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1.
Dendroecological techniques were employed to explore the growth response of subalpine fir (Abies fargesii) to climatic conditions across its altitudinal range in both the north and south aspects in the Shennongjia Mountains, central China. Correlation function analyses indicated that temperatures in current summer were significantly negatively correlated with fir radial growth at the lower limits, while temperatures in previous autumn and in current spring showed significantly positive correlations with fir radial growth at the mid- and high-elevations in both aspects. Radial growth of the subalpine fir was significantly and positively influenced by precipitation in previous autumn and in current spring at the lower elevations and by precipitation in current spring at the mid-elevations, while precipitation had no significant effects on its radial growth at the upper elevations. Moving correlation functions showed that temperatures in early spring of the current year (i.e., February-April) had a relatively stable effect on tree growth over time at the mid- and upper-elevations in both aspects. Thus, the growth of the subalpine fir responded differently to climatic conditions along the altitudinal gradient, showing that the importance of temperatures for the fir radial growth increased while the importance of precipitation decreased with increasing altitude in both aspects in the Shennongjia Mountains, central China.  相似文献   

2.
We used dendroclimatology to quantify inter-annual to multi-decadal climatic variation effects on white spruce radial growth in southwest Yukon, Canada. Local climate is dry and cold, such that tree growth was primarily moisture- rather than temperature-limited, although the mechanisms varied temporally. During the 20th century, significant increases in precipitation countered warming temperatures, so that heat?moisture indices have not changed significantly. Directional climatic change, superimposed on variation due to the Pacific Decadal Oscillation (PDO), resulted in unstable climate?growth relations. Prior to 1977, ring widths were positively correlated with previous growing season precipitation and warm temperatures had a negative impact, exacerbating moisture limitations in dry years especially during the cool, dry negative PDO phase (1946?1976). After 1977, correlations with previous growing season precipitation became negative and correlations with previous fall and winter precipitation and current year July and August temperatures became positive, although not statistically significant. These changes suggest precipitation and temperature increases over recent decades benefitted white spruce growth. Climate projections for this region include further temperature and precipitation increases, which may promote white spruce growth depending on the seasonality and interactions between temperature and precipitation. This study demonstrated the complexity of potential responses of white spruce to climate variation and change.  相似文献   

3.
Summary An analysis of correlation coefficients for climatological data covering the period 1901–1994 or 1931–1994 for six locations in Switzerland has been made in order to highlight the relationships between temperature, precipitation (rain and snow) and snow in summer and in winter. The results show that colder summers tend to be associated with more precipitation, mainly in terms of the frequency of occurrence of precipitation, but also in terms of its abundancy. In winter, sites located at lower altitudes behave differently from those at higher elevations. At lower altitudes, warmer winters tend to be rainier and to have less snow (only a small part of winter precipitation falls in the form of snow). Above 1000–1500 m, correlations between temperature on the one hand, and precipitation or snow on the other, tend to be weaker than at lower elevations; warmer winters are associated with less snow but also with less precipitation in general, while the relationship between precipitation and snow is stronger.These results confirm that during cold periods of the past, such as Löbben Phase (1400 BC — 1230 BC) cold summers were probably linked to frequent and abundant precipitation. These conditions led to increased mortality as well as to population migrations. In terms of potential future global warming, if the current temperature/precipitation relationships remain unchanged, then warmer summers will likely be linked to a decrease in precipitation. Higher winter temperatures can be expected to lead to a general decrease of snow and to a decrease in precipitation, but only at higher elevations; warmer winters would conversely be associated with an increase in precipitation at lower altitudes.With 4 Figures  相似文献   

4.
基于1961—2013年中国台站的均一化气温数据、NOAA月平均海温资料和CMIP5气候模式数据,利用气候统计手段,定量分析太平洋年代际振荡（PDO）对中国冬季最低气温年代际变化的贡献。结果表明：PDO的年代际序列与年代际滤波后的最低气温场在全国大部分地区呈显著正相关,即PDO负位相时中国冬季最低气温偏低,反之偏高。2006年后中国冬季最低气温变暖减缓,造成这一现象的主要原因是自然变率起到的降温作用,而自然变率又主要由PDO起主导作用,约占自然变率贡献的40%左右。PDO对温度的贡献呈现出明显的年代际变化,在变暖减缓期对升温有明显的负贡献,且负贡献逐渐增大至超过50%。  相似文献   

