Reductions in seasonal climate forecast dependability as a result of downscaling

Authors: Schneider, Jeanne; Garbrecht, Jurgen

Submitted to: Transactions of the ASABE
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 11/1/2007
Publication Date: 5/1/2008
Citation: Schneider, J.M., Garbrecht, J.D. 2008. Reductions in seasonal climate forecast dependability as a result of downscaling. Transactions of the ASABE. 51(3):1-11.

Interpretive Summary: This research determines whether NOAA/CPC seasonal climate forecasts are skillful enough to retain utility after they have been downscaled for use in crop models. Utility is assessed using net dependability, the product of the large-scale 3-month forecast dependability and a factor accounting for losses in dependability due to the higher variability of 1-month station data. This loss factor is estimated from station data, for average temperature and precipitation, over a 10 year study period and 96 stations in the contiguous U.S. The resulting loss factors are 0.76 for average temperature, and 0.66 for total precipitation. The loss factors are then applied to produce estimates of the net reliability for downscaled forecasts at locations within each forecast division. The resulting guidance is dependent on region and forecast variable. Forecasts for above average temperature should be considered for use in agricultural applications over the majority of the contiguous U.S. The Northeast, the Great Lakes, parts of the Northern Great Plains, interior California and northwest Nevada are the only regions with insufficient net dependability, precluding immediate consideration. Forecasts for cooler than average temperature do not retain sufficient net dependability after downscaling to be an attractive option in any part of the contiguous U.S. at this time. Forecasts for wetter or drier than average conditions retained sufficient net dependability to encourage further development over only about 10% of the contiguous U.S., specifically in Florida, south Texas, southwest New Mexico, Arizona, central and southern California, and parts of Oregon, Washington, Idaho, and Montana.

Technical Abstract: This research determines whether NOAA/CPC seasonal climate forecasts are skillful enough to retain utility after they have been downscaled for use in crop models. Utility is assessed using net dependability, the product of the large-scale 3-month forecast dependability and a factor accounting for losses in dependability due to the higher variability of 1-month station data. This loss factor is estimated from station data, for average temperature and precipitation, over a 10 year study period and 96 stations in the contiguous U.S. The resulting loss factors are 0.76 for average temperature, and 0.66 for total precipitation. The loss factors are then applied to produce estimates of the net reliability for downscaled forecasts at locations within each forecast division. The resulting guidance is dependent on region and forecast variable. Forecasts for above average temperature should be considered for use in agricultural applications over the majority of the contiguous U.S. The Northeast, the Great Lakes, parts of the Northern Great Plains, interior California and northwest Nevada are the only regions with insufficient net dependability,precluding immediate consideration. Forecasts for cooler than average temperature do not retain sufficient net dependability after downscaling to be an attractive option in any part of the contiguous U.S. at this time. Forecasts for wetter or drier than average conditions retained sufficient net dependability to encourage further development over only about 10% of the contiguous U.S., specifically in Florida, south Texas, southwest New Mexico, Arizona, central and southern California, and parts of Oregon, Washington, Idaho, and Montana.