Guam Hazard Mitigation Plan - Western States Seismic Policy Council

SECTIONFIVERisk Assessment5.3.3 DroughtNatureDrought is a normal part of virtually every climate on the planet, including areas of both highand low rainfall. Drought is different from normal aridity, which is a permanent characteristic ofthe climate in areas of low rainfall. Drought is the result of a natural decline in the expectedprecipitation over an extended period of time, typically one or more seasons. The severity of adrought can be aggravated by other climatic factors, such as prolonged high winds and lowrelative humidity.Drought is a complex natural hazard. This complexity is reflected in the following fourdefinitions commonly used to describe it:• Meteorological drought is defined solely on the degree of dryness, expressed as a departureof actual precipitation from an expected average or normal amount based on monthly,seasonal, or annual time scales.• Hydrological drought is related to the effects of precipitation shortfalls on stream flows andreservoir, lake, and groundwater levels.• Agricultural drought is defined principally in terms of soil moisture deficiencies relative towater demands of plant life, usually crops.• Socioeconomic drought associates the supply and demand of economic goods or serviceswith elements of meteorological, hydrologic, and agricultural drought. Socioeconomicdrought occurs when the demand for water exceeds the supply as a result of weather-relatedsupply shortfall. This type of drought is also called a water management drought.A drought’s severity depends on numerous factors, including duration, intensity, geographicextent, the regional water supply capacity/resources, and the demands of humans and vegetation.Due to its multidimensional nature, drought is difficult to define and poses difficulties in terms ofcomprehensive risk assessments.Drought differs from other natural hazards in three ways. First, the onset and end of a droughtare difficult to determine due to the slow accumulation and lingering effects of an event after itsapparent end. Second, the lack of an exact and universally accepted definition of drought adds tothe confusion about its existence and severity. Third, in contrast to other natural hazards, theimpact of drought is not always obvious and may be spread over a large geographic area. Thesecharacteristics hinder the preparation of drought contingency or mitigation plans by manygovernments.Drought can cause a shortage of water for human and industrial consumption, hydroelectricpower, recreation, and navigation. Water quality can also decline, and the number and severity ofwildland fires can increase. A severe drought can result in the loss of agricultural crops andforest products, undernourished wildlife and livestock, lower land values, and higherunemployment.LocationThe entire island is susceptible to drought.5-15