An integrated modeling approach for coupled risk management of regional Blue- and Greenwater under changing land-use patterns

land use change had a considerable impact on the regional water cycle throughout the past century, leading to an influence on water security. Bluewater (BW) and Greenwater (GW) concepts have found broad application in evaluating the water accessibility of both socioeconomic and ecological systems. However, regarding the interactions between BW and GW systems and their coupled risk under land use change, there has been limited research in this area. This study aims to address this gap by developing an integrated Hydrology and Water Security Modeling Framework (HWSMF) that combines a hydrological model (Soil and Water Assessment Tool), a copula-coupled risk model, and a water security assessment model to assess the impact of land use change on regional water security. As an example, the methodology was utilized in the East River basin (ERB) located in China's Pearl River Delta. Results showed that the sensitivity of GW to forest land change was significant. In general, land use change had a notable impact on the GW coefficient at a rate of more than 4% of change and in certain areas, it was over 8%. Due to land use change the freshwater availability per individual in each city of this basin decreased. When the probability of coupled risk is defined, the BW required is greater than the GW required in this basin. Land use change can lead to fluctuations in the coupled risk of the regional BluewaterGreenwater nexus system (BGN), which implies that appropriate land use management could be promising for regional water system risk mitigation. The results of this study will be valuable for policymakers and managers of watersheds in their endeavors to manage water resources sustainably amidst evolving land use patterns.