A Century of Drought in Hawai‘i

Contributed by Abby Frazier (abbyf@hawaii.edu)

Drought is a regular and natural component of the climate in Hawaiʻi with severe effects across many sectors statewide. This paper provides a comprehensive synthesis of past drought effects in Hawaiʻi that we integrate with geospatial analysis of drought characteristics using a newly developed 100-year (1920–2019) gridded Standardized Precipitation Index (SPI) dataset. The synthesis examines past droughts classified into five categories: Meteorological, agricultural, hydrological, ecological, and socioeconomic drought. The assessment of current drought literature revealed large gaps in our knowledge of socioeconomic and ecological drought effects in Hawaiʻi.

Figure 6. Droughts identified from the statewide average 12-month SPI time series (SPI-12). Intensity (absolute value of SPI values), peak intensity, average intensity, magnitude, and percent area in moderate drought or worse (SPI < −1) are shown for each drought; magnitude and percent area are shown on reverse axis.

Spatiotemporal analysis of a new gridded drought index revealed that the two worst droughts for the State of Hawaiʻi in the past century were 2007–2014 and 1998–2002 (Figure 6). The island-level analysis identified that the 2007–2014 drought was the worst for Hawaiʻi Island, whereas the 1998–2002 drought was more severe for Kauaʻi, Oʻahu, and Maui Nui, with different spatial patterns (Figure 9). Significant trends were found in decadal drought duration and magnitude (droughts in Hawai‘i have gotten longer and more severe) (Figure 8), consistent with trends found in other Pacific Islands. Droughts have resulted in over $80 million in agricultural relief since 1996 and have increased wildfire risk, especially during El Niño years.

By coupling quantitative SPI analysis with a review of the economic and ecological effects of drought across different sectors, a more thorough understanding of historical drought trends can be used to better understand future projections in a given region. Although drought is experienced differently across landscapes, this combined analysis provides a framework that enables a holistic yet spatiotemporally relevant view that can contribute to more effective management.

Figure 8. Drought maps based on SPI-12 for the two worst droughts (based on ranks in Table 1): (a) 2007–2014; (b) 1998–2002. Color indicates weighted proportion of drought intensity (mild drought in yellow to extreme drought in dark red). Size of points indicates proportion of time spent in drought (smallest points: 0–25% time in drought, largest points: 85–100% time in drought during drought years).
Figure 9. State and island drought frequency (DF; number of events) (a,b), total drought duration (TDD; number of months) (c,d), and total drought magnitude (TDM; unitless) (e,f) by decade from 1920–2019. Statewide trends (a,c,e) are shown for SPI-6 (darker colors, dashed trend line) and SPI-12 (lighter colors, solid trend line). Island trends (b, d, f) are shown for SPI-12; Ka = Kauaʻi, Oa = Oʻahu, Ma = Maui Nui, and Ha = Hawaiʻi Island. p < 0.05 indicated with asterisk *.

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