Temperature and precipitation long-term trends and variations in the Ili-Balkhash Basin

This study analyzed the long-term trends and variations of temperature and precipitation on annual timescale in the Ili-Balkhash Basin (IBB), Kazakhstan. Some statistical tools were employed to detect any climate variations at four stations in the IBB during the period between 1936 and 2005. These methods included the Mann–Kendall trend test, the Theil–Sen approach, and the sequential Mann–Kendall test. The results showed that in temporal scale, the climate in the IBB has been becoming warmer and wetter in the past several decades as a whole. The annual mean temperature and the annual precipitation in the IBB showed an increasing trend since the 1970s and the 1940s, respectively. The significance of the annual mean temperature and annual precipitation trends in the IBB was tested at >95 % confidence level. The slope of the increasing trend of annual mean temperature ranges from 0.019 to 0.029 °C/year, and that of the annual precipitation ranges from 0.654 to 2.179 mm/year. In spatial scale, the multiyear mean values of temperature and precipitation are greater in the southern mountain region than those in the northern plain and hilly land area of the basin. The multiyear mean temperature decreases with the increasing latitudes, while increases with the increasing altitudes except for Karaganda; the multiyear mean precipitation increase with the increasing altitudes, while decreases centered with the Lake Balkhash from the surrounding area. The results may provide climatic backgrounds for solving the problems related to water sources of the IBB.     

Multidecadal changes in the relationship between extreme temperature events in Uruguay and the general atmospheric circulation

We analyze changes in the relationship between extreme temperature events and the large scale atmospheric circulation before and after the 1976 climate shift. To do so we first constructed a set of two temperature indices that describe the occurrence of warm nights (TN90) and cold nights (TN10) based on a long daily observed minimum temperature database that spans the period 1946?C2005, and then divided the period into two subperiods of 30?years each (1946?C1975 and 1976?C2005). We focus on summer (TN10) and winter (TN90) seasons. During austral summer before 1976 the interannual variability of cold nights was characterized by a negative phase of the Southern Annular Mode (SAM) with a cyclonic anomaly centered off Uruguay that favoured the entrance of cold air from the south. After 1976 cold nights are associated not with the SAM, but with an isolated vortex at upper levels over South Eastern South America. During austral winter before 1976, the El Ni?o phenomenon dominated the interannual variability of warm nights through an increase in the northerly warm flow into Uruguay. However, after 1976 the El Ni?o connection weakened and the variability of warm nights is dominated by a barotropic anticyclonic anomaly located in the South Atlantic and a low pressure center over South America. This configuration also strengthens the northward flow of warm air into Uruguay. Our results suggest that changes in El Ni?o evolution after 1976 may have played a role in altering the relationship between temperature extreme events in Uruguay and the atmospheric circulation.     

Day-of-the-week variations of urban temperature and their long-term trends in Japan

Temperature differences among days of the week and their long-term trends were evaluated using 29 years of hourly data from the Automated Meteorological Data Acquisition System network of Japan. Stations were categorized with respect to the population density around each site, and an urban temperature anomaly (δT*) was defined as a departure from the spatial average of nearby rural stations. On Saturdays and holidays (Sundays and national holidays), δT* was lower than on weekdays by 0.2–0.25°C at Tokyo, by 0.1–0.2°C at Osaka, and by about 0.02°C at stations where the population density was 300 to 1,000 km^–2. Moreover, δT* showed a relative decreasing trend over the long term on Mondays and an increasing trend on Fridays, at a rate of about 0.05–0.1°C decade^–1 at Tokyo and about 0.02°C decade^–1 at stations where the population density was 100 to 1,000 km^–2, but no significant difference in δT* trends was observed between weekdays and weekend days.     

Consistency of observed winter precipitation trends in northern Europe with regional climate change projections

Often it is claimed that the recent changes in northern European climate are at least partly anthropogenic even though a human influence has not yet been successfully detected. Hence we investigate whether the recent changes are consistent with regional climate change projections. Therefore, trends in winter (DJF) mean precipitation in northern Europe are compared to human induced changes as predicted by a set of four regional climate model simulations. The patterns of recent trends and predicted changes match reasonably well as indicated by pattern correlation and the similarity is very likely not random. However, the model projections generally underestimate the recent change in winter precipitation. That is, the signal-to-noise ratio of the anthropogenic precipitation change is either rather low or the presently used simulations are significantly flawed in their ability to project changes into the future. European trends contain large signals related to the North Atlantic Oscillation (NAO), of which a major unknown part may be unrelated to the anthropogenic signal. Therefore, we also examine the consistency of recent and projected changes after subtracting the NAO signal in both the observations and in the projections. It turns out that even after the removal of the NAO signal, the pattern of trends in the observations is similar to those projected by the models. At the same time, the magnitude of the trends is considerably reduced and closer to the magnitude of the change in the projections.     

