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Photo of Maunalua Bay, Oahu. (Photo by Scot Izuka)

HAWAII VOLCANIC-ROCK AQUIFER STUDY

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HAWAII VOLCANIC-ROCK AQUIFER STUDY


CHANGES THAT AFFECT GROUNDWATER

Photo of irrigation-ditch diversion on upper Wailua River, Kauai. Diversions such as this took large amounts of water from streams for irrigation in the 20th Century. By 2000 all but a few sugarcane plantations in Hawaii closed. (Photo by Scot Izuka).

Irrigation-ditch diversion on upper Wailua River, Kauai. Diversions such as this took large amounts of water from streams for sugarcane irrigation in the 20th Century. By 2000 all but a few sugarcane plantations in Hawaii closed. (Photo by Scot Izuka).

In addition to the multiyear cyclic variations linked to oceanic climate cycles such as ENSO and PDO, Hawaii's climate shows a long-term average drying trend over the last century that may be linked to climate change. Stream-gage data also show a downward trend in stream base flow over the last century that indicates decreasing groundwater in storage.

Land-use changes such as expanding urbanization, deforestation, the introduction and eventual cessation of large-scale sugarcane (a high-water-demand crop) cultivation, and adoption of more efficient irrigation methods have affected groundwater recharge.

Changes in vegetation in Hawaii have also resulted from reforestation programs and replacement of native forests by non-native plant species. Changes in vegetation can alter evapotranspiration rates, and thus affect groundwater recharge.

Growing and shifting populations and industry, changes in agriculture, and changes in the way groundwater is managed have altered the distribution of groundwater withdrawals across the state since large-scale development of groundwater began in the late 19th century.

[References: Woodcock (2003), Oki (2004), Chu and Chen (2005), Asner and others (2008), Kruk and Levinson (2008), Kagawa and others (2009), Chu and others (2010), Bassiouni and Oki (2012)]

Graph showing declining stream base flow in Hawaii. Stream base flow, which comes from groundwater, has shown statistically significant downward trends in the last century (modified from Oki, 2004 and Bassiouni and Oki, 2012). Click image on image for larger view.

Stream base flow, which comes from groundwater, has
shown statistically significant downward trends in the
last century (modified from Oki, 2004 and Bassiouni and
Oki, 2012). Click image for larger view.



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