Abstract

This study addresses a need to document changes in streamflow and base flow (groundwater discharge to streams) in Hawaii during the past century. Statistically significant long-term (19132008) downward trends were detected (using the nonparametric MannKendall 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 19131943 and 19432008. 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 Hawaii, 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 19432008 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 (c) 2012 John Wiley & Sons, Ltd.

Keywords

streamflow; groundwater; base flow; trends; climate; Hawai"i

Published in

Hydrological Processes
2013, Volume: 27, number: 10, pages: 1484-1500
Publisher: WILEY

UKÄ Subject classification

Climate Research


Publication identifier

DOI: https://doi.org/10.1002/hyp.9298

Permanent link to this page (URI)

https://res.slu.se/id/publ/105942