Groundwater and Surface Water Interaction at the Regional-scale - A Review with Focus on Regional Integrated Models

Scientists and practitioners agree that integrated water resource management is necessary, with an increasing need for research at the regional scale (10(3) to 10(5) km(2)). At this scale interactions between environmental and human systems are fully developed and global change is linked to local actions. The groundwater-surface water interaction (GW-SW) is of particular interest. Herein we review the scientific journal literature and examine GW-SW at the regional scale. We briefly review all existing literature on GW-SW, then summarise its characteristics at different scales and identify specific challenges of the regional scale. We explore whether GW-SW should be treated differently at regional and local scales. Regional GW-SW is rarely examined in experimental field studies, which almost exclusively cover small areas. However, GW-SW is often integral to large scale coupled models. Thus, we collate information about existing models and their regional applications. Fully coupled, physics-based models have great potential to meet the technical challenges. However, limited data availability hampers the application of complex models at the regional scale and loosely coupled schemes are more widely applied. Many integrated modelling concepts have been published, but none have been applied in a wide range of settings. Thus, it is impossible to compare the performance of different approaches. Comparative analyses of existing regional scale integrated models in the context of different data availability and geographic conditions are needed. Unfortunately, peer-reviewed journal literature no longer provides a representative picture of the subject as models are becoming "too big to be published" or too pragmatic.