Recent climatic trends in the tropical Atlantic

A homogeneous monthly data set of sea surface temperature (SST) and pseudo wind stress based on in situ observations is used to investigate the climatic trends over the tropical Atlantic during the last five decades (1964–2012). After a decrease of SST by about 1 °C during 1964–1975, most apparent in the northern tropical region, the entire tropical basin warmed up. That warming was the most substantial (>1 °C) in the eastern tropical ocean and in the longitudinal band of the intertropical convergence zone. Surprisingly, the trade wind system also strengthened over the peirod 1964–2012. Complementary information extracted from other observational data sources confirms the simultaneity of SST warming and the strengthening of the surface winds. Examining data sets of surface heat flux during the last few decades for the same region, we find that the SST warming was not a consequence of atmospheric heat flux forcing. Conversely, we suggest that long-term SST warming drives changes in atmosphere parameters at the sea surface, most notably an increase in latent heat flux, and that an acceleration of the hydrological cycle induces a strengthening of the trade winds and an acceleration of the Hadley circulation. These trends are also accompanied by rising sea levels and upper ocean heat content over similar multi-decadal time scales in the tropical Atlantic. Though more work is needed to fully understand these long term trends, especially what happens from the mid-1970’s, it is likely that changes in ocean circulation involving some combination of the Atlantic meridional overtuning circulation and the subtropical cells are required to explain the observations.     

Wintertime climatic trends in the western Himalayas

Northern Indian rivers are primarily fed by wintertime (December, January, February—DJF) precipitation, in the form of snow—yielded by eastward moving synoptic weather systems called Western Disturbances (WDs), over the western Himalayas (WH). This accumulated snow melts during ablation period. In the context of today’s warming atmosphere, it is imperative to study the changes in the temperature and precipitation patterns over the WH to assess the impact of global warming on climatic conditions of the region. Keeping that in mind, observational analysis of temperature and precipitation fields is planned. In the present study various climatic indices are analyzed based on wintertime (DJF) data of 30?years (1975–2006) obtained from the Snow and Avalanche Study Establishment (SASE), India. Results indicate enhancement in the surface air temperature across the WH. Percent number of warm (cold) days have increased (decreased) during 1975–2006 over the WH. Further analysis of precipitation reveals slightly decreasing but inconsistent trends.     

Uncertainties of estimates of climatic change: A review

While climate modeling gives substantial information about the future climate, there are still many uncertainties. This review addresses the question of the response of the climate system to forcing by increasing atmospheric trace gases. The uncertainties of greatest concern are: the transient adjustment controlled by ocean heat uptake; the cover of snow and ice in high latitudes; the change in cloud radiative properties; and shifts in regional patterns connected to the ocean and land surfaces and to the internal dynamics of the atmosphere.The National Center for Atmospheric Research is sponsored by the National Science Foundation.     

Prevailing trends of climatic extremes across Indus-Delta of Sindh-Pakistan

This study examines the variability and change in the patterns of climatic extremes experienced in Indus-Delta of Sindh province of Pakistan, comprising regions of Karachi, Badin, Mohenjodaro, and Rohri. The homogenized daily minimum and maximum temperature and precipitation data for a 36-year period were used to calculate 13 and 11 indices of temperature and precipitation extremes with the help of RClimDex, a program written in the statistical software package R. A non-parametric Mann–Kendall test and Sen’s slope estimates were used to determine the statistical significance and magnitude of the calculated trend. Temperatures of summer days and tropical nights increased in the region with overall significant warming trends for monthly maximum temperature as well as for warm days and nights reflecting dry conditions in the study area. The warm extremes and nighttime temperature indices showed greater trends than cold extremes and daytime indices depicting an overall warming trends in the Delta. Historic decrease in the acreage of major crops and over 33% decrease in agriculture credit for Sindh are the indicators of adverse impacts of warmer and drier weather on Sindh agriculture. Trends reported for Karachi and Badin are expected to decrease rice cultivation, hatching of fisheries, and mangroves forest surrounding these cities. Increase in the prevailing temperature trends will lead to increasingly hotter and drier summers resulting to constraints on cotton, wheat, and rice yield in Rohri and Mohenjodaro areas due to increased crop water requirements that may be met with additional groundwater pumping; nonetheless, the depleted groundwater resources would have a direct impact on the region’s economy.     

