/ 2 November 2018

Warm world: Floods are our future

The destruction of wetlands and forests — and a warmer climate — will lead to more severe flooding in South Africa and around the world.
The destruction of wetlands and forests — and a warmer climate — will lead to more severe flooding in South Africa and around the world. (David Harrison)

We keep building in wetlands and near to rivers, breaking down the natural systems that slow down and control flood waters. New research shows how bad a mistake this is, as bigger storms and heavier flooding become normal.

Wetlands are referred to as the lungs of river systems. Water runs through them and all sorts of natural filters, cleaning it. Those filters also slow the water down, acting as a critical dampener for angry, turbulent floodwaters.

But wetlands are also beautiful, so they attract estate builders. In South Africa’s major metros, this has meant building shopping centres, parking lots and homes in and around the wetlands, or squeezing them into curated water features in sprawling estates.

As a result, broken wetlands are now the norm. In isolated cases, like the Ekangala strategic water resource area in southern Mpumalanga, the government has moved in to stop development in important wetlands. But even there, mining is fighting for the right to mine in the wetlands and local government is allowing this to go ahead.

New research by Columbia University’s school for engineering and applied science has pointed out how dangerous this disregard for wetlands (and all the other things that slow water down, like forests) is at a global level. With wetlands either broken down, or missing entirely, the research says floodwaters move at a much more rapid pace.

Without those natural systems in place, governments then have to build infrastructure to channel and slow down the water. This costs money, and it isn’t being done on a large enough scale, because, as the team warns, the models being used play down the damage that will be done by torrents of water.

Large Increases in Global Storm Runoff Extremes Driven by Climate and Anthropogenic Changes was published in the journal Nature Communications earlier this month.

It started by looking at the current damage done globally by weather extremes: R400-billion a year, each year for the past decade. Most research has gone from this point and looked at how a warming world will mean more rainfall, but the Colombia research is the first global project that has looked at how that rainfall will translate into water flooding through communities, forests and farmland.

The team says, in the research, that “we are trying to find the physical mechanisms behind why precipitation and runoff extremes are increasing all over the globe”. By discovering this, they can then suggest ways to fix the problems. This will save lives, ecosystems and property.

For South Africa, this research is timeous because government climate projections show that the west will get drier and the east will get wetter.

For the east, along the Drakensberg, rain will fall in fewer days and in heavier bouts. That means more water falling on to the earth, eroding valuable topsoil, swelling rivers and washing through towns and cities. The violence of this rainfall will also mean that little will drain into the soil and refill groundwater aquifers, and dams will have to release the floodwaters to avoid breaking.

The Colombia team took data from the Global Runoff Data Centre and the Global Summary of the Day to work out what more, heavier rainfall will mean. They conclude: “Flash floods attributed to storm runoff extremes are projected to become more frequent and damaging.”

The team warns that the torrents of water will then go on to do more damage, thanks to trees having been chopped down, the soil will hold less water and, with wetlands being destroyed, the water would have little to slow it down.

Importantly, they say a big driver of this change is human-related emissions of carbon dioxide, which is making the world warmer. The United Nation’s Intergovernmental Panel on Climate Change released a report last month saying this warming could be slowed down and even stopped. But, given current emissions, the panel believes this is likely.

Instead, the temperature increases that the Columbia team are working on are the most likely scenario, which means a warmer world, with more water evaporating. A warmer atmosphere can hold more water, which will lead to much more rain falling back to the ground.

The team says the amount of floodwaters has been underestimated in all major climate models. This means governments are planning for the future with models that do not show the reality of how bad things will be.

As a result, they say countries face “large threats to ecosystem and community resilience under future warming conditions”. This means that there is an “urgent need to increase societal resilience to both climate change and our changing environment”.

Using now-outdated models, planning permission will continue to be given to estates to build on wetlands and companies to mine in them.