The global dialogue surrounding water security and climate change has taken on new momentum. Several important calls-to-action and affiliated initiatives are in play across the highest levels of government, business, and civil society. While COVID uncovered the impact of a global emergency, water ranks near the top of concerns expressed by world leaders. As one example, water security is among the World Economic Forum’s highest impact risks to the global economy, fueled by a combination stresses produced by climate change, resource mismanagement and overuse, and lack of sufficient infrastructure to deliver reliable water services. At the same time, there is growing interest in the role of using natural capital productively and sustainably in development, like using protected watersheds for urban water supply. While this strategy has been adopted worldwide, environmental degradation has continued to compromise such systems and traditionally engineered solutions are invested in heavily to remediate this impairment. Furthermore, there is persistent skepticism around the value of nature-based systems toward achieving water security, particularly in the developing world and fueling an ongoing debate. The research reported here suggests there is enormous practical potential to enhance water security for the 2.5 billion people who live downstream of significant endowments of natural capital, which—if sufficiently protected—could provide to society a myriad water and non-water related co-benefits. Quantitative framing of these important issues will help to shift the debate away from generalizations and toward evidence-based evaluation.
Our study quantifies growing threats to human water security during the period of the Sustainable Development Goals and beyond. We provide, for the first time, systematic estimates of the economic value of water threat protection that is provided by existing natural capital. Today, the value of such protection greatly exceeds the costs of engineered threat control and by 2050 its contribution more than doubles to nearly $3 trillion. At the same time, we project that traditionally engineered water management will continue to expand throughout the century. Under a business-as-usual approach, annual water engineering costs triple to $2.3 trillion by 2050, but with a nearly equivalent amount needed to eradicate residual, unmitigated threat. We also find that when natural capital is lost, replacing the equivalent level of threat suppression by traditional engineering will on average be at least twice as expensive—a penalty for poor environmental stewardship. These estimates suggest that the economic importance of natural capital in water threat suppression is and will continue to be an essential and cost effective global-scale component of future water resource management. In turn, environmental protection and blended green-gray water resource approaches can serve as a central component of the sustainable development agenda on water.