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Delwyn S Oki

Delwyn Oki is a hydrologist with the Pacific Islands Water Science Center in Honolulu, Hawaiʻi.

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Cliffs falling into the ocean with pebbles and driftwood on the beach.

Characterization of Flood-Producing Mechanisms in Watersheds with a High-Elevation Area in Southeast Alaska and Hawaiʻi

Major floods in Southeast Alaska and Hawaiʻi that potentially threaten life, property, and culturally significant resources and ecosystems are caused by mechanisms related to intense precipitation for both locations as well as snow melt-based processes for Alaska. Small, high-gradient, and heavily vegetated watersheds with direct contribution to the ocean are common in both locations. To understan...
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Climate Adaptation Science Centers
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Characterization of Flood-Producing Mechanisms in Watersheds with a High-Elevation Area in Southeast Alaska and Hawaiʻi

Major floods in Southeast Alaska and Hawaiʻi that potentially threaten life, property, and culturally significant resources and ecosystems are caused by mechanisms related to intense precipitation for both locations as well as snow melt-based processes for Alaska. Small, high-gradient, and heavily vegetated watersheds with direct contribution to the ocean are common in both locations. To understan...
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Water flowing in the Wailuku River in Hawai'i

Changes in Water Flow through Hawaiian Forests due to Invasive Species and Changing Rainfall Patterns

Precipitation in Hawaiʻi’s higher elevation upland areas provides needed water to both people and ecosystems. Once it reaches the ground, rain can either run off and contribute to water flow in streams, or it can infiltrate into the ground and provide water for plants and recharge aquifers and groundwater. The exact route that water takes is controlled by many factors, including the duration and i...
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Climate Adaptation Science Centers
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Changes in Water Flow through Hawaiian Forests due to Invasive Species and Changing Rainfall Patterns

Precipitation in Hawaiʻi’s higher elevation upland areas provides needed water to both people and ecosystems. Once it reaches the ground, rain can either run off and contribute to water flow in streams, or it can infiltrate into the ground and provide water for plants and recharge aquifers and groundwater. The exact route that water takes is controlled by many factors, including the duration and i...
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Cliffs meet the ocean in the North Kohala District of Hawaii

Influences of Climate Change, Climate Variability, and Drought on Human Communities and Ecosystems in Hawaiʻi

Over the past century, Hawaiʻi has experienced a pronounced decline in precipitation and stream flow and a number of severe droughts. These changes can have wide-reaching implications, affecting the water supply, native vegetation and wildlife, wildfire patterns, and the spread of invasive species. Several climate-related factors are influencing Hawaiˈi’s landscapes and contributing to these chang...
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Climate Adaptation Science Centers
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Influences of Climate Change, Climate Variability, and Drought on Human Communities and Ecosystems in Hawaiʻi

Over the past century, Hawaiʻi has experienced a pronounced decline in precipitation and stream flow and a number of severe droughts. These changes can have wide-reaching implications, affecting the water supply, native vegetation and wildlife, wildfire patterns, and the spread of invasive species. Several climate-related factors are influencing Hawaiˈi’s landscapes and contributing to these chang...
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Rocky coastline with rocky island on a sunny day.

Assessing the Potential Effects of Climate Change on Vegetation in Hawaiʻi Volcanoes National Park

Climate change in Hawaiʻi is expected to result in increasing temperatures and varying precipitation through the twenty-first century. Already, high elevation areas have experienced rapidly increasing temperatures and there has been an increase in the frequency of drought across the Islands. These climatic changes could have significant impacts on Hawaiʻi’s plants and animals. Changes in temperatu...
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Climate Adaptation Science Centers
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Assessing the Potential Effects of Climate Change on Vegetation in Hawaiʻi Volcanoes National Park

Climate change in Hawaiʻi is expected to result in increasing temperatures and varying precipitation through the twenty-first century. Already, high elevation areas have experienced rapidly increasing temperatures and there has been an increase in the frequency of drought across the Islands. These climatic changes could have significant impacts on Hawaiʻi’s plants and animals. Changes in temperatu...
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Selected streamgage sites and periods of record for consideration of flood-generating mechanisms in Hawai`i and Southeast Alaska, 1913-2022

