Rural Water - Quarter 2, 2008 - (Page 21) Hotels in Las Vegas waste water in elaborate fountains, despite the high evaporation rate in Nevada. A drought is a period in which there below-average is below-averag precipitation and replenishment of surface and ground was ter supplies. The key word here is “avsignifi erage.” The sign cance of an average depends on the length of time during which measurements are taken. Periodmeasurem icity in precipitation over time is considprecipita ered normal; we don’t question the lack of precipitation during summer months in Nevada. The longer-term variations in climate patterns due to El Nino or patte episodes of sunspot activity are also sun becoming understandable, somewhat unde therefore “normal.” Recpredictable and t longer-term periodicity is ognition of lon lack of records. hampered by a l The allocation of water in the Coloallocatio rado River between Nevada, California betw and Arizona was based on an average wa annual flow determined over what is now recognized as a wet period. Recordkeeping since then indicates that the period on which the flow allocation was based was not “normal,” and the interval over which the average flow should have been determined needed to be longer. The decline in the flow of the Colorado is not due to a drought but to human perceptions. According to writer Mike Davis, “Regional watersource planning has been based upon a 140-year rainfall record that, according to most paleoclimatologists, is one of the most anomalously wet periods in the last 4,000 years” (Emerson, 2002). There are, however, indications that real droughts – extreme variations from normal – have taken place. Various sources of evidence indicate that the American Southwest experienced a prolonged drought around 1300, making agriculture impractical. Records indicate that a severe drought affected the Jamestown settlement from 1606 to 1612 (Emerson, 2002). In the 1890s, 1910s and 1930s, major droughts led to widespread crop failures across the Great Plains (Burroughs, 2003). Nevada State Climatologist Jeff Underwood suggests that precipitation and ©www.ostockphoto.com/Vlad Sadovsky drought considerations in Nevada need to be evaluated on a basin-to-basin basis. Some basins in the state experience normal precipitation during years in which other basins do not. In addition, heavy snow years in one state, such as Colorado, mean low snow years in another state, such as Nevada. Favorable winter storm tracks in both areas are unlikely in the same year. It’s important to understand the difference between a drought and an arid climate. In places like the Great Basin, geological indications are that the climate was wetter 5,000 years ago and even temperate as much as 10,000 years ago. Ancient rock art in the Sahara des- ert shows hippos in the region, but no one would imply that the Sahara is presently experiencing a drought. The climate west of the Mississippi has not changed radically in the last hundred years. Pioneers crossing the Great Plains considered it a desert then, before they discovered that water could be drawn out of the ground with metal straws. >>22 Nevada State Climatologist Jeff Underwood suggests that precipitation and drought considerations in Nevada need to be evaluated on a basin-tobasin basis. Second Quarter 2008 • 21 ©www.istockphoto.com/Harry Hu
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