Final Comprehensive Conservation Plan - U.S. Fish and Wildlife ...

Hakalau Forest National Wildlife Refuge
Comprehensive Conservation Plan
humidity during the winter months is about 70 percent. In the spring and summer months, daily
humidity increases to about 85 percent. Daily differences in humidity are also present, with the
strongest humidity in the late afternoon and early evening (USFWS 2002a).
3.1.2 Kona Forest Unit Climate
Compared to the HFU on windward Mauna Kea, the climate on the Kona side (leeward) of Hawai‘i
Island is drier. In particular, South Kona is considered one of the most drought-prone regions in the
Hawaiian archipelago (USFWS 2008a). The moisture patterns in the area are driven primarily by
daytime surface heating and upslope winds that yield convective rainfall from roughly 2,000 -
5,900 ft. Unlike most areas in the State, the rainy season in Kona occurs during the summer months,
with peaks in June-September and low periods from November-February (Juvik and Juvik 1998).
Rainfall clearly decreases with elevation at KFU. Areas above 5,000 ft and below 2,000 ft elevation
are generally dry (Atkinson et al. 2005). Average annual rainfall at the lower and upper area of KFU
can differ by 39 in (USFWS 2008a). Between April 1995-November 1998, the average annual
rainfall varied from 5.63 inches at 2,000 ft to 2.05 inches at 6,000 ft. The climatic differences
between the elevations affect the types of species present and species distributions. Seasonal
fluctuations have also been observed at the Refuge. Annual and monthly rainfall averages are listed
in Table 3-1.
Table 3-1. Average Monthly Rainfall (inches) at the Kona Forest Unit, April 1995-
November 1998.
Month Elevation
2,000 ft 3,000 ft 4,000 ft 5,000 ft 6,000 ft
January 3.31 2.80 3.00 2.78 2.73
February 1.61 2.07 2.25 1.71 0.82
March 5.28 6.12 6.09 5.42 4.08
April 3.89 4.40 3.26 2.57 1.64
May 4.76 5.77 4.04 2.15 1.30
June 8.45 8.19 7.06 4.74 3.17
July 6.94 5.45 4.10 3.17 1.95
August 6.99 6.48 4.02 2.29 1.73
September 12.2 9.89 6.19 3.07 2.35
October 6.16 4.79 2.19 2.03 1.25
November 3.11 2.85 2.10 1.79 1.42
December 2.37 4.25 4.15 4.01 2.71
Annual Ave. 5.63 5.39 4.05 2.93 2.05
Source: USFWS, unpubl.
Rain is the primary moisture source at elevations from 2,000 - 2,700 ft, while areas above this
elevation also receive moisture from fog drip. The maximum amount of fog drip occurs from 3,000-
6,500 ft. Fog density peaks at about 5,000 ft (USFWS 2008a). “Vog”, volcanic gases and particulates
emitted from Kīlauea volcano, is another aspect of the climate on the Island of Hawai‘i. Vog forms a
distinctive haze and has been implicated in causing decreased rainfall and plant damage in Kona
forests (USFWS 2008a).
Chapter 3. Physical Environment 3-3