Source: October-December 2006 California Agriculture magazine

Historic weather data can be used to develop accurate yield predictions for a number of important California crops, according to a peer-reviewed study published in the October-December 2006 issue of the University of California's California Agriculture journal. The full article is posted online at http://californiaagriculture.ucop.edu.
 
Currently, the California Agricultural Statistics Service (CASS) develops estimates of coming harvests for major California crops, which are then used by growers and the food industry to plan strategies for crop harvest, storage and distribution. These labor-intensive predictions are based on phone interviews with hundreds of farmers, or on samples from hundreds of fields.
 
The authors obtained 24 years of actual yield data for 12 valuable California crops--including walnuts, oranges, processing tomatoes and grapes--and compared it with daily weather measurements from 382 stations throughout California over the same time period. The resulting statistical models were able to predict the yields of some crops "with fairly high accuracy," wrote the authors, based at Lawrence Livermore National Laboratory and the Carnegie Institution at Stanford University. For almonds, the model captured 80 percent of yield variance. The models also did particularly well at predicting low yields in almonds, processing tomatoes, oranges and cotton.
 
The authors note that while field-based surveys are likely to be more accurate than weather-based yield predictions, weather-based estimates are much less expensive to produce and are often able to provide reliable yield forecasts several months earlier in the growing season.
 
"This gives growers the opportunity to use the information to make decisions," says lead author David Lobell. "For example, our models for almonds and walnuts rely mainly on winter weather, while harvest does not begin until late summer."
 
Growers and others interested in yield forecasts for the current season are encouraged to contact Lobell at lobell2@llnl.gov or (925) 422-4148.
 
California Agriculture is the University of California's peer-reviewed journal of research in agricultural, human and natural resources. For a free subscription, go to: http://CaliforniaAgriculture.ucop.edu, call (510) 987-0044 or write to calag@ucop.edu. For a printed copy of California Agriculture, media should email janet.byron@ucop.edu or call (510) 987-0668.