Accounting for ecosystem service flows in water security assessment: A case study of the Yiluo River Watershed, China

The water-related ecosystem services (ESs) flow is a pivotal linkage between ecological and social systems, playing an integral role in water security. Previous research has primarily assessed water security in contexts with and without the presence of ES flows, but further research is necessary to understand the influence of water yield inflow(WY_inflow) and total nitrogen inflow(TN_inflow) as critical determinants of water security. To address dynamic water security assessment and its driving mechanisms, we developed a novel water security index (WSI) that incorporates water quality and ES flows. Additionally, we employed a spatial Durbin model to investigate the impact and spatial effects of related factors on water security, applying it to the Yiluo River Watershed in China. The results revealed that: 1) the dynamic WSI of sub-watersheds incorporating ES flows was an improvement over the static WSI; 2) precipitation and the proportion of cropland significantly positively impacted static WSI, but their impact on dynamic WSI was not significant; 3) WY_inflow intensity contributed positively to dynamic WSI, while TN_inflow intensity negatively influenced dynamic WSI; and 4) most determinants of water security, including WY_inflow and TN_inflow intensity, exhibited negligible spatial spillover effects. Notably, the contribution of ES flows to water security showed an upward trend, accounting for approximately 30% by 2018. Such insights are crucial for formulating sustainable management strategies, such as ecological compensation, to enhance long-term regional water security.