weekly notes Geol370
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This 2 page Class Notes was uploaded by Monica Huang on Tuesday March 24, 2015. The Class Notes belongs to Geol370 at San Francisco State University taught by Dr.Sklar in Fall. Since its upload, it has received 145 views. For similar materials see Geology in Geology at San Francisco State University.
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Date Created: 03/24/15
What is Drought Simple working de nition Drought drier conditions over an extended period of time Which of 3 class themes Variability in time and space What is Drought National Weather Service NWS de nition Drought is a reduction in precipitation over an extended period usually a season or more resulting in a water shortage causing adverse impacts on vegetation animals andor people Drought 0 is a normal recurrent feature of climate that occurs in virtually all climate zones from very wet to very dry 0 is a temporary deviation from typical climatic conditions thus the degree of dryness during drought can very signi cantly from one region to another 0 is different from aridity which is a permanent feature of climate in regions where low precipitation is the norm as in a desert Quantifying Drought Cumulative Departure Method Remember the water balance equation Input Output Change in Storage Actual Precip Average Precip Departure from Normal Positive departure means more precipitation than normal Negative departure means less precipitation than normal Cumulative departures method Add up the departures from normalyear after year after year 0 Several negative dry years in a row can take many years to recover from 0 Several positive wet years in a row can save up water for dry years Drought types de ned by impacts Drought can be categorized based on the types of impacts 0 Meteorological Drought 0 Agricultural Drought 0 Hydrological Drought 0 SocioEconomic Drought Meteorological Drought 0 based on the degree of dryness in comparison to some normal or average and the duration of the dry period 0 is different for each region since it relates to atmospheric conditions that differ from place to place 0 Drought periods begin with a meteorological drought Agricultural Drought 0 occurs when low precipitation and soil moisture affect crop yields 0 links meteorological drought to agricultural impacts focusing on precipitation shortages soil water de cits reduced groundwater or reservoir levels needed for irrigation etc 0 usually evolves slowly over time 0 economic losses can be signi cant tens of billions of each year in US Hydrological Drought 0 occurs following periods of extended precipitation shortfalls that impact water supply ie stream ow reservoir and lake levels groundwater potentially resulting in signi cant societal impacts 0 because regions are interconnected by hydrologic systems the impact of meteorological drought may extend beyond the borders of the precipitationde cient area Socioeconomic Drought 0 occurs when reduced water supply causes the demand for goods or services to exceed the supply such as when hydroelectric power production declines with reservoir depletion is a comprehensive de nition that considers water rationing wild re events loss of life and other widespread impacts of water shortfalls Impacts of current California drought on Central Valley 0 Central Valley alone expected costs at least 20 Billion Central Valley farmers have received about 13 of normal water deliveries which costs about 450 million to replace with groundwater 0 Some agricultural users are not getting any water from state water project this year gt500000 fallow acres this past growing season loss of about 15000 jobs 0 higher unemployment means more welfare expenses less tax revenue this year for local state and federal governments
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