Integrative Assessment of Water Scarcity: A Case Study in the Nooksack Watershed Addressing Human and Aquatic Life Needs

The accessibility of water resource, encompassing both water quantity and quality, is pivotal for public health and aquatic ecosystem. It has been recognized by water related Sustainable Development Goals (SDGs) such as life on land and below water. This study underscores the importance of integrating these goals in the context of water resource accessibility. We develop water scarcity assessment that accounts for water demands of human activities by further introducing water quantity and quality requirements for different aquatic life uses. This is applied in a case study for Nooksack watershed that featured diverse anadromous fish habitats. In this study, local data including hydrological flows modelled using regional records, local water quality data, and water withdrawal reports are applied for enhancing the geographical specificity of our analysis. Using different geographical scales including management areas, drainages, and NHD stream reaches, along with annual and monthly temporal scales, this study presents a comprehensive view of water scarcity. Our findings reveal different levels of water scarcity across tributaries with residential distributions and the downstream region of the Nooksack River, with the most severe level observed in agriculture intensified area (Lower Nooksack) and moderately to highly developed urban coastal region (Lummi Bay Watershed). Impaired water quality contributes to exacerbated scarcity, especially during summer, peaking in August. The detailed water scarcity examination at stream reach level specifically identifies the border streams located in the Fishtrap drainage of Lower Nooksack as critically affected by both quantity and quality induced water scarcity. It highlights the need of effective management of border watersheds. It is noteworthy that water quality induced deficiencies of instream flow required by aquatic life uses distribute at mostly first level tributaries overlapping with those most affected drainages, but do not surge at some specific locations. The This study offers a novel framework for assessing water resources accessibility at watershed scale, advocating the downscaled application of water scarcity assessment results to the NHD reach level, thereby providing more intuitive and granular insights.