Topic

Forests

Forests and trees influence the water cycle by intercepting rainfall, helping water enter the soil and returning moisture to the atmosphere through transpiration. These processes affect water quality, water availability and rainfall locally and further away. Understanding these connections helps decision-makers account for water when managing forests, planning agriculture and restoring landscapes.

Why forests matter for water

The role of trees in the water cycle extends from their roots to the atmosphere. Roots and leaf litter help maintain soil structure, influencing how rainfall infiltrates the ground. Trees take up soil moisture and release water vapour through their leaves, a process called transpiration. This moisture can travel through the atmosphere and contribute to rainfall elsewhere.

Forest soils and vegetation can also reduce erosion and help limit the sediment reaching rivers and lakes. These functions connect forest management with drinking water supplies, farming and ecosystem health. SIWI’s article on forests, trees and the water cycle examines these connections and their importance for agriculture.

However, more trees do not automatically mean more water everywhere. Trees also use water, and their effects on soil moisture, groundwater and river flows depend on species, climate, soils and landscape conditions. Forest protection and restoration therefore need to consider the water requirements of both ecosystems and people.

The governance challenge

Decisions about forests affect water beyond the boundaries of individual properties and administrative areas. Yet forestry, agriculture, water management and climate policy often have separate institutions, budgets and objectives. This can leave the water consequences of land-use decisions insufficiently considered.

A landscape approach connects these responsibilities by considering how land, water and ecosystems interact across an area. It requires evidence about water flows and competing needs, coordination between institutions, and participation by the people who manage and depend on the landscape. Recognizing green water, the rainfall stored in soil and available to plants, is an important part of this approach.

How SIWI contributes

SIWI connects science, policy and practice to strengthen how forests and water are considered together in governance and planning. Its work links forest management and restoration with agriculture, climate resilience and the full hydrological cycle, including soil moisture and atmospheric water flows.

SIWI’s Water-smart Forest and Landscape Restoration Tool helps planners and practitioners assess water risks and opportunities, identify relevant stakeholders and strengthen coordination. It supports decisions about where and how to restore landscapes while considering water availability and the needs of different users.

SIWI also contributes scientific expertise to research on forest–water relationships and translates findings into policy discussions and practical guidance. As explained in Beyond trees: why water often is a missing aspect of forest and landscape restoration, successful restoration requires attention to how landscapes function, including how they absorb, store and release water. The aim is to help forest and land-use decisions support water security, livelihoods and resilient ecosystems.