Spectroscopic measurements of atmospheric carbon monoxide and methane. 2: Seasonal variations and long-term trends

A spectroscopic technique for measuring CO and CH₄ contents is described and the latitudinal distributions of these gases are presented. Carbon monoxide abundance decreases southward, having two local maxima: in midlatitudes and in the tropics. The slope of latitude dependence varies according to the season of the year. The difference in CH₄ content does not exceed the accuracy of the method (±8%).     

National-scale analysis of low flow frequency: historical trends and potential future changes

The potential impact of climate change on hydrological extremes is of increasing concern across the globe. Here, a national-scale grid-based hydrological model is used to investigate historical trends and potential future changes in low flow frequency across Great Britain. The historical analyses use both observational data (1891–2015) and ensemble data from a regional climate model (1900–2006). The results show relatively few significant trends in historical low flows (2- or 20-year return period), whether based on 7- or 30-day annual minima. Significant negative trends seen in some limited parts of the country when using observational data are generally not seen when using climate model data. The future analyses use climate model ensemble data for both near future and far future time periods (2020–2049 and 2070–2099 respectively), which are compared to a baseline sub-period from the historical ensemble (1975–2004). The results show future reductions in low flows, which are generally larger in the south of the country, at the higher (20-year) return period, and for the later time period. Reductions are more limited if the estimates of future potential evaporation include the effect of increased carbon dioxide concentrations on stomatal resistance. Such reductions in river flow could have significant impacts on the aquatic environment and on agriculture, and present a challenge for water managers, especially as reductions in water supply are likely to occur alongside increases in demand.     

阿留申低压与东亚冬季风关系的年代际变化

东亚冬季风系统是北半球冬季最活跃的环流系统,通过与西伯利亚高压、阿留申低压、东亚大槽和东亚西风急流等系统之间的相互作用,对东亚地区的气候产生重要影响。本文主要关注阿留申低压与东亚冬季风关系的年代际变化特征,利用经验正交函数分析方法,提取阿留申低压的强度变化、南北移动、西北-东南传播型和东西移动模态,并研究这4种模态与冬季风的北部型、南部型模态关系。结果表明阿留申低压的强度变化与2种东亚冬季风型的关系都不显著。阿留申低压的南北移动与南部型冬季风的相关性较强且具有年代际变化特征。1995年后南北涛动中心受ENSO(El Niño-Southern Oscillation)影响向东移动,阿留申低压和西伯利亚高压的配置不利于中国东南部气压梯度的形成,导致阿留申低压的南北移动与南部型冬季风的相关性降低。另外,1975年后北大西洋涛动在中西伯利亚地区激发正位势高度异常,扩大传播型模态影响范围,给中高纬地区带来东北风异常,有利于北部型冬季风的形成,此时传播型模态与北部型冬季风显著相关。     

欧洲冬季５００ｈＰａ环流异常及与中国气候异常的关系

用中国160气象站月平均降水和气温资料以及NCEP/NCAR月平均再分析资料,采用EOF分析等方法,研究了冬季欧洲500 hPa高度异常的变化特征及其与中国气候的关系.结果表明:(1)EOF第1模态主要反映了欧洲东部大槽和西欧脊的空间变化特征,定义了主模态的两种异常型:西高东低型和西低东高型;(2)主模态时间系数与40°N以南中国中东部一直到华南地区的降水呈显著正相关关系,而与中国东北、内蒙古中东部以及长江下游沿海的气温呈显著正相关关系;(3)西高东低异常型年,有利于欧洲中高纬冷空气向中国南方地区传输,不利于向中国北方地区传输;有利于孟加拉湾水汽向中国华南地区输送,也有利于西北太平洋水汽向中国东部以及北方输送;欧亚高纬度高压系统减弱,而西北太平洋海面低压系统减弱,东亚冬季风减弱;反之亦然.     

