The NCAR Water System Program (WSP) is a cross-Laboratory program that aims to improve understanding of the current water cycle and its likely evolution in a future climate by conducting research in the following areas: 

1. Global analysis and diagnosis of the water cycle from satellite and climate models,
2. Regional analysis of the water cycle using high resolution climate simulations over the Colorado Headwaters and U.S. CONUS,
3. Observations and simulation of Mesoscale Convective Systems, 
4. Improving the representation of land-surface/hydrology processes in the community land surface models (NoahMP and the Community Land Model (CLM)). 

In addition, two hydrological community models—WRF-Hydro and Structure for Unifying Multiple Modeling Alternatives (SUMMA)—have been developed in collaboration with the US Bureau of Reclamation, US Army Corps of Engineers, and NOAA. A short description of these models follows the discussion of the research themes.

1. Global analysis and diagnosis of the water cycle from satellite and climate models 

Global WSP-related research has primarily focused on precipitation characteristics (amount, frequency, intensity and duration) and how they are simulated by climate models, although studies focusing on continental runoff, drought, and regional and global water and energy budgets have also been undertaken. The WSP research on the global water cycle has made significant contributions in understanding 1) characteristics of climate-model simulated precipitation; 2) historical and future changes in precipitation, streamflow and continental runoff (fig. 1); 3) regional and global water and energy budgets; and 4) historical and future changes in global drought. Besides publishing a number of influential and highly- cited papers, the WSP has produced several global datasets that have been widely used by the university community and other groups, such as a revised Palmer drought severity index (PDSI) dataset and global streamflow and discharge dataset. This work also involves collaboration with faculty and graduate students from a number of universities.

2. Regional analysis of the water cycle using high resolution climate simulations over the Colorado Headwaters and U.S. CONUS

The Colorado Headwaters effort was initiated in the spring of 2008 as a project within the NCAR Water System program. It has focused on assessing the impact of climate change on winter precipitation, snowpack and runoff processes in Colorado's headwater basins using a very high- resolution fully-coupled atmospheric–hydrologic model (WRF coupled with the Noah land surface model). This work is collaborative with researchers from the University of Vienna, George Mason University, and the University of Texas.  A paper published from this effort showed that accurate simulation of Colorado snowfall and snowpack required a minimum horizontal model resolution of 6 km and that future snowpack melted 2-3 weeks earlier in a future climate despite the potential for 10-15% more snowfall in winter.  This Journal of Climate paper received the UCAR Outstanding Publication  award in December 2015. 

CONUS Simulations: The Colorado Headwaters high-resolution climate modeling effort has been expanded to cover all of North America.  Thirteen years of current and future simulations have been completed at 4 km horizontal resolution. The model faithfully reproduces the observed precipitation and snowpack in most regions of the U.S.  The output of these model runs will be used by WSP and university scientists to examine snowfall and snowpack changes in a future climate, as well as convection in the central U.S. and hurricanes in the Gulf of Mexico. A journal paper has been published in Climate Dynamic about the dataset and to advertise its availability to the community. 

Liu, Changhai, Kyoko Ikeda, Roy Rasmussen, Michael Barlage, A. J. Newman, A. F. Prein, F. Chen, L. Chen, Martyn Clark, Aiguo Dai, Jimy Dudhia, Trude Eidhammer, David Gochis, Ethan Gutmann, Sopan Kurkute, Yanping Li, Gregory Thompson, David Yates, 2016:  Continental‑scale convection‑permitting modeling of the current and future climate of North America, Climate Dynamics, DOI 10.1007/s00382-016-3327-9. 

Access to the data can be gained through the following portal (web site or DOI): 

• DOI : https://rda.ucar.edu/datasets/ds612.0/
• Info on the DOI is at https://ezid.cdlib.org/id/doi:10.5065/D6V40SXP.

3. Observations and simulation of Mesoscale Convective Systems

The WSP global model diagnostic studies revealed that most global climate models do not capture the nocturnal maximum in precipitation associated with eastward propagating Mesoscale Convective Systems  in the central U.S.  These systems are important as they produce a significant fraction of the annual precipitation in these regions. To understand the dynamics and forcing of these systems, WSP scientists have used the WRF community model to conduct a variety of studies.  The most recent work considered a 12-day heavy precipitation corridor in the central U.S., where warm-season precipitation was confined to narrow latitudinal zones (~3-4°). 

Model sensitivity studies revealed important positive feedbacks to corridor persistence resulting from moistening of the tropospheric column and from daytime sensible heat flux gradients (owing to residual cloudiness), which enhanced the lower-tropospheric frontal zone where the nocturnal corridor precipitation occurred. However, additional sensitivity studies revealed that corridor persistence was most affected by large-scale external factors. Current work is focused on analyzing these systems in the 13-year CONUS simulations. Insights from this work are communicated to the research community via papers and are expected to benefit both regional and global climate modeling research. At NCAR, CGD scientists are using it to help understand and improve the simulation of nocturnal thunderstorms in the Community Atmospheric Model (CAM). 

4. Improving the representation of land-surface/hydrology in the Community Land Surface Models

WSP research is focused on improving the representation of land-surface and hydrologic processes in Earth System Models. The Noah and NoahMP land surface models are two of the most commonly used land surface parameterizations in the community WRF modeling system and in the suite of operational models at NCEP/NOAA.  The NoahMP model is also the core column land surface model operating within the new National Water Model.  The WSP, through its regional water cycle research activities and collaborations with university investigators, NASA, and NOAA groups, has contributed to several major enhancements to both the Noah and NoahMP model, particularly with regard to improving the representation of snowpack, soil hydrology, vegetation canopy structure and surface energy fluxes. Members of the NCAR WSP organize and participate in annual land model workshops to coordinate Noah/NoahMP research and development activities with the academic and agency communities. WSP scientists are working with NCEP collaborators to implement the enhanced NoahMP land model in NCEP GFS and CFS in order to improve our nation’s global and seasonal prediction capabilities.

NCAR WSP scientists have partnered with the Consortium of Universities for the Advancement of Hydrologic Sciences Incorporated (CUAHSI) to use the NCAR Community Land Model (CLM) as a vehicle for hydrologists to engage in community modeling. This effort has supported strong and effective collaboration among NCAR scientists and the university community, including contributions to the code development in CLM5 (using some concepts from SUMMA to improve simulations of the storage and transmission of water through soils). A community workshop was held at NCAR in October 2015, and the project team is now actively working to incorporate advanced representations of lateral subsurface flow processes in CLM.

Community Hydrological Modeling

A cornerstone of the NCAR Water Systems program is the development and support of community modeling tools for both process-based research and hydro-meteorological forecasting applications.  These tools are co-developed by NCAR in close collaboration with university researchers and government agencies in the U.S. and around the world.  Scientists from the NCAR WSP serve as focal points for training and collaboration in the hydro-meteorological community.

SUMMA Community Model