A Hundred Year History of Drought at Hawaiʻi Volcanoes National Park
Native dominated ecosystems in the park can be impacted during drought events in several ways, including: increased incidences of wildfire, loss of bird habitat, decreased availability of forage, increased growth of non-native shrubs and grasses, increased activity of invasive rodents, and more.
Extended dry periods can be a deadly situation for many native species across the park
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 increase wildfire risk, decrease tree growth, and increase the spread of invasive species. In Hawai‘i, drought is a significant feature in the climate system that has profound impacts on ecosystems.
If the severity of dryness reaches 1, it is considered a moderate drought; if it reaches 1.5, it is considered a severe drought; and if it is greater than 2, it is considered an extreme drought.
A Drought History at HAVO
A total of 17 (park-wide) droughts have occurred since 1920, but the three most severe droughts have all occurred since 2003. The longest drought lasted for a total 119 months (March 2008 to April 2018) and had the highest intensity of any drought in the record. Even though drought is a natural part of the climate system, when we look at drought events over time, we can see that drought frequency, duration, and intensity have increased over the past century. When individual park units are considered, droughts can be more common or less common depending on your location. Interestingly, drought is almost twice as likely to occur in the wet windward areas than in the relatively dry leeward areas of the park. For example, in the ‘Ōla‘a tract, which is the wettest area of park (156 inches of rain per year), a total of 26 droughts have occurred while in the relatively dry Kahuku forest (43 inches of rain per year), only 14 droughts have been observed over the same 100-year record.
Management Actions During Drought
Resource managers are tasked with the protection of park resources. Therefore, it is critically important that they are equipped with the tools and knowledge necessary to plan effective management strategies. These include an array of management actions that can be taken before, during, and after a drought event to minimize impacts. Effective management can be the key to reducing impacts on natural resources in the park
Before Drought
Manage invasive species; establish and maintain fire fuel breaks; restore native plant communities; raise public awareness; establish vegetation monitoring plots; collect and store seeds of native species.
During Drought
Close areas for fire prevention; supplement food/water for Nēnē; increase fence inspections; adjust restoration activities (no planting); invasive plant control and increase predator trapping.
After Drought
If fire occurred, conduct post-fire restoration with fire-tolerant native species; replace rare species; evaluate long-term change in vegetation and formulate a response.
Broomsedge burn rehabilitation area in the Mauna Loa Strip during July 2011 after 35 consecutive months of drought conditions which began in September 2008. The hō‘awa in the foreground of the photo is a native species that is planted to help rebuild the understory.
Photo courtesy of J.B. Friday
Why is This Important? Range of Impacts Across the Park
Increased frequency, duration, and intensity of drought events can put pressure on water supplies and alter ecosystems in ways that can increase their vulnerability. Drought impacts span a wide range, from small-scale, temporary responses such as stunted plant growth and increased dehydration stress in wildlife, to widespread and persistent ecosystem transformations such as vegetation type conversion or species range shifts. Many threatened and endangered plant species occur in areas susceptible to drought and where drought-related impacts are the greatest. Severe droughts can reduce species populations and sometimes be the driving mechanism for extinction. The risk of wildfire occurrence is also increased during times of drought which may cause managers to close parts of the park to avoid ignitions, which ultimately impacts visitor experiences in the park. Wildfire can also lead to other ecological consequences, including higher rates of erosion from burned areas and increased sediment delivery to streams and nearshore areas. This highlights the importance of management actions that reduce drought effects on wildfire risk. Some examples include, reducing invasive fire prone vegetation, such as fountain grass, and increasing fire resistance in specific sites by rebuilding the structure of the native understory. This increases shade and moisture, decreases wind and fuel bed temperatures, thereby reducing the risk of wildfire spreading into high priority areas
Future Climate Projections at Hawai‘i Volcanoes National Park
The park is expected to become drier and hotter by the end of the century
What is Climate Downscaling?
