Microclimatic Characteristics of the Heihe Oasis in the Hyperarid Zone of China

The microclimate of a desert oasis in hyper-arid zone of China was monitored using micrometeorological methods and compared with those of areas adjacent to forested land. Differences in ground-level photosynthetically active radiation (PAR) on clear, cloudy and dust storm days and their subtending causes are analysed and discussed. Desert oases serve the ecological functions of altering solar radiation, adjusting near-ground and land surface temperatures, reducing soil temperature differences, lowering wind velocity, and increasing soil and atmospheric humidity. The total solar radiation in the interior of the oasis was roughly half of that outside a forest canopy. During the growing season, air temperatures in Populus euphratica Oliv. (poplar) and Tamarix ramosissima Ledeb. (tamarisk) forests were 1.62degC and 0.83degC lower, respectively than those in the areas around the forests. Furthermore, the taller the forest cover, the greater the temperature drops; air temperatures in the upper storey were greater than those in the lower storey, i.e., air temperature rose with increasing height. Over the growing season, the relative humidities of the air in the poplar and tamarisk forests were 8.5% and 4.2% higher, respectively, than that in areas around the forests. Mean wind velocity in poplar-forested lands was 0.33 m s^-1, 2.31 m s^-1 lower than that in the surrounding area. During dust storm days the PAR was significantly lower than on cloudy or clear days, when it was high and varied in an irregular manner.