Transitioning to a Gridded Climate Divisional Dataset

Map of U.S. Climate Divisions

NCDC is transitioning from its traditional climate divisional dataset to a new divisional dataset, known as nClimDiv, which is based on Global Historical Climatology Network–Daily (GHCN-D) observations using a 5-km gridded approach. For many years, the traditional climate divisional dataset was the only long-term complete dataset with enough coverage to generate historical climate analyses for the contiguous United States. NCDC originally developed this divisional dataset to monitor climate-division, statewide, regional, national, and population-weighted drought, temperature, precipitation, and heating and cooling degree day values. Since the dataset was based on a divisional scale, it also naturally lent itself to agricultural and hydrological applications.

Originally, NCDC scientists computed climate division values from the monthly averages for all of the Cooperative Observer Network stations in each division for data between 1931 and the present. For 1895–1930 data, scientists computed statewide values directly from stations within each state and, subsequently, calculated the divisional values for this period using a statistical analysis on those statewide values.

The new nClimDiv divisional dataset will now be based on GHCN-D data with a similar station inventory as the previous divisional dataset. However, NCDC scientists are using new methodologies to compute temperature, precipitation, and drought for the United States climate divisions. These new methodologies include using a grid-based calculation, incorporating more stations for the pre-1930s era, and using NCDC’s modern array of quality-control algorithms. NCDC made the incorporation of the new station data possible through digitization of paper records throughout the past decade. All of these changes improve the data coverage and quality in the nClimDiv dataset.

NCDC has also created a visualization toolkit to help users examine snapshots of both the old and new climate divisional datasets for comparison. With this tool, you can compare changes in monthly, seasonal, and annual variability of parameters such as temperature, precipitation, and a variety of drought indices. The toolkit is scheduled to be fully operational by March 17, 2014.

For more information on the nClimDiv dataset, visit the U.S. Climate Divisions page.