Recent trends in winter temperature extremes in eastern China and their relationship with the Arctic Oscillation and ENSO

Interannual variations in the number of winter extreme warm and cold days over eastern China （EC） and their relationship with the Arctic Oscillation （AO） and E1 Nifio-Southern Oscillation （ENSO） were investigated using an updated temperature dataset comprising 542 Chinese stations during the period 1961- 2011. Results showed that the number of winter extreme warm （cold） days across EC experienced a significant increase （decrease） around the mid-1980s, which could be attributed to interdecadal variation of the East Asian Winter Monsoon （EAWM）. Probability distribution functions （PDFs） of winter temperature extremes in different phases of the AO and ENSO were estimated based on Generalized Extreme Value Distribution theory. Correlation analysis and the PDF technique consistently demonstrated that interannual variation of winter extreme cold days in the northern part of EC （NEC） is closely linked to the AO, while it is most strongly related to the ENSO in the southern part （SEC）. However, the number of winter extreme warm days across EC has little correlation with both AO and ENSO. Furthermore, results indicated that, whether before or after the mid-1980s shift, a significant connection existed between winter extreme cold days in NEC and the AO. However, a significant connection between winter extreme cold days in SEC and the ENSO was only found after the mid-1980s shift. These results highlight the different roles of the AO and ENSO in influencing winter temperature extremes in different parts of EC and in different periods, thus providing important clues for improving short-term climate prediction for winter temperature extremes.     

Analysis of long-term precipitation changes in West Bengal,India: An approach to detect monotonic trends influenced by autocorrelations

The precipitation of the entire Indian sub-continent is primarily driven by the monsoon wind system, which throws a tough challenge to model changes due to its natural variabilities. Additionally, the unique geographical location and diverse climatic condition of the Indian state of West Bengal (WB) accelerates this challenge even more. Such a situation can be more complicated if the assumption of randomness in the Mann-Kendall (MK) test is not taken care of. The present study inspects the dynamics of precipitation using the original MK test along with its three modified versions in WB. The modified versions are considered to incorporate all the significant autocorrelation coefficient (ACC) along with the short and long term persistence (STP and LTP) in the time series. Results showed that the presence of significant ACC was more common than the LTP behavior. The STP approach produced similar results to the original MK test, while the LTP approach reduced the number of significant trends. When the series was free from the scaling effect, consideration of all significant ACC gave better result in comparison to the STP approach. The annual precipitation is decreasing in large areas of WB, while the coastal areas are receiving increasing trends, which can intricate the estuarine and coastal processes. The Sub-Himalayan region and the western parts of WB are experiencing significant falling trend in monsoon season. Such a decreasing trend can enhance drought vulnerabilities, especially in the western parts of WB. However, the other three seasons (pre-monsoon, post-monsoon, and winter) witness the maximum number of non-significant trends.     

Interdecadal changes in the Asian winter monsoon variability and its relationship with ENSO and AO

Interdecadal changes in the Asian winter monsoon (AWM) variability are investigated using three surface air temperature datasets for the 55-year period of 1958–2012 from (1) the National Centers for Environmental Prediction-National Center for Atmospheric Research reanalysis 1 (NCEP), (2) combined datasets from the European Centre for Medium-range Weather Forecasts (ECMWF) 40-yr reanalysis and interim data (ERA), and (3) Japanese 55-year reanalysis (JRA). Particular attention has been paid to the first four empirical orthogonal function (EOF) modes of the AWM temperature variability that together account for 64% of the total variance and have been previously identified as predictable modes. The four modes are characterized as follows: the first mode by a southern warming over the Indo-western Pacific Ocean associated with a gradually increasing basin-wide warming trend; the second mode by northern warming with the interdecadal change after the late 1980s; the third and fourth modes by north-south triple pattern, which reveal a phase shift after the late 1970s. The three reanalyses agree well with each other when producing the first three modes, but show large discrepancy in capturing both spatial and temporal characteristics of the fourth mode. It is therefore considered that the first three leading modes are more reliable than the rest higher modes. Considerable interdecadal changes are found mainly in the first two modes. While the first mode shows gradually decreasing variance, the second mode exhibits larger interannual variance during the recent decade. In addition, after the late 1970s, the first mode has a weakening relationship with the El Niño-Southern Oscillation (ENSO) whereas the second mode has strengthening association with the Artic Oscillation (AO). This indicates an increasing role of AO but decreasing role of ENSO on the AWM variability. A better understanding of the interdecadal change in the dominant modes would contribute toward advancing in seasonal prediction and the predictability of the AWM variability.     

