USING DAILY STREAM RECORDS TO EVALUATE STREAM TRENDS IN WISCONSIN

In 2012 a study was completed examining annual streamflow records in the state of Wisconsin. Statistical analysis of historical discharge records over 50 years illustrated spatial variability in streamflow trends; these findings largely mimicked suggested trends in precipitation in a study that was published by the “Wisconsin Initiative on Climate Change Impacts.” The current study proposes an augmentation to the prior and argues that streamflow trends can be more accurately examined using daily discharge records rather than annual. For this reason a study was devised to analyze daily averages (at least 18,260 records) instead of annual (at least 50 years of records) per location. In addition, the study examined trends over numerous short and long term time intervals (2011-1987, 2011-1962, 2011-1937, 1986-1962 and 1961-1937) and compared trends in average daily flow with annual high and low flow rates (90^th and 10^th percentile) to decipher where permutations may be occurring within each river. Statistical approach required each gaging station to have complete records for each segmented time. Data was analyzed for significant trends using the Mann-Kendall equation as done prior. The juxtaposition of these studies shows similarities and difference, questioning statistical approaches to trend analyses. Suggestive cause to the adverse findings is the re-interpolation of all the data points that influence and constitute a calculated annual value. By employing these values on a daily basis, all measurements can affect the regression equation for the time period of interest. Viewing what is considered to be a more accurate representation of discharge trends shows clear spatial and temporal patterns in streamflow exist across Wisconsin.