Growing trees remains the most effective way to draw maximum value from rainwater, with several other added benefits.

Agricultural water management experts contend that trees are the world’s best water storage and recycling channel. Forests and trees can avert water scarcity and poor crop yields through healthier ecosystem services and use of ‘conservation agriculture’.

This week, the world marked World Water Day with the theme of Valuing Water. The Day is observed to raise awareness of the global water crisis and manage this finite, irreplaceable resource.

According to Maimbo Malesu, a water-management expert at World Agroforestry (ICRAF) in Nairobi, Kenya, growing trees remains a pivotal approach to reaping the maximum value from water.

'Forests offer the most conserved environment and an ideal land-use type to get the highest water value,’ he said. ‘Typically, 65 percent of rainwater should go through evapotranspiration or “greenwater” systems such as forests, grasslands, wetlands and croplands. Of these land-use types, forests offer the highest value for the rainwater given the benefits that result from it.’

The common practice of replacing forests with crops reduces rainwater use from 30–40% in trees to only 6–9% in crops. Expert says other benefits from trees — like wood products, medicine and the environment's stability — gives trees a greater edge.

Previous studies by ICRAF and the United Nations Environment Programme have shown that Kenya’s rainwater potential is more than 350 billion cubic meters. If captured and managed, the water is enough to support 233 million people or close to five times the country's current population.

Agricultural engineering experts say forests also help to preserve river sources, hence, making them a key player in maintaining the critical resource and a driver for attainment of Sustainable Development Goal Number 6: water and sanitation for all by 2030.
 

According to the United Nations World Water Development Report 2020, the changing climate is also likely to disrupt water availability, quality and quantity for potentially billions of people.

Trees are critical in reducing the effects of climate change, hence, reducing the possibility of sinking deeper into a water crisis.

Despite the critical role trees play in supporting ecosystems functions, low investment in forests still undercuts the potential gains. Rather than convert more forests, CIFOR-ICRAF experts encourage intensification of agriculture for increased crop productivity. They have shown that the use of agricultural conservation practices — such as minimum tillage, mulching and crop rotation — increases crop production threefold.

'At CIFOR-ICRAF, we encourage agroforestry — the inclusion of trees in croplands — to increase greenwater capture to add more value from water within cropland,’ said Malesu. ‘Trees within a farming system manage water better, increase productivity and enhance the value of water.’

According to him, farmers’ fear that trees may out-compete crops for available water during rainy periods is unfounded because water essentially goes to waste in the absence of trees. Besides, trees help in preventing soil erosion.