Surface Temperature Patterns and Lapse Rates: Implications for Water Resources and Studies of Mountain Climate Change

Abstract

Mountains are the water towers of the western United States, and some of the greatest concerns about climate change in this region involve snowmelt timing and water supply. A realistic description of how temperatures vary with elevation is crucial for models of basin-scale snowmelt and spring streamflow. However, measurements at high elevations are scarce, and studies of long-term temperature trends have reached strikingly different conclusions about whether the high mountains are warming faster or slower than the lowlands (Beniston et al. 1997; Pepin 2000). More high-frequency observations of the spatial and temporal variations of mountain temperatures are needed before these long-term trends can be fully explained. For example, observed surface temperatures vary diurnally, synoptically, and seasonally and only sometimes increase linearly with elevation. Local inversions and cold air drainage may make a long-term measurement site unrepresentative of temperatures across most of the surrounding topography.

Fortunately, small, low-cost temperature loggers can now be deployed at high densities incomplex mountain terrain. We use a prototypical array of over 40 such sensors in Yosemite National Park, California, combined with snow and streamflow measurements, to demonstrate the following:

1. how temperature patterns and lapse rates vary with synoptic weather conditions
2. how snowmelt patterns reflect recurring temperature differences
3. how spatial patterns of snowcover affect temperature.

Beniston, M., Diaz, H. F. and Bradley, R. S. 1997. Climatic change at high elevation sites: an overview. Clim. Change, 36, 233.

Pepin, N. 2000. Twentieth-century change in the climate record for the Front Range, Colorado, USA. Artic, Antarctic, and Alpine Res., 32, 135-146.