5.
The impact of interannual variability in temperature and precipitation on global terrestrial ecosystems is investigated using a dynamic global vegetation model driven by gridded climate observations for the twentieth century. Contrasting simulations are driven either by repeated mean climatology or raw climate data with interannual variability included. Interannual climate variability reduces net global vegetation cover, particularly over semi-arid regions, and favors the expansion of grass cover at the expense of tree cover, due to differences in growth rates, fire impacts, and interception. The area burnt by global fires is substantially enhanced by interannual precipitation variability. The current position of the central United States’ ecotone, with forests to the east and grasslands to the west, is largely attributed to climate variability. Among woody vegetation, climate variability supports expanded deciduous forest growth and diminished evergreen forest growth, due to difference in bioclimatic limits, leaf longevity, interception rates, and rooting depth. These results offer insight into future ecosystem distributions since climate models generally predict an increase in climate variability and extremes. CCR Contribution # 941  相似文献   

6.
We here present a reconstruction (1725–1999) of the winter Pacific North American (PNA) pattern based on three winter climate sensitive tree ring records from the western USA. Positive PNA phases in our record are associated with warm phases of ENSO and PDO and the reorganization of the PNA pattern towards a positive mode is strongest when ENSO and PDO are in phase. Regime shifts in our PNA record correspond to climatic shifts in other proxies of Pacific climate variability, including two well-documented shifts in the instrumental period (1976 and 1923). The correspondence breaks down in the early 19th century, when our record shows a prolonged period of positive PNA, with a peak in 1800–1820. This period corresponds to a period of low solar activity (Dalton Minimum), suggesting a ‘positive PNA like’ response to decreased solar irradiance. The distinct 30-year periodicity that dominates the PNA reconstruction in the 18th century and again from 1875 onwards is disrupted during this period.  相似文献   

7.
Summary ?In many instances, snow cover and duration are a major controlling factor on a range of environmental systems in mountain regions. When assessing the impacts of climatic change on mountain ecosystems and river basins whose origin lie in the Alps, one of the key controls on such systems will reside in changes in snow amount and duration. At present, regional climate models or statistical downscaling techniques, which are the principal methods applied to the derivation of climatic variables in a future, changing climate, do not provide adequate information at the scales required for investigations in which snow is playing a major role. A study has thus been undertaken on the behavior of snow in the Swiss Alps, in particular the duration of the seasonal snow-pack, on the basis of observational data from a number of Swiss climatological stations. It is seen that there is a distinct link between snow-cover duration and height (i.e., temperature), and that this link has a specific “signature” according to the type of winter. Milder winters are associated with higher precipitation levels than colder winters, but with more solid precipitation at elevations exceeding 1,700–2,000 m above sea-level, and more liquid precipitation below. These results can be combined within a single diagram, linking winter minimum temperature, winter precipitation, and snow-cover duration. The resulting contour surfaces can then be used to assess the manner in which the length of the snow-season may change according to specified shifts in temperature and precipitation. While the technique is clearly empirical, it can be combined with regional climate model information to provide a useful estimate of the length of the snow season with snow cover, for various climate-impacts studies. Received May 14, 2002; revised August 12, 2002; accepted August 17, 2002  相似文献   

8.
A new set of tree-ring records from the Andes of northern Patagonia, Argentina (41° S) was used to evaluate recent (i.e., last 250 years) regional trends in tree growth at upper treeline. Fifteen tree-ring chronologies from 1200 to 1750 m elevation were developed for Nothofagus pumilio, the dominant subalpine species. Samples were collected along three elevational transects located along the steep west-to-east precipitation gradient from the main Cordillera (mean annual precipitation >4000 mm) to an eastern outlier of the Andes (mean annual precipitation >2000 mm). Ring-width variation in higher elevation tree-ring records from the main Cordillera is mainly related to changes in temperature and precipitation during spring and summer. However, the response to climatic variation is also influenced by local site factors of elevation and exposure. Based on the relationships between Nothofagus growth and climate, we reconstructed changes in snow cover duration in late spring and variations in mean annual temperature since A.D. 1750. Abrupt interannual changes in the mean annual temperature reconstruction are associated with strong to very strong El Niño-Southern Oscillation events. At upper treeline, tree growth since 1977 has been anomalously high. A sharp rise in global average tropospheric temperatures has been recorded since the mid-1970s in response to an enhanced tropical hydrologic cycle due to an increase in temperature of the tropical Pacific. Temperatures in northern Patagonia have been anomalously high throughout the 1980s, which is consistent with positive temperature anomalies in the tropical Pacific and along the western coast of the Americas at c.a. 40° S latitude. Our 250-year temperature reconstruction indicates that although the persistently high temperatures of the 1980s are uncommon during this period, they are not unprecedented. Tropical climatic episodes similar to that observed during the 1980s may have occurred in the recent past under pre-industrial carbon dioxide levels.  相似文献   

