Estimating source regions for snowmelt runoff in a Rocky Mountain basin: tests of a data‐based conceptual modeling approach

Abstract

In many mountain basins, river discharge measurements are located far away from runoff source areas. This study tests whether a basic snowmelt runoff conceptual model can be used to estimate relative contributions of different elevation zones to basin‐scale discharge in the Cache la Poudre, a snowmelt‐dominated Rocky Mountain river. Model tests evaluate scenarios that vary model configuration, input variables, and parameter values to determine how these factors affect discharge simulation and the distribution of runoff generation with elevation. Results show that the model simulates basin discharge well (NSCE and R >0.90) when input precipitation and temperature are distributed with different lapse rates, with a rain‐snow threshold parameter between 0 and 3.3 °C, and with a melt rate parameter between 2 and 4 mm °C−1 d−1 because these variables and parameters can have compensating interactions with each other and with the runoff coefficient parameter. Only the hydrograph recession parameter can be uniquely defined with this model structure. These non‐unique model scenarios with different configurations, input variables, and parameter values all indicate that the majority of basin discharge comes from elevations above 2900 m, or less than 25% of the basin total area, with a steep increase in runoff generation above 2600 m. However, the simulations produce unrealistically low runoff ratios for elevations above 3000 m, highlighting the need for additional measurements of snow and discharge at under‐sampled elevations to evaluate the accuracy of simulated snow and runoff patterns. Copyright © 2013 John Wiley & Sons, Ltd.

Large snowmelt versus rainfall events in the mountains

“…Jarrett and Costa [] noted that above the 2300 m elevation threshold in the Big Thompson River basin, rain does not contribute to flood potential and rainfall discharges per unit drainage area are very small. Kampf and Richer [] found that the majority of modeled runoff in the Cache La Poudre River watershed came from elevations higher than 2900 m, where there was persistent seasonal snow accumulation.…”

Transition of dominant peak flow source from snowmelt to rainfall along the Colorado Front Range: Historical patterns, trends, and lessons from the 2013 Colorado Front Range floods

“…The model uses a daily temperature threshold ( T s ) to estimate whether precipitation on each day is rain or snow. Snow water equivalent (SWE) accumulates in each grid cell if temperature stays below T s ; if temperature rises above T s , snow is melted using the product of temperature and a melt coefficient (α) [ Kampf and Richer , ]. This simple modeling approach was selected because it requires only precipitation and temperature as forcing data and has only two parameters ( T s and α).…”

“…Model tests and prior research [ Kampf and Richer , ] both found that SWE simulations were more sensitive to T s than to α, so we calibrated TopoWx simulations using varying values of T s and holding α constant at 3.0 mm d −1 ºC −1 . Calibrations were conducted for each grid cell containing a Natural Resource Conservation Service (NRCS) snow telemetry (SNOTEL) monitoring site (Figure ).…”

How Temperature Sensor Change Affects Warming Trends and Modeling: An Evaluation Across the State of Colorado

“…To evaluate the two homogenization methods, a simple temperature‐based daily SWE model was applied to see which homogenization algorithm resulted in a better simulation of SWE after the model was calibrated. This model only uses observations of average temperature (T) in degrees Celsius, precipitation (P) in millimeters, and two parameters as follows: where α is the melt coefficient parameter in mm/day/degree C, T s is the threshold temperature (average daily temperature) parameter separating rain and snow, and i indicates day (Kampf & Richer, ).…”