Big Wood Basin - 1980-2009 Historic Trends
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This page highlights historic temperature, precipitation, snow, and streamflow trends from 1980 to 2009.

Data Sources

Historic temperature and precipitation trends were identified using data from what is referred to as METDATA (Abatzoglou, 2013) from the University of Idaho (see http://maca.northwestknowledge.net/ - Training Data for additional information). By incorporating METDATA in the Envision model, we were able to extrapolate the specific Big Wood study area which also allowed us to analyze historic trends for different elevation ranges.

Historic snow data shown here were obtained by the USDA Natural Resources Conservation Service (NRCS) Snow Survey Office in Boise, Idaho. The NRCS calculates a monthly “snow index” for the Big Wood Basin based on 7 Snowpack Telemetry (SNOTEL) monitoring sites that are within or very close to the drainage boundary. We used the April snow index, which is the sum of snow water equivalent on April 1 of each year at the following SNOTEL locations: Chocolate Gulch, Dollarhide, Galena, Galena Summit, Hyndman, Lost Wood Divide, and Vienna Mine. We show data from the entire period of record, which goes back to 1961

Lastly, the streamflow data records analyzed here were obtained for USGS gaging stations 13139510 (Big Wood River at Hailey Id) and 13141500 (Camas Creek Nr Blaine Id). These are daily average flow rates passing by the gage.

Air Temperature

In the Big Wood Basin, air temperature varies by elevation. The lower elevations are, on average, 10°F warmer than the higher elevations. The following chart shows the 1980-2009 average annual air temperature in the study area for three elevation ranges. The solid lines represent the 10-year average value (for example, the value of the blue line at 1980 (48.1°F) is the average annual temperature from 1980-1989 for all areas in the study area less than 4,000 feet in elevation). The shaded bands indicate the variability from that average during the decade (for example, looking at the blue band during the 1980s, the lowest annual temperature was 44.4°F and the highest was 50.5°F).

Although the data show annual variability of up to 5-6 degrees, on average the air temperature across the study area has increased over this time period by 1.5°F. The lower elevations have increased the least (1°F), the mid-elevations by 1.3°F, and the high elevations have increased the most (2.3°F).

Average Annual Temperature by Elevation Range, 1980-2009. This figure shows the ten-year average annual temperature by elevation zone (solid lines). The shaded area indicates variability from the average.

Precipitation

Precipitation in the Big Wood Basin is also highly dependent on elevation with the higher elevations receiving the most precipitation. Precipitation shows a high degree of variability from year to year. The chart below shows the average annual precipitation in the study area for three elevation ranges from 1980-2009. Over this period, the lower elevations received anywhere from 6-17 inches of precipitation; the mid elevations received from 8-22 inches, and the higher elevations from 17-37 inches in a year. The solid lines indicate the ten-year average precipitation value, with the shaded bars indicating the variability from that average.

It is important to take into account the large annual variability seen in the past; however, looking at 10-year decadal averages, the basin received nearly 15% less precipitation in the 2000-2009 decade than 1980-1989. On average, in the decade 2000-2009, lower elevations received 1.6 inches less precipitation than in 1980-1989; mid-elevations 2.3 inches less; and higher elevations 4.1 inches less.

Average Annual Precipitation by Elevation Range, 1980-2009. This figure shows the ten year average annual precipitation by elevation zone (solid lines). The shaded area indicates variability from the average.

Snow Water Equivalent

In the Big Wood Basin, as in many river basins in the Western United States, most of the annual precipitation falls during the winter months yet the highest demands for water use are seen in the summer and fall. Ideally, river basins have the capability to store water from the wet season until it is needed. The largest storage of water in the Big Wood Basin occurs naturally through the annual snowpack. Here, we analyzed the April 1 Snow Index from the USDA Natural Resources Conservation Service Snow Survey Office in Boise, Idaho (see description above under Data Sources). These data were available as far back as 1961.

Considering the variability in annual precipitation, it is not surprising that the snowpack is also variable. As a water user or manager, it is very important to consider this variability; however, in general, the 10-year average April 1 Snow Index decreased from about 155 in the 1960s to about 123 in the 2000-2009 decade.

Big Wood above Hailey April 1 Snow Index, 1961-2009. The snow index is the sum of snow water equivalent at 7 different SNOTEL gages in or near the watershed boundary. Data from USDA NRCS Idaho Snow Survey Office.
Historic SWE

Quantity and Timing of Surface Water

Two metrics that water users are generally interested in are the quantity of water available in a given time period and the timing of the water, or when it flows through the river system. Timing can be measured in many different ways, but here we consider timing of peak flows and the center of timing.

The chart below shows daily streamflows averaged over the time period 1980-2009 for two different locations where USGS stream gages are present. The data are shown by water years, which run from October 1 to September 30. Over that period, peak flows for the Big Wood River at Hailey generally occurred around May 29, but occurred as early as May 8 and as late as June 18. Date of peak flow for Camas Creek near Blaine ranged from February 25 – May 20, with the average peak flow occurring on April 4.

Average Daily Streamflow – Big Wood River at Hailey and Camas Creek near Blaine, 1980-2009. Data from USGS.

The center of timing (CT) refers to the point in time at which half of the annual streamflow has passed a certain location. It is usually measured over a water year (October to September). Looking at the historic center of timing for the Big Wood at Hailey by decade shows no clear trends. During the 1980s, CT varied by 10 days averaging around May 24. In the 1990s, CT varied slightly less (7 days) but on average occurred 8 days later (June 1). Between 2000-2009, CT showed the largest variability of 19 days and the average (May 23) was similar to the 1980s.

Decadal range and average center of timing (CT) of streamflow for Big Wood at Hailey. Data from USGS.
DecadeEarliest CTLatest CTAverage CT
1980-1989May 19May 29May 24
1990-1999May 27June 2June 1
2000-2009May 10May 28May 23

Center of timing for streamflow at Camas Creek near Blaine does not show any clear changes in the historical period either. The decadal variability of CT reduced slightly from 23 days in the 1980s to 19 days in 2000-2009. The average CT in the 1980s was on April 9 while the last two decades both averaged April 13.

Decadal range and average center of timing (CT) of streamflow for Camas Creek Nr Blaine. Data from USGS.
DecadeEarliest CTLatest CTAverage CT
1980-1989March 29April 20April 9
1990-1999April 2April 23April 13
2000-2009April 4April 22April 13

Total annual streamflow is a measure of the volume of water passing by a certain location over a water year (October – September). The chart below shows total annual streamflow for two locations: the Big Wood River at Hailey and Camas Creek near Blaine from 1980-2009. Total streamflow fluctuates greatly from year to year based on the amount of precipitation. The driest year in this historic period for the Big Wood at Hailey was 1994 which saw about 147,800 ac-ft of water pass the streamgage and the wettest year was 1983 when over 609,500 ac-ft of water passed. In Camas Creek, the driest year was 1992 when around 11,000 ac-ft passed the Camas Creek near Blaine gage and the wettest year was 1983 when nearly 325,000 ac-ft passed.

Total annual streamflow volume – Big Wood at Hailey and Camas Creek near Blaine, 1980-2009.

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