Chelsea Decker and Dr. Matthew Bekker, Geography Department
The arid and heavily populated Wasatch Front in Utah is dependent on streamflow from snowmelt. Historical records of streamflow go back about 100 years but this is insufficient to provide a complete picture of streamflow variability in the area. Water managers would greatly benefit from a more extensive record of streamflow in the area to adequately plan for future population growth along the Wasatch Front.
The Wasatch Dendroclimatology Research (WADR) Group, including researchers from Brigham Young and Utah State Universities, has begun a campaign to reconstruct streamflow from tree rings for several Wasatch Front rivers. Several sites in the area have been sampled and new chronologies have been developed to provide more data for the Wasatch Front.
By taking these unpublished chronologies and the chronologies from the International Tree-Ring Data Bank, we show correlations between these moisture sensitive sites and the Provo and Weber Rivers.
Highcorrelations indicate which chronologies are potential candidates for inclusion as predictors of streamflow for use in reconstruction models. We have mapped the correlations using isolines to highlight areas where the tree ring chronologies have a strong relationship with streamflow records.
To determine which chronologies to include in this analysis, we used a 200 mile radius from the headwaters of the Provo and Weber Rivers. We then decided to include chronologies that were developed using drought sensitive trees.
The species we included were singleleaf pinyon pine, pinyon pine, douglas fir, rocky mountain juniper, Utah juniper, and ponderosa pine.
We took the raw measurements from all of the chronologies that corresponded to these requirements and ran them through Arstan using the same detrending methodology for each site. We took the standard measurements from the Arstan results and used these to calculate the correlations between tree ring width and the Provo and Weber River streamflow records.
We created a map of high and low correlation regions through inverse distance weighted interpolation from our 39 sites.
Results and Discussion
Below are the two maps that were created, Provo and Weber Rivers. We noticed that higher correlations were shown in an east – west pattern across the Wasatch front.
The darker areas on the maps show where the correlation between the site chronology and the river were highly correlated. As we expected, the sites close to the headwaters show high correlations with the streamflow records. A few high-elevation Douglas Fir sites exhibit low correlation values despite their proximity to the headwaters. Future studies should include elevation as a third dimension in the spatial analysis.
Our results indicate that the relationship between tree ring chronologies and streamflow data is subject to distance decay, particularly in distance North and South of the river headwaters, while the relationship remains strong at great distances East and West.
This knowledge can assist the WADR Group and others in determining where additional tree ring samples can be taken to strengthen streamflow reconstruction models.
With this research project I was able to put together a poster to present at the Annual Association of American Geographers Conference in April 2013 held in Los Angeles. The Geography Department came to the conference with several students presenting research that contributed greatly to the conference.
This research, in particular, is part of a bigger project that Dr. Bekker has been involved in along with me and his research assistants. Our maps can provide insight into our next sampling sites.