A climatological study of the Keetch/Byram Drought Index and fire activity in the Hawaiian Islands

Abstract

The Hawaiian Islands experience damaging wildfires on a yearly basis. Periods without substantial rain are part of the natural annual cycle as well as part of natural climate fluctuations. Soil moisture, or lack thereof, influences the amount and flammability of vegetation. Incorporating daily maximum temperatures and daily rainfall amounts, the Keetch and Byram Drought Index (KBDI) estimates the amount of soil moisture by tracking daily maximum temperatures and rainfall. For the first time, the climatological relationship between the KBDI and fire activity is examined using a number of different techniques. The KBDI is tested separately on four major Hawaiian Islands against total acres burned (TAB). This relationship is explored using various statistical methods and a strong relationship is found between these two variables. The annual cycle of the KBDI is investigated through the use of harmonic analysis. 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 various time scales. Individual stations are found to have different sensitivities to large-scale climatic fluctuations. An EI Nino signal is shown to have a strong relationship with leeward stations through the application of a band-pass filter. Large-scale atmospheric circulations are also investigated for seasons when KBDI is extremely high and low. Anomalous anticyclonic (cyclonic) circulations and surface divergence (convergence) are found over the island chain for times when the KBDI is high (low).