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2015 URBAN WATER MANAGEMENT PLAN <br />3.6.4 Single -Dry Year Reliability Comparison <br />A single -dry year is defined as a single year of no to minimal rainfall within a period that average <br />precipitation is expected to occur. The water demand forecasting model developed for the OC Reliability <br />Study (described in Section 2.4.1) isolated the impacts that weather and future climate can have on water <br />demand through the use of a statistical model. The impacts of hot/dry weather condition are reflected as a <br />percentage increase in water demands from the average condition (1990- 2014). For a single dry year <br />condition (FY2013 -14), the model projects a six percent increase in demand for the OC Basin area where <br />the City's service area is located (CDM Smith, Final Technical Memorandum #1 of Orange County <br />Reliability Study, April 2016). Detailed information of the model is included in Appendix G. <br />The City has documented that it is 100 percent reliable for single dry year demands from 2020 through <br />2040 with a demand increase of six percent from normal demand with significant reserves held by <br />Metropolitan, local groundwater supplies, and conservation. <br />3.6.5 Multiple -Dry Year Period Reliability Comparison <br />Multiple -dry years are defined as three or more consecutive years with minimal rainfall within a period of <br />average precipitation. The water demand forecasting model developed for the OC Reliability Study <br />(described in Section 2.4.1) isolated the impacts that weather and future climate can have on water <br />demand through the use of a statistical model. The impacts of hot/dry weather condition are reflected as a <br />percentage increase in water demands from the average condition (1990- 2014). For a single dry year <br />condition (FY2013 -14), the model projects a six percent increase in demand for the OC Basin area where <br />the City's service area is located (CDM Smith, Final Technical Memorandum #1 of Orange County <br />Reliability Study, April 2016). It is conservatively assumed that a three -year multi dry year scenario is a <br />repeat of the single dry year over three consecutive years (FY 2011 -12 through FY 2013 -14). <br />The City is capable of meeting all customers' demands with significant reserves held by Metropolitan, <br />local groundwater supplies, and conservation in multiple dry years from 2020 through 2040 with a <br />demand increase of six percent from normal demand with significant reserves held by Metropolitan, local <br />groundwater supplies, and conservation. The basis of the water year is displayed in Table 3 -5. <br />arcadis.com <br />S B� w1 3-20 <br />