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Estimating Soil Moisture, Actual Evapotranspiration, Climatic Water Deficit, and Groundwater Recharge during Periods of Drought for Current and Future Climate Conditions in Hawaii

Project Chief: Alan Mair
Project Period: 2016 through 2018
Cooperator: U.S. Department of the Interior, Pacific Islands Climate Science Center
Collaborators: USGS Pacific Island Ecosystems Research Center; U.S. Forest Service, Institute of Pacific Islands Forestry; University of Hawaii at Manoa, Department of Geography; University of Hawaii at Manoa, International Pacific Research Center; University of Hawaii at Manoa, Department of Natural Resources and Environmental Management
Location: Islands of Kauai, Oahu, Molokai, Maui, and Hawaii


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 Hawaii’s rain forests may play an important role in providing moisture for plants, reducing wildfire risk within the fog zone, and contributing to groundwater recharge that sustains water flow in streams during dry periods. Estimates of the changes in soil moisture and water availability during periods of drought are critical to Hawaii’s water, forest, and wildfire managers and planners, as well as to agriculturists and ranchers for developing adaptive management strategies.


Specific objectives of the study are (1) to estimate changes in soil moisture, evapotranspiration, and groundwater recharge during periods of drought for current and projected climate conditions, and (2) to estimate the combined impact of drought and reduced cloud-water interception on soil moisture, evapotranspiration, and groundwater recharge.

Relevance and Benefits

The results from this study will inform resource managers of the potential impacts of climate change on water resources and the importance of cloud-water interception in mitigating the impacts of drought. This study will also provide needed input for supporting science-based strategies for managing critical groundwater recharge areas and identifying areas vulnerable to wildfires. The results will be of 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, during periods of drought and soil-moisture stress, by facilitating the sharing of fire knowledge. By quantifying the impacts of drought on water resources and the importance of cloud-water interception in mitigating the impacts of drought, this study broadly supports three of the six science directions in the USGS Science Strategy: (1) understanding ecosystems and predicting ecosystem change, (2) climate variability and change, and (3) a water census of the United States.


To meet the objectives of this study, the USGS will (1) compile available soil-moisture monitoring data from a companion study of cloud-water interception and other studies in Hawaii, (2) estimate plot-scale groundwater-recharge rates at three plot sites using soil-moisture measurements and other plot-scale measurements, (3) estimate soil moisture, evapotranspiration, and groundwater recharge using projected future climate conditions developed from dynamical and statistical downscaling approaches, and a set of water-budget models developed for the main Hawaiian Islands, (4) publish the results in a USGS Scientific Investigations Report and prepare geospatial datasets of model results for public access on the internet, and (5) give presentations of study results to stakeholders.

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