019
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world water day

Extreme weather: Between deluge and drought, freshwater sources are struggling to replenish

Worldwide, heavy rainfall and flooding are wreaking havoc from Mozambique to the US. At the same time, ancient water sources are drying up. On World Water Day, DW looks at extreme weather's threat to freshwater sources.

It's hard to grapple with the reality of a shrinking water supply when places like Mozambique are saturated to the point of obliteration.

In the last few days, some of the worst flooding ever recorded — triggered by cyclone Idai — has devastated southeast Africa. Storm surge floods up to six meters (about 20 feet) deep have destroyed nearly 90 percent of Mozambique, as well as neighboring Zimbabwe and Malawi, decimating almost all water and power infrastructure. 

Between extreme floods and drought, global warming is disrupting the planet's water cycle.

Worldwide flooding

Across the Atlantic, flooding in the US state of Nebraska has been so bad an entire city was walled off from the outside world. In southeast Asia, more than 80 people have been killed in flash floods brought on by torrential rain in the Papua Province of Indonesia. Some areas of the province recorded almost 200 mm (7.8 inches) of rain in 24 hours.

A hotter global climate — in which a warmer atmosphere holds more moisture — is causing stronger, more frequent rainfall. As the Intergovernmental Panel on Climate Change outlined in their 2018 report, it's likely that anthropogenic influences have affected the global water cycle since 1960. 

Heavy rainfall and floods are a natural part of the world's weather cycle, but climate change is exacerbating them.

Read more: The Floods are Coming

Drought, heat and fire

On the other end of the spectrum of extremes, vital water sources — like lakes, rivers and wetlands — are drying up. For places like Iraq, Australia and China, drought, heat and fire are becoming the new normal.

In China, 28,000 rivers and waterways have dried up over the past 25 years. The country's Yellow River — the second-longest in Asia — is now a mere tenth of what it once was in the 1940s. In late 2018, former Chinese premier Wen Jiabao said the nation's acute water crisis was a threat to its very survival.

Read more: One year after the water crisis, Cape Town recovers from tourism drought

Parts of Australia's Murray-Darling Basin, one of the country's biggest water networks, have experienced huge drops in flows in recent years. Extended drought, prompted by intense heatwaves, in part led to the death of one million fish in the basin over a two-week period in January 2019.

In the Middle East, the Mesopotamian marshlands in southern Iraq, once the largest wetland ecosystem in Western Eurasia, are at risk of disappearing after years of drought.

Read more: German utilities call for more water infrastructure investment

Infographic global hotspots of flooding and drought

While the links between some weather extremes and climate change are more complicated than others, Jascha Lehmann from the Potsdam Institute for Climate Impact Research says the line drawn between floods, drought and global warming is clear. 

"There is a lot of evidence pointing to the fact that climate change means we have more weather extremes globally, and this is especially true for heat extremes, for heavy rainfall events and for droughts," he told DW. 

Pegged to gain an extra 2 degrees Celsius (3.6 degrees Fahrenheit) by 2100 if emissions aren't reduced, the world's climate may yet see the worst of such extremes.

The secret is in the soil

One important impact of temperature rise is greater evaporation rates and plant transpiration, which leads to drier soils. When rainfall does occur, these dry soils absorb more of it.  

This, according to Ashish Sharma, professor from the school of civil and environmental engineering at the University of New South Wales, is a crucial aspect of climate change's impact on the water cycle.

Infografik Where is all the extra rain going? EN

A study Sharma co-authored on the topic found that where soils were once moist before heavy rainfall and storms — allowing excess rainfall to runoff into lakes and rivers — they are now so dry they absorb most of the water.

This means, in many parts of the world, increased rainfall is contributing less to "blue water" that flows through lakes, rivers and dams and is extracted for human use, and more to "green water," which is soaked up by the landscape.

"What's happening is the first significant chunk of the rainfall has to be used up to wet the soil before the overland flow can occur and before the big flood can form," Sharma told DW.

This is more so the case with "moderate" floods that flow into dams, the professor said, rather than extreme floods, which tend to lead to more rapid movement of the water from the atmosphere back into the oceans  — preventing it from being stored and used.

"It's these moderate floods that supply water to our dams and it's the dams that basically give us water for our irrigation systems for our communities," Sharma said. The problem, Sharma surmised, "is the temperature rise."

Australian drought

An entire state in Australia was declared in drought for the second half of 2018

Water wars

Less water in our rivers, lakes and dams means less water for drinking, sanitation, food production, energy, and many other vital uses. It can also fuel conflict, and drive people from their homelands.

Age-old tribes like the Marsh Arabs in Iraq are being deprived of their livelihoods on the marshlands. The worst drought in Syria's history, from 2007 to 2010, has been credited as triggering political unrest and instability in the region, leading to a surge of refugees into Europe. 

As Friederike Otto, associate professor at the Environmental Change Institute at Oxford University outlines — and as climate change is continually showing — it is the world's poorest and most marginalized that disproportionately suffer.

"It's important in these debates not to forget just who and what is in harm's way, about vulnerability and exposure, by blaming [all extreme weather events] on climate change," she told DW. 

"We shouldn't assume that just because it's 'climate change' that we can't do anything. We can."

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