近58 a我国西北地区干期与湿期变化特征

Change characteristics of dry and wet spells in northwest China during the past 58 years

利用西北地区1960-2017年68个站点逐日降雨气象数据,分别将日降雨小于(大于等于)0.1 mm和1 mm定义为旱日(湿日),从干期和湿期变化特征的角度分析西北地区雨日年内分配变化。结果表明:西北地区东部年降雨量变化不明显,降雨频率下降,平均降雨强度增加;西北地区西部年降雨量、降雨频率和平均降雨强度均呈现增加趋势,平均降雨强度增加主要是由于降雨量增加速率快于降雨频率增加速率。结合干期和湿期变化特征,发现西北地区东部虽然干期旱日总数增加,但干期平均长度、干期次数和最长干期旱日数变化不明显,同时湿期湿日数和次数减少,说明西北地区东部在降雨量不变情况下,降雨更加集中。在西北地区西部,干期次数增加,但干期旱日总数、干期平均长度以及最长干期旱日数减少,湿期湿日数和湿期次数增加,湿期平均长度不变,西北地区西部在降雨量和降雨频率增加过程中,干期持续时间缩短,对该区域农业生产和生态环境有利。另外,使用不同阈值会影响特征值变化趋势大小及其显著性,甚至会得到相反的变化趋势,说明选择合理阈值对于研究降雨、干期以及湿期变化十分重要,需要结合区域气候特征进一步研究。

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.