Characteristics of Snow Water Equivalent to Precipitation Ratios in Utah

Snow water equivalent (SWE) to precipitation (PCP) ratios have recently been used as evidence to support climate change. The assumption is that when a site or region's SWE to PCP ratio declines, temperature is a driving mechanism. In fact, there is a reasonable linear statistical relation between these two variables, but there may be other influencing factors involved in both the site and regional SWE to PCP relations. There are distinctly different physical phenomena occurring at land surface relative to the location of the orifice of a precipitation gage some distance above that surface, such as vegetation and wind direction, run and general velocity. There also is a large 'scale' difference in exposed area of data collection between a 3.05 meter diameter snow pillow and a 30.5 cm diameter precipitation gage. SWE to PCP ratios change throughout the snow accumulation season and SWE, in general, outpaces precipitation accumulation. Therefore, a SWE to PCP ratio analysis on some arbitrary date such as April 1 may have strong systematic bias. The result is that the overall magnitude of SWE in any given year may be a strong indicator of the eventual SWE to PCP ratio.