To increase awareness and understanding about the many ways forests contribute to improving food security and nutrition, especially in developing countries, the FAO hosted an International Conference on Forests for Food Security and Nutrition  (May 13-15) in collaboration with the World Bank and with PROFOR .
Trees and forests provide a critical role in ensuring food security, in ways which often are poorly understood and as such are not adequately reflected in policy decision. One of the less direct and often undervalued services provided by forests and trees is their vital role in provisioning water and in maintaining the health of watersheds through water regulation and purification, erosion control, and other ecosystems services. These services complement other critical aspects of forests and trees which help build resilience  at the household level to food insecurity.
Traditionally only monetized products such as timber got the needed government attention, and in this context the role of forests in the hydrologic (water) cycle was too often been overlooked. A forested watershed by filtering freshwater and reducing soil erosion and sedimentation helps maintain clean water supplies. Moreover, forest canopy provides a protective cover for the landscape by intercepting rainfall and cycling much of water precipitation back to the atmosphere. As a matter of fact, a World Bank and WWF study  found that approximately one-third of the world’s 105 largest cities source a significant portion of their drinking water from protected forested watersheds.
An appreciation of the value of forests and the ecosystem services they provide including their capacity in provisioning water will enable decision-makers to better assess trade-offs associated with alternative land- and water-use choices. Besides water stored in biomass there is also soil moisture stored below the forest and both disappear from the area when the forest disappears.For instance, a study  by the FAO estimated the economic value of the water storage function of China’s forests as 7.5 trillion Yuan (approximately US$1 trillion), three times the value of the wood in those forests.
By improving water quality and regulating flow, forests and trees can reduce the risks of flooding or the drying up of rivers during dryer seasons. In Haiti, for instance, as one of the conference presenters explained, widespread deforestation in the 1960s, has meant nowadays only 2% of the once verdant forest cover remains, contributing to desertification, erosion and flooding and in turn increased vulnerability to natural disasters with a drastic impact on food and water security.
While in the past, ecosystem services provisioned by forests, such as water purification have been difficult to quantify and value, new research into natural capital accounting  and innovative market approaches such as Payments for Ecosystem Services, provide an opportunity to foster a growing appreciation of forests importance for long-term water security. The good news is there is growing demand  from developed and developing countries to integrate natural capital considerations into their decision-making processes.
With the recently published report Turn Down the Heat: Why a 4°C Warmer World Must be Avoided , suggesting that world temperatures could rise by 4 degrees Celsius this century, the stakes of recognizing the contribution of forests to water security are raised dramatically as availability of freshwater resources are predicted to become increasingly scarce in a warming, crowded, and challenging future, with estimations that by 2025, two-thirds of all nations will confront water supply stress.