Humans and Hydroclimate in the United States

A New Regional Hydroclimate Project in the United States


Since the Global Energy and Water Exchanges (GEWEX) Continental-Scale International Project (GCIP) in the 1990s and the GEWEX Americas Prediction Project (GAPP) in the 2000s, the GEWEX community has sought to organize a new Regional Hydroclimate Project (RHP) in the United States that evolves and builds from these earlier experiments, and speaks directly to the dynamically evolving Earth systems challenges we face.


The Humans and Hydroclimate in the United States (H2US) Project is envisioned as a ten-year effort to understand and characterize the water, energy, and carbon cycles (physical processes) in the Anthropocene, driven by a need for useful modeling tools and actionable products developed in collaboration with a multitude of stakeholders to address climate justice, and support water, food, and energy security for natural and human systems in a changing future.n systems in a changing future.

Goals and Working Groups

Goal #1:
To determine the extent to which Earth’s water cycle can be predicted.  This Goal is framed around making quantitative progress on three related areas: the fast reservoirs of water, flux exchanges with the Earth’s main reservoirs of water, and precipitation extremes.

Goal # 2:
Quantify the inter-relationships between Earth’s energy, water, and carbon cycles to advance our understanding of the system and our ability to predict it across scales. 

Goal # 3:
Quantify anthropogenic influences on the water cycle and our ability to understand and predict changes to Earth’s water cycle.

To address these goals we have formed seven working groups around their associated Thematic Research Areas, as illustrated in fig. 1.”

Fig. 1 The Humans and Hydroclimate in the United States (H2US) Project Thematic Research Areas

Geographic Scope and Activities

The rather expansive focus of the H2US is the CONUS. The CONUS encompasses a wide range of geomorphologies, land uses and land cover, weather phenomena, and localized climates. The CONUS also interacts with, and is influenced by global phenomena such as dynamical processes (e.g. El Nino/La Nina, teleconnections), climate change, and large scale events (dust storms, volcanic eruptions, etc.).

There will be a range of modeling activities that span spatial and temporal scales: from the global to the regional (CONUS in this sense) to the hyperlocal (e.g. a watershed). These modeling efforts will be supported by sub-regional focal studies, driven by observational campaigns, which are optimally coordinated into transects that leverage existing as well as new assets (fig. 2).

Fig. 2: Humans and Hydroclimate in the United States (H2US) Project Conus and modeling efforts

The map in the center of fig. 2 prescribes our definition of CONUS for the purposes of H2US, and notionally illustrates the idea of observational “transects” (the gray ellipses are not actual or even proposed transects, they are simply possible ones for illustrative purposes). It should be noted that the initial bounding box for H2US represented by this map is partly informed by geographic scope of what can be modeled today at finely-resolved scales (~4 km resolution) over climate timeframes.


Since GCIP and GAPP, the rest of the world has conducted numerous RHPs and the U.S. is lagging behind. Now is the time for a new large, coordinated effort focused on land-atmosphere processes. This calls for an RHP that reflects the physical realities presented by the Anthropocene that are unique to our geography, and that integrates and represents the human dimensions that exert a strong influence on the natural systems.

Fig. 3: The Earth’s surface coupled system

For the Humans and Hydroclimate in the United States (H2US) Project Summary Science plan click here or visit the website at