Analysis of Precipitation Differences and Their Local Causes in the Last 50 Years around the Qinling Mountains

Using daily precipitation data for more than 50 years around the Qinling Mountains from 54 meteorological observation stations, precipitation differences in this area of complicated terrain are analyzed, and their local causes are discussed. The results showed that: (1) The annual rainfall is generally high in the south and low in the north, and also high in the west and low in the east, which reflects the barrier effect of the Qinling Mountains and the influence of a westward return current of valley wind. (2) A reduction in yearly precipitation dominates the last 50 years; only nine eastern stations among the 54 exhibited increased precipitation. Further, the summer precipitation increased in most stations and decreased only in a few stations on the flat-topped ridge of the Qinling Mountains and in the western part. The precipitation obviously tends to be concentrated in the summer. (3) The yearly amounts and number of days with daily precipitation of less than 5 mm decreased obviously, and the number of days of daily precipitation greater than 50 mm clearly increased, suggesting an increase in heavy rain and a decrease in light rain. (4) All of these results in the precipitation variation, as well as the precipitation variation with latitude and longitude, reflect the facts that aerosols inhibit orographic precipitation and that ice formation may restore at least some of the inhibited precipitation, which suggests that aerosols play an essential role in the local causes of precipitation differences. (5) The topographic effect and regional energy balance are also important factors in the precipitation differences.