Droughts in the Hawaiian Islands can enhance wildfire risk, diminish freshwater resources, and devastate threatened and endangered species on land and in nearshore ecosystems. During periods of drought, cloud-water interception in Hawai‘i’s rain forests, also known as fog drip, may play an important role in providing moisture for plants, reducing wildfire risk within the fog zone, and contributing to groundwater recharge that sustains flow in streams during dry periods. Estimates of changes in groundwater recharge, soil moisture, and evapotranspiration during periods of drought are critical to Hawai‘i’s water managers, planners, agriculturists, ranchers, and forest, watershed, and wildfire managers for developing adaptive management strategies.
This study addresses a specific need to collect information that will lead to a better understanding of the hydrologic impacts of drought throughout the State of Hawai‘i. Specific objectives of the study are (1) to estimate changes in soil moisture, evapotranspiration, and groundwater recharge during periods of drought for current and future climate conditions, and (2) to estimate the combined impact of drought and reduced fog drip on soil moisture, evapotranspiration, and groundwater recharge. The proposed study area covers the islands of Hawai‘i, Kaua‘i, Maui, Moloka‘i, and O‘ahu.
To accomplish the study objectives, the following five tasks will be implemented: (1) soil-moisture data compilation, (2) plot-scale recharge-rate estimation using available data, (3) regional water-budget modeling, (4) report and geospatial dataset preparation, and (5) stakeholder engagement. The methods and results of this study will be documented in a USGS Scientific Investigations Report. Geospatial datasets of soil moisture, evapotranspiration, and groundwater recharge for current and future climate conditions will be prepared and made publicly available. The study will start in September 2016 and take about three years to complete.
The results from this study will inform resource managers of the potential impacts of climate change on water resources and the importance of fog drip in mitigating the impacts of drought, and provide needed input for supporting science-based strategies for managing critical recharge areas and identifying areas vulnerable to wildfires. Hence, the results will be a great value to forest and water-resource managers, watershed partnerships striving to protect, preserve, and restore large areas of forested watersheds for water-resource and conservation values, and outreach agents seeking to reduce the threat of wildfire to ecosystems and communities by facilitating the sharing of fire knowledge.