Assessing seasonal precipitation trends in India using parametric and non-parametric statistical techniques

This paper provides an insight into the long-term trends of the four seasonal and annual precipitations in various climatological regions and sub-regions in India. The trends were useful to investigate whether Indian seasonal rainfall is changing in terms of magnitude or location-wise. Trends were assessed over the period of 1954?C2003 using parametric ordinary least square fits and non-parametric Mann?CKendall technique. The trend significance was tested at the 95% confidence level. Apart from the trends for individual climatological regions in India and the average for the whole of India, trends were also specifically determined for the possible smaller geographical areas in order to understand how different the trends would be from the bigger spatial scales. The smaller geographical regions consist of the whole southwestern continental state of Kerala. It was shown that there are decreasing trends in the spring and monsoon rainfall and increasing trends in the autumn and winter rainfalls. These changes are not always homogeneous over various regions, even in the very short scales implying a careful regional analysis would be necessary for drawing conclusions regarding agro-ecological or other local projects requiring change in rainfall information. Furthermore, the differences between the trend magnitudes and directions from the two different methods are significantly small and fall well within the significance limit for all the cases investigated in Indian regions (except where noted).     

On climatic fluctuations and climate trends of modern Moscow

Considered are the results of the investigation of climatic fluctuations, supercentury climate trend, and 30-year trends in modern Moscow based on the time series of monthly mean values of air temperature for 1879?C2010. The data of air temperature anomalies in the Northern Hemisphere for the same period were used for the comparison. The computation of characteristics was carried out using the method of singular spectral analysis.     

中国雨日数的气候特征及趋势变化

使用国家气象信息中心整编的全国2 425个观测站1961年1月—2013年2月的52 a逐日降水观测资料,美国气象环境预报中心(NCEP)和美国国家大气研究中心(NCAR)资料。通过计算气候场、雨日概率、倾向值、M-K突变检验等现代统计诊断方法,研究了中国各等级雨日数的年、季节的时空分布特征和不同等级雨日数的趋势变化特征以及相关的背景环流。得到以下结论:(1)中国年总雨日数高值区在四川东部、贵州、江南及云南西南部,以小雨日数占比最高;中雨、大雨日数高值区在江南东部和云南西南部;50 mm以上雨日数中心分别在华南沿海和闽—浙—赣交界,前者强后者弱;(2)年内总雨日概率分布表现为3类:平缓型、单峰型、双峰型,南方地区除云南外均为平缓型;西藏东部、川西、陕甘宁3省南部、青海东部为双峰型;全国其余地区为单峰型;(3)中国季风区小雨日数在1970s末—1980s初发生突变,呈趋势性显著减少,除东北外,四季均减少,以秋冬季云南、上海等地减少最显著,而干旱半干旱区小雨日数呈增加趋势;(4)西南地区东部的年中雨日数在2000年后显著减少,秋季减少最明显,而京、沪、粤3大城市群年中雨日数呈增加趋势;西南地区东部秋季、云南夏季大雨以上日数在2003年后显著减少,而夏冬两季长江中下游中雨以上等级的雨日数明显增加;(5)川东、贵州、江南中部的雨日高值区与青藏高原东部低层回流冷空气形成的静止锋或辐合带相联系。     

Quantification of the influence of snow course measurement date on climatic trends

The Natural Resources Conservation Service measures high elevation snowpack manually at snow courses across the western US. In addition to supporting the production of seasonal snowmelt-driven streamflow forecasts, this long-term dataset is widely used throughout the research community to study historical climatic change impacts. Therefore it is critical to understand what factors may affect the quality of the measurements, especially if those non-climatic factors possess long-term trends. For example, the snowpack measurement dates are nominally the first and fifteenth of the month although they actually average approximately 2?days earlier. This study found that the variability of measurement dates are determined by, 1) the epoch of the measurement, 2) the day of the week of the nominal measurement date, 3) the presence or absence of snow at the site and 4) if the measurement is for the first or the fifteenth of the month. The measurement date is less variable if snow is absent from the site. Mid-month data are collected closer to the nominal measurement date, and first of month data have a greater early bias. Since 1957, there has been a stronger aversion to collecting data on Fridays and weekends. Measurements are taken today on average 1.35?days earlier than they were before 1957. The effect on measurement bias depended on the time of year and was generally less than 5?% of the measurement. Therefore, changes in measurement date only slightly mask one’s ability to accurately detect long-term climatic trends.     

