drought – Hawaiʻi Climate Data Portal

A Century of Drought in Hawai‘i

aimeesch@hawaii.edu — Mon, 24 Oct 2022 23:40:13 +0000

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 *.

Diagnosing Hawai‘i’s Recent Drought

aimeesch@hawaii.edu — Fri, 24 Jun 2022 02:03:45 +0000

Contributed by Henry Diaz (hfdiaz@hawaii.edu)

Read the full article:

Hawai‘i’s recent drought is among the most severe on record. Wet-season (November-April) rainfall deficits during 2010–2019 rank second lowest among consecutive 10-yr periods since 1900. Various lines of empirical and model evidence indicate a principal natural atmospheric cause for the low rainfall, mostly unrelated to either internal oceanic variability or external forcing.

Empirical analysis reveals traditional factors favored wetness not drought in recent decades, including a cold phase of the Pacific Decadal Oscillation in sea surface temperatures (SSTs) and a weakened Aleutian low in atmospheric circulation. But correlations of Hawaiian rainfall with patterns of Pacific sea level pressure and SSTs that explained a majority of its variability during the 20th Century collapsed in the 21st Century. Atmospheric model simulations indicate a forced decadal signal (2010–2019 vs 1981–2000) of Aleutian low weakening, consistent with recent observed North Pacific circulation. However, model ensemble means do not generate reduced Hawaiian rainfall indicating that neither oceanic boundary forcing nor a weakened Aleutian low caused recent low Hawaiian rainfall.

Additional atmospheric model experiments explored the role of anthropogenic forcing. These reveal a strong sensitivity of Hawaiian rainfall to details of long-term SST change patterns. Under an assumption that anthropogenic forcing drives zonally uniform SST warming, Hawaiian rainfall declines, with a range 3%–9% among three models. Under an assumption that anthropogenic forcing also increases the equatorial Pacific zonal SST gradient, Hawaiian rainfall increases 2%–6%. Large spread among ensemble members indicates that neither forced signals are detectable.

Pacific Drought Knowledge Exchange

aimeesch@hawaii.edu — Mon, 26 Jul 2021 18:28:57 +0000

Climate change, climate variability, and drought (CCVD) will exert a growing impact on landscapes, watersheds, and nearshore areas in the Pacific Islands. Droughts in the Pacific Islands can be extremely severe, causing drinking water shortages, extensive crop damage, and increases in the size, severity and extent of wildfires that burn incredibly large percentages of island land areas. A recent analysis of historical drought in Hawai‘i found that drought duration, magnitude, and frequency have all increased significantly, consistent with trends found in other Pacific Islands. While land managers are tasked with utilizing the “best available science”, they often are confronted with data products that are difficult to access and there is no facilitated communication process with researchers to meet the needs of resource managers. To address this gap, we established the PDKE to explore knowledge co-production among researchers and resource managers with the goal of expanding the utility of drought-related info

Principal Investigators: Christian Giardina (christian.p.giardina@usda.gov) and Abby Frazier (abbyf@hawaii.edu)

Names / Affiliations of other Cooperators and Partners: Ryan Longman (East-West Center); Clay Trauernicht and Thomas Giambelluca (University of Hawaii at Manoa); Victoria Keener and Laura Brewington (NOAA Pacific RISA); USGS Pacific Islands Climate Adaptation Science Center (PI-CASC); NOAA’s National Integrated Drought Information System (NIDIS); USDA Southwest Climate Hub

What is Drought?

The term “drought” is generally used to describe a prolonged period with less-than-average amounts of rain in a particular area. A lack of rainfall can reduce soil moisture or groundwater, reduce stream flow, and cause water shortages. Low rainfall can also be associated with higher-than-average temperatures and reduced cloud cover. An individual drought event may last for weeks, months, or even years and the severity of a drought will depend on how long the area receives below-average rainfall. Hot temperatures can make droughts worse by evaporating moisture from the soil. Drought can also create environmental conditions that lead to wildland fire, stunted tree growth or mortality, and the spread of invasive species. In Hawai‘i, drought is a significant feature in the climate system that has profound impacts on ecosystems.

During the PDKE pilot project we worked with Elliot Parsons and Edith Adkins from Pu‘u Wa‘awa‘a Hawai‘i Experimental Tropical Forest and Sierra McDaniel from Hawaii Volcanoes National Park to develop a series of factsheets for both resource managers and conservation practitioners to better understand the the impacts of drought in those landscapes.

