Abstract
Abstract Precipitation phase determination is a known source of uncertainty in surface-based hydrological, ecological, safety, and climate models. This is primarily due to the surface precipitation phase being a result of cloud and atmospheric properties not measured at surface meteorological or hydrological stations. Adding to the uncertainty, many conceptual hydrological models use a 24-h average air temperature to determine the precipitation phase. However, meteorological changes to atmospheric properties that control the precipitation phase often substantially change at sub-daily timescales. Model uncertainty (precipitation phase error) using air temperature (AT), dew-point temperature (DP), and wet-bulb temperature (WB) thresholds were compared using averaged and time of observation readings at 1-, 3-, 6-, 12-, and 24-h periods. Precipitation phase uncertainty grew 35–65% from the use of 1–24 h data. Within a sub-dataset of observations occurring between AT −6 and 6 °C representing 57% of annual precipitation, misclassified precipitation was 7.9% 1 h and 11.8% 24 h. Of note, there was also little difference between 1 and 3 h uncertainty, typical time steps for surface meteorological observations.
Highlights
An essential question for all cold region hydrological models is: was the precipitation mass in the form of rain, snow, or a mix of the solid and liquid phase (Harpold et al b)? To answer this question, hydrologists have used precipitation phase determination schemes (PPDS) in their surfacebased conceptual models
Observations with air temperature (AT), dew-point temperature (DP), and wet-bulb temperature (WB) between À6 and 6 C accounted for 57% AT and 63% DP and WB precipitation observations in each of the 1, 3, 6, 12, and 24-h datasets
Harpold et al ( b) stated in their review that PPDS accuracy is generally increased at finer timescales and or with the inclusion of RH data
Summary
An essential question for all cold region hydrological models is: was the precipitation mass in the form of rain, snow, or a mix of the solid and liquid phase (Harpold et al b)? To answer this question, hydrologists have used precipitation phase determination schemes (PPDS) in their surfacebased conceptual models. An essential question for all cold region hydrological models is: was the precipitation mass in the form of rain, snow, or a mix of the solid and liquid phase (Harpold et al b)? In the Scandinavian Peninsula, 41.77% of annual precipitation occurred with air temperatures (AT) À3 to 5 C in Norway, and 38.49% in Sweden with station maximum and minimum of 61.12% and 20.08%, respectively (Grigg et al ) This abundance of precipitation occurring in near-freezing temperatures leads to a fair amount of precipitation phase uncertainty within conceptual models. Conceptual hydrological models often use a set TRS calibrated over a large area regardless of changes in physiography, vegetation, or other characteristics that may affect local/regional average atmospheric conditions (Grigg et al ). The misclassified precipitation findings from this climatological study should translate to model uncertainty when applied in a cold region hydrological model
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