中国冬季暖夜频率变化特征及其与海温的关系

采用排除台站迁移对逐日资料均一性影响的中国201个台站1960—2009年冬季逐日最低气温资料,NCEP/NCAR再分析的月平均500 h Pa位势高度场资料,及由NOAA重构的海温场资料,对中国冬季暖夜频率(frequence of warm winter night,FWWN)的时空变化特征及暖夜频率与全球海温的关系进行了分析。结果表明:近50 a中国冬季暖夜频率显著增加,并于1988年前后发生突变;冬季暖夜频率的变化幅度及趋势均是在西北地区东部最大,西南地区最小;中国冬季暖夜频率可以分为5个各自变化特征比较一致的区域;赤道印度洋到赤道西太平洋海区、黑潮区、北大西洋海区及南太平洋海区的海温指数均与中国冬季暖夜频率在全国大部分地区呈显著正相关;4个海区海温指数的异常年对应的大气环流场背景均能反映出它们分别与中国冬季暖夜频率呈正相关的事实。     

Present-day characteristics and trends of long-term changes in ecological and toxicological conditions of the Tsimlyansk Reservoir

The analysis of ecological and toxicological conditions of the Tsimlyansk Reservoir and of trends of long-term variations of hydrochemical, hydrobiological, and biotesting parameters is carried out on the basis of long-term data of Roshydromet regular observations (1984?C1991) and authors?? studies (1990, 2006?C2007). It is revealed that, according to the complex of chemical parameters, the water pollution level decreased by the end of the period and is relatively low at present, although the pollution is of stable nature and the toxic and carcinogenic compounds are discovered in the water and in bottom sediments. The most dangerous display of the reservoir eutrophication is a ??bloom?? of algae characterized by the prevalence of blue-green algae (Cyanophyta) amounting to 100% of the total biomass in some samples; the species being able to discharge the toxins to the water (Aphanisomenon flos-aquae, Microcystis aeruginosa, Anabaena flos-aquae) often prevail. During biotesting, the samples of water and bottom sediments in a number of cases exerted a toxic effect on the water organisms and, most likely, the toxicity increases with time. Although different parts of the reservoir differ considerably in ecological and toxicological parameters, an ecologically unfavorable situation emerged in the reservoir ecosystem due to the pollution, eutrophication, and toxicophication.     

Temperature variations and rice yields in China: historical contributions and future trends

Temperature is the principal factor that determines rice growth, development and ultimately grain yield. In this study, normal growing-degree-days (NGDD) and killing growing-degree-days (KGDD) were used to capture the different effects of normal and extreme temperatures on rice yields, respectively. Based on these indexes, we assessed the contributions of temperature variations to county-level rice yields across China during the historical period (1980–2008), and estimated the potential exposure of rice to extreme temperature stress in the near future (2021–2050). The results showed that historical temperature variations had measurable impacts on rice yields with a distinct spatial pattern: for different regions, such variations had contributed much to the increased rice yields in Northeast China (Region I) (0.59 % yield year^?1) and some portions of the Yunnan-Guizhou Plateau (Region II) (0.34 % yield year^?1), but seriously hindered the improvements of rice yields in the Sichuan Basin (SB) (?0.29 % yield year^?1) and the southern cultivation areas (Region IV) (?0.17 % yield year^?1); for the entire country, half of the contributions were positive and the other half were negative, resulting in a balance pattern with an average of 0.01 % yield year^?1. Under the RCP8.5 scenario, climate warming during 2021–2050 would substantially reduce cold stress but increase heat stress in the rice planting areas across China. For the future period, Region I, II and eastern China would be continually exposed to more severe cold stress than the other regions; Region III (including SB and the mid-lower reaches of Yangtze River (MLRYR)) would be the hot spot of heat stress.     

The warm winter in the Russian Arctic and anomalous cold in Europe

Considered are synoptic mechanisms of the formation of abnormally warm weather and high anticyclones in the Russian Arctic as well as the generation of the series of cold cyclones in the middle troposphere over southern Europe in January–February 2012. Obtained are the typical schemes of thermobaric fields of the macro-scale reconstruction of atmospheric circulation and of the set-in of the eastern air transport from Siberia to the central and southern areas of the European part of Russia and to the Mediterranean countries. Proposed is an algorithm for predicting processes of atmospheric blocking with the help of quantitative criteria that enable to assess the existence, intensity, and lifetime of the circulation impeding the westerlies.     

Sensitivity of discharge and flood frequency to twenty-first century and late Holocene changes in climate and land use (River Meuse,northwest Europe)

We used a calibrated coupled climate–hydrological model to simulate Meuse discharge over the late Holocene (4000–3000 BP and 1000–2000 AD). We then used this model to simulate discharge in the twenty-first century under SRES emission scenarios A2 and B1, with and without future land use change. Mean discharge and medium-sized high-flow (e.g. Q₉₉) frequency are higher in 1000–2000 AD than in 4000–3000 BP; almost all of this increase can be attributed to the conversion of forest to agriculture. In the twentieth century, mean discharge and the frequency of medium-sized high-flow events are higher than in the nineteenth century; this increase can be attributed to increased (winter half-year) precipitation. Between the twentieth and twenty-first centuries, anthropogenic climate change causes a further increase in discharge and medium-sized high-flow frequency; this increase is of a similar order of magnitude to the changes over the last 4,000 years. The magnitude of extreme flood events (return period 1,250-years) is higher in the twenty-first century than in any preceding period of the time-slices studied. In contrast to the long-term influence of deforestation on mean discharge, changes in forest cover have had little effect on these extreme floods, even on the millennial timescale.     