Pu‘u Wa‘awa‘a Hawai‘i Factsheets

Hawaii Volcanoes National Park Factsheets

The PDKE also worked with Melissa Kunz from the Department of Natural Resource and Environmental Management to publish a series of factsheets that focused on state-wide drought impacts.

State-wide impacts of drought Factsheets

Drought and wildfire at Hawai‘i Volcanoes National Park

aimeesch@hawaii.edu — Mon, 19 Jul 2021 18:27:34 +0000

During the 2002–2003 drought, relative humidity values dropped into the single digits, and wildfire spread into “safe areas” of Hawai‘i Volcanoes National Park, including wet forests, with tree ferns (Cibotium menziesii) and uluhe ferns (Dicranopteris linearis) as the main carriers. Despite dozens of firefighters, miles of fuel breaks, and helicopter water drops, the fire spread into the East Rift Special Ecological Area, burning important habitat and damaging the ungulate proof fence. Immediate action was required to replace the fence and prevent pig ingress to the area. This series of fires also impacted the lower elevation wet/ mesic forest, with sword fern (Nephrolepis multifora) as the main carrier. Post-fire restoration work included monitoring along with seeding and planting fire-tolerant native species. Years of lab and field trials (Loh et al. 2009) were conducted to determine which species are fire-tolerant and then to collect and bank seeds from those species (McDaniel et al. 2008). Future projects will re-survey the plots to examine longer term changes in community composition.

To learn more, read the by Frazier et al.

Long-Term, Gridded Standardized Precipitation Index for Hawai‘i

aimeesch@hawaii.edu — Mon, 19 Jul 2021 17:32:56 +0000

Percent area drought time series (2000–2012) for the State of Hawai‘i for: (a) monthly aggregated U.S. Drought Monitor; and (b) gridded SPI-3 converted to USDM categories.

to read the publication by Matthew Lucas.

Spatially explicit, wall-to-wall rainfall data provide foundational climatic information but alone are inadequate for characterizing meteorological, hydrological, agricultural, or ecological drought. The Standardized Precipitation Index (SPI) is one of the most widely used indicators of drought and defines localized conditions of both drought and excess rainfall based on period-specific (e.g., 1-month, 6-month, 12-month) accumulated precipitation relative to multi-year averages. A 93-year (1920–2012), high-resolution (250 m) gridded dataset of monthly rainfall available for the State of Hawai‘i was used to derive gridded, monthly SPI values for 1-, 3-, 6-, 9-, 12-, 24-, 36-, 48-, and 60-month intervals. Gridded SPI data were validated against independent, station-based calculations of SPI provided by the National Weather Service. The gridded SPI product was also compared with the U.S. Drought Monitor during the overlapping period. This SPI product provides several advantages over currently available drought indices for Hawai‘i in that it has statewide coverage over a long historical period at high spatial resolution to capture fine-scale climatic gradients and monitor changes in local drought severity.

Drought effects on drinking water supply on Maui

aimeesch@hawaii.edu — Mon, 19 Jul 2021 17:21:44 +0000

Reduced rainfall from meteorological drought can have direct effects on social-ecological systems; the most obvious consequence is reduced runoff and streamflow. Streams provide important ecological services on tropical islands, including water for hydropower production, habitat for freshwater fauna, irrigation of agriculture, and potable water supply. On Maui Island, surface water is a critical source of potable water supply, supplying 26.7 percent of total water for the island. Some regions are more dependent on surface water supply than others. For example, surface water sources supply most of the water systems in upcountry Maui (84.6 percent) and west Maui (65.1 percent) (fg. 5.3). These streams are vulnerable to drought, leading to frequent declarations of stage 1 water shortages (voluntary reductions in water use), where anticipated water demand is projected to exceed available water supply by 1–15 percent. Reservoirs in these regions help buffer the water system against shifts in surface water availability. However, if drought conditions continue and water conservation measures do not limit short term use, stage 2 or stage 3 water shortages may be declared, requiring mandatory reductions in water use.

To learn more, read the by Frazier et al.

Maui County Department of Water Supply mean daily groundwater versus surface potable water use for central drought-pest interactions have led to tree mortality of Maui, upcountry Maui, and west Maui regions, 2016–2017