SINGAPORE - Climate change likely increased the intense rainfall that flooded large parts of Pakistan in recent weeks, and the nation needs to adapt to a future of more periods of extreme rains, an analysis by an international team of scientists says.

The study by the World Weather Attribution (WWA) initiative, which investigates to what extent climate change has played a role in a major weather event, found that extreme rainfall in the Pakistan region increased 50 per cent to 75 per cent in recent decades.

"Our evidence suggests that climate change played an important role in the event, although our analysis doesn't allow us to quantify how big the role was," Dr Friederike Otto, WWA co-founder and senior lecturer at the Grantham Institute for Climate Change and the Environment in London, said in a statement.

She said what occurred in Pakistan was exactly what climate projections have been predicting for years.

"The real lesson here is that this (extreme rainfall) will become more likely and probably a lot more likely. So being more resilient to these kinds of events is a very high priority," Dr Otto told a media briefing.

Pakistan received more than three times its usual rainfall in August, making it the wettest August since 1961. The southern provinces of Sindh and Balochistan recorded their wettest August, receiving seven and eight times their usual monthly totals respectively.

More than 33 million people were affected by the rains and floods, which destroyed 1.7 million homes and killed more than 1,300 people.

WWA's rapid analysis of the disaster involved more than two dozen scientists. They analysed weather data and simulations from 31 computer climate models to compare the climate today, after about 1.2 deg C of global warming since the late 1800s, with the climate of the past, using peer-reviewed methods.

The researchers focused on the 60-day period of heaviest rainfall over the Indus River basin between June and September, and the five-day period of heaviest rainfall in Sindh and Balochistan.

Modern climate models cannot fully simulate monsoon rainfall because that region is at the western edge of the monsoon belt and its rainfall pattern is extremely variable from year to year. This meant there were large uncertainties in climate modelling of the 60-day rainfall period in the Indus basin.

Consequently, the scientists could not quantify the influence of climate change as accurately as has been possible in other studies of extreme weather events. For example, WWA found the March to May heatwave that parched India and Pakistan this year was 30 times more likely because of climate change.

The results were clearer for the five-day total rainfall. Some of the computer models suggest that climate change increased the rainfall in Sindh and Balochistan by up to 50 per cent.

And this tallies with recent United Nations' assessments projecting more intense rains in the region and with historical weather records showing these heavy rainfall episodes have increased 75 per cent in the region in the past few decades.

Other factors also exacerbated the floods.

Extremely hot summer temperatures sped up the melting of Pakistan's 7,000 glaciers that feed the Indus River, while the unusually hot weather in spring and summer enhanced rain-bearing storm systems from the Arabian Sea, bringing heavy rainfall to the southern provinces.

In addition, a La Nina event in the Pacific also enhanced rainfall. La Nina typically causes warmer ocean waters to pile up in the western Pacific and around South-east Asia, enhancing the monsoon in South Asia.

Pakistan's 220 million people remain extremely vulnerable to weather-related disasters, especially floods. Many of them live near flood plains, leaving houses, infrastructure and farmlands exposed to future disasters.

Poverty also limits access to funds to build stronger houses, flood defences and information on steps to reduce risks. Better early warning systems and river management are life-saving steps.

The researchers said rebuilding provides an opportunity to strengthen resilience and avoid future risk through stronger infrastructure and better understanding of flood risk when deciding where to rebuild.