9.
The ability of the Parallel Climate Model (PCM) to reproduce the mean and variability of hydrologically relevant climate variables was evaluated by comparing PCM historical climate runs with observations over temporal scales from sub-daily to annual. The domain was the continental U.S, and the model spatial resolution was T42 (about 2.8 degrees latitude by longitude). The climate variables evaluated include precipitation, surface air temperature, net surface solar radiation, soil moisture, and snow water equivalent. The results show that PCM has a winter dry bias in the Pacific Northwest and a summer wet bias in the central plains. The diurnal precipitation variation in summer is much stronger than observed, with an afternoon maximum in summer precipitation over much of the U.S. interior, in contrast with an observed nocturnal maximum in parts of the interior. PCM has a cold bias in annual mean temperature over most of the U.S., with deviations as large as ?8 K. The PCM daily temperature range is lower than observed, especiallyin the central U.S. PCM generally overestimates the net solar radiation over most of the U.S, although the diurnal cycle is simulated well in spring, summer and winter. In autumn PCM has a pronounced noontime peak in solar radiation that differs by 5–10% from observations. PCM'ssimulated soil moisture is less variable than that of a sophisticated land-surface hydrology model, especially in the interior of the country. PCM simulates the wetter conditions over the southeastern U.S. and California during warm (El Niño) events, but shifts the drier conditions in the PacificNorthwest northward and underestimates their magnitude. The temperature response to the North Pacific Oscillation is generally captured by PCM, but the amplitude of this response is overestimated by a factor of about two.  相似文献   

10.
Tendencies of climatic variability indicate that northern Mexico will soon suffer from severe drought. Modeling the influence of climate and ecological processes would help researchers better understand the future implication of climatic variations. Here, we reconstructed historical seasonal precipitation using dendrochronological indices of Pinus cooperi and El Niño southern oscillation (ENSO). Correlation analysis was conducted to establish the precipitation response period; then a reconstruction model using independent variables was constructed using regression procedures. Available data were calibrated and verified to strengthen and validate the modeled reconstruction. Precipitation from the previous winter was best correlated with tree growth. Regression procedures showed that the residual chronology associated in a linear model with El Niño 3.4 explained 47 % of seasonal precipitation variability. This study contributes to a better understanding of historical variations in precipitation and the influence of ENSO in common tree species of northern Mexico to help land managers improve local forest management in a climate change scenario.  相似文献   

11.
In this study, we investigated the response of trees growing at the cold margins of the boreal forest to climate variation in the 20th century. Working at eight sites at and near alpine and arctic treeline in three regions in Alaska, we compared tree growth (from measured tree ring-widths) to historical climate data to document how growth has responded to climate variation in the 20th century. We found that there was substantial regional variability in response to climate variation. Contrary to our expectations, we found that after 1950 warmer temperatures were associated with decreased tree growth in all but the wettest region, the Alaska Range. Although tree growth increased from 1900–1950 at almost all sites, significant declines in tree growth were common after 1950 in all but the Alaska Range sites. We also found that there was substantial variability in response to climate variation according to distance to treeline. Inverse growth responses to temperature were more common at sites below the forest margin than at sites at the forest margin. Together, these results suggest that inverse responses to temperature are widespread, affecting even the coldest parts of the boreal forest. Even in such close proximity to treeline, warm temperatures after 1950 have been associated with reduced tree growth. Growth declines were most common in the warmer and drier sites, and thus support the hypothesis that drought-stress may accompany increased warming in the boreal forest.  相似文献   

12.
The impacts of year-to-year and decade-to-decade climatic variations on some of the Pacific Northwest's key natural resources can be quantified to estimate sensitivity to regional climatic changes expected as part of anthropogenic global climatic change. Warmer, drier years, often associated with El Niño events and/or the warm phase of the Pacific Decadal Oscillation, tend to be associated with below-average snowpack, streamflow, and flood risk, below-average salmon survival, below-average forest growth, and above-average risk of forest fire. During the 20th century, the region experienced a warming of 0.8 °C. Using output from eight climate models, we project a further warming of 0.5–2.5 °C (central estimate 1.5 °C) by the 2020s, 1.5–3.2°C (2.3 °C) by the 2040s, and an increase in precipitation except in summer. The foremost impact of a warming climate will be the reduction of regional snowpack, which presently supplies water for ecosystems and human uses during the dry summers. Our understanding of past climate also illustrates the responses of human management systems to climatic stresses, and suggests that a warming of the rate projected would pose significant challenges to the management of natural resources. Resource managers and planners currently have few plans for adapting to or mitigating the ecological and economic effects of climatic change.  相似文献   

