Factors Affecting United States Geological Survey Irrigation Freshwater Withdrawal Estimates In Utah: Bureau of Reclamation Reservoir Levels Analysis Results

This Resource serves to explain and contain the methodology and results of the Bureau of Reclamation (BOR) reservoir levels freshwater supply key indicator analysis for my thesis. For more information, see my thesis at the USU Digital Commons.

Freshwater availability in the state can be summarized using streamflow, reservoir level, precipitation, and temperature data. Climate data for this study have a period of record greater than 30 years, preferably extending beyond 1950, and are representative of natural conditions at the county-level.

BOR reservoir level data are representative of major statewide surface water supplies. These data are available online and were downloaded as comma-separated files from the BOR website. For BOR reservoir levels, 1 June was selected to represent each water year. This date is towards the beginning of the summer irrigation season and typically after spring snow melt. When 1 June data were missing, the closest available adjacent date in June or May was chosen.

Freshwater availability key indicators were non-parametrically separated per temporal/spatial delineation into quintiles representing Very Wet/Very High/Hot (top 20% of values), Wet/High/Hot (60-80%), Moderate/Mid-level (40-60%), Dry/Low/Cool (20-40%), to Very Dry/Very Low/Cool (bottom 20%).
Each quintile bin was assigned a rank value 1-5, with ‘5’ being the value of the top quintile, in preparation for the Kendall Tau-b correlation analysis. These results, along with USGS irrigation withdrawal and acreage data, were loaded into R. State-level quintile results were matched according to USGS report year. County quintile results were matched with corresponding USGS irrigation withdrawal and acreage county-level data per report year for all other areas of interest. Using the base R function cor(), with the “kendall” method selected (which is, by default, the Kendall Tau-b calculation), relationship correlation matrices were produced for all areas of interest. The USGS irrigation withdrawal and acreage data correlation analysis matrices were created using the R ‘corrplot’ package, for all areas of interest.