Characteristics of the Climate Change in West China in Recent 50 Years

Using the surface observational data and upper air data from 1951 to 2000 at 194 stations in China, the inter annual and inter decadal characteristics of climate in West China are analyzed. The results show that in the middle of 1970s, an evident climate sudden change happens to yearly average surface temperature, air temperature, precipitation, total cloud amount, low cloud amount and solar radiation. There is a rising trend of the annual mean temperature in West China. The most evident warming occurs in Hetao and Xinjiang regions; in Tibet and Hexi regions warming is also evident, and in Southwest China the warming trend is less evident. The surface temperature changes in the same trend of the air temperature, and its variation is more significant. Particularly, the surface temperature in West China is getting higher since the middle of the 1970s, but it doesn't reach the level of that in 1950s, therefore shows a dropping trend in linear from 1951 to 2000. Annual mean precipitation takes on a rising trend all the regions in West China except for Hetao region, and the largest increase of rainfall occurs in Xinjiang and Tibet regions. Both the annual mean and season mean rainfall increases significantly in Xinjiang and Tibet regions, and the annual mean precipitation in 1990s increases 50% than that in 1950s. The precipitation in Xinjiang region keeps increasing in every season particularly in winter. Actually the precipitation is nearly zero in winter before 1978(except 1950s), and it begins to grow after that. The total cloudiness and the low cloudiness decrease linearly in West China in recent 50 years. The decreasing trends of annual mean low cloudiness are observed in all the areas, with the most remarkable decreasing rate in Hetao region and Southwest China, especially in Hetao region where the rate is -1.7%/10 a. In Xinjiang region the cloudiness hasn't decreased much. The total radiation drops over the west regions, particularly in Tibet region. The change of solar direct radiation in the whole areas in West China is similar with that of total radiation. The southwest region experiences an increasing trend in solar diffuse radiation, while a dropping trend in the other four areas and the most evident decreasing occurs in Xinjiang and Tibet regions. The cloud amount and aerosol consistency have a close connection with solar diffuse radiation. In Southwest China, the solar diffuse radiation decreases as the cloud amount increases, so it's guessed that the decreasing of solar diffuse radiation is caused by the increasing of aerosol consistency.