More than five billion people are expected to face a shortage of access to water at least once a month each year by 2050 as a result of extremes such as flooding and drought, the UN said on Tuesday.
Climate change is reducing river levels and melting glaciers as global temperatures are more than 1.1°C higher than in pre-industrial times, according to a report by the UN's World Meteorological Organsiation (WMO).
Large areas around the world have been drier than usual last year, when precipitation patterns were influenced by climate change, the report said.
The report, named The State of Global Water Resources for 2021, is the first comprehensive review of water resources by the WMO.
It will be published on an annual basis starting from this year due to calls for more accurate data in a time of increasing demand and limited supplies, WMO said.
"Currently, 3.6 billion people face inadequate access to water at least a month per year and this is expected to increase to more than five billion by 2050," said the report.
From 2001 to 2018, 74 per cent of all natural disasters were water-related, according to UN studies.
Last year, all regions suffered devastating water extremes, the report said.
Record-breaking floods in western Europe and the Amazon were reported, while water levels in rivers in Paraguay and southern Brazil dropped to an all-time low.
Major river basins in the Americas and central Africa saw water volumes shrink. Rivers in northern India and southern Africa saw above average increases.
Flooding around the world in 2022 - in pictures
The report highlighted that inconsistent measurements and a lack of data collected on the ground made it hard to understand some of the effects that climate change was having on water systems.
At Cop27, the recent UN climate change conference held in Egypt, governments were urged to further integrate water into adaptation efforts.
The WMO secretary, Prof Petteri Taalas, said climate change effects were usually felt through water in the form of more intense and frequent droughts, flooding, erratic seasonal rainfall and melting glaciers.
"With cascading effects on economies, ecosystems and all aspects of our daily lives, there is insufficient understanding of changes in the distribution, quantity and quality of freshwater resources," he said.
Extreme drought was experienced in 2020 in Iran, Iraq and Syria, followed by a warm winter that continued into last year.
Up to 12 million people in Iraq and Syria and 4.8 million in Iran were affected by the droughts. Protests directly resulted in deadly clashes in the Khuzestan province.
Drought in the Horn of Africa has led to a devastating food crisis affecting 18 million people. Not even intense rainfall between December 2020 to February 2021, typically the dry season in the region, helped alleviate the situation.
On the other hand, the report said about 1.9 billion people lived in areas where drinking water was supplied by glaciers and snow melt but these glaciers are melting increasingly fast.
The report said governments must increase their actions in introducing of early warning systems for floods and droughts to help reduce the effects of water extremes.