Fluctuations and trends of annual precipitation in different climatic regions of Croatia

Summary Secular series of annual precipitation over Croatia have been studied at three stations representing the different climatic regions of Croatia: Osijek (continental precipitation climate), Zagreb-Gri (continental precipitation climate with maritime influence) and Crikvenica (maritime precipitation climate).The time series analysis has been deduced by using a quick test for stationarity according to Schönwiese and Malcher, moving average filters, the Mann-Kendall rank statistic, and a progressive test for trend according to Sneyers. From this analysis, the stationarity in time series of annual precipitation totals is stated over the entire interval at all locations except for a very short interval during the first decade of the twentieth century over the continental lowland (Osijek). A generally decreasing trend is present over the entire interval, but is statistically significant only in the continental lowland (Osijek).With 4 Figures     

Socio-economic and climatic changes lead to contrasting global urban vegetation trends

Urban greening can enhance quality of life by generating ecosystem services and has been proposed as a way of mitigating adverse consequences of global warming for human health. However, there is limited knowledge on global trends in urban vegetation and their relation to economic development and climate change. Here we studied 1,688 major cities worldwide and show that 70% (1,181) show an increase in vegetation derived from satellite observations (2000–2018). For 68% (1,138) of the cities studied, the increase in the urban vegetation is less strong as compared to the vegetation increase found in the surroundings of these cities. Overall, positive vegetation trends are widely observed in cities in Europe and North America, whereas negative vegetation trends in cities occur primarily in Africa, South America and Asia. Gross Domestic Product growth, population growth as well as temperature are found to be the main underlying drivers of the observed contrasts in changes in urban vegetation as compared to surrounding areas across continents. From a global synthesis of urban vegetation change, we quantify the role of social-economic development and climate change in regulating urban vegetation growth, and the contrasting imprint on cities of developed and developing countries.     

Comparison of climatic trends and variability among glacierized environments in the Western Himalayas

The climate and hydrology of the Western Himalayas is complex and a function of snow and glacier melt, land use, topography, and Indian summer and winter monsoon dynamics. Improving our knowledge about these processes is important from societal and agricultural points of view. In this study, an observational analysis is carried out to assess the changing climatic trends and the associated interannual variability in winter temperature and precipitation at three glacierized regions of Western Himalayas having distinctly different sub-regional characteristics. In situ observations of 23 years (1985–2007) are used. These observations are passed through rigorous statistical quality control checks. Results show higher interannual variability with increasing temperature trends in the glacierized regions of the Siachen (Karakoram Range) and Chotasigri (Great Himalayan Range). Karakoram Range has higher warming trends than the Great Himalayan Range. In case of precipitation, an overall decrease in precipitation is observed with contrasting trends in the last decade. Nino3.4 index is positively correlated with winter precipitation with similar interannual variability. In addition, at Siachen temperature and precipitation show strong negative correlation, and precipitation to spell length correlation is opposite at Siachen and Chotasigri.     

1951—2009年天津市主要极端气候指数变化趋势

利用1951—2009年天津市逐日气温和降水量资料,计算了极端气候指数,并研讨了其中11个主要指数的变化特征。结果表明：天津市暖日、冷夜具有基本相反的变化趋势,暖日显著增加,冷夜显著减少,且冷夜的变化幅度远大于暖日。持续暖期、霜日呈显著增加趋势,持续冷期呈显著减少趋势。降水指数中连续干日呈增加趋势,最大连续5 d降水量...     

1951—2009年天津市主要极端气候指数变化趋势

利用1951—2009年天津市逐日气温和降水量资料,计算了极端气候指数,并研讨了其中11个主要指数的变化特征。结果表明：天津市暖日、冷夜具有基本相反的变化趋势,暖日显著增加,冷夜显著减少,且冷夜的变化幅度远大于暖日。持续暖期、霜日呈显著增加趋势,持续冷期呈显著减少趋势。降水指数中连续干日呈增加趋势,最大连续5 d降水量、日降水强度、强降水率和极强降水率及连续湿日均呈减少趋势,表明天津市干旱化倾向明显。与气温有关的极端指数大多在1993年前后出现突变,周期特征不明显。与降水有关的极端指数未现突变,但周期特征明显,大多出现10 a和4 a的周期。     

Long term (100 yr) climatic trends for agriculture at selected locations in Canada

