Extrapolation of synoptic meteorological data in mountainous terrain and its use for simulating forest evapotranspiration and photosynthesis

Abstract

A model for calculating daily microclimate conditions in mountainous terrain is presented. Maximum–minimum daily air temperatures, precipitation, and dew point are extrapolated from valley stations to adjacent mountain slopes, after making elevation- and aspect-related corrections. The model (MT-CLIM) produces estimates of daily incoming shortwave radiation, air temperature, humidity and vapor pressure deficit, and precipitation for any mountain study site. MT-CLIM was tested against measured meteorological data on six study sites consisting of three north–south slope pairs in western Montana. Correlations between predicted and observed daily conditions on the six study sites for the period April–November 1983 were air temperature, R 2 = 0.88–0.92 with standard errors <0.48 °C; relative humidity R 2 = 0.63–0.72 with standard errors <15%; radiation R 2 = 0.60–0.78 with standard errors <100 W m−2. To test the utility of the model, data from MT-CLIM were used to run the DAYSTRANS/PSN model of evapotranspiration (ET) and photosynthesis (PSN) for western coniferous forests. Seasonal ET calculated from MT-CLIM data deviated by less than 5% from ET calculated from measured meteorological conditions on the six sites. Estimates of seasonal PSN agreed to within 10% of estimates derived from measured meteorological data on all sites except one. For each of the north–south slope study pairs, the combined MT-CLIMDAYTRANS/PSN simulation predicted that north slopes would have higher (5–31%) seasonal PSN than the comparable south slopes, which agrees with observed patterns of forest productivity in this semiarid region.