|Sacramento Valley Fall Burn
Donald Schukraft,WeatherNews, Inc.
Rice acreage was in excess of 600,000 acres last year, yet the amount of acreage burned continues to dwindle. The rice industry created the Sacramento Valley Fall Burn Program to manage this limited open field burning with minimal impact to the air quality in the Sacramento Valley and beyond.
The 2004 fall burn ran from September 1 through November 12, a total of 73 days. Total rice acreage burned was 28,404 acres, a decline of about 5,500 acres from the previous year. Other agricultural burning, such as orchard prunings, totaled 11,784 acres, a decrease of approximately 7,200 acres from the previous year. A few other facts from 2004 include:
Weathernews Americas Inc. is the Chico-based firm under contract with the Rice Research Board to provide real-time meteorological information from a network of 19 remote weather stations to county air pollution control officials. These officials decide the amount and location of acreage to be burned, depending on weather conditions and prescribed allotments. Existing law limits rice straw burning for disease control to the lesser of 25 percent of each grower’s planted acreage up to an annual total of 125,000 acres in the Sacramento Valley Air Basin. Of the 125,000-acre total, a maximum of 90,000 acres can be burned during the fall.
The information from the automated weather stations is made available to all rice growers in the Sacramento Valley on a year-round basis at the Rice Research Board’s password-protected Web site. Growers can also use the data to calculate growing degree-days, phenology models and field temperatures to assess blanking and other weather-related rice issues.
Monthly weather review
In September 2004 a progressive weather pattern brought two distinct periods of cooling in the latter half of the month. An initial period of cooling culminated with scattered shower activity over sections of the valley on Sept. 19. A second, less robust trough initiated a strong onshore surge of marine air into the north state interior late in the month but generated few clouds and no precipitation across the valley. The improved atmospheric circulation during this period allowed for greater burning than a typical September.
In October 2004 the usual early fall high-pressure system failed to materialize. The first half of the month was generally dry with fluctuating temperatures. A weak trough passing on Oct. 8-9 improved air circulation enough to burn 2,500 acres on the 8th and a more limited amount on the 9th because of overnight rain. This was the only day more than 2,000 acres were burned and proved to be the day with the greatest acreage burned during the fall. Incoming storm systems finally gained sufficient moisture and thermal support that left the last half of October significantly cooler and wetter. The frequent storm activity set rainfall records in the Sacramento Valley for the month of October, with Chico receiving 4.91 inches. The previous maximum over the last 30 years was 3.20 inches of rainfall in Chico for the month of October.
Much dryer conditions prevailed across the Sacramento Valley during the first week of November. Unfortunately, the lateness of the season with its shorter days, increasingly shallow sun angle, and nightly fog formation slowed field drying. Nevertheless, Nov. 2 and Nov. 9 saw more than 2,000 acres burned each day. Two weather systems, although milder than late October’s, brought enough precipitation to interfere with burning operations and bringing a close to the fall burn on Nov. 12.
New air quality standards
New air quality standards were in effect for the 2004 fall burn. In previous years the coefficient of haze (COH) had been used to measure air quality. Fine particulate matter (PM) of 2.5 microns or less (PM2.5) is now the air quality measurement in use. The ambient air quality standards for the state were not exceeded during the 2004 fall burn.
The number of citizen complaints has been recorded each fall since the program began in 1981. The state Air Resources Board recorded very few complaints in the last few years. Of the complaints recorded in 2004, most came from Butte County with 11. Sutter and Yuba counties each recorded two. Glenn, Placer, Sacramento, Shasta and Tehama counties recorded one each. No complaints were recorded in Colusa, Yolo or Solano counties.
Field burning is limited on days of poor air quality and poor atmospheric dispersion and maximized during days of good air quality and good atmospheric dispersion. This greatly minimizes the impact of agricultural burning on the air quality in the Sacramento Valley Air Basin, just as intended. The air quality during the fall is often more influenced by other sources of pollution, such as forest or other wildfires, vehicular traffic and residential burning, than by the burning of rice fields, as was the case in 2004. Two days were declared no burn days due to wildfire smoke.