More trees more water

September 1, 2016

By Tony Rinaudo – World Vision Australia

More Trees, more water.Under Australian climatic conditions and where we use Eucalypts as biological pumps to lower water tables, this statement doesn’t make sense. Even Mussolini used our red gums (Eucalyptus camaldulensis) to drain malarial swamps in Italy.

However new research backs up the observation and experience of thousands of third world farmers – that more trees mean more water! Scientists have proven that intermediate (moderate) tree cover can maximize groundwater recharge in the seasonally dry tropics.

Where FMNR has been conducted at scale such as in Niger and Ethiopia we have documented cases of water tables rising, and springs which had long dried up flowing perennially again. A number of factors can explain this. Most of the soils in the seasonally dry tropics have lost significant amounts of moisture-retaining organic matter. In addition, the removal of vegetative cover and continuous grazing has compacted these soils to the extent that they now shed water – in extreme cases, over 90% of the rain that falls does not soak in, but flows away, causing erosion and flooding in the process. Additionally, storms in the seasonally dry tropics tend to deliver large volumes of rainfall in a short period of time, further negatively affecting the ability of already compromised soils to absorb moisture.  Finally, while Eucalypts are notoriously famous at sucking up water, many of the indigenous species occurring in the semi-arid tropics have much lower transpiration rates, hence there is less loss of moisture from the soil.

Tigray Region is one of the most water insecure regions of Ethiopia. However, Tigriyan communities which have combined soil and water conservation measures with natural regeneration of trees on the hills and valleys, have become the most water secure communities in all of Ethiopia. In Abreha Weatsbha the community made a decision to no longer over exploit the vegetation on the hills and trees soon began regenerating. In addition they dug many kilometres of contour banks and converted deep gullies into dams resulted.

More water began to soak into the ground recharging water tables. In the valleys the water table rose from a depth of 9 meters to less than 3 from the surface in just two years. Community leader Aba Hawi calls this “Water banking”. He says “we make our deposit in the hills, and withdraw it in the valley”. This community which had been threatened with relocation because conditions had become so dire went onto dig over 600 shallow wells. In several places the water table has risen to such an extent that it is even coming out of the ground under pressure. Now even in drought years they grow two to three crops per year through irrigation by drawing on their “deposit”.

Today, this community which was vulnerable to both drought and flooding, is not only now food secure, but they produce a surplus. Flooding has stopped and their “water deposit” ensures that they have nothing to fear during drought.

On Mount Damota in Southern Ethiopia heavy deforestation had contributed to most of the springs drying up completely, or only flowing after rain. Within a few years of regenerating the trees on 500 hectares 12 formerly dry springs ‘returned’ and one completely new spring appeared. Nine of these springs now flow permanently through the year.

The importance of these experiences and the scientific findings cannot be underestimated. Two of the most serious issues facing communities globally in the semi-arid zones are water and food shortages. Ironically, many of these very same regions are subject to seasonal flooding during the rainy season. By the simple act of restoring tree cover through FMNR, flooding can be greatly reduced and more water can be ‘banked’ for times of need. For the semi-arid tropics at least, more trees does indeed mean more water.