Urban water security relies on tropical forests

Image courtesy of Bruno Melo

Alex Morrice

The strong possibility of Cape Town running out of water, before recent storms, recently placed a spotlight on urban water security. As climate change accelerates, populations grow and cities expand, the stress on rivers, reservoirs and aquifers will further intensify.

With UN-backed projections showing global demand for water will exceed supply by 40% by 2030, it is not just Cape Town that is affected. Sao Paulo suffered a major drought in 2015, with the availability of water from its main reservoir falling to below 4% of its total capacity. Similar events are expected in major cities and watersheds around the globe over the next decade.

This is a complex problem with a range of potential mitigating and exacerbating factors. However, what is clear is that one method for boosting water security and mitigating climate change at the same time is simple — protecting and restoring forests.

Water availability at the local and regional scale is heavily reliant on forests. Deforestation drives reduced rainfall and water availability. A recent publication led by Global Canopy examines the important relationship between forest cover and water availability in the Cumbaza basin in the San Martin region of Peru. Losing forests in watersheds means more sediment enters water courses, as the ability of forests to retain that sediment is compromised or removed. This in turn affects water availability, and deforestation is already causing water insecurity for smallholder farmers and urban households in the region.

Forests also protect settlements from floods. They act like a sponge, soaking up the water and slowly releasing it into nearby water courses, and provide a physical barrier for flood waters. With urbanisation, migration and agricultural development around cities increasing pressure on water resources and land availability, it will become ever more important to maintain the crucial ecosystem services provided by forests.

Climate change is impacting on the supply of water, at both the local and regional scale. As many regions of the planet warm over the next decade, aquifers, reservoirs and watercourses will be subject to greater stress from reduced availability and increased demand.

Deforestation drives greater climate change and water stress, but forests also represent an opportunity to slow or reverse these trends. Half the emissions reductions needed to meet the Paris Agreement aim of keeping global average temperature rise below a 2 degree increase can be delivered with the same method.

Encouragingly, this is increasingly recognised. Many countries’ nationally determined contributions (NDCs) to the Paris agreement have included forests. Forests are identified as fundamental to water supply in the UN’s Sustainable Development Goals (SDGs). It is now essential that time-bound, ambitious targets are set to meet these goals.

To read more about our research on the crucial role forests play in supporting climate stability, water security and the livelihoods of millions, visit our new website at www.globalcanopy.org.

This blog is the fifth instalment of a weekly five-part series on why we rely on tropical forests, focusing on water. Previous pieces have covered their importance for the climate, finance, biodiversity and public health.