Agricultural Burn



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Don Schukraft - certified meterologist, Weather Network, Inc.

The 1994 fall burn will be remembered as a year when the program was severely tested. On November 1 a storm front acted unpredictably, kicking up north winds that blew rice smoke into many urban areas of the Sacramento Valley. Unfortunately, this was also the same day the most acreage was burned. Not surprisingly this set of circumstances generated the greatest number of complaints since the inception of the agricultural burning program. If not for this event, last year's program would have been noteworthy only because it ended so early due to the onset of a very wet winter.

FieldBurn.jpg (119388 bytes)The fall burn ran from September 15 to November 10. A total of 113,073 acres was burned. The most acreage, as previously noted, was on November 1 and totaled 14,337 acres. The daily average acreage burned last fall was 1,984 acres, 500 acres higher than the previous year. A total of 333 citizen complaints were received, 215 of them on November 1.

Although there were only seven no burn days, burning was once again concentrated on a handful of days. The five days with the most acreage burned accounted for 35 percent of the total acreage burned.

AMOS Monitoring

Preparation for the fall burn began last summer when staff from Weather Network visited the network of Automatic Meteorological Observing Stations (AMOS) scattered throughout the Sacramento

Valley to ensure proper operation of each station's sensor array, datalogger, radio and modem. A new phone line was installed at the Woodland weather station in September. Because of interference from nearby buildings and trees, reaching particular weather station via radio telemetry had become difficult. Meteorologists are now assured consistent observations from the station.

Weather Conditions

Weather conditions played a significant role in the amount of acreage burned. An abundance of hot, dry, stable weather through most of September restricted early season burning. Burning conditions improved in October when several, largely dry, fronts passed through the valley. Storm activity picked up in November resulting in the two highest acreage burn totals of the fall but eventually shutting the program down by the 10th of the month because fields never got a chance to dry out.

South winds were more common Iast fall, occurring on 28 percent of the days. Normally south winds occur less than a quarter of the time each fall. North wind days were down 10 percent from normal, while days with a significant wind shift -either north to south or vice versa- occurred with greater frequency than usual.

Program Changes

One of the keys to avoiding a November 1 incident in the future is to be able to better distinguish between "problem" storm systems and the more classic storm systems such as one that pushed across the north state just three days later.

Agricultural burning program personnel and participating counties are implementing several changes for the 1995 burn program. One change involves the installation of rain gauges at more valley AMOS locations. The hourly precipitation data from these weather stations will be transmitted to the computer database from which decisions about burning are made. Also, the current frontal position and expected time of frontal passage will be added to Weather Network's forecasting files. Finally, a new policy will be established to not release any additional acreage for burning to counties where measurable precipitation has been reported.

Air Quality Readings

With the exception of the November 1 incident, days of greater acreage burn coincided well with periods of low COH readings and periods of higher COH coincided with days when little or no agricultural burning was allowed.

There was a substantial difference in the air quality of the 13 sites where coefficient of haze (COH) is monitored. Comparing the cleanest of these locations, Colusa, with the dirtiest, Sacramento, leads to some interesting conclusions (see graph). The 8 a.m. COH peak in Sacramento is directly related to the morning commute. The 10 p.m. peak is related to home heating. Neither graph shows any significant afternoon increase in COH, yet this is when a majority of the agricultural burning would be taking place. As in past years, this suggests that the program continues to be successful it minimizing the impact rice straw burning has on the air quality of the Sacramento Valley.

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The problem on November 1 illustrates that even with the best of intentions things sometimes go haywire due to the inherent uncertainty of weather. Despite these problems, rice burning remains only a small constituent of valley air pollution. Because of the program's safeguards, rice burning is never a contributor to valley air pollution for any extended period of air stagnation during the fall.

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