Annual mesoscale study of water balance in a Great Basin heterogeneous desert valley

We studied the annual mesoscale water balance in northeastern Nevada, USA, in a Great Basin heterogeneous semi-and desert valley (the Goshute Valley) at 40 degrees 44'N, 114 degrees 26'W, with elevation of 1707 m above mean sea-level. This north-south-oriented flat valley has an area of about 1113 km2 and is partially covered mostly by sagebrush, greasewood, shadscale, desert molly, cheatgrass. and winter fat bushes. Five Bowen ratio stations measured the incoming and outgoing (reflected) solar radiation, net radiation, air temperatures and moisture at 1 and 2 m, the aggregated (soil + vegetation) surface temperature, wind speed and direction at 10 m, soil heat flux at 8 cm (three locations at each station), soil temperatures at 2 and 6 cm above each soil flux plate, and precipitation every 5 s averaged to 20 mm throughout the valley from 1 May 1993 to 30 September 1994. Locations of stations were based upon the vegetation types and percentage of coverage by bushes. The topsoil (10 cm) moisture content was measured either by time domain reflectometer or gravimetric method at least once a week. We used the Bowen ratio energy balance (BREB) method for the measurement of 20 mm evapotranspiration throughout the experiment. During the dry water year 1993-1994 (beginning from 1 October) the average amount of aggregated (soil + bushes) evapotranspiration (ETa) among stations measured by the BREB method was almost equal to the average total precipitation for the entire valley (160.9 mm vs. 157.7 mm, respectively). Variations of precipitation among stations (ranging from 173.7 mm at Station 2 to 130.5 mm at Station 1) were attributed to winter orographic effects and summer thermal lows. ETa ranged from 181.2 mm at Station 3 to 142.7 mm at Station 2. Variations were related mostly to vegetation types and percentage of the soil coverage. All stations showed slight water losses (ETa greater than precipitation) in the dry water year 1993-1994, except at Station 2, where water gain was about 31.1 mm. The 1993-1994 water losses at Stations 1, 3, 4 and 5 were 29.7 mm, 7.5 mm. 8.1 mm and 2 mm, respectively. The additional water for the process of evapotranspiration at these stations may be due to extraction of moisture from the air during the cool early mornings throughout the water year or to extraction of moisture from the soil. A set of relationships between the incoming solar and net radiation, surface and 2 m air temperatures, and surface and 8 cm soil heat fluxes among stations was also developed. This study showed how the mesoscale water balance was achieved during a dry water year in a desert valley. The findings could be applied to similar valleys.