Future projections of both rainfall and temperature are available for most of the Earth’s surface from a wide variety of global climate models. These models use mathematical equations to characterize how energy and matter interact in different parts of the ocean and atmosphere over time. Climate downscaling, is a technique used to translate the global model projections at a finer resolution. A range of future climate projections (that use different downscaling methods) for both rainfall and temperature are available for Hawai‘i for two distinct future climate scenarios. These scenarios include: 1) a future in which societies work together to reduce the amount of greenhouse gases (GHGs) in the earth’s atmosphere (“Low Emissions” scenario), and 2) a future where no effort is made to reduce GHGs (“High Emissions” scenario). Understanding how climate is projected to change under different scenarios is critical to an effective management response that incorporates a wide range of adaptation options, for example, ecosystem-based adaptation, ecosystem restoration to avoid degradation and deforestation, biodiversity management, and incorporating local and indigenous knowledge into decision making. Adapting to a changing climate helps to reduce the risks to both natural and managed ecosystems.
Future Climate Change in Hawaii Volcanoes National Park
Future rainfall extremes for both the low and high emissions scenarios for Hawai‘i Island are shown in Figure 1. For the low emissions scenario, Hawaii Volcanoes National Park (HAVO) is projected to see a moderate, 7% (-4 inch) decline in average annual rainfall by the end of the century. The driest projections are for the windward (eastern) areas of the park. For the high emissions scenario, HAVO is projected to see a 38% (22 inch) reduction in rainfall. In this scenario, pronounced drying is projected for both windward and leeward (western) areas and most pronounced low elevations (<5000 ft) across the park. For temperature (Figure 2), accelerated warming is expected under both future scenarios. For the low emissions scenario, end-of-century average temperatures across the park are projected to be 3.4°F warmer than temperature today. For the high emissions scenario, average temperatures across the park are projected to be 7.1°F warmer. For both scenarios the highest warming rates are projected for the highest elevations. For example at the Mauna Loa unit (~10,000 ft), an additional 4.0°F to 8.6°F of warming is projected under the low and high emissions scenarios respectively.
Left image
Figure 1: Future projections of rainfall on Hawai‘i Island for year 2100, under a low1 (left) and high2 (right) emissions scenario.
Right image
Figure 2: Future projections of temperature on Hawai‘i Island for year 2100, under low2 (left) and high1 (right) emissions scenarios
Figure 3: Picture of the endemic scarlet ‘I‘iwi in Hawaiʻi Volcanoes National Park. At present ‘i‘iwi are restricted to elevations above 5,000 ft where the disease vector mosquito for avian malaria is absent. ‘I‘iwi are present at low densities relative to most species across the park.
NPS Photo/J.Wei
Why is This Important? A Range of Impacts Across the Park
Future changes in temperature and rainfall will undoubtedly affect the plant and animal species that reside in the park. As the climate becomes warmer and drier a range of impacts are expected including dramatic range shifts of native and non-native species, increased wildfire risk, expansion of disease and increased risk of extinction. It is also important to understand that climate change is not just a future scenario, as many of these impacts are being realized today. The primary threat to native Hawaiian forest birds is avian malaria, which is transmitted by the bite of non-native mosquitoes. In the past, low temperatures at high elevations created disease free forest refuges. However, environmental warming allows the mosquitoes to move further upslope thus reducing the area of safe habitat and resulting in population declines. Current climate based population models predict approximately 1/3rd of all Hawaiian honeycreepers will lose more than 90% of their current range by 2080. The iconic ‘I‘iwi (Figure 3) now only persists in a narrow band of forest between mosquito range and sparsely forested sub-alpine lava flows of Mauna Loa. In the absence of significant intervention, many native Hawaiian species will suffer major population declines or extinction due to increasing risk from avian malaria during the 21st century. Understanding how climate is projected to change is critical to an effective management response that incorporates a wide range of adaptation options to promote healthy ecosystems. Land managers are working to build climate resilient native ecosystems by excluding invasive species, partnering with researchers to investigate strategies for reducing mosquitoes on a landscape scale, seed banking, and restoring rare plant species across the ecological range. Actions such as these, combined with new innovative approaches and working with our partners beyond park boundaries, will increase the potential that our native plants and animals will persist for future generations.
