NASA’s GMAO on the the simulation and global gridded analysis of current climate, in conjunction with the assimilation of satellite and other data.

These centers vary in the size and scope of their activities devoted to modeling (see Chapter 7 for a discussion on the climate modeling workforce). The two largest centers in the United States are NCAR and GFDL. USGCRP (2011) estimates that of the $2.18 billion spent annually by federal agencies on climate research, 11 percent (~$239 million) is allocated for “improving our capability to model and predict future conditions and impacts.” That spending supports activities in both global and regional modeling at the large modeling centers, as well as smaller activities in federal laboratories, universities, and private companies.

Finding 13.1: The United States has a distributed system for global climate modeling, with a small number of “core modeling efforts.” These efforts have a long history and their structure derives from both modeling functions and agency funding structures. There is a separation of modeling activities across time scales, with operational weather and seasonal prediction centers largely separated from longer-term climate variability and change efforts.

CURRENT REGIONAL MODELING ACTIVITIES IN THE UNITED STATES

Regional climate modeling activities are focused on developing and using climate models with fine spatial resolution to better resolve small-scale climate features over a limited geographic domain. These models can be defined only over this limited domain, with specified boundary conditions at the perimeter of the domain, or they can be global models with varying spatial resolution in which the fine resolution is focused over the region of interest. For the limited domain regional models, boundary conditions can be supplied from a reanalysis or from some other climate model, for example, from a global simulation of future climate change.

Regional modeling activities are also distributed in the United States. Some have primary affiliation in universities, while others have strong affiliations with some of the modeling centers described above. Most of the regional models used are derived from models developed at one of the global modeling centers. For example, a number of regional modeling efforts use the Weather Research and Forecasting (WRF) regional model that is developed through efforts involving NCAR and NOAA. This modeling system is then tailored to specific applications in various institutions according to their scientific foci and goals. WRF supports many different options for physical parameterization, and a centralized effort has not yet evolved to quantitatively evaluate which of these options are most appropriate for a regional climate model. Based on local expe-



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