近40年我国极端温度变化趋势和季节特征

利用1961—2000年我国194个测站逐日最高温度和最低温度器测资料,结合具有实际意义的季节极端温度指数,分析了我国近40年极端温度事件的年变化趋势和季节特征。对年极端气候指数的研究表明:绝对阈值定义的冷暖指数由于无法考虑南北气候差异,其结果不理想。百分比阈值所得的冷暖指数中,冷日指数和暖日指数具有不对称性,冷夜指数和暖夜指数具有较强的对称性。对季节极端温度指数研究表明:冬季极端冷指数变化趋势最为明显,夏季极端暖指数的变化趋势次之,春、秋两季极端冷指数的变化趋势不明显;年和季节尺度的极端冷暖指数均反映出增暖趋势。     

Changes in Mean and Extreme Temperature and Precipitation over the Arid Region of Northwestern China:Observation and Projection

This paper reports a comprehensive study on the observed and projected spatiotemporal changes in mean and extreme climate over the arid region of northwestern China, based on gridded observation data and CMIP5 simulations under the RCP4.5 and RCP8.5 scenarios. The observational results reveal an increase in annual mean temperature since 1961, largely attributable to the increase in minimum temperature. The annual mean precipitation also exhibits a significant increasing tendency. The precipitation amount in the most recent decade was greater than in any preceding decade since 1961. Seasonally,the greatest increase in temperature and precipitation appears in winter and in summer, respectively. Widespread significant changes in temperature-related extremes are consistent with warming, with decreases in cold extremes and increases in warm extremes. The warming of the coldest night is greater than that of the warmest day, and changes in cold and warm nights are more evident than for cold and warm days. Extreme precipitation and wet days exhibit an increasing trend, and the maximum number of consecutive dry days shows a tendency toward shorter duration. Multi-model ensemble mean projections indicate an overall continual increase in temperature and precipitation during the 21 st century. Decreases in cold extremes, increases in warm extremes, intensification of extreme precipitation, increases in wet days, and decreases in consecutive dry days, are expected under both emissions scenarios, with larger changes corresponding to stronger radiative forcing.     

Trends of Temperature Extremes in China and its Relationship with Global temperature anomalies Relationship with Global Temperature Anomalies

Changes of temperature extremes over China were evaluated using daily maximum and minimum temperature data from 591 stations for the period 1961--2002. A set of indices of warm extremes, cold extremes and daily temperature range (DTR) extremes was studied with a focus on trends. The results showed that the frequency of warm extremes (F_WE) increased obviously in most parts of China, and the intensity of warm extremes (I_WE) increased significantly in northern China. The opposite distribution was found in the frequency and intensity of cold extremes. The frequency of high DTR extremes was relatively uniform with that of intensity: an obvious increasing trend was located over western China and the east coast, while significant decreases occurred in central, southeastern and northeastern China; the opposite distribution was found for low DTR extreme days. Seasonal trends illustrated that both F_WE and I_WE showed significant increasing trends, especially over northeastern China and along the Yangtze Valley basin in spring and winter. A correlation technique was used to link extreme temperature anomalies over China with global temperature anomalies. Three key regions were identified, as follows: northeastern China and its coastal areas, the high-latitude regions above 40^oN, and southwestern China and the equatorial eastern Pacific.     

Influence of Strong Tropical Volcanic Eruptions on Daily Temperature and Precipitation Extremes Across the Globe

This study investigates the influences of strong tropical volcanic eruptions(SVEs) on daily temperature and precipitation extreme events using long-term simulations from the Hadley Centre Coupled Model version 3(HadCM3) and the Community Earth System Model version 1.1(CESM1). The results indicate that the occurrences of daily hot extremes and daily heavy precipitation extremes decrease over most parts of the world in the peak forcing years of SVEs. Due to the volcanic cooling effect, the average probability of daily hot extremes decreases by approximately50% across the globe. The decrease in intensity is stronger for midlatitude land regions and tropical South America.In contrast, daily cold extremes occur more frequently over most parts of continental regions. Globally, a cold extreme event expected once every 3 years under non-volcanic conditions can be expected every 1.5 years on average in the peak forcing years. Overall, the SVE-induced cooling effect plays a dominant role in regulating daily cold and hot extremes. Over high-latitude Eurasian regions, in contrast to other continental regions, the probability and intensity of daily cold extremes decrease due to an SVE-strengthened polar vortex and the associated temperature advection anomalies. With regard to daily heavy precipitation extremes, the probability and intensity both decrease over most monsoon areas. Further analysis suggests that the reduced probability and intensity of daily heavy precipitation extremes are mainly due to the SVE-induced global decrease in the water-holding capacity.     