Observed precipitation in the Paraná-Plata hydrological basin: long-term trends, extreme conditions and ENSO teleconnections

The Paraná-Plata basin is the second largest hydrological basin in South America and is of great importance for the countries of the region (Argentina, Bolivia, Brazil, Paraguay and Uruguay). The present study focuses on the long-term trends in basin-scale precipitation with special emphasis on the role of distribution changes in extreme large-scale precipitation events and on the characteristics and evolution of ENSO teleconnections over the last 50 years. First, we defined a Paraná-Plata basin total precipitation index (PTPI) as the precipitations spatially averaged over the hydrological basin. On interannual time scales, such an index is mainly representative of anomalous monsoon precipitations in the northern part of the basin and large convective precipitation anomalies in the center of the basin (Paraguay-southern Brazil-Uruguay-northern Argentina) typical of the canonical ENSO teleconnection pattern. Our major findings clearly highlight a positive trend in yearly averaged PTPI mainly from the late 1960s to the early 1980s with a strong dependence from month-to-month. The largest precipitation increase is observed from November to May in southern Brazil and Argentina. A close examination of PTPI distributions during the two halves of the period 1950–2001 shows that the changes in the mean state from 1950–1975 to 1976–2001 result from significant changes in each calendar month mean state and in the tails of the PTPI anomaly distributions in May with lesser and weaker large-scale dry events and stronger large-scale wet events. Further studies will be needed to assess whether the observed trend in large-scale extreme precipitation conditions can be related to natural climate variability or anthropogenic activities and whether it is associated to changes in local/regional extreme events. The stronger wet conditions in different months seem to be associated to changes in ENSO characteristics (amplitude, propagation, spatial structure, ...) since the 1982–1983 El Niño. Indeed, spatial ENSO teleconnections (stronger in November and April–May) have greatly evolved from 1950–1975 to 1976–2001. Moreover, we demonstrate that there is a strong modulation and displacement of the teleconnection patterns from one event to another, impeding the definition of robust statistical relationship between ENSO and precipitation in the Paraná-Plata basin (except maybe over a very limited area near the common border between Paraguay, Argentina and Brazil). Finally, the non-antisymmetrical patterns of precipitation between El Niño and La Niña conditions and the non-linear relationship between precipitation and either Niño3.4 or Niño1+2 sea surface temperature indices show that linear statistical forecast systems are actually of very limited use for impact predictions on society on a local or regional scale.     

Snow climate baseline conditions and trends in Croatia relevant to winter tourism

The presence of snow along a portion of the Croatian highlands has enabled the development of winter tourism that is primarily oriented toward snow-related activities. Snow is more abundant and stays on the ground longer in the mountainous district of Gorski kotar (south eastern edge of the Alps) and on Mount Velebit (Dinaric Alps), which have elevations of up to 1,600?m and are close to the Adriatic coast than over the inland hilly region of north western Croatia where the summits are not more than approximately 1,000?m high. Basic information about the snow conditions at these locations was gathered for this study, including the annual cycle and probabilities for various snow parameters at different altitudes. As requested by the Croatian Ski Association, the relation between the air temperature and the relative humidity was investigated to determine the feasibility of artificial snowmaking. The snow parameters are highly correlated to air temperature, surface air pressure and precipitation, with certain differences occurring as a result of the altitude. Since the beginning of the second half of the twentieth century, winter warming and a significant increase in the mean air pressure (more anticyclonic situations) have been detected at all sites. Winter precipitation totals decreased at medium altitudes and increased at the summit of Mount Velebit, but these trends were not significant. The frequency of precipitation days and of snowfall decreased whereas an increasing fraction of the precipitation days at high altitudes involved solid precipitation. In contrast, a decreasing fraction of the precipitation days at medium altitudes involved solid precipitation, probably because of the different warming intensities at different altitudes. The mean daily snow depth and the duration of snow cover both slightly decreased at medium altitudes whereas the snow cover duration slightly increased at the mountainous summit of Mount Velebit.