13.
Tree-ring estimates of Pacific decadal climate variability   总被引：10，自引：0，他引：10  
 Decadal-scale oscillatory modes of atmosphere-ocean variability have recently been identified in instrumental studies of the Pacific sector. The regime shift around 1976 is one example of such a fluctuation, which has been shown to have significantly impacted climate and the environment along the coastline of the western N and S Americas. The length of meteorological data for the Pacific and western Americas critically limits analyses of such decadal-scale climate variability. Here we present reconstructions of the annual Pacific Decadal Oscillation (PDO) index based on western North American tree-ring records which account for up to 53% of the instrumental variance and extend as far back as AD 1700. The PDO reconstructions indicate that decadal-scale climatic shifts have occurred prior to the period of instrumental record. Evaluation of temperature and precipitation-sensitive tree-ring series from the northeast Pacific as well as these reconstructions reveals evidence for a shift towards less pronounced interdecadal variability after about the middle 1800s. Our analyses also suggest that sites from both the northeast Pacific coast as well as the subtropical Americas need to be included in proxy data sets used to reconstruct the PDO. Received: 15 September 2000 / Accepted: 30 March 2001  相似文献   

14.
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.  相似文献   

15.
我国华南3月份降水年代际变化的特征   总被引：5，自引：2，他引：3  
利用1951～2005年华南3月份降水资料、太平洋年代际振荡(PDO)指数以及NCEP再分析资料,对华南3月份降水年代际变化特征、及其对应的大尺度环流以及与PDO的关系进行了分析。结果表明,华南3月份降水存在显著的年代际变化特征,并且Mann-Kendal突变检验表明华南3月份降水在1978年左右发生年代际突变,从之前的降水偏少转变为降水偏多。我国华南3月份降水与PDO有着显著的相关。进一步研究表明,在年代际降水偏少时期,PDO处于负位相(北太平洋海温偏高,中东太平洋海温偏低),北太平洋海平面气压场和高度场偏高,亚洲大陆海平面气压场和高度场偏低,赤道西太平洋到赤道东印度洋附近的海平面气压场偏低,赤道辐合带附近地区的高度场偏低,东亚对流层大气偏暖,西太平洋副热带高压偏东,东亚高空急流偏北,东亚Hadley环流偏弱。在年代际降水偏多时期,PDO处于正位相,情况则与降水偏少时期相反。  相似文献   

16.
Growth of trees at their altitudinal and latitudinal range limits is expected to increase as climate warms, but trees often exhibit unexplained spatial and temporal variation in climate-growth responses, particularly in alpine regions. Until this variability is explained, predictions of future tree growth are unlikely to be accurate. We sampled Picea glauca (white spruce) growing at forest and tree line on north and south aspects in two mountain ranges of southwest Yukon to determine how and why ring-width patterns vary between topographic settings, and over time. We used multivariate statistical analysis to characterize variation in ring-width patterns between topographic factors and time periods, and calculated correlations between ring-width indices and climate variables to explain this variation. Ring-width patterns varied more between mountain ranges than elevations or aspects, particularly in recent decades when ring-widths increased in one mountain range but not the other. Growth responses to summer temperature were notably weaker during warmer time periods, but growth was not positively correlated to summer precipitation, suggesting trees may not be suffering from temperature-induced drought stress. Rather, ring-width indices began responding positively to spring snow depth after 1976. We conclude that tree growth is unlikely to increase in synchrony with rising air temperatures across subarctic tree lines in southwest Yukon. Instead, they may decline in areas that are prone to thin snowpacks or rapid spring runoff due to the negative influence warming springs will have on snow depth and, consequently, early growing season soil moisture.  相似文献   

