Countries around the globe are striving to meet the UN's 17 Sustainable Development Goals of the 2030 Agenda for Sustainable Development. Goal 15 is focused on ‘sustainable forest management'. With about 30% of the world's land surface covered by forests, this goal is vitally needed against a backdrop of stunning change. Most of this is occurring in the headwaters of larger watersheds. These headwaters are where partitioning occurs between water used by vegetation and the water that leaves the watershed via streamflow. At risk are the forested headwaters that support the water supply for billions of people worldwide.
Paired watershed studies where one watershed serves as a reference, while the adjacent watersheds are harvested have been the standard approach for over 100 years for quantifying the effects of forest cover change on streamflow in the headwaters. But even with >150 paired watersheds to date around the world, we're still unable to predict streamflow response to harvesting. Paired watershed studies have revealed increases, decreases or no change in annual streamflow in response to harvesting: some studies with 100% forest removal show no response of annual streamflow, whereas some watersheds with < 20% forest removal show an observable response. All this illustrates the difficulty in predicting, a priori, the outcome of forest cover change on streamflow. This is problematic for Goal 15 because variable outcomes of paired watershed experiments contribute to uncertainty about how forests should be managed for water sustainability.
This talk outlines the current situation and presents new analysis that suggests a way forward. The talk builds on recent commentary (McDonnell et al., 2018, Nature-Sustainability) and focuses on a hitherto largely unexplored factor in paired watershed analysis: below ground storage. The talk will show how storage may be one of the most critical factors for understanding hydrological change and presents a vision for future work in forest hydrology to quantify storage in paired watershed studies to inform how to manage water sustainably in forested landscapes.
Responsable(s): Prof. Jeffrey J. McDonnell (University of Saskatchewan, Canada).
Avec le soutien de Section des Sciences de l’Institut Grand-ducal & musée national d'histoire naturelle.
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