The roles of convective and stratiform precipitation in the observed precipitation trends in Northwest China during 1961–2000

• The annual precipitation has increased in the western region and decreased in the eastern region of Northwest China.
• The increase of the heaviest precipitation in summer dominates the annual increasing trend in the western region.
• The increase of the heaviest precipitation in summer in the western region is convective-dominated.
• The decrease of the heaviest precipitation in autumn dominates the annual decreasing trend in the eastern region.
• The decrease of the heaviest precipitation in autumn in the eastern region is stratiform-dominated.

Northwest China is one of the most arid areas in East Asia. Previous studies pointed out that some regions of Northwest China experienced a dry to wet climate change in the past half century. This study analyzed the observed daily precipitation during 1961–2000 in Northwest China. Results show that the annual precipitation in Northwest China has different trends in the western region and the eastern region. The western region has a significant increasing trend as shown in previous studies, while the eastern region has a decreasing trend. It is found that the increasing trend in the western region is caused by the increase of the heaviest precipitation in summer, while the decreasing trend in the eastern region is caused by the decrease of the heaviest precipitation in autumn. In order to find out the dominating precipitation type in the change of precipitation, a simple parameter is used to distinguish convective precipitation from stratiform precipitation. It is found that the increase of the heaviest precipitation in summer in the western region resulted from the increased frequency of convective precipitation, and the decrease of the heaviest precipitation in autumn in the eastern region was caused by the decreased frequency of stratiform precipitation.