Very wet and very dry: unprecedented droughts and hyper-damaging floods in the future

The studies, both published in Nature Communications, find that billions of people are exposed to once-in-100-year floods, and many others will be exposed to "unprecedented" droughts within the next 30 years, under global warming scenarios.

The drought study examines the probability of severe drought in a variety of vulnerable places around the world.

The researchers modelled river discharge around the world until the end of the 21st century, under both high and low greenhouse gas-emissions scenarios.

"Regarding precipitation and temperature, preceding studies report the timing at which the impact of climate change emerges," says co-author Tokuta Yokohata, chief senior researcher at the Earth System Division in Japan's National Institute for Environmental Studies.

"However, no study had successfully estimated the timing in terms of drought focusing on river discharge at a global scale."

The modelling showed that 25 per cent of the world's land can expect an increase in drought frequency by 2050 in a low-emissions scenario. With high emissions, this rises to 28 per cent.

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"The projected impacts of warming show significant regional disparities in their intensity and the pace of their growth over time," says co-author Yusuke Satoh, a research associate professor at Korea Advanced Institute of Science & Technology, South Korea.

Mediterranean regions, southern and central South America, and Australia are particularly vulnerable regions.

"Appropriate and feasible climate mitigation and adaptation plans are essential for overcoming the expected extraordinarily severe dry conditions," says Satoh.

"Particularly regarding adaptation, it is crucial to improve our preparedness in the given time horizon before unprecedented drought conditions emerge."

This sentiment is reflected in the flood study which finds that right now, 1.81 billion people live in places that could experience depths of at least 15cm if a once-in-100-year flood were to occur. This represents nearly a quarter of the world's population.

Of this population, 780 million are living on less than $US5.50 ($A7.95) a day. Indeed, 89 per cent of flood-exposed people live in low and middle-income countries.

South and East Asia had the highest populations exposed to flood risk - China and India make up a third of the 1.81 billion (395 million people in China, and 390 million in India). The researchers point out that climate change is likely to exacerbate this risk.

"Estimates from 11 climate models converge to the conclusion that flood frequencies in Southeast Asia, East and Central Africa, and large parts of Latin America could increase substantially by 2100," they write in their paper.

The researchers combined a flood exposure assessment of 188 countries with the World Bank's Global Subnational Atlas of Poverty to complete their analysis.

"Flooding is a risk with global prevalence, and systematic risk mitigation measures are crucial to prevent the loss of lives and livelihoods, and reversals of development progress," write the authors.