Less rainfall stirs concern about greater water demand

By EDWIN TANJI, City Editor
KAHULUI — With rainfall sharply down through most of February and the first week of March, county Water Director Jeff Eng on Friday expressed concern over growing demand on the Upcountry and Central Maui water systems.

The monthly rainfall report for February showed most areas of Maui County had below-normal rainfall — with the exception of East Maui areas that were drenched in early February.

The West Wailua Iki rain gauge in the East Maui watershed recorded 22.31 inches in February, 149 percent of normal for the month. But National Weather Service hydrologist Kevin Kodama said most of the moisture fell early in the month, with a high of 6.22 inches recorded Feb. 2.

February opened with heavy rains, with an upper-level trough causing instability that led to significant rainfall and flooding particularly on the Big Island. Big Island regions received 20 to 40 inches of rain over five days at the beginning of the month, he reported.

But by Feb. 9, he said, a more stable trade wind pattern returned with a southward shift in the surface-level, high-pressure system normally located 1,000 miles northeast of the islands.

“The resulting stable, light-wind pattern persisted through most of the remainder of the month, broken briefly by the passage of a weak cold front on February 24 and 25,” he said.

For the month, rainfall totals across Maui County ranged from the high of 22.31 inches at West Wailua Iki to a low of 0.91 inch in Kihei, 41 percent of normal for February.

Over the first two months of 2008, key watersheds have received healthy rainfall — but Kodama acknowledged that the rainfall occurred in spurts that aren’t helpful for consistent water flow.

“I guess the difficulty is that the Upcountry areas can have all the water in the world, but if it goes three weeks to a month with little rain, then it gets into trouble right away,” he said.

“That’s an issue related to storage capacity, whether they can capture the rain when it falls. That’s their reality.”

Flows into the Upcountry water system reflect the diminished rainfall. From March 1 through Friday, the flow in the Wailoa Ditch — which provides domestic water through the Kamole Weir Treatment Plant — fell steadily from 50.8 million gallons a day to 40 mgd. The water department reported water levels in Upcountry reservoirs were down from 128 million gallons on March 1 to 115.6 million gallons on Friday.

At the same time, water demand is increasing, Eng said. Consumption on the Upcountry system edged up from 6.13 mgd the previous week to 6.87 mgd last week.

Demand in Central and South Maui also rose, from 22.59 mgd the previous week to 23.2 mgd last week.

“Both the Upcountry and Central/South Maui systems saw increases in production demand,” Eng said. “Due to the lack of rain, the department began pumping water up from the Makawao system to supplement the Lower Kula system.”

That doubled the demand at the Kamole Weir from 2 mgd to 4 mgd, but the pumping eased the flow out of the Kahakapao and Piiholo reservoirs. Flows into the reservoirs were reported to be minimal, with no water at all flowing into the Waikamoi Reservoirs for nearly two weeks.

Kodama said the jet stream has shifted to a east-west flow, which affects the movement of cold fronts that would otherwise swing across the islands, bringing in periodic Kona winds and tropical moisture. With the shift, the winter season cold fronts are pushing across from Asia to the Pacific Northwest, while forcing a high-pressure ridge closer to the islands, cutting the intensity of the trade winds.

“The winter storms are still coming across the North Pacific. It’s just that right now, over the past weeks, the jet stream has been on more of an east-west flow, and those frontal systems have just been moving straight across the Pacific very quickly,” he said.

“When the pattern is shifted this way, we’re very stable, with the high-pressure ridge moving closer to the islands so the trades die or are very weak — reducing the trade showers.”

In January, when the Maui watersheds were still getting steady rains, the frontal systems were contributing more to the islands’ water systems.

“Sometimes, during the winter months, you get these shear lines embedded in the trade. They contain more showers and the windward areas get more rain,” Kodama said.

For most of February and the beginning of March, the pattern has been light trades and little rain, with Kodama reporting the computer models indicating that similar conditions will prevail for at least another week.

On Maui, it will mean mostly clear morning skies but increased vog because of the light winds, cooler nights and convectional warming during the day that will increase cloud cover over the slopes — nearly ideal conditions for visitors.

“Unfortunately you can’t rely on HVB weather to provide sufficient rainfall,” Kodama said.

Eng expressed his concern that residents are pumping more water onto their lawns and landscaping, which could increase demand past the safe yield limits of the Central Maui system.

“The Central and South Maui demand is being closely monitored,” he said. “The department may be looking at instituting outdoor watering rules if increasing demand warrants them.”



• Edwin Tanji can be reached at citydesk@mauinews.com.