Trends in Temperature Extremes in Association with Weather-Intraseasonal Fluctuations in Eastern China

Trends in the frequencies of four temperature extremes (the occurrence of warm days, cold days, warm nights and cold nights) with respect to a modulated annual cycle (MAC), and those associated exclusively with weather-intraseasonal fluctuations (WIF) in eastern China were investigated based on an updated homogenized daily maximum and minimum temperature dataset for 1960–2008. The Ensemble Empirical Mode Decomposition (EEMD) method was used to isolate the WIF, MAC, and longer-term components from the temperature series. The annual, winter and summer occurrences of warm (cold) nights were found to have increased (decreased) significantly almost everywhere, while those of warm (cold) days have increased (decreased) in northern China (north of 40°N). However, the four temperature extremes associated exclusively with WIF for winter have decreased almost everywhere, while those for summer have decreased in the north but increased in the south. These characteristics agree with changes in the amplitude of WIF. In particular, winter WIF of maximum temperature tended to weaken almost everywhere, especially in eastern coastal areas (by 10%–20%); summer WIF tended to intensify in southern China by 10%–20%. It is notable that in northern China, the occurrence of warm days has increased, even where that associated with WIF has decreased significantly. This suggests that the recent increasing frequency of warm extremes is due to a considerable rise in the mean temperature level, which surpasses the effect of the weakening weather fluctuations in northern China.     

Changes in temperature and precipitation extremes in the CMIP5 ensemble

Twenty-year temperature and precipitation extremes and their projected future changes are evaluated in an ensemble of climate models participating in the Coupled Model Intercomparison Project Phase 5 (CMIP5), updating a similar study based on the CMIP3 ensemble. The projected changes are documented for three radiative forcing scenarios. The performance of the CMIP5 models in simulating 20-year temperature and precipitation extremes is comparable to that of the CMIP3 ensemble. The models simulate late 20th century warm extremes reasonably well, compared to estimates from reanalyses. The model discrepancies in simulating cold extremes are generally larger than those for warm extremes. Simulated late 20th century precipitation extremes are plausible in the extratropics but uncertainty in extreme precipitation in the tropics and subtropics remains very large, both in the models and the observationally-constrained datasets. Consistent with CMIP3 results, CMIP5 cold extremes generally warm faster than warm extremes, mainly in regions where snow and sea-ice retreat with global warming. There are tropical and subtropical regions where warming rates of warm extremes exceed those of cold extremes. Relative changes in the intensity of precipitation extremes generally exceed relative changes in annual mean precipitation. The corresponding waiting times for late 20th century extreme precipitation events are reduced almost everywhere, except for a few subtropical regions. The CMIP5 planetary sensitivity in extreme precipitation is about 6 %/°C, with generally lower values over extratropical land.     

