Environment

Trade Winds Declining in Hawaii

Experts say trade winds are declining, a drop that’s slowly changing life across the islands. Part of what makes living in Hawaii so pleasant is the gentle breeze. Arriving from the northeast, it’s light enough that it is barely noticeable but strong enough to chase away the humidity.

The effects of the decline in the trade winds can be seen from the relatively minor - such as residents unaccustomed to the humidity complaining about the weather and having to use their fans and air conditioning more often - to the more consequential - including winds being too weak to blow away volcanic smog. The winds also help bring the rains, and their decline means less water. It’s one reason officials are moving to restore the health of the mountainous forests that hold the state’s water supply and encourage water conservation. Scholars are studying ways for farmers to plant crops differently.

It’s not clear what’s behind the shift in the winds. A study has shown a decades-long decline, including a 28 per cent drop in northeast trade wind days at Honolulu’s airport since the early 1970s.

These days there are fewer waves to surf because the winds are arriving less often. Sometimes the winds are too weak to blow away the volcanic smog, or vog, created by sulfur dioxide erupting from Kilauea volcano on the Big Island, leaving a white or brownish haze hanging over Honolulu. This aggravates asthma and other respiratory problems.

For now, the most important consequence will be declining rainfall and a drop in the water supply, particularly as Hawaii’s population grows and uses more water. Trade winds deliver rain to Hawaii when clouds carried from the northeast hit mountainous islands built by millions of years of volcanic eruptions. These rains, together with rainfall from winter storms, are the state’s primary sources of water. On Oahu, the rain feeds ground aquifers that supply water to about 950,000 people in Honolulu and surrounding towns. Residents are reporting streams near their homes are flowing lower than before. Scientists don't know if this is a downward trend or just the lower leg of a long-term cycle.