Implications of Climate Change for Hawaii’s Water Resources
How exactly climate change will impact Oahu’s groundwater supply by changing precipitation and evaporation rates is difficult to determine. Recent studies noted that a temperature rise of 3 oC would result in a 10% increase in evaporation in Oahu’s Pearl Harbor basin. Even an accompanying precipitation rate increase of 10% would be too little to sustain the groundwater reservoir at present water usage levels. It is important to note again that predicting how future climate change will impact island weather-related processes (e.g., orographic patterns) is currently difficult because the present climate models’ spatial scale resolution is too course (course means large) to model successfully how these smaller-scale weather-related processes will be impacted by climate change. However, it is likely that as population continues to grow on Oahu, the groundwater supply will be taxed more and more, especially if climate change further makes the problem worse.
The economic and social impacts of changing climate on the Hawaiian Islands are intimately tied to changes in rainfall and sea level. Given that the state’s economy is heavily dependent upon the tourism industry (as of 2003, 26% of the state's economy), any water shortage or restrictions imposed on the 100,000 or so visitors at any one time in Waikiki could severely stress the state’s economy. Waikiki, one square mile of the total area of Honolulu, is associated with supporting 11% of the state’s civilian jobs, 12% of the state and local tax revenues, and is responsible for $3.6 billion or 46% of statewide tourism’s total contribution to the 2002 Gross State Product.
In 2002 and 2003, several government and local organization did ground-water-level surveys in the Pearl Harbor area of Oahu, Hawaii. On October 31, 2002, water levels at 24 wells (wells are holes dug in the ground to see where the water table level is at) were measured during a two and a half hour time period (9:00 a.m. to 11:30 a.m.). On May 15, 2003, water levels at 23 wells were measured between 9:00 a.m. and 11:30 a.m. Organizations and agencies participating included the U.S. Geological Survey, the Honolulu Board of Water Supply, the Hawaii Commission on Water Resource Management, the U.S. Air Force (through their consultant, URS Corporation), and the U.S. Navy.
Water levels measured on October 31, 2002 in the Pearl Harbor area ranged from 13.6 to 20.4 feet above the average sea level. Water levels measured on May 15, 2003 in the Pearl Harbor area ranged from 13.1 to 19.7 feet above the average sea level. In general, measured water levels were lowest near the southeastern and southwestern parts of the Pearl Harbor area and were highest in the inland, northern part of the area. The water-level measurements of October 31, 2002 and May 15, 2003 shared a total of 21 well sites in common. At each of these common sites, the change in water level can be determined. For three wells in the western part of the Pearl Harbor area, water levels changed by 0.1 foot or less. For the remaining 18 common sites, water levels measured on May 15, 2003 were about 0.4 to 1.6 feet lower than water levels measured on October 31, 2002. With fresh water use on Oahu already exceeding sustainable use by some estimates, the drop in ground water levels in the Pearl Habor basin is troubling.
Figure. October 31, 2002, Pearl Harbor area water level survey.
Figure. May 15, 2003, Pearl Harbor area water level survey.
