近57年中国北方气候干湿变化及与太平洋年代际振荡的关系

Relationship of Dry-Wet Climate Changes in Northern China in the Past 57 Years with Pacific Decadal Oscillation(PDO)

利用中国北方424个气象站点1960—2016年逐日地面观测资料,应用联合国粮农组织(FAO)Penman-Monteith模型计算潜在蒸散(ET0),基于降水量和潜在蒸散计算的湿润指数研究了1960—2016年中国北方干湿气候时空变化特征,分析了太平洋年代际振荡(PDO)对气候干湿变化的影响。结果表明:北方总体干湿变化不显著,空间上表现为西北、青藏高原、内蒙古湿润化而华北干旱化的特征。极端干旱区面积显著缩小,干旱区、半干旱区则明显扩张,表明气候敏感区域在扩张。极端干旱区和干旱区显著变湿润,半干旱区有变湿润的趋势。1960—1990年至1991—2016年,北方经历了变湿润的过程。西北西部、青藏高原湿润化趋势明显,极端干旱—干旱区的界线呈西界东移、南北界线收缩的变化。干旱化趋势主要发生在华北和东北部分地区,华北黄河沿线一带半干旱—半湿润区界线向东南方向扩张。东北中部和西北西部由于降水增加而ET0减少,气候变湿润。华北中西部、内蒙古东部和东北部分地区降水减少、ET0增加,气候变干旱。在PDO暖位相,西北、东北北部及内蒙古东部地区地表气候偏湿润;在PDO冷位相,地表气候偏干旱。而华北则相反。

【Objective】Global warming has caused heterogeneous changes in precipitation intensity and distribution, which inevitably impacts dry and wet status of the climate. In order to explore changes in distribution of dry and wet climate zones occurring in recent 57 years (1960-2016) in the northern part of the China , this paper characterize the spatiotemporal variation of dry-wet climate in the northern part of China over the period, analyzed the variation for impacts of the Pacific Decadal Oscillation (PDO), and explored potential causes of the variation.【Method】The meteorological data used in this study were downloaded from the “China Surface Climate Daily Data” and “China Surface Climate Data & Daily Data V3.0” of the National Meteorological Information Center, including daily mean temperature, mean minimum temperature, mean maximum temperature, precipitation, relative humidity, mean wind velocity at 10 m height and sunshine hours. Based on the daily climate data of the 424 meteorological stations in northern part of China from 1960 to 2016, ET0 was calculated with the Penman-Monteith method, humid indices(HI) were analyzed for spatio-temporal variation of the wet-dry climate, impacts of the Pacific Decadal Oscillation (PDO) on variation of the wet-dry climate were explored with the correlation analysis method, and spatio-temporal variation of the dry and wet climate was characterized with the linear trend analysis method and the multiple linear regression spatial interpolation method.【Result】Results showed: the overall wet-dry status of the northern part of China fluctuated up and down the mean of the 57 years and did not follow any obvious linear variation trend. Spatially, it displayed as wetting in Northwest China, Qinghai-Tibetan Plateau, Inner Mongolia and Xinjiang, and drying in North China. The extremely arid region was shrinking in area, while the semi-arid, and arid regions expanding, which indicates that the climate-sensitive regions are overspreading. Apparent wetting trends were observed in the extremely arid, arid and semi-arid regions. All the findings show that the boundary between the wet and dry regions was shifting during the period of 1991-2016 to the period of 1960-1990. The northern part of the country experienced a wetting process and the northwestern and western parts of the country and the Qinghai- Tibetan Plateau did a significant one, too. The west boundaries of the extremely arid and arid regions shifted towards the east, and their south and north boundaries retreated inwardly. The trend of aridification was found in North China and parts of the Northeast China. The central section of the boundary of the semiarid and semi-humid regions along the Yellow River in North China moved southeastward. The climate in the central part of Northeast China and western part of Northwest China was turning humid because of increasing precipitation and decreasing ET0. On the contrast, the climate in the central and western parts of North China, and eastern and northeastern parts of Inner Mongolia was turning arid because of decreasing precipitation and increasing ET0. In the eastern part of Northwest China, western part of Northwest China and eastern part of Inner Mongolia, PDO index was positively related to dry and wet climate, that is to say, when PDO is in its positive phase, precipitation in those regions would be higher and the surface climate relatively wet. When PDO is in its negative phase, precipitation in the above regions would be lower and the surface climate relatively dry. The case in North China was just opposite. Variation of the wet-dry climate was negatively related to PDO, namely when PDO is in its positive phase precipitation in North China tends to be lower and the surface climate relatively dry. When PDO is in its negative phase, precipitation in North China would be higher and the surface climate relatively wet.【Conclusion】All the findings in this paper suggest that the climate in northern part of the country was on the process of getting wet in two time period (period 1: 1960-1990;period 2: 1991-2016) and PDO is closely related to the dry-wet climate.