This article is a US Government work and is in the public domain in the USA.
Trends and shifts in streamflow in Hawai‘i, 1913–2008†
Article first published online: 1 MAY 2012
Copyright © 2012 John Wiley & Sons, Ltd.
Volume 27, Issue 10, pages 1484–1500, 15 May 2013
How to Cite
Bassiouni, M. and Oki, D. S. (2013), Trends and shifts in streamflow in Hawai‘i, 1913–2008. Hydrol. Process., 27: 1484–1500. doi: 10.1002/hyp.9298
- Issue published online: 2 MAY 2013
- Article first published online: 1 MAY 2012
- Accepted manuscript online: 8 MAR 2012 04:18AM EST
- Manuscript Accepted: 2 MAR 2012
- Manuscript Received: 10 NOV 2011
- base flow;
This study addresses a need to document changes in streamflow and base flow (groundwater discharge to streams) in Hawai‘i during the past century. Statistically significant long-term (1913–2008) downward trends were detected (using the nonparametric Mann–Kendall test) in low-streamflow and base-flow records. These long-term downward trends are likely related to a statistically significant downward shift around 1943 detected (using the nonparametric Pettitt test) in index records of streamflow and base flow. The downward shift corresponds to a decrease of 22% in median streamflow and a decrease of 23% in median base flow between the periods 1913–1943 and 1943–2008. The shift coincides with other local and regional factors, including a change from a positive to a negative phase in the Pacific Decadal Oscillation, shifts in the direction of the trade winds over Hawai‘i, and a reforestation programme. The detected shift and long-term trends reflect region-wide changes in climatic and land-cover factors. A weak pattern of downward trends in base flows during the period 1943–2008 may indicate a continued decrease in base flows after the 1943 shift.
Downward trends were detected more commonly in base-flow records than in high-streamflow, peak-flow, and rainfall records. The decrease in base flow is likely related to a decrease in groundwater storage and recharge and therefore is a valuable indicator of decreasing water availability and watershed vulnerability to hydrologic changes. Whether the downward trends will continue is largely uncertain given the uncertainty in climate-change projections and watershed responses to changes. Copyright © 2012 John Wiley & Sons, Ltd.