Freshwater & Drought

Freshwater resources are essential to life on Pacific Islands. Water is needed for human consumption, as well as for agriculture, industry, ecosystems and public health. Each island location relies on a different mix of freshwater sources, including groundwater, surface water, and rainwater catchment, but the small size of islands means that these resources are limited. Climate change may pose serious challenges for island freshwater resources.

Key Message

Warmer and drier conditions mean that freshwater supplies will decrease on some Pacific Islands. Atolls and low-lying islands are especially vulnerable to freshwater shortages due to their small size and limited resources.

Observed Trends

Central North Pacific: Hawai‘i

Average air temperature in Hawai‘i has risen significantly in the past 100 years. This rise in air temperature has accelerated in the past 30 years.
In recent decades, higher elevation areas are warming more rapidly compared to lower elevation areas.
Annual precipitation has decreased significantly in the past 100 years.
In the past 30 years, all Hawaiian Islands have experienced greater numbers of consecutive dry days and fewer days of intense rainfall.
Base flow, the groundwater component of streamflow, has shown significant downward trends of 20% to 70% in the past 100 years. This trend indicates a decrease in groundwater resources. This could be serious for Hawai‘i’s domestic drinking water supply, 99% of which comes from groundwater.
Hawai‘i has experienced a decrease in climate monitoring stations. The ability to meaningfully assess future climate changes in detail is at risk.

Western North Pacific: Guam, Palau, Federated States of Micronesia, Marshall Islands, Northern Mariana Islands

Although highly variable, maximum and minimum air temperatures have increased over the past 60 years.
The Eastern Micronesian islands, including RMI and Kosrae and Pohnpei in FSM, show a statistically significant drying trend, losing nearly 15% of annual rainfall over the past 60 years.
Western Micronesia, including Guam, Palau, and Yap and Chuuk in FSM, shows a slight tendency toward wetter conditions over the past 60 years.
Since the 1950s, there have been fewer extreme rainfall events (exceeding 10 inches in 24 hours) in Guam and the CNMI.
The smallest islands are extremely vulnerable to droughts of any severity.
The number of climate monitoring stations in Micronesia is declining and currently is not adequate to assess future climate changes in meaningful detail.

Central South Pacific: American Samoa

In the past 60 years, average, minimum, and maximum air temperatures have been increasing. The largest observed increases have been in minimum air temperatures.
In Sāmoa, precipitation records in the past 100 years have shown no trend.
The frequency of extreme precipitation and drought events has not changed significantly in the past 60 years.
No significant trends were detected in streamflow, which may be due to the short length of record.
Like Micronesia, the Sāmoa region suffers from a declining number of climate monitoring stations, which will make it impossible to assess future climate changes in meaningful detail.

Future Projections

Surface air temperatures are projected to increase across the region. In Hawai‘i and the Central North Pacific, a temperature increase of 1° to 2°F is expected by 2035. In Micronesia, average air temperature is projected to increase in the range of 1.1° to 1.3°F by 2030 and 1.1° to 2.6°F by 2055. In American Samoa and the Central South Pacific, the average air temperature is projected to increase 1.1° to 1.3°F by 2030 and 1.9° to 2.5°F by 2055.
In Micronesia and the Western North Pacific, the wet season is projected to get wetter and the dry season is projected to get drier. An overall increase in mean annual rainfall is expected for this region.

In Hawai‘i (updated June 2016):
- The windward sides of the Hawaiian Islands will become increasingly wetter in the winter season, with the trend most prominent on Hawai‘i Island and Maui Island (high confidence; Elison Timm et al. 2015).
- Leeward sides will become increasingly drier in the summer season (medium confidence; Elison Timm et al. 2015).
- The height of the trade wind inversion layer will decrease very slightly, and the occurrence frequency of trade wind inversion (number of days present) will increase by the end of the century if the current levels of greenhouse gas production continue (medium confidence; Lauer et al., 2013).

Download “Freshwater and Drought on Pacific Islands” chapter from the 2012 PIRCA Report

Freshwater and Drought on Pacific Islands (1.5 MB)

Download Chapter (1.5 MB)

The preceding text (excluding the 2016 updated projections) is excerpted and abridged from this chapter, which should be cited as:

Keener, V. W., Izuka, S. K., & Anthony, S. (2012). Freshwater and Drought on Pacific Islands. In V. W. Keener, J. J. Marra, M. L. Finucane, D. Spooner, & M. H. Smith (Eds.), Climate Change and Pacific Islands: Indicators and Impacts. Report for the 2012 Pacific Islands Regional Climate Assessment (PIRCA). Washington, DC: Island Press.