Average wet season climate conditions during El Niño and La Niña phases of ENSO.
Impacts of El Niño on Climate in Hawai‘i Volcanoes National Park
Understanding and anticipating climate variations during El Niño events allows us to protect park resources
El Niño vs. La Niña
The El Niño-Southern Oscillation (ENSO) is a naturally recurring feature in the Earth’s climate system that involves a change in sea surface temperatures in the eastern and central tropical Pacific Ocean. This change in temperature is brought on by changes in surface winds that move water from east to west across the Pacific basin. During the La Niña (cool) phase of ENSO, strong winds move cool water quickly from east to west across the basin, resulting in cooler water temperatures around Hawai‘i. During the El Niño (warm) phase winds are weaker, so the slower moving water has the ability to absorb more heat energy, resulting in warmer sea surface temperatures.
El Niño Weather in Hawai’i
In Hawai’i, both rainfall and temperature are strongly influenced by both El Niño and La Niña events. El Niño events are typically associated with less rainfall and warmer temperatures during the traditional wet (winter) season (November to April) while La Niña events are associated with greater rainfall and cooler temperatures during this season. During the dry (summer) season (May to October) these rainfall patterns are reversed: El Niño summers are typically wet, and La Niña summers are typically dry. Individual El Niño and La Niña events can vary in strength and are often classified as either strong or weak depending on how warm or cool the sea surface temperatures are. Winters in Hawai‘i are almost always drier than normal during a strong El Niño event, while during a weak El Niño we see a range of conditions (dry and wet).
January average rainfall (left) and January 2010 rainfall (right).
The Effects of El Niño at Hawaiʻi Volcanoes National Park
Average monthly wet season rainfall is about 5 inches per month at Hawai’i Volcanoes National Park (HAVO), but during an El Niño event, average rainfall typically declines by 2 inches per month. During a strong El Niño in January 2010, rainfall was 5.9 inches (94%) drier than the long-term average for that month and maximum temperatures (measured at the park headquarters) were 3.1˚F warmer than normal.n fact, during the consecutive 6-month period leading up to the fire, total rainfall was 66% drier than normal and maximum temperatures were 1.7˚F warmer. The resulting dry conditions allowed the fire to spread in uluhe wet forest and ‘ōhi’a/swordfern mesic forest. Fire risk in this area of the park is generally low due to high frequency of rainfall, but fire can occur after short dry periods. Understanding the timing, intensity, and duration of an El Niño event is critical to an effective management response, which can include securing resources (equipment and staff), growing seedlings for restoration, invasive species control, and saving seeds of rare species. The phase of ENSO and the strength of the event can usually be identified several months in advance, therefore, resource managers can make the necessary adjustments in restoration schedules or take the necessary precautions in fire management activities.
2003 Luhi Fire. Inset shows location of the fire relative to Park Headquarters.
NPS Photo
Why is This Important? A Range of Impacts in the Park
Some of the most intense droughts observed in the park have been associated with El Niño events that have occurred during the wet season. These extreme changes in seasonal rainfall can result in a range of direct and indirect impacts on natural resources including survival of native plants (seedlings and adults), invasive plant expansion, and survival of endangered animals. In addition, decreases in rainfall accompanied by decreases in relative humidity are conducive to wildland fires (with an ignition source). In May 2003, following a moderately strong El Niño, the Luhi Fire burned approximately 4,900 acres in the Kīlauea unit of the Park. This fire was ignited by lava and spread during a period of extremely low relative humidity and strong winds. In addition, the rainfall leading up to the fire event was extremely low
Authors: Ryan J. Longman (East-West Center), Sierra McDaniel (Hawai‘i Volcanoes National Park), Abby G. Frazier (East-West Center), and Christian P. Giardina (USDA Forest Service). Design and layout: Brooks Bays (SOEST Publication Services.
