Testing the PRISM Temperature Model in Complex Terrain: Implications for Mountain Ecohydrology

Abstract:

Studies in mountainous terrain related to ecology and hydrology often use interpolated climate products because of a lack of local observations. One dataset frequently used to develop plot-to-watershed scale climatologies is the PRISM (Parameter-elevation Regression on Independent Slopes Model) temperature model. Benefits of this approach include geographically-weighted station observations and topographic positioning modifiers, which become important factors for predicting temperature in complex topography. Because of the paucity of long-term climate records in mountain environments, validation of PRISM algorithms across diverse regions remains challenging, with end users instead relying on atmospheric relationships derived in sometimes distant geographic settings. Recent developments of the PRISM model have increased temporal resolution capability from monthly to daily, which in turn has allowed a reasonable test of PRISM performance during a single season at distributed points across a large watershed. Presented are results from testing instrumental observations of daily max/min temperature on 16 sites in the Walker Basin, CA-NV, located on open woodland slopes ranging from 1967 to 3111 m in elevation. Individual site MAE varies from 1.34 to 4.22 C with better performance observed during summertime as opposed to winter. We observe a consistent bias in minimum temperatures for all seasons across all sites, with bias in maximum temperatures varying with season. Model error for minimum is associated strongly with elevation, whereas model error for maximum is associated with topographic radiative indices (solar exposure and heat loading). These results indicate that actual temperature conditions across open mountain woodland slopes are more heterogeneous than interpolated models (such as PRISM) indicate, which in turn impacts prediction/modeling of landscape processes such as ecological niches, bioclimatic refugia, and snow hydrology.