Detection of urbanization signals in extreme winter minimum temperature changes over Northern China

Although previous studies show that urbanization contributes to less than 10 % of the long-term regional total warming trend of mean surface air temperature in northeast China (Li et al. 2010), the urban heat island (UHI) impact on extreme temperatures could be more significant. This paper examines the urbanization impact on extreme winter minimum temperatures from 33 stations in North China during the period of 1957–2010. We use the Generalized Extreme Value (GEV) distribution to analyze the distribution of extreme minimum temperatures and the long-term variations of the three distributional characteristics parameters. Results suggest that among the three distribution parameters, the position parameter is the most representative in terms of the long-term extreme minimum temperature change. A new classification method based on the intercommunity (factors analysis method) of the temperature change is developed to detect the urbanization effect on winter extreme minimum temperatures in different cities. During the period of rapid urbanization (after 1980), the magnitude of variations of the three distribution parameters for the urban station group is larger than that for the reference station group, indicating a higher chance of occurrence of warmer weather and a larger fluctuation of temperatures. Among different types of cities, the three parameters of extreme minimum temperature distribution of the urban station group are, without exception, higher than those of the reference station group. The urbanization of different types of cities all show a warming effect, with small-size cities have the most evident effects on extreme minimum temperatures.     

中国东部地区夏季极端高温的特征分析

利用中国东部地区449个气象站的日最高气温资料,应用趋势分析法等,分析了1960-2012年夏季极端高温日数、持续高温日数的时空变化特征。分析发现:北方地区、华南地区和杭州湾周围地区两个高温指数都呈现增加趋势,长江与黄河之间的中部地区都减小。而在长江下游南部地区极端高温日数显著增加,但持续高温日数却明显减少。从季节特征上看,淮河以北的地区两个高温指数主要集中在6、7月;而以南的区域主要集中在7、8月。各个地区的这两个高温指数与降水日数均呈现显著的负相关,但南北有明显的差异,北方地区负相关的在年际变率以及5 a尺度都很显著,而中部地区则只在年际尺度上显著。杭州湾与华南地区持续高温日数与降水日数的相关体现在5 a尺度上。北方极端高温的显著增加与该地区降水日数与降水量明显减少密切相关。西北太平洋副热带高压显著的西伸,与东南地区的两个高温指数的变化有关。     

Local recent changes in extreme air temperature

Daily minimum and maximum air temperatures recorded in Naples (1872–1982) and in surrounding areas have been analysed in order to set up a statistical model for investigating climatic changes of extreme air temperature. We have analysed on various time-scales the mean values of minimum air temperature lower than the 10th percentile (Tmin₁₀) and the mean values of the maximum air temperature greater than the 90th percentile (Tmax₉₀). The results have shown for the city: (i) a significant secular trend both for yearly Tmin₁₀ and Tmax₉₀, mostly due to the process of urbanization, that is also responsible for (ii) the ascertained change in the character of the annual cycle, (iii) a reasonable ability to forecast winter Tmin₁₀ and summer Tmax₉₀ in statistical terms using a markovian model, and (iv) a significant 11-yr cycle with an amplitude of 0.5 °C directly related to solar activity which has never been succesfully determined before.     

近年华中地区不同级别强降水事件变化趋势

利用1981—2017年近37 a华中区域241个气象观测站年最大小时降水资料,分析了该区域年极端小时降水的时空分布特征。结果表明：阈值分别为30~ < 40 mm·h^-1、40~ < 50 mm·h^-1和≥50 mm·h^-1的年极端小时降水频次,河南和湖北中东部均较高,湖南则随其阈值增大而降低;年极端小时降水频次日变化特征较为明显,午后至傍晚发生最多,前半夜至凌晨次之,后半夜至早晨、上午至午后明显减少;年极端小时降水平均强度大值区多集中在河南和湖北的中东部地区,湖北最强年极端小时降水大值区主要位于沿江汉平原边缘地带;年极端小时降水频次日峰值主要出现在午后至傍晚和后半夜至早晨,其区域性差异较为明显;不同阈值的年极端小时降水频次均表现出明显的年际和年代际变化特征,1980年代呈波动减小趋势,1990年代呈波动增加趋势,21世纪初期呈现低频波动变化,之后波动加大;不同阈值的极端小时降水频次日变化均表现为明显的单峰型特征,峰值出现在17时前后。

     

