Abstract
AbstractFresh water—the bloodstream of the biosphere—is at the center of the planetary drama of the Anthropocene. Water fluxes and stores regulate the Earth's climate and are essential for thriving aquatic and terrestrial ecosystems, as well as water, food, and energy security. But the water cycle is also being modified by humans at an unprecedented scale and rate. A holistic understanding of freshwater's role for Earth system resilience and the detection and monitoring of anthropogenic water cycle modifications across scales is urgent, yet existing methods and frameworks are not well suited for this. In this paper we highlight four core Earth system functions of water (hydroclimatic regulation, hydroecological regulation, storage, and transport) and key related processes. Building on systems and resilience theory, we review the evidence of regional‐scale regime shifts and disruptions of the Earth system functions of water. We then propose a framework for detecting, monitoring, and establishing safe limits to water cycle modifications and identify four possible spatially explicit methods for their quantification. In sum, this paper presents an ambitious scientific and policy grand challenge that could substantially improve our understanding of the role of water in the Earth system and cross‐scale management of water cycle modifications that would be a complementary approach to existing water management tools.
Highlights
Freshwater is crucially important for all life on Earth
The water cycle is the bloodstream of Earth, yet it is startling that we do not know if human modifications of the water cycle will cause major disruptions of the Earth System
By reviewing water’s role in the Earth System, and regions where the water cycle is already being disrupted, we present an ambitious scientific and policy Grand Challenge to improve our understanding of the role of freshwater in the Earth System and water management
Summary
To motivate the following overview of resilience theory, we start with the potential role of human modifications of the water cycle in planetary-scale Earth System regime shift. In the Anthropocene, continued human pressure may accumulate water cycle modifications to threats of planetary-scale tipping through four general pathways (Barnosky et al, 2012; Lenton et al, 2008; Steffen et al, 2018, Rocha et al, 2018): (1) extensive local scale changes that trigger critical transitions over a large area; (2) global forcing that trigger local changes; (3) synergy, feedbacks, and cross-scale interactions through complex networks; and (4) tipping of major subsystems of the Earth System.
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