Delwyn S Oki
Delwyn Oki is a hydrologist with the Pacific Islands Water Science Center in Honolulu, Hawaiʻi.
Science and Products
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
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
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
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
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
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
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,
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
Filter Total Items: 47
Correlation analysis of groundwater and hydrologic data, Kaloko-Honokōhau National Historical Park, Hawai‘i
Designated in 1978, Kaloko-Honokōhau National Historical Park is located on the west coast of the Island of Hawaiʻi. The Kaloko-Honokōhau National Historical Park encompasses about 1,200 acres of coastal land and nearshore ecosystems, which include wetlands, anchialine pools (landlocked bodies of brackish water with hydrologic connections to the ocean), fishponds, a fishtrap, and coral reefs. Thes
Authors
Brytne K. Okuhata, Delwyn S. Oki
Estimated groundwater recharge for mid-century and end-of-century climate projections, Kaua‘i, O‘ahu, Moloka‘i, Lāna‘i, Maui, and the Island of Hawai‘i
Demand for freshwater in the State of Hawaiʻi is expected to increase by roughly 13 percent from 2020 to 2035. Groundwater availability in Hawaiʻi is affected by a number of factors, including land cover, rainfall, runoff, evapotranspiration, and climate change. To evaluate the availability of fresh groundwater under projected future-climate conditions, estimates of groundwater recharge are needed
Authors
Heidi L. Kāne, Alan Mair, Adam G. Johnson, Kolja Rotzoll, James Mifflin, Delwyn S. Oki
Effects of drought and cloud-water interception on groundwater recharge and wildfire hazard for recent and future climate conditions, Kauaʻi, Oʻahu, Molokaʻi, Maui, and the Island of Hawaiʻi
The Water-budget Accounting for Tropical Regions Model (WATRMod) code was used for Kauaʻi, Oʻahu, Molokaʻi, Maui, and the Island of Hawaiʻi to estimate the spatial distribution of groundwater recharge, soil moisture, evapotranspiration, and climatic water deficit for a set of water-budget scenarios. The scenarios included historical and future drought conditions, and a land-cover condition where s
Authors
Alan Mair, Delwyn S. Oki, Heidi L. Kāne, Adam G. Johnson, Kolja Rotzoll
Identifying the relative importance of water-budget information needed to quantify how land-cover change affects recharge, Hawaiian Islands
This report describes a sensitivity analysis of a water-budget model that was completed to identify the most important types of hydrologic information needed to reduce the uncertainty of model recharge estimates. The sensitivity of model recharge estimates for the Hawaiian Islands of Oʻahu and Maui was analyzed for seven model parameters potentially affected by land-cover changes within a watershe
Authors
Adam G. Johnson, Alan Mair, Delwyn S. Oki
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
Authors
Abby G. Frazier, Christian P. Giardina, Thomas W Giambelluca, Laura Brewington, Yi-Leng Chen, Pao-Shin Chu, Lucas Fortini, David Helweg, Victoria W. Keener, Ryan J Longman, Matthew P Lucas, Alan Mair, Delwyn S. Oki, Julian J Reyes, Stephanie G. Yelenik, Clay Trauernicht
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
Authors
Rylen K. Nakama, Jackson N. Mitchell, Delwyn S. Oki
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
Authors
Kolja Rotzoll, Delwyn S. Oki, Adam G. Johnson, William R. Souza
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,
Authors
Delwyn S. Oki
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
Authors
Rylen K. Nakama, Jackson N. Mitchell, Delwyn S. Oki
Estimating soil moisture, actual evapotranspiration, climatic water deficit, and groundwater recharge during periods of drought for current and future climate conditions in Hawaiʻi
Mid- and end-of-century climate projections for the Hawaiian Islands indicate that rainfall is projected to decrease across large areas. In areas affected by drought or where the future climate becomes drier, reduced groundwater recharge can affect freshwater availability. Reduced rainfall can also reduce soil moisture, which can increase the risk of wildfire. Cloud-water interception, or fog drip
Authors
Alan Mair, Delwyn S. Oki
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
Authors
Rylen K. Nakama, Jackson N. Mitchell, Delwyn S. Oki