Trends of Extreme Temperatures in Europe and China Based on Daily Observations

Ten of the longest daily temperature series presently available in Europe and China are analysed, focusing on changes in extremes since pre-industrial times. We consider extremes in both a relative (with respect to the time of year) and an absolute sense. To distinguish changes in extremes from changes affecting the main part of the temperature distribution, a percentile smaller than 10 (and/or larger than 90) is recommended for defining an extreme. Three periods of changes in temperature extremes are identified: decreasing warm extremes before the late 19th century; decreasing cold extremes since then and increasing warm extremes since the 1960s. The early decreases and recent increases of warm extremes dominate in summer, while the decrease of cold extremes for winter persists throughout the whole period. There were more frequent combined (warm plus cold) extremes during the 18th century and the recent warming period since 1961 at most of the ten stations, especially for summer. Since 1961, the annual frequency of cold extremes has decreased by about 7% per century with warm extremes increasing by more than 10% per century but with large spatial variability. Compared with recent annual mean warming of about 2–3 ° C/century, the coldest winter temperatures have increased atthree times this rate, causing a reduced within-season range and therefore less variable winters. Changes in the warmest summer temperatures since 1961 exhibit large spatial variability, with rates of change ranging from slightly negative to 6 ° C/century. More extensive station observations since 1961 indicate that the single site results are representative of larger regions, implying also that the extremes studied are the result of large-scale changes. Recent circulation changes in daily gridded pressure data, used as an indicator of wind speed changes, support the results by explaining some of the trends.     

Towards a better understanding of changes in wintertime cold extremes over Europe: a pilot study with CNRM and IPSL atmospheric models

Recent winter seasons have evidenced that global warming does not exclude the occurrence of exceptionally cold and/or snowy episodes in the Northern mid-latitudes. The expected rarefaction of such events is likely to exacerbate both their societal and environmental impacts. This paper therefore aims to evaluate model uncertainties underlying the fate of wintertime cold extremes over Europe. Understanding why climate models (1) still show deficiencies in simulating present-day features and (2) differ in their responses under future scenarios for the twentyfirst century indeed constitutes a crucial challenge. Here we propose a weather-regime approach in order to separate the contributions of large-scale circulation and non-dynamical processes to biases or changes in the simulated mean and extreme temperatures. We illustrate our methodology from the wintertime occurrence of extremely cold days in idealized atmosphere-only experiments performed with two of the CMIP5 climate models (CNRM-CM5 and IPSL-CM5A-LR). First we find that most of the present-day temperature biases are due to systematic errors in non-dynamical processes, while the main features of the large-scale dynamics are well captured in such experiments driven by observed sea-surface temperatures, with the exception of a generalized underestimation of blocking episodes. Then we show that uncertainties associated with changes in large-scale circulation modulate the depletion in cold extremes under an idealized scenario for the late twentyfirst century. These preliminary results suggest that the original methodology proposed in this paper can be helpful for understanding spreads of larger model-ensembles when simulating the response of temperature extremes to climate change.     

Global changes in extreme events: regional and seasonal dimension

This study systematically analyzes the complete IPCC AR4 (CMIP3) ensemble of GCM simulations with respect to changes in extreme event characteristics at the end of the 21st century compared to present-day conditions. It complements previous studies by investigating a more comprehensive database and considering seasonal changes beside the annual time scale. Confirming previous studies, the agreement between the GCMs is generally high for temperature-related extremes, indicating increases of warm day occurrences and heatwave lengths, and decreases of cold extremes. However, we identify issues with the choice of indices used to quantify heatwave lengths, which do overall not affect the sign of the changes, but strongly impact the magnitude and patterns of projected changes in heatwave characteristics. Projected changes in precipitation and dryness extremes are more ambiguous than those in temperature extremes, despite some robust features, such as increasing dryness over the Mediterranean and increasing heavy precipitation over the Northern high latitudes. We also find that the assessment of projected changes in dryness depends on the index choice, and that models show less agreement regarding changes in soil moisture than in the commonly used ‘consecutive dry days’ index, which is based on precipitation data only. Finally an analysis of the scaling of changes of extreme temperature quantiles with global, regional and seasonal warming shows that much of the extreme quantile changes are due to a seasonal scaling of the regional annual-mean warming. This emphasizes the importance of the seasonal time scale also for extremes. Changes in extreme quantiles of temperature on land scale with changes in global annual mean temperature by a factor of more than 2 in some regions and seasons, implying large changes in extremes in several countries, even for the commonly discussed global 2°C-warming target.     

