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Theoretical background on pwsFWI: Difference between revisions
Theoretical background on pwsFWI (view source)
Revision as of 15:01, 13 April 2021
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== Some reasoning == | == Some reasoning == | ||
The whole process of evaporation and drying is implicit. I will not try to quantify the waterbalance exactly which would result in a quantification of the [[Charts_-_Misc_charts#Daily_EVT_.28Evapotranspiration.29|Evapotranspiration]]. Evaporation is an extremely complex process | The whole process of evaporation and drying is implicit. I will not try to quantify the waterbalance exactly which would result in a quantification of the [[Charts_-_Misc_charts#Daily_EVT_.28Evapotranspiration.29|Evapotranspiration]]. Evaporation is an extremely complex process, too much for this wiki page, see some pages on the wikipedia <ref>[https://en.wikipedia.org/wiki/Evaporation Evaporation], [https://en.wikipedia.org/wiki/Hydrology_(agriculture) Hydrology (agriculture)] and the [http://www.fao.org/3/X0490E/x0490e00.htm FAO Irrigation and drainage paper 56].</ref>, which is far beyond the scope of a fire weather index. But even for professionals it is a complex phenomenon, as it is influenced by vegetation, crop, soil etc… In short, the whole environment. That would be a bit too much although I think in principle it can be done. | ||
High VPD implies also high evaporation. | High VPD implies also high evaporation. | ||
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Wind, although not a direct factor in igniting fire, contributes very much to the drying process and after ignition, it contributes to the propagation. Strong winds will quickly create dangerous fire weather. The longer the period of dry (and strong) wind and high temperatures, the drier the fuel will be and the easier it will ignite. | Wind, although not a direct factor in igniting fire, contributes very much to the drying process and after ignition, it contributes to the propagation. Strong winds will quickly create dangerous fire weather. The longer the period of dry (and strong) wind and high temperatures, the drier the fuel will be and the easier it will ignite. | ||
So, relative humidity (fraction), wind (in km/h) and temperature (in °C) are the measurements used for the daily calculation as shown above. Furthermore the effect of the duration of dry and (possibly windy) weather needs to be taken into account and that is done through a process of testing and adjusting (a kind of calibration) until the output delivers consistent warning levels comparable with experience and existing fire weather indices. | So, relative humidity (fraction), wind (in km/h) and temperature (in °C) are the measurements used for the daily calculation as shown above. Furthermore the effect of the duration of dry and (possibly windy) weather needs to be taken into account and that is done through a process of testing and adjusting (a kind of calibration) until the output delivers consistent warning levels comparable with experience and existing fire weather indices. | ||
== Quenching and smoothing the fire weather index == | == Quenching and smoothing the fire weather index == | ||