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| Titel |
Effects of slope orientation on fine surface fuel moisture content: implications for ignition probabilities and connectivity of fuels |
| VerfasserIn |
Petter Nyman, Daniel Metzen, Phil Noske, Thomas Duff, Gary Sheridan |
| Konferenz |
EGU General Assembly 2015
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| Medientyp |
Artikel
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| Sprache |
Englisch
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| Digitales Dokument |
PDF |
| Erschienen |
In: GRA - Volume 17 (2015) |
| Datensatznummer |
250107654
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| Publikation (Nr.) |
 EGU/EGU2015-7363.pdf |
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| Zusammenfassung |
| This study quantifies topographic effects on microclimate and moisture dynamics in litter and
near surface soil with the aim to improve spatial representation of fine surface fuel moisture
content (FFMC) in mountainous terrain where forest fires typically operate. FFMC was
monitored at 30-minute intervals using a novel field method for measuring moisture content
of litter, providing unique data on the spatial-temporal variation in FFMC throughout a fire
season. Moisture sensors were inserted into litter packs at sites on different slope aspects
(North, South, West and East) and paired with manual measurement of gravimetric water
content to relate sensor output to water content. Hydrochron sensors (or iButtons) were
placed within the litter packs, measuring temperature at the interface between the litter
layer and the soil. During the monitoring period the mean daily moisture content in
the litter layer ranged from 0.07-1.30 kg kg-1 on the north-facing slope and from
0.11–1.83 kg kg-1 on the south-facing slope. The number of days during the fire
season when the litter was below the fiber saturation point (~0.35 kg kg -1) was 49
and 128 on the south and north aspects, respectively, highlighting the very large
aspect-driven variation in FFMC and the need for spatially explicit data on microclimate.
Differences in moisture content were caused by aspect-related variation in incoming
radiation which resulted in large temperature differences within the litter layer. On
the warmest day of the monitoring period (38.9Ë C on 17 January), for example,
the difference in litter temperature between North and South aspect was 14Ë C.
Differences in surface temperature were driven mainly by the systematic variation
in vegetation cover, and hence shading, which emerge as a result of aspect (i.e.
eco-hydrologic effect) and partly by the effects of slope orientation (i.e. geometric effect) on
incoming radiation. Furthermore, the differences in FFMC due to evaporative demand
were augmented by the systematic increase in litter depth (and thus the overall
water holding capacity of the fuel bed) with decreasing incoming radiation. The
combined effects of slope orientation, vegetation and litter bed properties on FFMC was
up-scaled to explore how ignition probabilities and fuel connectivity vary in space and
time during drying and wetting cycles throughout a fire season. Results from the
study will be used to improve the spatial modeling of microclimate and FFMC
and provide a basis for i) more spatially explicit predictions of fuel availability for
wildfires and ii) more targeted, safe and effective scheduling of fuel reduction burns. |
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