17.
基于最新版本的全球降水气候中心(Global Precipitation Climatology Centre Version 7,GPCC_V7)资料与欧洲中期数值预报中心20世纪再分析资料(ERA-20C)融合的百年尺度逐月降水资料(1901~2012年),运用集合经验模态分解方法(EEMD)、合成分析等方法系统分析了我国北方干旱半干旱区降水多年代际变化特征及与太平洋年代际振荡(PDO)之间的相互关系。结果表明:北方干旱半干旱区大多数区域降水都具有50~60年的平均变化周期,而PDO对大多数地区降水多年代际变化特征具有明显的调制作用;其中新疆北部和内蒙古北部的降水与PDO呈现出显著的正相关,而河套东西部地区的降水则与PDO的变化呈现显著负相关。进一步分析表明,当PDO为暖相位时,径向环流增强使得北冰洋水汽南下,当遇到低空北上的阿拉伯海域暖湿气流时,会造成新疆中南部的降水增多;另一方面,PDO暖相位时赤道西太平洋及印度洋区域通过对流加热的作用激发了太平洋—日本/东亚—太平洋(PJ/EAP)遥相关型的产生,这有利于渤海湾暖湿水汽输送至干旱半干旱区北部区域,增大降水概率;同时,当偏北和偏西气流在河套北部区域相遇时会形成降水中心。当PDO位于冷位相时,结论则反之。  相似文献   

18.
Outputs from a 10,000-year simulation with a coupled global climatic model for present climatic conditions have been used to investigate the behaviour of the Pacific Decadal Oscillation (PDO), the North Pacific Oscillation (NPO) and related phenomena. The analysis reveals a wide range of temporal variability for these Oscillations, suggesting that observations to date provide only a limited sample of possible outcomes. In addition, the simulation suggests that the current observed phase relation between the PDO and NPO may not be typical of longer-term variability. Climatic jumps appear to be a ubiquitous feature of climatic variability, and while, as observed, the most common interval between such jumps is about 20 years, intervals of up to 100 years occur in the simulation. The probability density functions of the PDO and NPO are very close to Gaussian, with the PDO being represented by an auto-regressive function of order one, while the NPO consisted of white noise. An FFT analysis of PC1 of the PDO revealed periodicities concentrated near 10 years, while for the NPO the principal periodicities were decadal to bidecadal. Global distributions of the distributions of the correlations between PC1 or the NPO and selected climatic variables were similar, and in agreement with observations. These correlations highlight the inter-relationships between these two Oscillations. The above correlations were not necessarily stable in time for a given geographical point, with transitions occurring between positive and negative extremes. Climatic jumps were identified with transitions of both the PDO and NPO, with magnitudes of importance as regards climatic perturbations. Spatial patterns of the changes associated with such jumps have global scales, and the need to consider the implications of these jumps in regard to greenhouse induced climatic change is noted.  相似文献   

19.
This paper highlights the relationship between precipitation variability at the sub-regional level in the Southwest United States and the SOI and PDO climate teleconnection indices during the period 1950–2000. Statistical correlations at α = 0.05 and 0.01 levels are calculated for fall, winter, and spring precipitation in the Southwest, and contemporaneous and antecedent seasonal SOI and PDO index values. A strong SOI-winter precipitation signal is seen to progress across Arizona and New Mexico from southwest to northeast over a three-season lagged period. The PDO also exhibits a strong relationship with winter and spring precipitation in New Mexico; however, the PDO is not well correlated with precipitation in Arizona. The results underscore the non-uniform spatio-temporal relationships of the SOI and PDO indices as they relate to the precipitation regime of the Southwest, and provide a framework for future diagnostic analyses of these relationships.  相似文献   

20.
The Intra-Americas Sea (IAS) low-level jet has been studied mainly for the summer and winter seasons. In contrast, spring conditions have been studied less. Here we analyze the boreal spring variability of the IAS low-level jet (IA-LLJ) and its relation with precipitation and tornadic activity in the region of the lower Mississippi, Tennessee and Ohio River basins (MORB). The main mode of variability of the spring IA-LLJ is obtained from a combined principal component analysis of zonal and meridional winds at 925-hPa. The first empirical orthogonal function of the IA-LLJ is a strengthening of the climatological flow with stronger easterlies in the Caribbean and stronger southeasterlies in the Gulf of Mexico. This first mode of variability of the IA-LLJ is related mainly to the Pacific North American (PNA) teleconnection pattern as the PNA modulates the pressure in the southeast region of the U.S. Consequently, there is an increase in precipitation over the MORB region as the moisture fluxes associated with the IA-LLJ increase. Tornadic activity in nine states spanning the MORB region is also significantly related to the IA-LLJ and the PNA index for March, in addition to the Pacific decadal oscillation (PDO) and the Ni?o indexes. Among the environmental factors that influence tornadic activity are southwesterly wind shear, dry transients at the mid-troposphere, moist transients at low levels, and an increase in convective available potential energy (CAPE). The decadal shifts in MORB precipitation and tornado activity appear to be related to the decadal shift of the IA-LLJ.  相似文献   

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