Sea Surface Temperature Extremes of Different Intensity in the China Seas During the Global Warming Acceleration and Hiatus Periods

Based on the daily OISST V2 with 0.25o horizontal resolutions, we study the variations of sea surface temperature (SST) extremes in the China Seas for different segments of the period 1982-2013. The two segments include the warming acceleration period from 1982 to 1997 and hiatus period from 1998 to 2013 when the global surface mean temperature (GSMT) was not significantly warming as expected during the past decades, or even cooling in some areas. First, we construct the regional average time series over the entire China Seas (15o–45oN, 105o–130oE) for these SST extremes. During the hiatus period, the regionally averaged 10th, 1th and 0.1th percentile of SSTs in each year decreased significantly by 0.40°C, 0.56°C and 0.58°C per decade, respectively. The regionally averaged 90th, 99th and 99.9th percentile of SSTs in each year decreased slightly or insignificantly. Our work confirmed that the regional hiatus was primarily reflected by wintertime cold extremes. Spatially, the trends of cold extremes in different intensity were non-uniformly distributed. Cold extremes in the near-shore areas are much more sensitivity to the global warming hiatus. Hot extremes trends exhibited non-significant tendency in the China Seas during the hiatus period. In word, the variations of the SST extremes in the two periods were non-uniform spatially and asymmetric seasonally. It is unexpected that the hot and cold extremes of each year in 1998–2013 were still higher than those extremes in 1982–1997. It is obvious that relative to the warming acceleration period, hot extremes are far more likely to occur in the recent hiatus as a result of a 0.3°C warmer shift in the mean temperature distribution. Moreover, hot extremes in the China Seas will be sustained or amplified with the end of warming hiatus and the continuous anthropogenic warming.     

Changes in temperature extremes based on a 6-hourly dataset in China from 1961–2005

Changes in Chinese temperature extremes are presented based on a six-hourly surface air temperature dataset for the period 1961--2005. These temperature series are manually observed at 0200, 0800, 1400, and 2000 Beijing Time (LST), and percentile based extreme indices of these time series are chosen for analysis. Although there is a difference in time among the different time zones across China, as more than 80% of the stations are located in two adjacent time zones, these indices for all the stations are called warm (cold) nights (0200 LST), warm (cold) mornings (0800 LST), warm (cold) days (1400 LST), and warm (cold) evenings (2000 LST), respectively for convenience. The frequency of the annual warm extremes has generally increased, while the frequency of the annual cold extremes has decreased, and significant changes are mainly observed in northern China, the Tibetan Plateau, and the southernmost part of China. Based on the national average, annual warm (cold) nights increase (decrease) at a rate of 5.66 (-5.92) d (10 yr)^-1, annual warm (cold) days increase (decrease) at a rate of 3.97 (-2.98) d (10 yr)^-1, and the trends for the annual warm (cold) mornings and evenings are 4.35 (-4.96) and 5.95 (-4.35) d (10 yr)^-1, respectively. For China as a whole, the increasing rates for the occurrence of seasonal warm extremes are larger in the nighttime (0200, 2000 LST) than these in the daytime (0800, 1400 LST), the maximal increase occurs at 2000 LST except in the summer and the minimal increase occurs at 1400 LST except in autumn; the maximal decrease in the occurrence of seasonal cold extremes occurs at 0200 LST and the minimal decrease occurs at 1400 LST.     

1957-2005年河南省降水和温度极端事件变化

利用河南省1957-2005年逐日降水,最高、最低和日平均气温资料,分析了近50 a河南省极端天气事件的变化趋势。结果表明：1957-2005年河南省暴雨日数、极端降水事件和严重干燥事件发生频率都在增加,但其线性趋势并不显著;暴雨和极端降水的变化趋势呈明显的南北差异;异常高温事件增加而异常低温事件减少,暖冬的趋势比较显著;高温日数和低温日数都显著减少,其变化趋势的空间分布具有很好的一致性。     

Changes in European temperature extremes can be predicted from changes in PDF central statistics

Although uncertainties are still large, many potentially dangerous effects have already been identified concerning the impacts of global warming on human societies. For example, the record-breaking 2003 summer heat wave in Europe has given a glimpse of possible future European climate conditions. Here we use an ensemble of regional climate simulations for the end of the twentieth and twenty-first centuries over Europe to show that frequency, length and intensity changes in warm and cold temperature extremes can be derived to a close approximation from the knowledge of changes in three central statistics, the mean, standard deviation and skewness of the Probability Distribution Function, for which current climate models are better suited. In particular, the effect of the skewness parameter appears to be crucial, especially in the case of cold extremes, since it mostly explains the relative warming of these events compared to the whole distribution. An application of this finding is that the future impacts of extreme heat waves and cold spells on non-climatological variables (e.g., mortality) can be estimated to a first-order approximation from observed time series of daily temperature transformed in order to account for simulated changes in these three statistics.     