This data release consists of a comma-delimited ascii file with attributes for 21 U.S. Geological Survey streamgage sites in Hawai`i and Southeast Alaska selected to enable assessment of how floods might change in a future climate. Floods in Hawai`i and Southeast Alaska have led to loss of human life; damage to agricultural crops, cultural and biological resources, infrastructure, and property; th
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Pacific Islands Water Science Center

WATRMod, a Water-budget accounting for tropical regions model--source code, executable file, and example files

This data release contains the source code, executable file, and example files for WATRMod, a Water-budget Accounting for Tropical Regions Model code that is documented in U.S. Geological Survey Open-File Report 2022-1013 available at https://doi.org/10.3133/ofr20221013. The source code is written in the Fortran computer language. The model source code was compiled using Intel(R) Visual Fortran In
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Pacific Islands Water Science Center

SUTRA model used to evaluate the effects of groundwater withdrawal and injection, Kaloko-Honokohau National Historical Park, Hawaii

A three-dimensional, variable-density solute-transport model (SUTRA) was developed to evaluate the effects of three selected withdrawal/injection scenarios on salinity of groundwater (as simulated at damselfly anchialine-pool habitat) and discharge of freshwater to the nearshore environment of Kaloko-Honokohau National Historical Park (KAHO), Hawaii. A base model was constructed using water-level,
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Pacific Islands Water Science Center

SUTRA model used to evaluate groundwater availability in central Molokai, Hawaii

A three-dimensional, variable-density solute-transport model (SUTRA) was developed to evaluate the effects of nine selected withdrawal/recharge scenarios on salinity of groundwater and discharge of freshwater to the nearshore environment of central Molokai, Hawaii. The model was constructed using water-level and salinity data available for the period from 1940 to 2012. Groundwater recharge for the
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Pacific Islands Water Science Center
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A century of drought in Hawai‘i: Geospatial analysis and synthesis across hydrological, ecological, and socioeconomic scales

Drought is a prominent feature of Hawaiʻi’s climate. However, it has been over 30 years since the last comprehensive meteorological drought analysis, and recent drying trends have emphasized the need to better understand drought dynamics and multi-sector effects in Hawaiʻi. Here, we provide a comprehensive synthesis of past drought effects in Hawaiʻi that we integrate with geospatial analysis of d
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Ecosystems, Pacific Island Ecosystems Research Center

Groundwater-level monitoring from January 17 to March 3, 2022, Hālawa area, O‘ahu, Hawai‘i

A reported fuel release in November 2021 at the Red Hill Bulk Fuel Storage Facility within the naval reservation at Red Hill led to the shutdown of several production wells in the Hālawa area, O‘ahu, Hawai‘i. Red Hill Shaft—one of the high-capacity production wells that shut down—was reactivated on January 29, 2022. Submersible pressure transducers were deployed at 20 wells in the Hālawa area to m
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Water Resources, Pacific Islands Water Science Center

Long-term groundwater availability in the Waihe‘e, ‘Īao, and Waikapū aquifer systems, Maui, Hawai‘i

Groundwater levels have declined since the 1940s in the Wailuku area of central Maui, Hawai‘i, on the eastern flank of West Maui volcano, mainly in response to increased groundwater withdrawals. Available data since the 1980s also indicate a thinning of the freshwater lens and an increase in chloride concentrations of pumped water from production wells. These trends, combined with projected increa
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Water Resources, Pacific Islands Water Science Center

Water-budget accounting for tropical regions model (WATRMod) documentation

Regional groundwater recharge commonly is estimated using a threshold-type water-budget approach in which groundwater recharge is assumed to occur when water in the plant-root zone exceeds the soil’s moisture storage capacity. A water budget of the plant-soil system accounts for water inputs (rainfall, fog interception, irrigation, septic-system leachate, and other inputs), water outputs (runoff,
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Water Resources, Pacific Islands Water Science Center

January 18, 2022, Red Hill synoptic groundwater-level survey, Hālawa area, O‘ahu, Hawai‘i

