Rice Straw Burning
Program-99

 
 

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Don Schukraft, Certified Consulting Meterologist, WeatherNews, Inc.

Each fall a plan is developed in collaboration with air quality officials to allow for the controlled burning of rice straw and other agricultural waste.  The plan is designed to minimize the impact of burning to air quality and to protect the health and safety of Sacramento Valley residents.  The 1999 fall burn program was characterized by spurts of burning with extended periods when little or no burning took place.  Complaints about rice straw burning affecting air quality were virtually nonexistent — with good reason.   The efficiency of the program allows a quantified amount of field burning to take place only when the atmospheric conditions are conducive to dispersing the smoke so as to minimize the impact on the population in the Sacramento Valley.

Annual Tune-up

As usual, preparations for the fall burn began with late summer visits by Weathernews technicians to the Automatic Meteorological Observing Stations (AMOS) scattered throughout the Sacramento Valley.  All stations were checked for proper operation.   Dataloggers, meteorological sensors and radio equipment were repaired or replaced if necessary.  The Weathernews meteorological team also expanded information available on the Fall Burn website.  New links were established to access data from the state Air Resources Board and the Central Computer Operator (Fife Environmental).   Radar and satellite imagery and airport observations, as well as data from the Rice Research Board’s automated weather stations were also posted on the Fall Burn website.

Season Overview

Burning commenced September 15 and concluded 64 days later on November 17.  During this period 73,000 acres of total agricultural waste was burned, about 80 percent of it rice stubble.  Not surprisingly, only one complaint was filed with the ARB, an all-time low, but a gauge that may not necessarily reflect the success or failure of the program.  More on that below.

Dry weather after the conclusion of the organized phase of the fall burn allowed another 32,000 acres to be burned before the end of the year.  Altogether, 80,000 acres of rice stubble was burned between September 1 and December 31 — 10,000 acres less than the legislated maximum limit.  That acreage was to be credited toward a spring 2000 burn allowing up to 120,000 acres to be burned.  Although the amount of rice stubble burned has varied widely since 1993, the amount of other agricultural waste burned during this time has remained remarkably consistent.

Ten days were declared "no burn" days during the 1999 fall burn.  The no burn days were prompted by forest fire smoke trapped in the Valley, creating some of the worst air quality in recent memory.

Burning began slowly in September.  Delays in harvesting, the conservative policies of air quality regulators, along with inconvenient weather and the wildfire smoke combined to limit September acreage to 7,500 acres.  This was the second lowest for September since 1985.

Dry weather dominated in October, with only two storm fronts of any significance.   Ahead of these storms, consistent southerly winds helped disperse smoke.  The first storm front brought only sprinkles to the valley and could have been better utilized, according to program meteorologists.  Slightly more than 7,600 acres were burned during this two-day period.  A second, more powerful storm pushed across the north state late in the month and was more successfully taken advantage of before the valley got soaked with a healthy dose of rain.  Overall, October saw 36,130 acres burned, fairly typical when compared to recent past years.

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Burning in November started out more modestly as fields were slow to dry following the late October storm.  This changed abruptly, however, when a vigorous system approached Northern California on November 7.   On that day, with precipitation holding off until the afternoon, 13,512 acres were burned, the most burned on any single day since 1996.  This one day accounted for nearly a fifth of all acreage burned.

Wildfire Increases Pollutants

The coefficient of haze (COH), an important measure of air quality, surprisingly did not trend upward through the fall as it has in past years.  Meteorologists suspect there may be several reasons for this.  The lower atmosphere was more stable in September and October than in November, thus trapping more non-agricultural pollution than usual.  Second, agricultural burning is concentrated during periods of good dispersion and ventilation, thus unlike most other sources of pollution it does not linger within the airshed.  And third, wildlife smoke produced two large spikes in the daily average COH, with the second episode producing some of the worst air quality in recent years.

BurnCh2.jpg (8800 bytes)Total citizen complaints were close to an all-time low. Nevertheless, these complaints are not necessarily a good measure of the program’s success or failure.  While they can point out problems in burn placement, they can too easily be manipulated.  The amount of acreage burned during the fall continues to have little correlation with regional air quality.  The average amount of acreage burned on a daily basis continued to decline; however, seasonal COH did not.    Since the early 1980s when this program began, average acreage burned has dropped by 80 percent, while COH has improved far less.   This underscores the fact that agricultural burning is not a large constituent of valley air pollution, certainly not as much as is perceived by the general public.

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