Hawai’i Groundwater Recharge Tool

An interactive website created by the University of Hawaiʻi and U.S. Geological Survey

The primary source of freshwater to Hawai‘i’s groundwater systems is recharge. Accurate estimates of recharge are critical for groundwater-resource management and planning. The Hawai‘i Groundwater Recharge Tool allows users to evaluate the potential effects of land-cover and climate changes on groundwater recharge. This is a pilot website that is currently limited to the island of O‘ahu, but the website has been designed to be expandable so that other islands and conditions can be added in the future.

Recharge primarily originates as precipitation. In Hawai‘i, most precipitation is in the form of rain, with some contribution from fog. Only a fraction of the water from precipitation contributes to recharge; the remainder runs off to the ocean by way of streams, or returns to the atmosphere through evapotranspiration (evaporation and transpiration by plants).

Changes in precipitation caused by climate changes can affect recharge rates. Changes in land cover can also affect recharge because different types of vegetation and land uses have different rates of evapotranspiration (different land cover types also have different runoff rates, but these differences are not considered in the Hawai‘i Groundwater Recharge Tool). Irrigation of crops, parks, and golf courses can affect recharge. In urban areas, leaking water mains and seepage from septic systems can also affect recharge.

This website provides a baseline estimate of recharge representing recent conditions of precipitation (1978–2008 average) and land cover (2010). Users can change land cover and rainfall conditions to evaluate the effects on groundwater recharge. Results will be displayed as on-screen maps, and users will be given options to generate interpretive graphics or export results in various formats.

Results from this website are based on soil water-balance models. The user is responsible for understanding the website’s methods and limitations. The user is also responsible for the appropriate use of the web interface.

Access Recharge Tool