TY - Generic T1 - Forecasting the Effects of Snow Drought on Streamflow Volumes in the Western U.S. T2 - 87th Annual Western Snow Conference Y1 - 2019 A1 - Joshua T. Sturtevant A1 - Adrian A. Harpold KW - climate change KW - NRCS KW - snow drought KW - streamflow KW - Water supply forecasting AB -

Mountain snowpack supplies critical water resources to natural ecosystems and downstream populations, particularly in semi-arid regions such as the Western U.S. Extremely low snowpack, or snow drought, can arise from inter-annual climate variability but is worsened by long-term declines in snowpack. Snow drought has negative implications for water availability as earlier, slower, and smaller snowmelt fundamentally changes runoff patterns including runoff efficiency and groundwater recharge rates. We explored the implications of snow drought on streamflow in the Western U.S. through the investigation of historical (1980-2014) observational data from the U.S. Geological Survey and Natural Resource Conservation Service for 59 watersheds. Our primary focus was evaluating the accuracy of April-July streamflow volume forecasts using the statistical method of Principal Component Regression (PCR). Early results indicate that forecast errors are highest during snow drought years, but that these errors vary across basins and are affected by precipitation received after the forecast issue date. We also show that forecast errors have a strong positive correlation with the inter-annual variability of runoff efficiency. Our objective is to refine statistically-based forecasting methods by introducing non-linearities into the forecast equations or subsetting the data into dry and wet years in order to improve streamflow volume forecasts during snow drought years.

JF - 87th Annual Western Snow Conference CY - Reno, NV UR - /files/PDFs/2019Sturtevant.pdf ER - TY - CONF T1 - Effects of Temperature on the Propylene Glycol/Ethanol (PGE) Solutions Used in Mountain Precipitation Gauges with the Polysorbate Emulsifier Additive T2 - 80th Annual Western Snow Conference Y1 - 2012 A1 - Lea, Rowyn A1 - Lea, Jon A1 - Lea, Jolyne KW - NRCS KW - precipitation gauge KW - propylene glycol/ ethanol (PGE) KW - SNOTEL AB -

The object of this study was to verify the earlier test to determine the temperatures at which various dilutions of equal proportions of propylene glycol and ethanol (PGE) with the addition of an emulsifier Polysorbate 20 (brand name Tween 20) would freeze. Earlier tests were conducted with straight mixture of 50 percent by volume of propylene glycol and 50 percent ethanol by volume without an emulsifier. This repeat study was to determine if the Tween 20 emulsifier had an effect on the freezing properties and specific gravity as tested in the earlier experiment. This experiment was also to observe if the 3 percent by volume Tween 20 would keep the 48.5 percent by volume propylene glycol and 48.5 percent by volume ethanol solution from separating at high temperatures which could occur at the remote site locations.

JF - 80th Annual Western Snow Conference PB - Omnipress CY - Anchorage, Alaska UR - sites/westernsnowconference.org/PDFs/2012Lea-R.pdf ER - TY - Generic T1 - Improved Estimates of Snow Water Equivalent at NRCS Aerial Markers Using New Statistical Methodology T2 - 80th Annual Western Snow Conference Y1 - 2012 A1 - Lea, Jon A1 - Sturm, Matthew A1 - Lea, Jolyne KW - aerial markers KW - Bayesian analysis KW - bulk density KW - climate (snow) class KW - NRCS KW - Snow water equivalent KW - SWE AB -

Natural Resources Conservation Service (NRCS) Aerial Markers snow depth data have been measured since the late 1940s and are located in remote areas of the West. These stations would typically take hours or days of ground travel to visit, so are measured by aircraft over-flights to get a monthly depth reading. This depth reading and an estimate of the snowpack density are used to estimate snow water equivalent (SWE) for use in water supply forecasting. The NRCS historically has used an empirical method described in the agency National Engineering Handbook (Davis, R. T., et al.) to calculate densities. Using Bayesian analysis technique, Sturm et al. developed densification parameters from worldwide snow pack data. With these parameters, the accuracy of the estimates of density can be improved using only the snow depth, day of the year, and climate class of the snowpack. These parameters were applied to a subset of data from February 1, 2012, NRCS Cooperative snow surveys where measurements of SWE and depth were measured. The density of the snow pack using the observed data was compared to the modeled density. Differences between the modeled and the measured densities were about 1%. With additional refinement, this method can be applied to depth readings throughout the NRCS Aerial Marker network to calculate SWE values in a consistent and repeatable fashion.

JF - 80th Annual Western Snow Conference T3 - Proceedings of the Western Snow Conference PB - Omnipress CY - Anchorage, Alaska UR - sites/westernsnowconference.org/PDFs/2012Lea-J.pdf ER -