A green-gray path to global water security and sustainable infrastructure

Charles J Vörösmarty,Ben Stewart-Koster,Pamela A Green,Edward L Boone,Martina Flörke,Günther Fischer,David A Wiberg,Stuart E Bunn,Anik Bhaduri,Peter B Mcintyre,Claudia Sadoff,Hongxing Liu,David Stifel

doi:10.1016/j.gloenvcha.2021.102344

Abstract

Sustainable development demands reliable water resources, yet traditional water management has broadly failed to avoid environmental degradation and contain infrastructure costs. We explore the global-scale feasibility of combining natural capital with engineering-based (green-gray) approaches to meet water security threats over the 21st century. Threats to water resource systems are projected to rise throughout this period, together with a significant expansion in engineering deployments and progressive loss of natural capital. In many parts of the world, strong path dependencies are projected to arise from the legacy of prior environmental degradation that constrains future water management to a heavy reliance on engineering-based approaches. Elsewhere, retaining existing stocks of natural capital creates opportunities to employ blended green-gray water infrastructure. By 2050, annual engineering expenditures are projected to triple to $2.3 trillion, invested mainly in developing economies. In contrast, preserving natural capital for threat suppression represents a potential $3.0 trillion in avoided replacement costs by mid-century. Society pays a premium whenever these nature-based assets are lost, as the engineering costs necessary to achieve an equivalent level of threat management are, on average, twice as expensive. Countries projected to rapidly expand their engineering investments while losing natural capital will be most constrained in realizing green-gray water management. The situation is expected to be most restrictive across the developing world, where the economic, technical, and governance capacities to overcome such challenges remain limited. Our results demonstrate that policies that support blended green-gray approaches offer a pathway to future global water security but will require a strategic commitment to preserving natural capital. Absent such stewardship, the costs of water resource infrastructure and services will likely rise substantially and frustrate efforts to attain universal and sustainable water security.

Highlights

IntroductionRecent studies on human water security reveal globally significant threats from population and economic growth, mismanaged water use, climate extremes and a general failure to effectively protect landscapes and inland waterways (Vorosmarty et al, 2010; Chaplin-Kramer et al, 2019; Harrison et al, 2016; Gleick, 2018; Tickner et al, 2020; Díaz et al, 2019)
We evaluate the contribu tions of traditional engineering (TE) and natural capital (NC) to threat management should present-day approaches to water management persist over the remainder of the century
In the context of human water security (HWS), we define natural capital as a type of infrastructure that constitutes a broad category of physical entities, collectively representing terrestrial and aquatic ecosystems that are intimately connected to the hydrologic cycle

Summary

Introduction

Recent studies on human water security reveal globally significant threats from population and economic growth, mismanaged water use, climate extremes and a general failure to effectively protect landscapes and inland waterways (Vorosmarty et al, 2010; Chaplin-Kramer et al, 2019; Harrison et al, 2016; Gleick, 2018; Tickner et al, 2020; Díaz et al, 2019). Solutions are routinely applied to substantially reduce the attendant risks (Vorosmarty et al, 2010; Green et al, 2015). Such “gray” engi neering is essential in delivering and improving upon the quality of water used by society (HLPW, 2018; OECD, 2012), and un derpins an economic sector with annual gross revenues approaching $0.8 trillion (Ashley and Cashman, 2006; McKinsey & Company, 2009). Persistent shortfalls in funding for traditionallyengineered systems (Rodriguez et al, 2012; ASCE, 2011) and the negative and long-lived impacts they often present to the environment (Vorosmarty et al, 2010; Zarfl et al, 2015; Palmer et al, 2015) illustrate the need for alternatives, like those associated with natural capital (Chaplin-Kramer et al, 2019; Harrison et al, 2016; Palmer et al, 2015; Costanza et al, 2017)

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