Assessment of historic ground-water recharge in central and west Maui, Hawaiʻi

Abstract

Concern surrounding recent evidence of over-pumping in the Iao aquifer on Maui has prompted an investigation into the long-term sustainability of current and future withdrawal scenarios. As part of this investigation, a water budget of the central and west Maui region was computed from which (1) historic ground-water recharge was estimated and (2) the effects of agricultural land use and drought were analyzed. Estimated annual ground-water recharge decreased 44 percent from 1979 to 2004 in central and west Maui Reduction in agricultural irrigation, resulting from more efficient irrigation methods and reduction in agricultural land, is largely responsible for declining recharge. Recently, periods of lower-than-average rainfall have had an exacerbating effect. Simulations of hypothetical future conditions indicate that a cessation of agriculture in central and west Maui would reduce annual ground-water recharge by 18 percent over current conditions, and a period of drought, identical to 1998-2002, would reduce annual recharge by 27 percent over current conditions.