Demand for freshwater on the Island of Maui is expected to grow. to assess the availability of fresh groundwater,estimates of groundwater recharge are needed. A water-budget model with a daily computation interval was developed and used to estimate the spatial distribution of recharge on Maui for average climate conditions (1978–2007 rainfall and 2010 land cover) and for drought conditions (1998–2002 rainfall and 2010 land cover). For average climate conditions, mean annual recharge for Maui is approximately 1309 million gallons per day, or approximately 44 percent of precipitation (rainfall and fog interception). Recharge for average climate conditions is approximately 39 percent of total water inflow consisting of precipitation,irrigation, septic leachate, and seepage from reservoirs and cesspools. Most recharge occurs on the wet,windward slopes of Haleakalā and on the wet, uplands of West Maui Mountain. Dry, and coastal areas generally have low recharge. In the dry isthmus,however, irrigated fields have greater recharge than nearby unirrigated areas. For drought conditions, or mean annual recharge for Maui is approximately 1010 million gallons per day,which is 23 percent less than recharge for average climate conditions. For individual aquifer-system areas used for groundwater management, recharge for drought conditions is approximately 8 to 51 percent less than recharge for average climate conditions. The spatial distribution of rainfall is the primary factor determining spatially distributed recharge estimates for most areas on Maui. In wet areas, and recharge estimates are also sensitive to water-budget parameters that are related to runoff,fog interception, and forest-canopy evaporation. In dry areas, and recharge estimates are most sensitive to irrigated crop areas and parameters related to evapotranspiration.
Source: usgs.gov