Journal cover Journal topic
Natural Hazards and Earth System Sciences An interactive open-access journal of the European Geosciences Union
Nat. Hazards Earth Syst. Sci., 16, 403-415, 2016
https://doi.org/10.5194/nhess-16-403-2016
© Author(s) 2016. This work is distributed under
the Creative Commons Attribution 3.0 License.
Research article
09 Feb 2016
Comparison of different methods for the in situ measurement of forest litter moisture content
C. Schunk1, B. Ruth2,*, M. Leuchner1,3,a, C. Wastl1,b, and A. Menzel1,3 1Ecoclimatology, Technische Universität München, Hans-Carl-von-Carlowitz-Platz 2, 85354 Freising, Germany
2Institute of Soil Ecology, Helmholtz Zentrum München – German Research Center for Environmental Health, Ingolstädter Landstraße 1, 85764 Neuherberg, Germany
3Institute for Advanced Study, Technische Universität München, Lichtenbergstraße 2a, 85748 Garching, Germany
anow at: Springer Science + Business Media B.V., Dordrecht, the Netherlands
bnow at: Central Institute for Meteorology and Geodynamics, Vienna, Austria
*retired
Abstract. Dead fine fuel (e.g., litter) moisture content is an important parameter for both forest fire and ecological applications as it is related to ignitability, fire behavior and soil respiration. Real-time availability of this value would thus be a great benefit to fire risk management and prevention. However, the comprehensive literature review in this paper shows that there is no easy-to-use method for automated measurements available. This study investigates the applicability of four different sensor types (permittivity and electrical resistance measuring principles) for this measurement. Comparisons were made to manual gravimetric reference measurements carried out almost daily for one fire season and overall agreement was good (highly significant correlations with 0.792 <  =  r <  =  0.947, p  <  0.001). Standard deviations within sensor types were linearly correlated to daily sensor mean values; however, above a certain threshold they became irregular, which may be linked to exceedance of the working ranges. Thus, measurements with irregular standard deviations were considered unusable and relationships between gravimetric and automatic measurements of all individual sensors were compared only for useable periods. A large drift in these relationships became obvious from drought to drought period. This drift may be related to installation effects or settling and decomposition of the litter layer throughout the fire season. Because of the drift and the in situ calibration necessary, it cannot be recommended to use the methods presented here for monitoring purposes and thus operational hazard management. However, they may be interesting for scientific studies when some manual fuel moisture measurements are made anyway. Additionally, a number of potential methodological improvements are suggested.

Citation: Schunk, C., Ruth, B., Leuchner, M., Wastl, C., and Menzel, A.: Comparison of different methods for the in situ measurement of forest litter moisture content, Nat. Hazards Earth Syst. Sci., 16, 403-415, https://doi.org/10.5194/nhess-16-403-2016, 2016.
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Short summary
Dead fine fuel (e.g. litter) moisture is a key parameter for wildfire and ecological applications, as it is related to ignitability, fire behavior and soil respiration. For example, fire ignition is highly likely at moisture contents below 10 %, yet nearly impossible above 25 %. Thus, fine fuel moisture measurements are very desirable; however, there is no easy-to-use automated technique available to date. This study investigates the applicability of different sensor types for this measurement.
Dead fine fuel (e.g. litter) moisture is a key parameter for wildfire and ecological...
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