Rain fails to run the course to dry rivers

We are getting more intense rain but our rivers are drying. Why is that?

I know lots of people in regional, rural and urban areas who struggle to understand how our water supplies can be shrinking at the same time as climate change is generating more intense rain.

I have been part of a research group who have studied this paradox and found the culprit is the drying of our soils, not just here in Australia, but worldwide.

In our study, we expected to find that extreme rainfall was increasing because warmer air stores more moisture.

But despite all that extra rain our large rivers are drying out.

We found that in the past, soils were more moist so when a big storm hit all the excess rainfall would run off into the rivers.

Today, as global warming evaporates more moisture from the soil, the drier soil absorbs much more of the rain when it falls.

That also means floods are actually decreasing in magnitude.

If the soil is wet before a storm, you find that 62 per cent of extreme storms become equivalent extreme floods.

But when soils are dry, that number drops to just 13 per cent.

With smaller rainfall inflows into reservoirs, the biggest impact is felt by local communities suffering water restrictions.

Add to that the fact that farmers have higher demands on the water supply as they need more water to grow crops in soils that are drier than they used to be.

Conditions in the most arid parts of Australia could become the new normal for populated regional communities.

Just consider what happened in Cape Town, South Africa last year.

Water restrictions became so acute that each person was entitled to only one bucket worth of water for the entire day.

This is a major challenge for scientists and engineers and let's be honest, there is no simple fix.

But knowing what the problem is means that we can prepare for what lies ahead.

We have to be proactive and re-engineer our water systems to better adapt and be more efficient.

This is possible, but it requires major investment.

However, the cost of inaction could make whole swathes of Australia not just impossible to farm but unlivable.

Governments and business must act as one to ensure the water security upon which we all depend.

Ashish Sharma is Professor, School of Civil and Environmental Engineering, UNSW