人为气溶胶对中国东部冬季风影响的模拟研究

采用美国国家大气研究中心(NCAR)的公共大气模式CAM5.1研究了人为气溶胶排放增加对中国东部冬季风的影响,同时通过对比中国东部地区不同人为气溶胶排放源的敏感性试验结果,探讨了人为硫酸盐、黑碳及总人为气溶胶(硫酸盐+黑碳)增加对东亚冬季风的影响。结果表明:冬季硫酸盐气溶胶排放增加的直接和第一间接效应减少了到达地表的短波辐射通量,引起了陆地地表和对流层低层降温,海平面气压升高,增加了海陆间气压梯度,使得东亚冬季风增强。其第二间接效应导致中国南部大尺度降水率减少;黑碳气溶胶排放增加导致到达地表的短波辐射通量减少和大气中短波辐射通量增加,其半直接效应部分抵消了直接效应,故地表温度变化微小且不显著。加热的对流层低层导致中国南部对流活动和对流降水率增加;总人为气溶胶排放增加导致的大气温度变化表现为弱的降温作用,引起中国北部对流和大尺度降水率减少,而南部对流降水率增加。总人为气溶胶和黑碳气溶胶排放增加是导致中国北(南)部的东亚冬季风增强(减弱)的重要因素。     

中国极端温度的群发性研究

从极端事件再现时间的角度研究了中国极端高、低温事件再现时间序列的长程相关性、群发性以及二者的关系。发现极端温度事件再现时间序列具有长程相关性,表征长程相关性的标度指数分布存在着明显的区域性特征,并与大气环流有关,当中国大陆在盛夏或隆冬稳定的西风环流控制下,极端温度的长程相关性较好,标度指数较大。通过定义极端事件的群发指数,对极端高、低温进行研究,发现具有长程相关性再现时间序列的极端温度呈现群发现象,且极端温度再现时间序列的标度指数和群发指数二者在空间分布上有较好的对应,极端温度再现时间序列的长程相关性可能是导致极端温度群发性的原因。从年际变化的角度看,极端高温Ⅰ级群发区域的群发指数增长趋于平缓,而极端低温Ⅰ级群发区域的群发指数有下降趋势,这与近几十年来全球变暖一致。在年代际尺度上,群发指数分布的演变特征明显,极端高温Ⅰ级群发区域总体面积变化不大,而极端低温Ⅰ级群发区域面积明显减少。因此,极端低温事件群发性减弱很可能是年代际气候变暖的主要原因。     

A new approach to detection of anthropogenic temperature changes in the Australian region

Summary A new method has been applied for detecting a human influence on regional temperature changes in Australia over the last 50 years, including the whole of Australia, the southern half of Australia and the southeastern sector of Australia. There was a strong relationship between interannual variations of rainfall and temperature in different regions in Australia. The rainfall-related component of the temperature variations was removed using linear regression and the residual temperature variations were much smaller for maximum and mean temperature, and diurnal temperature range. Model simulations of regional temperature and rainfall variations agreed reasonably well with observations.Trends in the residual variations of maximum, mean and minimum temperature over the last 50 years could not be explained by natural climate variations in all the regions considered and were consistent with the response to increasing greenhouse gases and sulphate aerosols in the climate models. This new approach has been able to enhance the signal-to-noise ratio for anthropogenic temperature change signals in the Australian region and to show that there is a clear anthropogenic warming signal in observed regional temperature trends, even for regions as small as the southeastern sector of Australia.     

城市化对江苏气候变化影响的数值模拟个例分析

利用MM5模式对2003年夏季6、7两个月典型区域气候极端事件进行数值模拟,研究城市化急剧扩张对区域气候极端事件的影响和可能机制.研究发现:苏南及邻近地区城市化区域的扩张,会引起区域降水分布的变化.在城市化区域,降水将减少,而在城市化的下风区会有局地的降水增加;同时,在苏南城市化区域中,太湖等湖泊的影响也很重要,会加强其邻近地区局地降水强度.城市化区域的地面气温有明显的上升,对高温天气的作用更大.城市化也会影响地面风场,阻挡穿越城市化区域的风;苏南沿海城市化区域扩张,会使海陆风环流增强,加大了海面向陆面的风.城市化区域的潜热通量明显减少,而感热通量显著增加.城市化增暖产生的局地热源,使城市化区域及邻近地区局地环流发生变化,增强了低层城市化区域向周边辐散的强度.随着高度的增加,城市化的影响也越来越小.     

近50年中国气温、降水极值分区的时空变化特征

在全球增暖背景下,当前极端天气气候事件频发,由此引发的气象灾害及其所带来的社会经济损失日益增加.深入了解与社会生活密切相关的气温和降水极值的特征,对开展防灾减灾工作有指导意义.文中用百分位阈值求算变量极值的概率密度值,从极值概率角度用系统聚类分析法合并站点,根据方差稳定性特征和变量最概然值的均值确定划分区域个数和对区域...     

