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: 43
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
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
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
Authors
Delwyn S. Oki, John A. Engott, Kolja Rotzoll
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
Authors
Abby G. Frazier, Jonathan Deenik, Neal Fujii, Greg Funderburk, Thomas Giambelluca, Christian Giardina, David A. Helweg, Victoria Keener, Donald Mair, John Marra, Sierra McDaniel, Lenore Ohye, Delwyn S. Oki, Elliott Parsons, Ayron Strauch, Clay Trauernicht
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
Authors
Alan Mair, Adam G. Johnson, Kolja Rotzoll, Delwyn S. Oki
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
Authors
Shellie Habel, Charles H. Fletcher, Kolja Rotzoll, Aly I. El-Kadi, Delwyn S. Oki
Science and Products
- Science
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... - Data
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; thWATRMod, 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 InSUTRA 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 - Publications
Filter Total Items: 43
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 watersheAuthorsAdam G. Johnson, Alan Mair, Delwyn S. OkiA 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 dAuthorsAbby 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 TrauernichtGroundwater-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 mAuthorsRylen K. Nakama, Jackson N. Mitchell, Delwyn S. OkiLong-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 increaAuthorsKolja Rotzoll, Delwyn S. Oki, Adam G. Johnson, William R. SouzaWater-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,AuthorsDelwyn S. OkiJanuary 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. FollowingAuthorsRylen K. Nakama, Jackson N. Mitchell, Delwyn S. OkiDecember 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. FollowingAuthorsRylen K. Nakama, Jackson N. Mitchell, Delwyn S. OkiNumerical 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. InAuthorsDelwyn S. OkiNumerical 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 managemAuthorsDelwyn S. Oki, John A. Engott, Kolja RotzollManaging 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 effecAuthorsAbby G. Frazier, Jonathan Deenik, Neal Fujii, Greg Funderburk, Thomas Giambelluca, Christian Giardina, David A. Helweg, Victoria Keener, Donald Mair, John Marra, Sierra McDaniel, Lenore Ohye, Delwyn S. Oki, Elliott Parsons, Ayron Strauch, Clay TrauernichtEstimated 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-budgeAuthorsAlan Mair, Adam G. Johnson, Kolja Rotzoll, Delwyn S. OkiComparison 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 adaptatiAuthorsShellie Habel, Charles H. Fletcher, Kolja Rotzoll, Aly I. El-Kadi, Delwyn S. Oki