The surface-water resources of Hawaii have significant cultural, aesthetic, ecologic, and economic importance. Proper management of the surface-water resources of the State requires an understanding of the long- and short-term variability in streamflow characteristics that may occur. The U.S. Geological Survey maintains a network of stream-gaging stations in Hawaii, including a number of stations with long-term streamflow records that can be used to evaluate long-term trends and short-term variability in flow characteristics.
The overall objective of this study is to obtain a better understanding of long-term trends and variations in streamflow on the islands of Hawaii, Maui, Molokai, Oahu, and Kauai, where long-term stream-gaging stations exist. This study includes (1) an analysis of long-term trends in flows (both total flow and estimated base flow) at 16 stream-gaging stations, (2) a description of patterns in trends within the State, and (3) discussion of possible regional factors (including rainfall) that are related to the observed trends and variations.
Results of this study indicate the following:
1. From 1913 to 2002 base flows generally decreased in streams for which data are available, and this trend is consistent with the long-term downward trend in annual rainfall over much of the State during that period.
2. Monthly mean base flows generally were above the long-term average from 1913 to the early 1940s and below average after the early 1940s to 2002, and this pattern is consistent with the detected downward trends in base flows from 1913 to 2002.
3. Long-term downward trends in base flows of streams may indicate a reduction in ground-water discharge to streams caused by a long-term decrease in ground-water storage and recharge.
4. From 1973 to 2002, trends in streamflow were spatially variable (up in some streams and down in others) and, with a few exceptions, generally were not statistically significant.
5. Short-term variability in streamflow is related to the seasons and to the EL Niño-Southern Oscillation phenomenon that may be partly modulated by the phase of the Pacific Decadal Oscillation.
6. At almost all of the long-term stream-gaging stations considered in this study, average total flow (and to a lesser extent average base flow) during the winter months of January to March tended to be low following El Niño periods and high following La Niña periods, and this tendency was accentuated during positive phases of the Pacific Decadal Oscillation.
7. The El Niño-Southern Oscillation phenomenon occurs at a relatively short time scale (a few to several years) and appears to be more strongly related to processes controlling rainfall and direct runoff than ground-water storage and base flow.
Long-term downward trends in base flows of streams may indicate a reduction in ground-water storage and recharge. Because ground water provides about 99 percent of Hawaii's domestic drinking water, a reduction in ground-water storage and recharge has serious implications for drinking-water availability. In addition, reduction in stream base flows may reduce habitat availability for native stream fauna and water availability for irrigation purposes.
Further study is needed to determine (1) whether the downward trends in base flows from 1913 to 2002 will continue or whether the observed pattern is part of a long-term cycle in which base flows may eventually return to levels measured during 1913 to the early 1940s, (2) the physical causes for the detected trends and variations in streamflow, and (3) whether regional climate indicators successfully can be used to predict streamflow trends and variations throughout the State. These needs for future study underscore the importance of maintaining a network of long-term-trend stream-gaging stations in Hawaii.
ABSTRACT
INTRODUCTION
Objectives
Purpose and Scope
BACKGROUND
Atmospheric Circulation
Climate
Rainfall
Surface Water
El Niño-Southern Oscillation and the Pacific Decadal Oscillation
DATA
METHODS
Estimation of Base Flow
Cumulative Monthly Departures
Statistical Analysis of Long-Term Trends
Analysis of the Relation Among Flow, Southern Oscillation Index, and Pacific Decadal Oscillation
LONG-TERM TRENDS IN FLOW
Water Years 1913-2002
Water Years 1933-2002
Water Years 1953-2002
Water Years 1973-2002
Summary of Patterns in Long-Term Trends
RELATION AMONG STREAMFLOW, SOUTHERN OSCILLATION INDEX, AND PACIFIC DECADAL OSCILLATION
January to March
April to June
July to September
October to December
Summary of Patterns in Relations Among Flow, Southern Oscillation Index, and Pacific Decadal Oscillation
SUMMARY
REFERENCES CITED
APPENDIX A. ANNUAL FLOW STATISTICS AT LONG-TERM STREAM-GAGING STATIONS, HAWAII
APPENDIX B. ANNUAL RAINFALL AT SELECTED LONG-TERM RAIN-GAGING STATIONS, HAWAII
APPENDIX C. MANN-KENDALL TEST
APPENDIX D. TABLES 2-5
For sale by
U.S. Geological Survey,
Information Services
Box 25286, Denver Federal Center
Denver, CO 80225
For more information about the USGS and its products:
Telephone: 1-888-ASK-USGS
World Wide Web: http://www.usgs.gov/
For more information about USGS activities in Hawaii, visit the USGS Hawaii District home page.
Any use of trade, product, or firm names in this publication is for descriptive purposes only and does not imply endorsement by the U.S. Government.Although this report is in the public domain, permission must be secured from the individual copyright owners to reproduce any copyrighted materials contained within this report.
Suggested citation:
Citation: Oki, D.S., 2004, Trends in Streamflow Characteristics at Long-Term Gaging Stations, Hawaii: U.S. Geological Survey Scientific Investigations Report 2004-5080, 120 p.
This report is available online in Portable Document Format (PDF). If you do not have the Adobe Acrobat PDF Reader, it is available for free download from Adobe Systems Incorporated.
Download the text of the report (PDF, 27.6 MB)
Document Accessibility: Adobe Systems Incorporated has information about PDFs and the visually impaired. This information provides tools to help make PDF files accessible. These tools convert Adobe PDF documents into HTML or ASCII text, which then can be read by a number of common screen-reading programs that synthesize text as audible speech. In addition, an accessible version of Acrobat Reader 5.0 for Windows (English only), which contains support for screen readers, is available. These tools and the accessible reader may be obtained free from Adobe at Adobe Access.
For more information about USGS activities in Hawaii, visit the USGS Hawaii District home page.
| AccessibilityFOIAPrivacyPolicies and Notices | |
  |
|