7638 - Laserfiche WebLink

Home Browse Search

. . HaiJ. The ecological effects of hail have rarely been investigated; however, hail storms are common on the Colorado Plateau. Hailstones up to 4.5 cm in diameter have been reported, with tens of thousands of dollars of damage to crops, and occasional damage to homes (Rykaczewski 1981). Hailstorms tend to occur during the summer monsoon period (July through September) on the Plateau. FJooding. The Colorado River is a snowmelt river, and flooding is a ubiquitous form of disturbance in its riparian systems. Flooding is directly related to climate (see Chapter 4). Spring melt-off flooding and summer drawdown affect all aspects of water quality and fluvial ecology: backwater habitat availability, sediment transport, nutrient availability, turbidity, germination, and survivorship of riparian biota. The precipitation events that induce flooding therefore influence ecosystem processes. . . . Evaporation Evaporation rates are influenced by elevation, temperature and relative humidity. The arid Colorado Plateau has low ambient humidity and pan evaporation rates in excess of 2.3 m/yr characterize lower elevations. It has been estimated that riparian species, such as PopuJus fremontii, Tamarix ramosissima, and Prosopis gJanduJosa, transpire the weight of their foliage every hour at a temperature of 300 C (Davenport 1978). This evapotranspiration rate is considerably greater than that of exposed ground surface, and thus, the presence of riparian vegetation increases local relative humidity as well as increasing loss of water to the atmosphere. As an interesting aside, dense growth of riparian vegetation at low elevations may serve to reduce moisture stress on individual plants by protection from wind, increased humidity and reduced ambient temperature. This constitutes a unique form of beneficence. Wind . . . Persistent winds are common in the upper Colorado River drainage, seasonally' varying from the southwest in spring and summer to the north in winter. Winds contribute strongly to desiccation and occasionally damage crops and homes (Rykaczewski 1981), with speeds reported in excess of 160 km/hr. Strong winds are common at low elevations in the late winter and spring in the southern part of the region, while winter winds exert pronounced ecological impacts at high elevations in the northern section of the Colorado River basin. Annual wind data were compiled for Hanksville, Utah from 1948 through 1954 (Rykaczewski 1981). While this station was affected . . 18 .