A Science Plan for a Coordinated Regional Hydroclimate Project in the United States Focussed on Land-Atmosphere Processes

It has been well over 10 years since the US has hosted a major coordinated study of the water, energy and carbon cycles over the Contiguous United States (CONUS). Since that time, our modeling capabilities have advanced to the point where they are beginning to outstrip our current observational capabilities; both in terms of process fidelity and model grid spacing. In addition, new observations are coming on line (e.g. the USGS Next Generation Water Observing System, NGWOS) and new concepts are emerging, such as the GEWEX Land/Atmosphere Feedback Observatory (GLAFO) that can be leveraged. We argue that the time is now for a large-scale, sustained, and convergent research project to address our understanding of, and tools to monitor and predict, the water and energy cycles across the land-atmosphere interface. Under the auspices of GEWEX, and in coordination with the GEWEX Hydroclimate Panel, a public Affinity Group was formed in June 2021, which is broadly representative of the hydroclimate scientific community. This diverse group is developing a plan to propose a new US Regional Hydroclimate Project (RHP). The plan adopts a big tent approach that is inclusive and interdisciplinary, and integrates our understanding of land-atmosphere processes across the CONUS. This metaphorical tent is supported by tall pole activities that encompass key themes under this broad concept that are representative of regionally focused, process specific studies. We will describe our process to date and the current state of the plan and how to get involved. The project will be aimed at addressing current high priority science issues both at Federal as well as state and local level. It is envisioned that a successful project will (i) advance understanding and tools to monitor and predict key components of the water and energy cycles at the Earths surface; and (ii) engage stakeholders and the scientific community to ensure practical and applicable outcomes (action-oriented science) that benefit communities and ecosystems in the United States and globally.