Critical freshwater requirements for meeting the Paris Agreement

Intact land and freshwater ecosystems are a prerequisite for limiting global warming in accordance with the Paris Agreement. However, the critical co-dependence of climate mitigation outcomes and freshwater dynamics tends to be neglected in both research and policies. Here, we suggest a framework for systematically quantifying the indispensable freshwater requirements for mitigation measures, focused on natural and managed terrestrial systems upholding the land carbon sink. We assert that while huge freshwater volumes are involved in this biospheric service per se, a substantial fraction of these volumes and their spatial connectivity need to remain inside a certain variability corridor in order to maintain the current mitigation potential and to enable measures creating further ‘negative emissions’. Moreover, we highlight that the freshwater volumes and flows required are limited both by the equally substantial water requirements for other societal goals such as food security and by the potential resilience loss due to aggravating impacts of ongoing climate change. In view of high uncertainties and knowledge gaps regarding the underlying processes and feedbacks, coordinated inter- and transdisciplinary research is needed to comprehensively assess global freshwater flows and uses with explicit consideration of water-resilient climate mitigation.