Most people outside of farming circles are unaware of the extensive, careful monitoring of atmospheric conditions during the fall, when farmers have traditionally burned rice fields, orchard prunings and other agricultural wastes.

Weathernews is a meteorological firm based in Chico under contract with the rice industry through the Rice Research Board that feeds data from a network of remote weather stations scattered throughout the Sacramento Valley to county Air Pollution Control offices.  These officials, acting under an air quality plan for the Sacramento Valley, determine the very limited amounts of rice acreage that can be burned each fall.  As of last year, only burning for disease control is now permitted, and that is limited to a maximum of 90,000 acres.

Total rice acreage burned last year was 37,373 acres, down significantly from the 43,680 acres in the previous year and a record low since the agricultural burning program began in 1981.  Another 11,478 acres of other agricultural residue was also burned.  Peak burning days (all crops) included November 6 (4,322 acres), October 10 (2,018 acres) and September 27 (1,804 acres).  Average daily burn was 908 acres; the average allocation 2,005 acres.  There were no declared “no burn” days; however, only orchard prunings were permitted on five days.

Monthly Review

The fall burn program officially began Monday, September 16, during a period of mild late summer weather and the influence of pronounced onshore winds.  These pleasant weather conditions allowed for moderate burning, but gave way to a heat wave that significantly reduced burning.  During the final days of September, more cooler marine air vastly improved valley ventilation.

October began cool and very windy, putting a damper on burning for a couple of days due to serious fire control problems.  A couple of weeks of warmer, less windy but fairly stable weather allowed steady but modest burning to be undertaken.  A weak storm front passed through the north state October 16 through October 18, but conditions were not conducive for extensive burning.  Weak disturbances late in the month provided better atmospheric mixing, allowing several days of increased burning.  Despite less than desirable conditions much of the month, nearly 30,000 acres of agricultural residue were burned in October, the most burned during any month last fall.

In early November, very little burning took place because of the return of very stable weather conditions.  The storm track made a dramatic breakthrough across Northern California November 6, when the first in a wave of Pacific storms made its way inland over the valley.  More than 4,000 acres were burned that day — the highest daily total for the season.  The storm dumped more than two inches of rain within the next three days, bringing an early end to the organized phase of the fall burn program.

Air Quality Objectives

The primary objective of the Sacramento Valley Agricultural Burn Plan is to allow agricultural field burning to exist, while maintaining good air quality in the Sacramento Valley air quality basin.  When the atmosphere cannot disperse the smoke from fires efficiently, the burning activity is decreased. That may help explain the minimal number of citizen complaints recorded during fall 2002.  Only 13 complaints were recorded last year throughout the entire Sacramento Valley during the three-month burning period.  The air quality during the fall is more often influenced by other sources of pollution, such as forest fires, vehicular traffic and residential burning than by rice field burning.

Fortunately, the 2002 fall burn was not affected by wildfire smoke as it had been in recent years.  Residential burning was also minimal due to extended periods of dry, generally warm weather.  In fact, this was the first time in program history where the COH (coefficient of haze), a measure of air quality never reached minimal levels.  COH is a crude but effective qualitative measure of how dirty the air is.  Unfortunately, COH makes no determination as to the size or source of particulate pollution present within the valley.