7638 - Laserfiche WebLink

Home Browse Search

. . Chapter 3. Climate of the Colorado Plateau Introduction The climate of the Colorado Plateau is highly variable, changing temporally on hourly, daily, seasonally, annually, and geological scales, and spatially on microscale, synoptic (local), mesoscale (regional) and macroscale (global) levels (Schaefer and Day 1981J. Lying squarely in the "Horse Latitudes" between 34.50 and 42.5 north latitude, the weather is arid and continental. The jet stream (a core of wind in the troposphere with speeds in excess of 80 kmjhr), wanders latitudinally, directing the movement of turbulent cyclones (low pressure storm systems) and anticyclones (high pressure systems) that pass over the region on a seasonal basis. The transfer of thermal (solar) energy from the tropics northward and the rotation of the earth create prevailingly southwesterly winds, which are often turbulent on the Plateau during spring and autumn. Furthermore, the Colorado Plateau includes more than 4,000 m of topographic relief from the headwaters in the Rocky Mountains to the Grand Wash Cliffs in upper Lake Mead, and this topo~raphic relief exerts significant impacts on all climatic conditlons, including temperature, precipitation, snowfall, humidity, evaporation, and air movement. Temperature Temperature in the upper Colorado River drainage is regulated by latitude, elevation, intensity and duration of solar insolation, albedo, surface characteristics, vegetation cover, and energy exchange involved in water phase change, advection of air masses from tropic or polar sources, and vertical air movement (Rykacweski 1981; Schaefer and Day 1981). Plateau temperatures range from less than -500 C at higher elevations during winter to more than 500 C at lowest elevations during the summer (Table 4). Recording stations at higher elevations have a greater range between extreme temperatures (in excess of 450 C) as compared to those at lower elevations. For example, ambient temperatures in the Paria River drainage, which drains the south side of Bryce Canyon National Park, range from -330 to 330 C, while temperatures at the mouth near Lees Ferry range from -100 C to more than 460 C (Sellers and Hill 1974; Hereford 1984). Temperature variation is pronounced along the drainage in the bedrock constrained channels. Thermal radiation off canyon walls tends to keep air temperatures in narrow canyons warmer during the summer months. Exposure differences in sinuous canyons and subsidence of cold air from surrounding rims and highlands create strong thermal gradients in riparian channels. At low elevations in the Grand Canyon, Stevens (1989) reported increased species richness of perennial plants on south-facing slopes and higher channel terraces and attributed these patterns, at least . . . . . . . . 15 .