Impact of recent climatic change on growth of low elevation eastern Mediterranean forest trees

Evidence is presented of how Pinus halepensis Miller from dry habitats at <300 m elevation of four Greek island regions have responded to climatic conditions of the last two centuries. We compared historical periods of low growth due to low precipitation with the recent period of significant precipitation decline. In all cases trees?? growth patterns across the twentieth century were consistent with trends in annual (rather than seasonal) precipitation, with lowest values in both precipitation and radial growth during the last two decades of the twentieth century, the worst conditions for tree growth in more than 200 years. The data are compared with trends across different vegetation belts of the northern Mediterranean basin. Drought related tree mortality in Greece in 2000 and 2007 coincided with the most severe fire outbreaks on record. IPCC WG I (2007) climate scenarios for the Mediterranean suggest a further decline in precipitation, particularly in the eastern regions. Should this occur, growth reduction in trees, tree mortality and damage from forest fires are likely to become more severe.     

华山松树木年轮对气候响应的模拟分析

采用树木年轮生长模型,从细胞尺度对华山松在不同时期的树木生长状况,包括早材和晚材的细胞大小等年轮结构变化进行了模拟。所建立的细胞大小年表对气候的响应函数结果,揭示出华山松的生长主要受生长季中4～7月份以及滞后一年降水的影响,而温度只是在生长季节开始的4月份起限制作用。利用气候资料对华山松的细胞大小及变化趋势的模拟结果表明,它与实测值十分接近。     

巴丹吉林南缘近两百年来年降水重建及初步分析

沙漠及其边缘地区生态环境脆弱,对气候变化敏感。但沙漠地区有限的森林资源限制了区域百年到千年尺度上的历史气候变化研究。利用采自巴丹吉林南缘的青海云杉年轮宽度资料,重建了区域近191 a(1815—2005年)来的年降水(前一年7月至当年8月的总降水量)变化序列。重建的相关系数是0.636,方差解释量为40.4%,调整自由度后的解释方差R2adj为0.392。重建结果稳定可靠。分析区域过去年降水变化结果可见,19世纪该区域干湿变化频繁,20世纪前半段主要以干旱为主,干湿转变较少。20世纪20年代的干旱事件在巴丹吉林南缘的干旱持续时间更长。周期分析的结果表明,区域年降水量变化有2 a、4 a、64 a等周期。     

Climatic trends and different drought adaptive capacity and vulnerability in a mixed Abies pinsapo�CPinus halepensis forest

The projected temperature rise, rainfall decrease and concentration of rainfall in extreme events could induce growth decline and die-off on tree populations located at the geographical distribution limit of the species. Understanding of adaptive capacity and regional vulnerability to climate change in Mediterranean forests is not well developed and requires more focused research efforts. We studied the relationships between spatiotemporal patterns of temperature and precipitation along the southwestern edge of the Betic range (southern Spain) and measured basal area increment (BAI) and carbon isotope (??) in tree ring series of Abies pinsapo and Pinus halepensis, two Mediterranean conifer trees with contrasting drought adaptive capacity. Climatic information was obtained from a network covering a wide range of elevations and distances from the Atlantic and Mediterranean coasts. Temperature trends were tested by the Mann?CKendall test, and precipitation was thoroughly analyzed by quantile regression. Climatic data showed a warming trend, enhanced since the 1970s, while quantile regressions revealed that drought events worsened during the course of the twentieth century. Long-term decrease of A. pinsapo BAI was related to regional warming and changing precipitation patterns, suggesting increasing drought stress on this species. Both temperature and precipitation in the summer influenced wood ?? in P. halepensis, whereas negative correlation between wood ?? and current autumn temperature was yielded for A. pinsapo. Increased intrinsic water use efficiency was inferred from wood ?? in both species; however, A. pinsapo showed sudden growth reductions under drier conditions, while pine trees were able to maintain almost constant BAI values and lower water costs under increasing long-term water stress.     