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
Authors
Delwyn S. Oki
Science and Products
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
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
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
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
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
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
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,
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
Filter Total Items: 47
Correlation analysis of groundwater and hydrologic data, Kaloko-Honokōhau National Historical Park, Hawai‘i
Designated in 1978, Kaloko-Honokōhau National Historical Park is located on the west coast of the Island of Hawaiʻi. The Kaloko-Honokōhau National Historical Park encompasses about 1,200 acres of coastal land and nearshore ecosystems, which include wetlands, anchialine pools (landlocked bodies of brackish water with hydrologic connections to the ocean), fishponds, a fishtrap, and coral reefs. Thes
Authors
Brytne K. Okuhata, Delwyn S. Oki
Estimated groundwater recharge for mid-century and end-of-century climate projections, Kaua‘i, O‘ahu, Moloka‘i, Lāna‘i, Maui, and the Island of Hawai‘i
Demand for freshwater in the State of Hawaiʻi is expected to increase by roughly 13 percent from 2020 to 2035. Groundwater availability in Hawaiʻi is affected by a number of factors, including land cover, rainfall, runoff, evapotranspiration, and climate change. To evaluate the availability of fresh groundwater under projected future-climate conditions, estimates of groundwater recharge are needed
Authors
Heidi L. Kāne, Alan Mair, Adam G. Johnson, Kolja Rotzoll, James Mifflin, Delwyn S. Oki
Effects of drought and cloud-water interception on groundwater recharge and wildfire hazard for recent and future climate conditions, Kauaʻi, Oʻahu, Molokaʻi, Maui, and the Island of Hawaiʻi
The Water-budget Accounting for Tropical Regions Model (WATRMod) code was used for Kauaʻi, Oʻahu, Molokaʻi, Maui, and the Island of Hawaiʻi to estimate the spatial distribution of groundwater recharge, soil moisture, evapotranspiration, and climatic water deficit for a set of water-budget scenarios. The scenarios included historical and future drought conditions, and a land-cover condition where s
Authors
Alan Mair, Delwyn S. Oki, Heidi L. Kāne, Adam G. Johnson, Kolja Rotzoll
Identifying the relative importance of water-budget information needed to quantify how land-cover change affects recharge, Hawaiian Islands
This report describes a sensitivity analysis of a water-budget model that was completed to identify the most important types of hydrologic information needed to reduce the uncertainty of model recharge estimates. The sensitivity of model recharge estimates for the Hawaiian Islands of Oʻahu and Maui was analyzed for seven model parameters potentially affected by land-cover changes within a watershe
Authors
Adam G. Johnson, Alan Mair, Delwyn S. Oki
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
Authors
Abby G. Frazier, Christian P. Giardina, Thomas W Giambelluca, Laura Brewington, Yi-Leng Chen, Pao-Shin Chu, Lucas Fortini, David Helweg, Victoria W. Keener, Ryan J Longman, Matthew P Lucas, Alan Mair, Delwyn S. Oki, Julian J Reyes, Stephanie G. Yelenik, Clay Trauernicht
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
Authors
Rylen K. Nakama, Jackson N. Mitchell, Delwyn S. Oki
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
Authors
Kolja Rotzoll, Delwyn S. Oki, Adam G. Johnson, William R. Souza
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,
Authors
Delwyn S. Oki
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
Authors
Rylen K. Nakama, Jackson N. Mitchell, Delwyn S. Oki
Estimating soil moisture, actual evapotranspiration, climatic water deficit, and groundwater recharge during periods of drought for current and future climate conditions in Hawaiʻi
Mid- and end-of-century climate projections for the Hawaiian Islands indicate that rainfall is projected to decrease across large areas. In areas affected by drought or where the future climate becomes drier, reduced groundwater recharge can affect freshwater availability. Reduced rainfall can also reduce soil moisture, which can increase the risk of wildfire. Cloud-water interception, or fog drip
Authors
Alan Mair, Delwyn S. Oki
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
Authors
Rylen K. Nakama, Jackson N. Mitchell, Delwyn S. Oki
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
Authors
Delwyn S. Oki