The heavy rains that followed Cyclone Jasper were a stark reminder of a changing climate’s potential impacts. Extreme rainfall and floods are becoming more frequent as the average global temperature rises.

Climate scientist Dr. Steve Turton says that for every temperature increase of one degree centigrade the atmosphere can hold an extra seven per cent of water vapour, and when the conditions are right it is released as intense rainfall.

“Last year was the warmest year on record and sea surface temperatures were record breaking every single day. Then along comes Cyclone Jasper and instead of moving away and taking the rain with it, the system remained stationery, bringing down moist air down and causing several days of torrential rain,” he says.

The water levels in the lower Barron River after Cyclone Jasper smashed a 41-year-old record, and in the Daintree River a 2019 record was broken by more than two metres. It caused huge landslides, punched a new river mouth into the coastline and caused major damage to homes and infrastructure.

Dr Han She Lim, a hydrology researcher at James Cook University, said the Barron River flood caught everyone by surprise.

“Cyclone Jasper itself didn’t cause too much damage but it was the rainfall after it passed that caused the damage. Nobody was expecting the flood that came afterwards,” she says.

“We live in an area that is prone to flooding and the more we build on flood plains, the greater our exposure to risk of flooding. While flood modelling and mapping has highlighted the areas that are most at risk, this flood reiterated that we can never be 100 per cent certain about where and what the impacts of floods will be.

“In this event, some areas were flooded that we didn’t expect, with one area affected by rocks and debris that washed downhill and blocked drains,” she says.

“But then on the other hand, there were areas that we would expect to be a higher flood risk, that didn’t flood. So, the key message is to know your flood risk by checking out your local council’s flood maps – but also to be prepared for the unexpected.

“As a community we did a really good job at rescue and recovery after the floods. The SES were efficient, and volunteers stepped up to help those affected. But many people – from newcomers to longtime locals – were not sure how to prepare or when to evacuate so we need to raise community awareness, just as we do for cyclones.”

Extreme events aside, Dr Richard Hunt from Wet Tropics Waterways says floods are a natural – and important – part of our region’s ecology.

“For most of the last eight to nine years, we’ve seen below average rainfall in the Wet Tropics,’’ he says. “But floods are important for connecting aquatic habitats, replenishing flood plains and wetlands, recharging groundwater supplies, dispersing and germinating seeds and helping cycle nutrients and sediments.”

“Many fish, birds and other wildlife also rely on high-flow events to trigger lifecycle events. For example, there is evidence that populations of fish species like barramundi often increase in response to floods.”

Flood Checklist

• Know your risk. If you live in a coastal area, check the flood maps and storm surge maps on your local council’s website.
• Understand the different types of flooding and check your insurance.

Prepare for flooding, including having an emergency household plan. (See your local council’s website).

Know your flood types

• Flooding – generally associated with a rise in river levels due to heavy rain, an infrastructural issue (such as a dam break or over-topping) or combination of high tides and heavy rain. Not necessarily associated with a cyclone.
• Flash flooding – More common in the Wet Tropics with waterways that appear benign on a day-to-day basis quickly becoming raging torrents.
• Storm surge (storm tide) – An abnormal rise in sea level associated with higher intensity cyclones that affects coastal communities and can be very dangerous due to its strength and reach.