Big Bog, Maui
# Big Bog, Maui

The Big Bog on the island of Maui is the largest high-altitude bog in the Hawaiian Islands. It is located on East Maui Volcano's east rift zone, at the border between Hāna Forest Reserve and Haleakalā National Park. It is alleged to be one of the wettest places on earth, with a reported annual rainfall of 404 inches (10,300 mm) for the period 1992-2018.

## Climate

The Big Bog has a tropical rainforest climate (Köppen Af), with no observable dry season and nearly constant torrential rainfall. Prior to the establishment of the station there in 1992, rainfall for Big Bog was estimated at around 4,600 millimetres (180 in) per year. However, the first full year of recorded data showed 13,995 millimetres (551.0 in) of rainfall, which is one of the highest annual rainfall totals measured in the Hawaiian Islands. Since then, the annual average has been recorded as 404 inches (10,300 mm). Clear days are essentially nonexistent, and even when it is not raining, it is almost certainly cloudy or foggy. The lack of adequate drainage has caused moisture to accumulate, forming the bog.

Climate data for Big Bog (HN-164) 1993-2011 :

| Month | Jan | Feb | Mar | Apr | May | Jun | Jul | Aug | Sep | Oct | Nov | Dec | Year |
| - | - | - | - | - | - | - | - | - | - | - | - | - | - |
| Average rainfall inches (mm) | 32.17 (817.0) | 24.94 (633.6) | 52.07 (1,322.7) | 38.51 (978.1) | 25.52 (648.2) | 28.51 (724.2) | 32.80 (833.0) | 31.04 (788.5) | 26.07 (662.2) | 38.31 (973.1) | 38.02 (965.8) | 36.42 (925.0) | 404.38 (10,271.4) |
| Source: ||||||||||||||

### Causes

The Big Bog lies at 5,400 feet (1,600 m), very close to the trade wind inversion layer, leading to persistent transport of moisture rich air by the northeast trade winds up the steep mountain slopes. These trade winds condense to form clouds and precipitation. Its moniker as the cloudiest place in the Hawaiian Islands is verified by the fact that its average solar radiation and potential evapotranspiration are the lowest amongst recorded locations, and relative humidity and cloud attenuation are the highest.

## Comparison with Mount Waiʻaleʻale

While the summit of Mount Waiʻaleʻale has long been considered the wettest place in the Hawaiian Islands, and thus Oceania, the Big Bog has a higher 30-year average. NOAA reports Wai’ale’ale's annual rainfall as 373.85 inches (9,495.8 mm), while the University of Hawaiʻi at Mānoa reports the Big Bog's as 404.3 inches (10,270 mm). This would make the Big Bog the wettest location in the Hawaiian Islands and in Oceania, although many amateur sources cite Mount Waiʻaleʻale's precipitation as higher.

