宁夏冬季气温变化与大气环流异常的关系

利用1961~2015年冬季(12月到次年2月)宁夏20个气象站月平均气温资料,NCEP/NCAR发布的500 h Pa位势高度场和海平面气压场,200 h Pa、850 h Pa风场月平均再分析资料,运用线性倾向估计、M-K法及合成分析等方法,在研究宁夏冬季平均气温的年际变化及年代际变化特征的基础上,分突变前后的冷、暖期时段进一步分析大气环流场不同影响因子与宁夏冬季气温异常的关系,揭示宁夏冬季气温异常的成因。结果表明:(1)宁夏冬季平均气温由冷变暖的趋势非常显著,在1985年之前为冷期,1985年以后为暖期;冬季平均气温年代际变化在20世纪增暖趋势显著,21世纪后上升趋势趋于平缓。(2)不仅500 h Pa位势高度场的乌拉尔山高压脊和西太平洋副高是影响宁夏冬季气温异常的主要系统,海平面气压场的西伯利亚高压也是影响宁夏冬季气温异常的关键系统;高低空的偏北气流和偏南暖湿气流异常流场也对宁夏冬季气温变化造成一定影响。

Climate Change Impacts and Adaptation Strategies in Northwest China

Climate change resulted in changes in crop growth duration and planting structure,northward movement of planting region,and more severe plant diseases and insect pests in Northwest China.It caused earlier seeding for spring crop,later seeding for autumn crop,accelerated crop growth,and reduced mortality for winter crop.To adapt to climate change,measures such as optimization of agricultural arrangement,adjustment of planting structure,expansion of thermophilic crops,and development of water-saving agriculture have been taken.Damaging consequences of imbalance between grassland and livestock were enhanced.The deterioration trend of grassland was intensified;both grass quantity and quality declined.With overgrazing,proportions of inferior grass,weeds and poisonous weeds increased in plateau pastoral areas.Returning farmland to grazing,returning grazing to grassland,fence enclosure and artificial grassland construction have been implemented to restore the grassland vegetation,to increase the grassland coverage,to reasonably control the livestock carrying capacity,to prevent overgrazing,to keep balance between grassland and livestock,and to develop the ecological animal husbandry.In Northwest China,because the amount of regional water resources had an overall decreasing trend,there was a continuous expansion in the regional land desertification,and soil erosion was very serious.A series of measures,such as development of artificial precipitation(snow),water resources control,regional water diversion,water storage project and so on,were used effectively to respond to water deficit.It had played a certain role in controlling soil erosion by natural forest protection and returning farmland to forest and grassland.In the early21st century,noticeable achievements had been made in prevention and control of desertification in Northwest China.The regional ecological environment has been improved obviously,and the desertification trend has shown sign of under control.

Analysis on Spatial and Temporal Changes of Extreme Precipitation Events in Ningxia in Recent 50 Years

[ Objective] The aim was to study the spatial and temporal changes of extreme precipitation events in Ningxia in recent 50 years. [ Method] Using dally precipitation data at 20 stations in Ningxia from 1961 to 2010, and defining the threshold value of extreme precipitation in each sta- tion by percentage method, choosing indicators such as precipitation, frequency and intensity of extreme precipitation events, the characteristics of the spatial and temporal distribution and linear trend of extreme precipitation events in Ningxia were analyzed based on linear regression and M-K non-parameter statistical test method. [ Result] The percentage method suggested the threshold value of average extreme precipitation in Ningxia in recent 50 years decreased from south to north. The large threshold value was in southern Haiyuan, Tongxin and northern Yancheng, which was similar to the distribution of mean annual precipitation in Ningxia. In recent 50 years, extreme precipitation frequency and extreme precipitation de- creased in most part of Ningxia but the intensity tended to strengthen. Study of extreme precipitation in Mahuang Mountain and Liupan Mountain in- dicated that precipitation frequency, intensity and extreme precipitation reduced. Annual extreme precipitation frequency narrowed and then in- creased after 1994 and had mutation in 2003. Annual extreme precipitation intensity enhanced since 1984. Mutation took place in 1984. Intensity in Liupan Mountain had weakened since 1978. [ Conclusion] The study provided theoretical basis for the mutation of climate in Ningxia.