Global Threats to Human Water Security and River Biodiversity

Model Overview

In this study, we assembled a global database of 23 drivers of environmental stress, categorized into four themes and organized as digital maps. These drivers reflect numerous pathways to ultimate threats to Human Water Security (HWS) and Biodiversity (BD) that can be mapped at the global scale. Each driver and theme was weighted according to its relative influence on threat by surveying expert opinion within the working group, which collectively represented a wide range of disciplinary expertise and work experience on most continents.

A three-step process was used to convert the geospatial driver values into standardized driver scores needed to calculate the aggregate HWS and BD threat indices. For these driver values:

  1. Firstly, we modeled the propagation of impacts downstream within drainage basins to reflect the influence of upstream stressors routed downstream through digital river networks;
  2. Secondly, the routed driver values were normalized by discharge to account for the dilution of stressors as water flow typically increases downstream; and,
  3. Finally, the normalized driver scores were standardized to a continuous 0-1 scale.

Standardized drivers were merged into the two aggregate indices of Incident HWS and Incident BD Threat using weightings from expert opinion at both the driver and theme levels. Separate weights were used to compute threat status with regard to HWS and BD, reflecting differences in threat posed to water resources for humans versus biodiversity.

To account for the beneficial impacts of technological advances in engineering and regulatory approaches to enhance HWS, we distinguished between the Incident HWS Threat index outlined above and an Adjusted HWS Threat index that accounts for investment in water infrastructure and management such as dams, sustainable water use practices, improved access to water resources, and improvements in clean drinking water supplies.

Details of the methods used in this study are available in the Supplementary Information on the Nature website.