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There is a high degree of interannual variability in precipitation within the Great Salt Lake Basin. In addition, the precipitation distribution is not normal, with bimodal tendencies toward wet or dry periods.

The interannual variability in precipitation at a station located in Salt Lake City is shown below. The first figure shows that total annual precipitation can vary to a huge degree from year to year, and that annual precipitation values tend to be located either above or below the average, with fewer years located near the average value (shown as the horizontal red line). The second figure is a histogram of the annual precipitation values for this location, which again accentuates this pattern.

Total Annual Percipitation from 1950-2004

Distribution of Annual Percipitation Precipitation data from Salt Lake City NWSFO, Utah (427598)
Source: Western Regional Climate Center

The annual variability in precipitation illustrated in these figures is common throughout the Great Salt Lake Basin and has profound effects on the availability of water for municipal and agricultural use from year to year as the region moves from wetter periods to periods of drought. The ecosystems of the Great Salt Lake Basin are also affected to a great degree, as streamflow and water levels in the Great Salt Lake and major water storage reservoirs rise and fall in response to changes in annual precipitation.

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