Transient twenty-first century changes in daily-scale temperature extremes in the United States

A key question for climate mitigation and adaptation decisions is how quickly significant changes in temperature extremes will emerge as greenhouse gas concentrations increase, and whether that emergence will be uniform between hot and cold extremes and across different geographic areas. We use a high-resolution, multi-member ensemble climate model experiment over the United States (U.S.) to investigate the transient response of the annual frequency, duration and magnitude of 8 daily-scale extreme temperature indices during the twenty-first century of the A1B emissions scenario. We evaluate the time of emergence of a permanent exceedance (PE) above the colder part of the historical (1980–2009) extremes distribution, and the time of emergence of a new norm (NN) centered on the historical maxima (for hot extremes) or minima (for cold extremes). We find that during the twenty-first century, hot extremes permanently exceed the historical distribution’s colder half over large areas of the U.S., and that the hot extremes distribution also becomes centered on or above the historical distribution’s maxima. The changes are particularly robust for the exceedance of the annual 95th percentile of daily maximum temperature over the West and the Northeast (with the earliest emergence of a PE by 2030 and of a NN by 2040), for warm days over the Southwest (with the earliest emergence of a PE by 2020 and of a NN by 2030), and tropical nights over the eastern U.S. (with the earliest emergence of a PE by 2020 and of a NN by 2030). Conversely, no widespread emergence of a PE or a NN is found for most cold extremes. Exceptions include frost day frequency (with a widespread emergence of a PE below the historical median frequency by 2030 and of a NN by 2040 over the western U.S.), and cold night frequency (with an emergence of a PE below the historical median frequency by 2040 and of a NN by 2060 in virtually the entire U.S.). Our analysis implies a transition over the next half century to a climate of recently unprecedented heat stress in many parts of the U.S., along with cold extremes that, although less frequent, remain at times as long and as severe as are found in the current climate.     

1957-2005年河南省降水和温度极端事件变化

 利用河南省1957-2005年逐日降水,最高、最低和日平均气温资料,分析了近50 a河南省极端天气事件的变化趋势。结果表明：1957-2005年河南省暴雨日数、极端降水事件和严重干燥事件发生频率都在增加,但其线性趋势并不显著;暴雨和极端降水的变化趋势呈明显的南北差异;异常高温事件增加而异常低温事件减少,暖冬的趋势比较显著;高温日数和低温日数都显著减少,其变化趋势的空间分布具有很好的一致性。     

Changes in weather and climate extremes: phenomenology and empirical approaches

The terms “weather extremes” and “climate extremes” are widely used in meteorology, often in relation to climate change. This paper reviews the empirical investigations into parallel changes in extreme events and climate change published in recent years and looks at their relevance for the global energy system. Empirical investigation into the correlation of extremes with global warming covers five groups: changes in temperature, precipitation, wind (storm) extremes, tropical and extra-tropical circulation phenomena. For temperature extremes, extensive analyses demonstrate that extreme hot days and nights will likely become more frequent, and extreme cold days and nights less frequent. Intense precipitation events will likely become more frequent in most continental regions. Scientific confidence in the trends of the frequency, duration, and intensity of tropical cyclones, is still low. A poleward shift is observed for extratropical cyclones, whereas no convincing tendencies of many smaller-scale phenomena, for example, tornados, or hail, can yet be detected. All these extremes have serious implications for the energy sector.     