Unstable climate−growth relations for white spruce in southwest Yukon, Canada

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.     

Linking two centuries of tree growth and glacier dynamics with climate changes in Kamchatka

Glaciers around the world retreated as the climate warmed substantially. For the majority of alpine and arctic areas, however, the lack of meteorological data over a long period makes it difficult to build long-term climate and glacial fluctuation relationships, emphasizing the importance of natural proxy archives. Here we use the 230-year record of stem radial growth of birch trees (Betula ermanii) from the treeline forests above the receding glaciers in eastern maritime Kamchatka to analyse temporal variations of climate as well as glacial advance and retreat. Glaciers in Kamchatka Peninsula represent the southern limit of glaciation in far eastern Eurasia, which makes them prone to global warming. Using instrumental climate data (1930–1996) from local meteorological stations, we find that the July temperature had most prominent positive impact on birch growth. On the contrary, smaller ring increments are associated with the positive summer and net annual ice mass balance of Koryto Glacier. The prevailing trend of higher summer temperatures and lower snowfall over the past 70 years has enhanced tree growth while causing the glacier’s surface to lower by about 35 m and its front to retreat by about 490 m. Assuming these same relationships between climate, tree growth, and glacier mass balance also existed in the past, we use tree rings as a proxy record of climatically induced temporary halts in the glacier’s retreat over the past two centuries, which in total was over 1,000 m. Both direct observations and tree ring proxies indicate several prolonged warm periods (1990s, 1960s, 1930–1940s, 1880–1900s) interspersed with cooler periods (1984–1985, 1970–1976, 1953–1957, 1912–1926, 1855–1875, 1830–1845, 1805–1820 and 1770–1780) when the glacier re-advanced, creating several consecutive terminal moraine ridges. We conclude that birch tree-rings are suitable for assessing tree growth/climate/glacial relationships over a longer timescale in maritime Kamchatka.     

A millennial long March–July precipitation reconstruction for southern-central England

We present a millennial long dendroclimatic reconstruction of spring/summer precipitation for southern-central England. Previous research identified a significant moisture stress signal in ring-width data measured from oak trees growing in southern England. In this study, we build upon this earlier work, specifically targeting south-central England, to derive a well replicated oak ring-width composite chronology using both living and historical material. The data-set includes 352 living trees (AD 1629–2009) and 1540 individual historical series (AD 663–1925). The period expressed by at least 50 trees in any year is AD 980–2009. Calibration experiments identify the optimal seasonal predictand target as March–July precipitation (1901–2007: r² = 0.33). However, comparison with the long Kew Gardens precipitation record indicates a weakening in tree-growth/climate response from ~1800 to 1920 which we speculate may be related to smoke and sulphur dioxide (SO₂) emissions at that time which may have also contributed to a decrease in tree productivity. The time-series derived using the regional curve standardisation method to capture lower frequency information shows a mediaeval period with alternating multi-decade-long dry and wet periods, with AD 1153–1172 being the wettest reconstructed 20-year period in the whole record. Drier conditions are prevalent from ~1300 to the early sixteenth century followed by a period of increasing precipitation levels. The most recent four centuries of the record appear similar to the mediaeval period with multiple decade-long dry and wet periods. The late twentieth century is the second reconstructed wettest period. These centennial hydroclimatic trends are in broad agreement with independent regional scale hydroclimatic reconstructions from tree-ring (East Anglia), historical, speleothem and peat water level proxy archives in the United Kingdom and appear coupled with reconstructed sea surface temperature changes in the North Atlantic which in turn influence the Atlantic meridional overturning circulation and westerly airflow across the UK.     

