Abstract:

Northwest China has become warmer and wetter during the past several decades, which has profound influence on the fragile ecological environment. In this study, using the daily precipitation data of 68 stations in northwest China from 1960 to 2017, setting daily precipitation less than (greater than or equal to) 0.1 mm and less than (greater than or equal to) 1 mm as dry day (wet day), respectively. The distribution of precipitation during the year was analyzed based on indicators of dry and wet spells. The results show that in addition to the change of number of dry and wet days, the distribution of the dry and wet days also changes during the year. There are spatial differences in the change characteristic of rainfall, dry spells and wet spells in the northwest China. In the eastern part of northwest China, the total number of dry periods was increased, the number of dry spells and mean length of dry spells and maximum length of dry spells did not change significantly, while wet days and wet spells were decreased. In the absence of significant changes in rainfall in the region, the frequency of rainfall was decreased significantly and the average rainfall intensity was increased significantly. In the western part of northwest China, the increase of rainfall is caused by the increase of rainfall intensity and frequency. The characteristics of dry and wet period change show that wet days were more dispersed during the year, and the total number of wet days in wet spells and the number of wet spells were increased, while there was no significant change in the mean length of wet spells. On the other hand, the number of dry spells was increased and the mean length of dry spells and maximum length of dry spells were decreased, which could alleviate the drought condition in the western part of northwest China. Different from the long-term drought research, the distribution of dry days and wet days during the year were analyzed from the perspective of the change characteristics of dry and wet spells. By this way, the short-term water condition in these regions can be better demonstrated. In addition, the threshold of wet days and dry days have obvious influence on the results, which needs to be further studied according to the regional climate condition.

Key words: dry spell')">dry spell, wet spell; distribution of precipitation, threshold