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Click on the icons below to learn more about the hazards detailed in the 2020 Maui HMP.
Drought is a normal occurrence in virtually all climatic regions, including areas with high and low average rainfall. Drought is the consequence of a natural reduction in precipitation expected over an extended period, usually lasting a season or more. High temperatures, high winds, and low humidity can exacerbate drought conditions. In addition, human actions, anthropogenic climate change, and demands for water resources can hasten drought-related impacts. See the five categories of drought classified by the US Drought Monitor in the image above.
The National Centers for Environmental Information (NCEI) identifies drought as a “creeping phenomenon that slowly sneaks up and impacts many sectors of the economy, and operates on many different time scales.”83 Thus, the National Drought Mitigation Center has classified droughts into five types:
Meteorological Drought: The degree of dryness or departure of actual precipitation from an expected average or normal amount based on monthly, seasonal, or annual time scales. (Dry weather patterns dominate an area; can begin/end rapidly).
Hydrological Drought: The effects of precipitation shortfalls on stream flows and reservoir, lake, and groundwater levels. (Low water supply is evident; conditions take longer to develop and then recover).
Agricultural Drought: Soil moisture deficiencies relative to water demands of plant life, usually crops. (Crops significantly affected).
Socioeconomic Drought: The effect of demands for water exceeding the supply because of a weather-related supply shortfall.
Ecological Drought: A prolonged and widespread deficit in naturally available water supplies — including changes in natural and managed hydrology — that create multiple stresses across ecosystems.
A drought is a regional event that is not confined to geographic or political boundaries; it can affect several areas at once. It can also vary in severity across those areas. While leeward facing areas, like Maui’s Upcountry are more prone to drought, all areas of Maui County are at risk to drought occurrence.
In order to understand the conditions of past drought, it can be helpful to understand the typical precipitation received each year. According to the Rainfall Atlas of Hawai’i, rainfall rates through Maui County are highly variable. Rainfall is highest on windward facing mountain slopes, and most of the county’s rainfall is attributed to northeasterly trade winds. For instance, the windward side of Haleakalā in East Maui receives the highest amount of rainfall in Hawai’i, with an average annual rainfall of 404 inches. In contrast, the Kīhei area and parts of eastern Molokaʻi receive as little as 10 inches of rainfall per year. A majority of the area’s rainfall is received in the winter months, with summer months being the driest.
In the 20-year period from 2000 – 2019, the U.S. Drought Monitor reports years 2010, 2012, and 2019 exhibiting the most intense droughts (weeks within the Exceptional Drought category). However, another notable trend is that some level of drought was present in each of the 20 years studied, indicating a long-term and ongoing drought concern. During the 2019 drought, Maui County officials declared a Stage 1 water shortage on May 24th. In the month after the declaration, upcountry water levels dropped and additional 16% and water usage by 36%, prompting county officials to ask residents to curb non-essential water usage, and impacting expected crop yields.
Extent can be defined by the highest drought monitor category: Exceptional Drought. Since the U.S. Drought Monitor began in 2000, there have been 16 weeks where all or part of Maui County experienced Exceptional Drought (in 2010, 2012, and 2019).
Drought severity can also be measured in terms of damages. In Hawai’i, the 2007-2014 drought period caused $44.5 million in losses for the ranching industry alone, and recovery is expected to take 10 to 14 years, at $4 - $6 million per year. It should be noted that more intense, prolonged droughts than those that have occurred in the past are possible.
An exact probability is difficult to quantify given the limited reporting period available from the Drought Monitor (20 years; 2000-2019). There have been reported drought conditions in every year on record for Maui County. Further, drought frequency and severity are projected to increase in Maui County in the future due to projected warmer temperatures and decreased rainfall associated changing climatic conditions.
Due to the regional nature of drought and the water cycle, all of Maui County, including all community planning areas, are considered to have the same drought probability. Based on historic data and information regarding future conditions, a probability of “highly likely” (greater than 90 percent annual probability) was assigned to the drought hazard in Maui County. It should be noted that drought events are likely to span several months, or even years, adding to the probability of occurrence.
It is assumed that all current and future buildings, infrastructure, populations, and critical facilities in Maui County are at risk to drought. The atmospheric nature of drought and lack of specific boundaries make it more conducive to a qualitative assessment as opposed to a quantitative analysis, such as GIS analysis. The majority of drought impacts, however, are not structural but societal in nature. A drought’s impacts on society result from the interplay between a natural event and the demand people place on water supply.
Buildings and Infrastructure: Drought has minimal impacts on buildings and infrastructure, although drought could have impacts on the functionality of a building if water supply is disrupted. In addition, structural issues could occur in the event that drought impacts building foundations or footings. There are no known losses associated with drought on buildings or infrastructure in Maui County.
Health and Safety: As drought is a slow developing hazard, drought is unlikely to have significant impacts on life safety, and it is not expected to result in warnings or evacuation. Drought occurrences may result in water use restrictions or require freshwater to be imported. Water is also needed to manage wildfires. A lack of, or limited, water supply presents wildfire management vulnerability. Substantial water is needed to fight wildfires, which are also more frequent in dry conditions. In addition, soil that is dry and loosened due to dead or barren vegetation is more prone to landslides and sedimentation when a drought is followed by a heavy rain event. Drought has the potential to impact public health by reducing the quality and quantity of available drinking water. The State of Hawai’i, including Maui County, is an isolated land mass with limited freshwater resources. Drought may substantially reduce surface water stream flows or result in saltwater intrusion into groundwater and other freshwater sources. While drought has never been severe enough to fully deprive the county of water, it is possible. Populations who rely on catchment for their water supply are especially vulnerable.
Economic Impacts: Drought has the potential to impact Maui County economically in several ways. Drought resulting in water shortage can also impact businesses (ranging from restaurants to manufacturing) which cannot operate without water. Maui’s robust tourism industry could be severely impacted by water shortages, and eco-tourism may be curbed during events where drought has measurable impacts on ecosystems. In addition, in the case of a water shortage, the cost of water may increase (or the county may be forced to import water or set up expensive desalination facilities), which would have ripple effects on the local economy. Additionally, drought has a history of negatively impacting agricultural holdings. Within the state, USDA paid $50 million in livestock insurance claims to Hawaiian ranchers for grazing losses from 2008-2017, and farmers in Hawai’i have received $10 million in federal crop insurance payments since 1996 due to drought losses. Further, the cultivation of traditional, culturally significant crops such as taro can be impacted.
Climate Change: In Maui County, climate change is projected to result in increased drought frequency and severity. Warming temperatures result in increased evaporation and evapotranspiration, reducing water levels and drying out plants and soils. Further, Maui County is experiencing decreased precipitation. A documented decrease in trade winds, which bring moisture to windward mountain slopes, over the last 40 years has subsequently resulted in decreased rainfall. Lastly, end-of-century rainfall projections for the entire state under a higher emissions scenario (RCP8.5) range from small increases to increases of to up to 30% in wet areas, and from small decreases to decreases of up to 60% in dry areas.