On January 18, 2022, groundwater levels were measured in selected wells in the Hālawa area, O‘ahu, Hawai‘i, constituting a synoptic groundwater-level survey (shortened herein to “synoptic survey”) of the area. Groundwater levels were measured mainly from 9:00 a.m. to 12:00 p.m. (times listed in Hawai‘i standard time) and provide a snapshot of groundwater levels during the survey period. Following
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Water Resources, Pacific Islands Water Science Center

December 23, 2021, Red Hill synoptic groundwater-level survey, Hālawa area, O‘ahu, Hawai‘i

On December 23, 2021, groundwater levels were measured in selected wells in the Hālawa area, O‘ahu, Hawai‘i, constituting a synoptic groundwater-level survey (shortened herein to “synoptic survey”) of the area. Groundwater levels were measured mainly from 9:00 a.m. to 12:00 p.m. (times listed in Hawai‘i standard time) and provide a snapshot of groundwater levels during the survey period. Following
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Water Resources, Pacific Islands Water Science Center

Numerical simulation of the effects of groundwater withdrawal and injection of high-salinity water on salinity and groundwater discharge, Kaloko-Honokōhau National Historical Park, Hawaiʻi

Kaloko-Honokōhau National Historical Park (KAHO) is located on the west coast of the island of Hawaiʻi and contains water resources exposed in fishponds, anchialine pools, and marine waters that are cultural resources and that provide habitat for threatened, endangered, and other culturally important native species. KAHO’s water resources are sustained by and dependent on groundwater discharge. In
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Water Resources, Pacific Islands Water Science Center

Numerical simulation of groundwater availability in central Moloka‘i, Hawai‘i

Since the 1990s, increased chloride concentrations of water pumped from wells (much of which is used for drinking water) and the effects of withdrawals on groundwater-dependent ecosystems have led to concerns over groundwater availability on the island of Molokaʻi, Hawaiʻi. An improved understanding of the hydrologic effects of proposed groundwater withdrawals is needed to ensure effective managem
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Water Resources, Pacific Islands Water Science Center

Managing effects of drought in Hawai’i and U.S.-affiliated Pacific Islands

How is drought expressed in Hawai‘i & USAPI? Drought is a significant climate feature in Hawai‘i and the U.S.-Affiliated Pacific Islands (USAPI), at times causing severe impacts across multiple sectors. Below average precipitation anomalies are often accompanied by higher than average temperatures and reduced cloud cover. The resulting higher insolation and evapotranspiration can magnify the effec
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Ecosystems, Climate Adaptation Science Centers

Estimated groundwater recharge from a water-budget model incorporating selected climate projections, Island of Maui, Hawai‘i

Demand for freshwater on the Island of Maui is expected to increase by 45 percent between 2015 and 2035. Groundwater availability on Maui is affected by changes in climate and agricultural irrigation. To evaluate the availability of fresh groundwater under projected future climate conditions and changing agricultural irrigation practices, estimates of groundwater recharge are needed. A water-budge
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Water Resources, Pacific Islands Water Science Center

Comparison of a simple hydrostatic and a data-intensive 3D numerical modeling method of simulating sea-level rise induced groundwater inundation for Honolulu, Hawai'i, USA

Groundwater inundation (GWI) is a particularly challenging consequence of sea-level rise (SLR), as it progressively inundates infrastructure located above and below the ground surface. Paths of flooding by GWI differ from other types of SLR flooding (i.e., wave overwash, storm-drain backflow) such that it is more difficult to mitigate, and thus requires a separate set of highly innovative adaptati
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Water Resources, Pacific Islands Water Science Center

Groundwater-level, groundwater-temperature, and barometric-pressure data, July 2017 to February 2018, Hālawa Area, Oʻahu, Hawaiʻi

The Red Hill Bulk Fuel Storage Facility, operated by the U.S. Navy and located in the Hālawa area, Oʻahu, Hawaiʻi, includes 20 underground storage tanks that can hold a total of 250 million gallons of fuel. In January 2014, the U.S. Navy notified the Hawaiʻi Department of Health and U.S. Environmental Protection Agency of release of an estimated 27,000 gallons of fuel from the Red Hill Bulk Fuel S
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Water Resources, Pacific Islands Water Science Center

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