Natural variability of the Keetch–Byram Drought Index in the Hawaiian Islands
Klaus Dolling A C , Pao-Shin Chu A and Francis Fujioka BA Department of Meteorology, School of Ocean and Earth Science and Technology, University of Hawaii, Honolulu, HI 96822, USA.
B USDA Forest Service, Pacific Southwest Research Station, 4955 Canyon Crest Drive, Riverside, CA 92507, USA.
C Corresponding author. Email: dolling@hawaii.edu
International Journal of Wildland Fire 18(4) 459-475 https://doi.org/10.1071/WF06146
Submitted: 11 November 2006 Accepted: 29 July 2008 Published: 29 June 2009
Abstract
The Hawaiian Islands experience damaging wildfires on a yearly basis. Soil moisture or lack thereof influences the amount and flammability of vegetation. Incorporating daily maximum temperatures and daily rainfall amounts, the Keetch–Byram Drought Index (KBDI) estimates the amount of soil moisture by tracking daily maximum temperatures and rainfall. A previous study found a strong link between the KBDI and total area burned on the four main Hawaiian Islands. The present paper further examines the natural variability of the KBDI. The times of year at which the KBDI is highest, representing the highest fire danger, are found at each of the 27 stations on the island chain. Spectral analysis is applied to investigate the variability of the KBDI on longer time scales. Windward and leeward stations are shown to have different sensitivities to large-scale climatic fluctuations. An El Niño signal displays a strong relationship with leeward stations, when examined with a band-pass filter and with a composite of standardized anomalies. Departure patterns of atmospheric circulations and sea surface temperatures over the North Pacific are investigated for composites of extremely high KBDI values when fire risk is high. The winter, spring, and fall show anomalous surface anticyclonic circulations, surface divergence, and subsidence over the islands for the upper quartile of KBDI. The winter, spring, and fall composites of equatorial sea surface temperatures for the upper quartile of KBDI are investigated for possible links to atmospheric circulations. These analyses are an effort to allow fire managers some lead time in predicting future fire risks.
Acknowledgements
The present study has been supported by the USDA Forest Service projects 01-CA-11272169–124 and 05-JV-11272165–015. We would like to thank the two anonymous reviewers and the associate editor for their helpful suggestions.
Chen Y-L , Nash AJ (1994) Diurnal variation of surface airflow and rainfall on the island of Hawaii. Monthly Weather Review 122, 34–55.
| Crossref | GoogleScholarGoogle Scholar |
Dolling KP, Chu P-S , Fujioka F (2005) A climatological study of the Keetch/Byram drought index and fire activity in the Hawaiian Islands. Agricultural and Forest Meteorology 133, 17–27.
| Crossref | GoogleScholarGoogle Scholar |
Heim RR (2002) A review of twentieth century drought indices used in the United States. Bulletin of the American Meteorological Society 83, 1149–1165.
Lee H-K, Chu P-S, Sui C-H , Lau K-M (1998) On the annual cycle of latent heat fluxes over the equatorial Pacific using TAO buoy observations. Journal of the Meteorological Society of Japan 76, 909–923.
Ramage CS (1962) The subtropical cyclone. Journal of Geophysical Research 67, 1401–1411.
| Crossref | GoogleScholarGoogle Scholar |
Ropelewski CF , Halpert MS (1987) Global and regional scale precipitation patterns associated with the El Niño/Southern Oscillation. Monthly Weather Review 115, 1606–1626.
| Crossref | GoogleScholarGoogle Scholar |
Trenberth KE (1997) The definition of El Niño. Bulletin of the American Meteorological Society 78, 2771–2777.
| Crossref | GoogleScholarGoogle Scholar |
Walker GT , Bliss EW (1932) World Weather V. Memoirs of the Royal Meteorological Society 4, 53–84.
