What role do wetlands play in flood mitigation?

Wetlands play a crucial role in flood mitigation primarily by absorbing excess rainfall. When heavy rains occur, wetlands act as natural sponges, capturing and holding water. This capacity for water retention helps to slow down the movement of water into downstream areas, reducing the risk of flooding. The intricate structure of wetland vegetation and soils allows them to efficiently trap water, which can then slowly release into surrounding ecosystems or waterways over time.

The other options do not accurately reflect the beneficial role of wetlands. Increasing water temperature is not a function of wetlands; in fact, they often help to moderate temperatures in adjacent water bodies. Promoting urban runoff contradicts the purpose of wetlands, as one of their key functions is to filter and hold water rather than facilitate its rapid movement away from the area. Decreasing biodiversity is also not applicable here, as wetlands typically support a rich variety of flora and fauna, contributing positively to ecosystem health. Thus, the correct answer highlights the vital function of wetlands in managing water during storm events and protecting adjacent landscapes from flooding.