Tendency of Dryness/Wetness over Northwest China in Recent 50 Years

A sort of drought index (DRI) is calculated in this paper to analyze the change of dryness/wetness in Northwest China during 1960-2005 by the use of 135 stations monthly data, processed by National Meteorological Information Center recently. Results show that warming aridification tendency is the main characteristic in Northwest China in recent 50 years; especially there is the most obvious warming aridification tendency in the eastern part of Northwest China. Although precipitation in most parts of Northwest China has significant increasing tendency, the dryness/wetness tendency in these regions is unmarked. This shows that the increasing precipitation cannot compensate the loss of water in soil due to the increasing of potential evaporation results from warming. It is noticeable that there are two areas in which the range of precipitation increasing is wider than the wetting range. The one area is the northwest part of Xinjiang; the other one is located in east and south of Qinghai. Being in these areas, the temperature has obvious warming, that means the warming can enhance the drought. In addition, the change cycle and trend of DRI is different from those of precipitation, and due to consider synthetically the temperature and precipitation, the DRI can be more objective than precipitation to reflect the change of dryness/wetness in Northwest China.