Long term (100 yr) trends of 17 selected annual climatic parameters were studied for 5 locations in Canada. Simple linear correlation coefficients (r) were computed for each variable with time. Temporal variations were not uniform over space, as might be expected over a large continent. Some variables differed significantly with time, while others did not. Forage aridity indices (FAI), or seasonal forage water deficits, had significant negativer values at Agassiz and Ottawa, indicating decreasing aridity over time, but no such trends were evident at the other 3 locations. Stations in western Canada were characterized byr values (mostly significant atP = 0.01) which indicated trends to earlier last spring frost (SF), later growing season end (GSE), later first fall frosts (FF) and increased frost-free period (FFP), growing degree-days (GDD) and Corn Heat Units (CHU). Stations in eastern Canada did not exhibit the same warming trends. No warming trends were observed in January mean temperature (JAN).Five-year moving averages and standard deviations were calculated and plotted forFAI, FF, GDD andGSL (growing season length). The climatic attributes were extremely variable, making detection of warming or cooling trends difficult. TheFAI for the last 30 yr or more at Agassiz and for the last 20 yr at Ottawa was well below the 100 yr normal. At Indian Head,FAI values were high during the 1930's and again around 1960, reflecting the drought conditions which occurred at those times. The other 3 variables showed a tendency to slightly increasing values over the past 50 yr at Agassiz, Indian Head, Brandon and Ottawa. Little, if any, systematic change in these elements was evident at Charlottetown. Standard deviations (S _d) fluctuated widely at all locations, with generally little evidence to suggest that the climate has become more or less variable. Cumulative frequency distribution for the total period and the first 70 yr were compared to the last 30 yr. There was an increased frequency of lowerFAI values at 2 locations for the 30-yr period.GDD increased significantly at lower probabilities at Indian Head. Differences in frequency distributions were generally slight for all other variables at the 5 locations.     

Spatial and temporal analysis of observed trends in extreme precipitation events in different climatic zones of Nigeria

Theoretical and Applied Climatology - The purpose of this study is to assess spatial and temporal changes in extreme precipitation events from 1983 to 2017 over different climatic regions of...     

Changes of atmospheric circulation in central Europe and their influence on climatic trends in the Czech Republic

This work deals with the influence of changes of atmospheric circulation on observed trends of 11 climatic elements at 21 stations in the Czech Republic in the period 1961–1998. Atmospheric circulation in central Europe is described by the German (Hess-Brezowsky) and Czech-Slovak (Brádka’s) subjective catalogues of synoptic types. In the study period there is a strong downward trend in the occurrence of anticyclonic types in Brádka’s catalogue in all seasons, this trend being most prominent in autumn. Westerly and northwesterly types become more frequent in autumn and winter, less frequent in spring and summer under both classifications. In the Hess-Brezowsky catalogue, the occurrence of anticyclonic types increases in winter, spring, and summer. To assess the effect of circulation changes on observed climate trends we have used the method of “hypothetical” seasonal trends that are calculated from a daily series, constructed by assigning the long-term monthly average of the given climatic element under a specific circulation type to each day classified with this type. The ratio of these circulation-conditioned trends and observed seasonal trends shows that changes in atmospheric circulation are the primary cause of massive winter warming and autumn cooling, which is connected with increasing precipitation and humidity. Summer climate trends are unrelated to changes in atmospheric circulation. Simultaneous use of more circulation classifications for the detection of climatic changes is highly recommended, as the long-term circulation trends depend on the catalogue applied.     

Variations and trends of onset, cessation and length of climatic growing season over Xinjiang, NW China

In this study, we assess spatial patterns of variations and trends of onset, cessation, and length of growing season using mean air temperature data recorded at 51 stations in Xinjiang province, NW China over the period 1959?C2008. Rank-based Mann?CKendall trend test and linear regression method are used to detect the significance and the magnitude of growing season change, respectively. Regionally, the average onset of the growing season has shifts 5.3?days earlier while the average ending date has moved 7.1?days later, increasing the length of the growing season by an average of 12.6?days. This study reveals a quite different result from previous studies. While the lengthening of the growing season in Xinjiang in the past 50?years is similar to that of previous studies, we find that the lengthening can be mainly attributed to delay of cessation in autumn rather than advance of onset in spring. The extended growing season will have strong implications in regional agricultural production of Xinjiang.     

Structure of climatic variability of the Mediterranean sea surface temperature. Part I. Standard deviations and linear trends

Interannual and longer-period variability of the Mediterranean sea surface temperature is studied in terms of standard deviations and linear trends based on the 1951–2000 data. It is shown that both standard deviations and linear SST trends in the Mediterranean Sea are clearly season-dependent. Seasonality of standard deviations is characterized by a zonally-oriented seesaw with opposite changes in standard deviations in the western and eastern parts of the basin from season to season. The SST trend seasonality is pronounced in winter in predominant negative SST trends, and in summer in positive trends. Such seasonal differences indicate that long-term Mediterranean SST variability has different mechanisms of formation.