Surface temperature adjustments to improve weather radar representation of multi-temporal winter precipitation accumulations S.R. Fassnacht * , N. Kouwen, E.D. Soulis Department of Civil Engineering, University of Waterloo, Waterloo, Ontario, Canada, N2L 3G1 Received 20 October 2000; revised 7 June 2001; accepted 12 June 2001 Abstract Hydrologists and water resources managers who work in areas that receive a signi®cant portion of the annual precipitation in the form of snowfall rely on good approximates of snow accumulation in order to assess snowpack volumes for snowmelt stream¯ow estimation. Weather radar rainfall estimation has been used for hydrological modelling and radar has been used for the estimation of snowfall from individual events, yet radar has rarely been used to measure snowfall accumulation over time periods longer. Snowfall estimates for weekly, monthly, and seasonal accumulation periods have been compared to measured Nipher-shielded Belfort precipitation gauge quantities. A local scaling issue that caused overestimates is discussed. To enhance the accumulation estimates, the conventional scan radar images were adjusted using the near surface air temperatures. The adjustment for mixed precipitation improved the accumulation estimates, while the subsequent particle shape adjustment for snow crystal shape did not further enhance the radar estimates. q 2001 Elsevier Science B.V. All rights reserved. Keywords: Snowfall; Snow accumulation; Weather radar; Mixed precipitation; Snow particles 1. Introduction Ground based weather radar is often used to estimate precipitation since it can provide maps of precipitation that are not readily produced from precipitation gauge data. There are also problems associated with measurement by gauges, especially the undercatch of snow due to wind Goodison et al., 1998). Radar precipitation measurement has its own problems Collier, 1996). However the distribu- ted estimates can be used to determine current condi- tions in a watershed and radar rainfall estimates can be used for stream¯ow forecasting Kouwen, 1988; Finnerty et al., 1997). During the winter, individual storms are usually not hydrologically in¯uential, as snowfall tends to accumulate over time. Thus the estimate of the volume of water stored in the snow- pack is crucial information for hydrologists and water resources managers Wright and Wright, 1991). Therefore in this study the emphasis is on the accu- mulation of snow over time. The seasonal, monthly and weekly accumulations of snow at several locations, as measured by precipitation gauges, are compared to the precipitation estimates for the winter period derived from ground-based weather radar imagery. A method is described to provide post- processing adjustments to the radar imagery to Journal of Hydrology 253 2001) 148±168 www.elsevier.com/locate/jhydrol 0022-1694/01/$ - see front matter q 2001 Elsevier Science B.V. All rights reserved. PII: S0022-169401)00479-6 * Corresponding author: now at Department of Hydrology and Water Resources, University of Arizona, Tucson, AZ 85721- 0011, USA. Tel.: 11-520-626-8522; fax: 11-520-621-1422. E-mail address: srfassna@hwr.arizona.edu S.R. Fassnacht).