前冬北半球环状模对春季中国东部北方地区极端低温的影响

对1959—2008年前冬(12—3月)北半球环状模与春季(3—5月)中国东部北方地区极端低温事件的关系进行诊断分析,发现前冬北半球环状模与春季中国东部北方地区极端低温事件存在显著负相关。当前冬北半球环状模偏强时,春季中国东部北方地区上空对流层高、低层分别出现位势高度的负、正异常,对应异常的下沉增温,东北冷涡偏弱,极端低温事件发生频次偏少,强度偏弱;反之,当前冬北半球环状模偏弱时,春季该地区极端低温事件发生的频次偏多,强度偏强。进一步研究表明,欧亚雪盖在前冬北半球环状模对春季中国东部北方地区极端低温的影响中起到潜在的桥梁作用,当前冬北半球环状模偏强(偏弱)时,同期欧亚大陆中高纬度地区偏暖(偏冷),欧亚雪盖面积较小(较大)。另外,欧亚雪盖面积异常具有较强的持续性,可以从前冬持续到春季。因此,当前冬欧亚雪盖面积较小时,春季欧亚雪盖面积也偏小,且对应春季东北冷涡强度偏弱,中国东部北方地区地表气温偏高,极端低温事件发生的频次偏少,强度偏弱;反之亦然。前冬北半球环状模与春季中国东部北方地区极端低温事件的负相关关系为预测中国东部北方地区春季极端低温事件的变化提供了一个潜在的前期信号。     

The contribution of anthropogenic forcings to regional changes in temperature during the last decade

Regional distributions of the mean annual temperature in the 2000s are computed with and without the effect of anthropogenic influences on the climate in several sub-continental regions. Simulated global patterns of the temperature response to external forcings are regressed against observations using optimal fingerprinting. The global analysis provides constraints which are then used to construct the regional temperature distributions. A similar approach was also employed in previous work, but here the methodology is extended to examine changes in any region, including areas with a poor observational coverage that were omitted in the earlier study. Two different General Circulation Models (GCMs) are used in the analysis. Anthropogenic forcings are found to have at least quadrupled the likelihood of occurrence of a year warmer than the warmest year since 1900 in 23 out of the 24 regions. The temperature distributions computed with the two models are very similar. While a more detailed assessment of model dependencies remains to be made once additional suitable GCM simulations become available, the present study introduces the statistical methodology and demonstrates its first application. The derived information concerning the effect of human influences on the regional climate is useful for adaptation planning. Moreover, by pre-computing the change in the likelihood of exceeding a temperature threshold over a range of thresholds, this kind of analysis enables a near real-time assessment of the anthropogenic impact on the observed regional temperatures.     

The performance of multiple datasets in characterizing the changes of extreme air temperature over China during 1979 to 2012

Theoretical and Applied Climatology - Using multiple datasets, including three grid datasets (ERA-Interim, WFDEI, and SURF) and one station dataset, we analyzed the climatological distributions and...     

Anthropogenic influence on the extreme drought in eastern China in 2022 and its future risk

2022年夏季中国东部地区遭遇了一次持续性极端高温干旱事件.本文利用CMIP6检测归因比较计划(DAMIP)数据,量化了人为强迫对类2022年极端干旱事件发生概率的影响,并基于未来不同增暖情景试验给出了此类极端干旱事件的未来变化预估.通过分析不同外强迫因子作用下此类极端干旱事件的发生概率变化,发现人为强迫使此类极端干旱事件的发生概率提高约56%,这主要与人为强迫下中国东部平均水汽减少和平均上升运动减弱有关.进一步通过分析此类极端干旱事件对不同温室气体排放情景(SSP1-2.6,SSP2-4.5,SSP5-8.5)的响应,发现在低排放情景下类2022年极端干旱事件的发生概率较当今气候显著下降,这主要与中国东部平均水汽的增加和平均环流的变化有关,而在高排放情景(SSP5-8.5)下,此类极端干旱事件的发生概率较当今气候增加约79%,这主要与高排放情景下平均下沉运动增强有关.该研究表明,人为强迫通过调制气候平均背景场从而引起极端事件发生频次的变化是人类活动影响极端气候事件的重要途径之一,极端干旱事件对温室气体排放量的响应可能是非线性的.     

利用CAM5.1模拟中国东部大规模城市化对东亚地区夏季大气环流及降水分布的影响

利用CAM5.1大气环流模式研究中国东部大规模城市化对东亚夏季大气环流及降水分布的影响。通过在模式中修改中国东部地区(22～42°N,110～125°E)城市比重的方法,探讨东亚地区夏季大气环流与降水等气象要素在一般城市化及极端城市化两种情景下的响应。结果表明:(1)CAM5.1模式能够很好地模拟出东亚地区夏季大气环流形势及降水分布。(2)城市比重增大后,晴空时地面吸收的净辐射增多,近地层气温升高,低层增温中心上空的大气由于受热产生上升运动,35°N以南的气流向增温区辐合,东亚夏季风出现增强的趋势,大量暖湿水汽往北输送,导致降水在中国北方地区增多而南方减少。(3)城市化的发展程度越高,它所产生的气候效应对各气象要素的影响就表现得越明显。