Solar Radiation and Forest Fuel Moisture. Byram, G. M. and Jemison, G. M. 67(4):149–176.
Solar Radiation and Forest Fuel Moisture [link]Paper  abstract   bibtex   
A major contribution to progress in forest fire prevention and control during the past 10 years has been the development and widespread application of methods of rating forest fire danger. Fire danger rating systems are now in use in all the forest regions of the United States. They have been described by Gisborne, Brown and Davis, Curry et al., Matthews, Jemison, and others. Under each of these systems the major factors affecting fire danger are measured and the measurements are integrated by means of charts, tables, or some mechanical device into ratings, on a numerical scale, which are free from the serious errors common in estimates of fire danger based on personal judgment alone. The numerical ratings are usually defined in terms of probable fire behavior or of manpower required for suppression. They serve as a guide to efficient distributIon of fire-control funds and personnel. [Excerpt: Summary] Forest fire-danger rating systems, now in use in all forest regions of the United States, are based chiefly on measurement of wind and of fuel moisture. While many workers have investigated atmospheric and related elements that control fuel moisture, little research has be.en done on solar radiation and its influence on fuel moisture equilibria and rates of drying. With a view to contributing to the refinement of fire-danger rating systems and application of the ratings, a study of solar radiation and fuel moisture was begun in the southern Appalachians in 1938. [] A method has been developed whereby radiation intensity can be determined for any season of year, hour of day, slope, and aspect. Examples are given showing the widely different radiation intensities that are to be expected under different combinations of these factors even though atmospheric conditions are the same. The relation of solar radiation intensity to surface fuel moisture equilibria and, to a lesser extent, its relation to rates of drying have been established on the basis of theory and of data obtained by use of an "artificial sun" apparatus, a specially constructed weather synthesizer. This apparatus permits both field and laboratory observation of moisture equilibria and rates of drying under various combinations of radiation, Wind, and humidity. Formulae have been developed so that for any combination of air temperature, relative humidity, and wind velocity, equilibrium moisture content of forest litter can be derived for any season, slope, and aspect. These formulae can be used universally, provided radiation intensities are adjusted for latitude. [] The influence of wind on fuel drying is emphasized. In bright sunlight, contrary to popular belief, wind maintains levels of fuel moisture higher than those in calm air. The reason is that for fuels in the sun the wind's cooling action more than offsets its drying action. This is important in some regions where fuels are fully exposed to sunlight during the fire season. [] Fuel moisture equilibrium maps are presented showing variations with season, aspect, and slope that result from variations 1n radiation intensity alone. A table is presented showing differences in drying rates caused by differences in radiation.
@article{byramSolarRadiationForest1943,
  title = {Solar Radiation and Forest Fuel Moisture},
  author = {Byram, George M. and Jemison, George M.},
  date = {1943},
  journaltitle = {Journal of Agricultural Research},
  volume = {67},
  pages = {149--176},
  issn = {0095-9758},
  url = {http://mfkp.org/INRMM/article/14073812},
  abstract = {A major contribution to progress in forest fire prevention and control during the past 10 years has been the development and widespread application of methods of rating forest fire danger. Fire danger rating systems are now in use in all the forest regions of the United States. They have been described by Gisborne, Brown and Davis, Curry et al., Matthews, Jemison, and others. Under each of these systems the major factors affecting fire danger are measured and the measurements are integrated by means of charts, tables, or some mechanical device into ratings, on a numerical scale, which are free from the serious errors common in estimates of fire danger based on personal judgment alone. The numerical ratings are usually defined in terms of probable fire behavior or of manpower required for suppression. They serve as a guide to efficient distributIon of fire-control funds and personnel.

[Excerpt: Summary] Forest fire-danger rating systems, now in use in all forest regions of the United States, are based chiefly on measurement of wind and of fuel moisture. While many workers have investigated atmospheric and related elements that control fuel moisture, little research has be.en done on solar radiation and its influence on fuel moisture equilibria and rates of drying. With a view to contributing to the refinement of fire-danger rating systems and application of the ratings, a study of solar radiation and fuel moisture was begun in the southern Appalachians in 1938.

[] A method has been developed whereby radiation intensity can be determined for any season of year, hour of day, slope, and aspect. Examples are given showing the widely different radiation intensities that are to be expected under different combinations of these factors even though atmospheric conditions are the same. The relation of solar radiation intensity to surface fuel moisture equilibria and, to a lesser extent, its relation to rates of drying have been established on the basis of theory and of data obtained by use of an "artificial sun" apparatus, a specially constructed weather synthesizer. This apparatus permits both field and laboratory observation of moisture equilibria and rates of drying under various combinations of radiation, Wind, and humidity. Formulae have been developed so that for any combination of air temperature, relative humidity, and wind velocity, equilibrium moisture content of forest litter can be derived for any season, slope, and aspect. These formulae can be used universally, provided radiation intensities are adjusted for latitude.

[] The influence of wind on fuel drying is emphasized. In bright sunlight, contrary to popular belief, wind maintains levels of fuel moisture higher than those in calm air. The reason is that for fuels in the sun the wind's cooling action more than offsets its drying action. This is important in some regions where fuels are fully exposed to sunlight during the fire season.

[] Fuel moisture equilibrium maps are presented showing variations with season, aspect, and slope that result from variations 1n radiation intensity alone. A table is presented showing differences in drying rates caused by differences in radiation.},
  keywords = {*imported-from-citeulike-INRMM,~INRMM-MiD:c-14073812,disturbances,environmental-modelling,fire-fuel,forest-resources,fuel-moisture,modelling,solar-radiation,wildfires},
  number = {4}
}
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