Exploring the impact of airtanker drops on in-stand temperature and relative humidity
Melanie Wheatley A B # * , Anne Cotton-Gagnon C # , Jonathan Boucher C , B. Mike Wotton B D , Colin B. McFayden A D , Natasha Jurko D and Jason Robinson AA Ontario Ministry of Natural Resources and Forestry, Aviation, Forest Fire and Emergency Services, Dryden Fire Management Centre, 95 Ghost Lake Road, P.O. Box 850, Dryden, ON P8N 2Z5, Canada.
B Institute of Forestry and Conservation, John H. Daniels Faculty of Architecture, Landscape and Design, University of Toronto, 33 Willcocks Street, Toronto, ON M5S 3B3, Canada.
C Laurentian Forestry Centre, Canadian Forest Service, Natural Resources Canada, 1055 rue du P.E.P.S., P.O. Box 10380, Québec City, QC G1V 4C7, Canada.
D Great Lakes Forestry Centre, Canadian Forest Service, Natural Resources Canada, 1219 Queen Street E., Sault Ste. Marie, ON P6A 2E5, Canada.
International Journal of Wildland Fire 32(8) 1269-1276 https://doi.org/10.1071/WF22218
Submitted: 18 November 2022 Accepted: 17 May 2023 Published: 2 June 2023
© 2023 The Author(s) (or their employer(s)). Published by CSIRO Publishing on behalf of IAWF. This is an open access article distributed under the Creative Commons Attribution 4.0 International License (CC BY).
Abstract
Background: There has been little quantification of the extent and duration of micrometeorological changes within a forest after airtanker drops of water-based suppressant. It has been speculated that a period of prolonged relative humidity – referred to as a ‘relative humidity (RH) bubble’ – temporarily exists in the canopy understorey post-drop.
Aims: We quantify the RH bubble from the drops of five airtankers commonly used by wildland fire management organisations in Canada.
Methods: We measured airtankers dropping water, foam concentrates, and gel enhancers in a mature jack pine stand. We examined the duration of change in RH and temperature using Generalised Additive Models, and the consequence of these changes on fine fuel moisture.
Key results: The average maximum RH increased and temperature decreased, indicating that the effects of the ‘RH bubble’ in-stand lasted from 25 to 76 min, depending upon the airtanker type and load configuration.
Conclusion: Airtanker drops cause an in-stand increase in RH and decrease in temperature, but this ambient change has a limited effect on potential fire behaviour.
Implications: The direct effect of water wetting the fuel is the most impactful effect of an airtanker drop. The ‘RH bubble’ created, though observable, does not change fine fuel moisture enough to impact fire behaviour.
Keywords: aerial suppression, enhancer, fine fuel moisture, fire management, general additive model, humidity dome, mature jack pine, RH bubble.
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