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<br /> . ....,._- '_u.""""""''''''~<t.',..\,. "....... <br /> I 5 ,I.~- 2.4- <br /> annual average temperature did not vary by more than 10F from its average of 70J"F and <br /> never had II difference greater than 3"F. Although greater dif:fcrcnces are.expe;. ienccd on <br /> II month-to-montb basis, they tend to average out over the year. This stability CI,~ates <br /> stability in annual water demand. Exhibit 5 plots temperature against montbJy Wlli':r-USe <br /> over 1975 to 2001. Water use and temperature are highly correlated. <br /> Annual rainfall, in contrast, is much more variable. However, rain tends to fall in the <br /> winter and early spring months when temperatures md iIrigation demands are relatively <br /> low. Hence, rainfall variability docs not tend to greatly impact annuaJ water demands.. <br /> Rainfall has a much bigger impact on water supply (Hc:tcb Hetchy) than demand. <br /> Our model colTClating water use with weather was specified to measure the deviations in <br /> water use (as shown in ExhibitS) from deviations in normal temperature and rainfall as <br /> follows: <br /> 12 <br /> WATERt = raix MONTHi,t+ {JIxTEMPDEVt + fJ2xRA1NDEVt <br /> /.l <br /> where, <br /> WATERt .. ratio ofWlltCr\lSe in montbttoa 12-rnonth moving avera,gc ofWATERt <br /> MONT Hi,! '" binary variable CI'C8ting one unique a intercept for each calendar month <br /> TEMPDEV/ ... temperature deviation in month t from the average for that month ("F) <br /> RAINDEVt =- rainfall deviation in month t from the average for that month (incbcs) <br /> ai, pI, fJ2 ... coefiicientscstimated using least squares regression <br /> After estimating the mode~ we used actual weather data from 1949 to 2001 to simulate <br /> the maximum impacts on annual water use. From tbi$ exeIcise, we determine that water <br /> use can be expected to vary +/- 2 percent from weather alone on annual basis. <br /> Page 8 <br /> _~..~._'. ."_'''M'~'_~.._..__'' ..,..._..'.~",~ "- <br />