Pacific Islands Water Science Center

Prepared in cooperation with the Office of Hawaiian Affairs, State of Hawai‘i

U.S. Geological Survey
Open-File Report 2007-1157
version 1.0

Water Use in Wetland Kalo Cultivation in Hawai‘i

By Stephen B. Gingerich, Chiu W. Yeung, Tracy-Joy N. Ibarra, and John A. Engott

2007

Closeup photo of taro plants.  The field of view is solid lush green leaves with purple veins and stems
Kalo or taro (Colocasia esculenta (L.) Schott) typically in Hawai‘i is grown in wetland patches (lo‘i) directly irrigated with water from rivers or streams. Nearly 300 forms of Hawaiian kalo have been recorded. As a food source it was so important that it was referred to simply as ‘ai, which means food in Hawaiian. Practically the entire plant is edible.

Abstract

Ten cultivation areas (8 windward, 2 leeward) were selected for a kalo water-use study, primarily on the basis of the diversity of environmental and agricultural conditions under which wetland kalo is grown and landowner permission and availability. Flow and water-temperature data were collected at the lo‘i complex level and at the individual lo‘i level. To ensure that flow and temperature data collected at different lo‘i reflect similar irrigation conditions (continuous flooding of the mature crop), only lo‘i with crops near the harvesting stage were selected for water-temperature data collection. The water need for kalo cultivation varies depending on the crop stage. In this study, data were collected during the dry season (June–October), when water requirements for cooling kalo approach upper limits. Flow measurements generally were made during the warmest part of the day, and temperature measurements were made every 15 minutes at each site for about a two-month period.

Flow and temperature data were collected from kalo cultivation areas on four islands—Kaua‘i, O‘ahu, Maui, and Hawai‘i. The average inflow value for the 19 lo‘i complexes measured in this study is 260,000 gallons per acre per day, and the median inflow value is 150,000 gallons per acre per day. The average inflow value for the 17 windward sites is 270,000 gallons per acre per day, and the median inflow value is 150,000 gallons per acre per day. The average inflow value for the two leeward sites is 150,000 gallons per acre per day. The average inflow value measured for six individual lo‘i is 350,000 gallons per acre per day, and the median inflow value is 270,000 gallons per acre per day. The average inflow value for the five windward lo‘i is 370,000 gallons per acre per day, and the median inflow value is 320,000 gallons per acre per day. The inflow value for the one leeward lo‘i is 210,000 gallons per acre per day. These inflow values are consistent with previously reported values for inflow and are significantly higher than values generally estimated for water consumption during kalo cultivation. These measurements of inflow are important for future considerations of water-use requirements for successful kalo cultivation.

Of the 17 lo‘i complexes where water inflow temperature was measured, only 3 had inflow temperatures that rose above 27 °C, the threshold temperature above which wetland kalo is more susceptible to fungi and associated rotting diseases. The coldest mean inflow temperature was 20.0 °C and the warmest inflow temperature was 24.9 °C. All 15 of the sites where outflow temperatures were measured had some temperatures greater than 27 °C. Outflow temperatures exceeded 27 °C between 2.5 percent and about 40 percent of the time. Mean outflow temperatures ranged from 23.0 °C to 26.7 °C.

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