The Changing Incidence of Extremes in Worldwide and Central England Temperatures to the End of the Twentieth Century

Annual and seasonal gridded ocean surface temperature anomalies show an increase in warm extremes and a decrease in cold extremes since the late 19th century attributable entirely to the overall warming trend. Over land, however, a reduction in the total incidence of extremes may reflect improved instrumental exposures. Our estimates of extremes are made by deriving percentiles from fits of anomalies on 5° latitude ×5° longitude resolution to modified 2-parameter gamma distributions. A non-parametric method is used to check the validity of the results. Fields of percentiles created using this technique can be used to map the distribution of unusual temperature anomalies across the globe on any time scale from a month to about a decade, from 1870 onwards. We apply a similar technique to assess changes in the incidence of extreme daily Central England temperature anomalies. The incidence of these extremes, relative to individual monthly average temperatures, has declined.     

BCC_CSM1．1全球模式中极端气温变化的归因分析

利用1°×1°的ERA-Interim再分析资料和气候系统模式BCC_CSM1．1历史模拟（Historical）试验及气候归因试验（只考虑温室气体变化Historica1GHG试验和只考虑自然强迫变化的Historica1Nat试验）的结果,考查了BCC_CSM1．1模式对中国和全球陆地地区极端气温指数的模拟能力,并在此基础上分析了温室气体和自然强迫这两种外强迫的变化对极端气温变化的贡献。结果表明：BCC_CSM1．1可以对中国乃至全球陆地区域极端气温指数的气候态及其变化趋势进行合理模拟,主要偏差表现为模式对极端低温指数模拟值偏低,而对极端高温指数模拟值偏高。对于20世纪末极端气温指数的变化,只有考虑了温室气体变化的外强迫时,模式可以再现再分析资料中极端气温的变化趋势。这表明温室气体的变化对极端气温的变化有着关键性的影响。     

Changing climate extremes in the Northeast United States: observations and projections from CMIP5

Climate extremes indices are evaluated for the northeast United States and adjacent Canada (Northeast) using gridded observations and twenty-three CMIP5 coupled models. Previous results have demonstrated observed increases in warm and wet extremes and decreases in cold extremes, consistent with changes expected in a warming world. Here, a significant shift is found in the distribution of observed total annual precipitation over 1981-2010. In addition, significant positive trends are seen in all observed wet precipitation indices over 1951-2010. For the Northeast region, CMIP5 models project significant shifts in the distributions of most temperature and precipitation indices by 2041-2070. By the late century, the coldest (driest) future extremes are projected to be warmer (wetter) than the warmest (wettest) extremes at present. The multimodel interquartile range compares well with observations, providing a measure of confidence in the projections in this region. Spatial analysis suggests that the largest increases in heavy precipitation extremes are projected for northern, coastal, and mountainous areas. Results suggest that the projected increase in total annual precipitation is strongly influenced by increases in winter wet extremes. The largest decreases in cold extremes are projected for northern and interior portions of the Northeast, while the largest increases in summer warm extremes are projected for densely populated southern, central, and coastal areas. This study provides a regional analysis and verification of the latest generation of CMIP global models specifically for the Northeast, useful to stakeholders focused on understanding and adapting to climate change and its impacts in the region.     

Spatial distribution of temperature trends and extremes over Maharashtra and Karnataka States of India

Earth surface temperatures are changing worldwide together with the changes in the extreme temperatures. The present study investigates trends and variations of monthly maximum and minimum temperatures and their effects on seasonal fluctuations at different climatological stations of Maharashtra and Karnataka states of India. Trend analysis was performed on annual and seasonal mean maximum temperature (TMAX) and mean minimum temperature (TMIN) for the period 1969 to 2006. During the last 38 years, an increase in annual TMAX and TMIN has occurred. At most of the locations, the increase in TMAX was faster than the TMIN, resulting in an increase in diurnal temperature range. At the same time, annual mean temperature (TM) showed a significant increase over the study area. Percentiles were used to identify extreme temperature indices. An increase in occurrence of warm extremes was observed at southern locations, and cold extremes increased over the central and northeastern part of the study area. Occurrences of cold wave conditions have decreased rapidly compared to heat wave conditions.