Wang Runyuan

Climatic changes of semi-arid region over the northwest China in recent 50a.

Using 33 stations temperature,precipitation,relative humidity,wind speed,evaporation in the semi-arid region of Northwest China from 1951 to 2004,some new characteristics of climatic changes were posted in virtue of statistics method.The result shows that precipitation displayed a descendant tendency in most areas of the semiarid region in Northwest China,the tendency rate was -59.168～-1.143 mm/10a,its maximum descendant tendency was in autumn and the second one in spring,but it displayed an ascendant tendency in some areas in summer and in most areas in winter,3a and 6～8a period was existed,whereas 3a period of oscillation was the strongest,as its centre during the period from 1962 to 1966,and 3a period of oscillation began to weaken from 1966,6～8a period of oscillation was the strongest,as its centre during the period from 1980 to 1985.The temperature showed an ascendant tendency,the tendency rate was 0.074～0.507℃/10a,it displayed anti-parabola type in most areas,and turning point was from the earlier stage of 1960s to the later stage of 1970s,its ascendant tendency was maximum in winter,the second one in spring and autumn,except for the common boundary of Shaanxi, Gansu and Ningxia Province,which showed a descendant tendency.The precipitation displayed a descendant tendency, whereas the temperature showed an ascendant tendency,which resulted in climate warming and drying in the semi-arid region of Northwest China.The relative humidity showed a wavelike variation.Evaporation also showed an ascendant tendency except for some individual areas in recent 50a.

An Assessment of Storage Terms in the Surface Energy Balance of a Subalpine Meadow in Northwest China

The heat storage terms in the soil-vegetation-atmosphere system may play an important role in the surface energy budget. In this paper, we evaluate the heat storage terms of a subalpine meadow based on a field experiment conducted in the complex terrain of the eastern Qilian Mountains of Northwest China and their impact on the closure of the surface energy balance under such non-ideal conditions. During the night, the average sum of the storage terms was −5.5 W m−2, which corresponded to 10.4% of net radiation. The sum of the terms became positive at 0730 LST and negative again at about 1500 LST, with a maximum value of 19 W m−2 observed at approximately 0830 LST. During the day, the average of the sum of the storage terms was 6.5 Wm−2, which corresponded to 4.0% of net radiation. According to the slopes obtained when linear regression of the net radiation and partitioned fluxes was forced through the origin, there is an imbalance of 14.0% in the subalpine meadow when the storage terms are not considered in the surface energy balance. This imbalance was improved by 3.4% by calculating the sum of the storage terms. The soil heat storage flux gave the highest contribution (1.59%), while the vegetation enthalpy change and the rest of the storage terms were responsible for improvements of 1.04% and 0.77%, respectively.