Evaluation of climate change over the continental United States using a moisture index

This paper uses a modified form of Thornthwaite’s moisture index to better quantify climate variability by integrating the effects of temperature and precipitation. Using the moisture index, trends were evaluated over the last 112 years (1895–2006), when unique changes in temperature and precipitation have been documented to have occurred. In addition, data on potential evapotranspiration and the moisture index were used to investigate changing climate and vegetation regions. The results show that the eastern half of the country has been getting wetter, even as temperatures have continued to increase in many areas. In particular, conditions have become wetter in the South, Northeast, and East North Central regions. The changing climate is illustrated by computing climate and vegetation regions for three 30-year periods (1910–1939, 1940–1969, and 1970–1999). Climate regions based on the moisture index show an expansion of the Humid region (where precipitation vastly exceeds climatic demands for water) across the East as well as a westward shift in the zero moisture index line. In terms of vegetation zones, the most dramatic change occurs across the Midwestern prairie peninsula where the wetter conditions lead to a westward expansion of conditions favorable for oak–hickory–pine vegetation.     

Historical and potential changes of precipitation and temperature of Alberta subjected to climate change impact: 1900–2100

We investigated changes to precipitation and temperature of Alberta for historical and future periods. First, the Mann-Kendall test and Sen’s slope were used to test for historical trends and trend magnitudes from the climate data of Alberta, respectively. Second, the Special Report on Emissions Scenarios (SRES) (A1B, A2, and B1) of CMIP3 (Phase 3 of Coupled Model Intercomparison Project), projected by seven general circulation models (GCM) of the Intergovernmental Panel on Climate Change (IPCC) for three 30 years periods (2020s, 2050s, and 2080s), were used to evaluate the potential impact of climate change on precipitation and temperature of Alberta. Third, trends of projected precipitation and temperature were investigated, and differences between historical versus projected trends were estimated. Using the 50-km resolution dataset from CANGRD (Canadian Grid Climate Data), we found that Alberta had become warmer and somewhat drier for the past 112 years (1900–2011), especially in central and southern Alberta. For observed precipitation, upward trends mainly occurred in northern Alberta and at the leeward side of Canadian Rocky Mountains. However, only about 13 to 22 % of observed precipitation showed statistically significant increasing trends at 5 % significant level. Most observed temperature showed significant increasing trends, up to 0.05 °C/year in DJF (December, January, and February) in northern Alberta. GCMs’ SRES projections indicated that seasonal precipitation of Alberta could change from ?25 to 36 %, while the temperature would increase from 2020s to 2080s, with the largest increase (6.8 °C) in DJF. In all 21 GCM-SRES cases considered, precipitation in both DJF and MAM (March, April, and May) is projected to increase, while temperature is consistently projected to increase in all seasons, which generally agree with the trends of historical precipitation and temperature. The SRES A1B scenario of CCSM3 might project more realistic future climate for Alberta, where its water resources can become more critical in the future as its streamflow is projected to decrease continually in the future.     

宁夏河东沙地近百年来气候背景变化分析

利用贺兰山树木年轮指数与河东沙地盐池代表站的年降水量及气温距平建立相关关系,对河东沙地近百年的降水量及气温距平序列进行拟合延长,分析河东沙地近百年来气候变化大趋势。同时利用河东沙地范围内6个代表性站气象资料,对近50年来河东沙地气候变化特征作较详细的分析。结果表明:河东沙地在30年代之前为干冷期;30年代以后逐渐向暖湿方向发展,一直持续到50年代中期;50年代中期以后是一个典型的寒冷湿润时期;60年代以后是一个相对干冷时期;80年代中期至今是近百年里的一个相对干暖时期。另外,在河东沙地不同时间、不同方位上气温、降水量、蒸发量、空气相对湿度及平均风速均存在着较大差异。     

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.     

长江源区近44年气候变化的若干统计分析

利用长江源区5个气象站44年的气温、降水量资料以及其中2个探空站500hPa露点资料,分析了该地区气候变化趋势、突变等情况。结果表明：近44年来长江源区气温普遍升高,冬季升温幅度较大,夏季增温趋势明显,进入21世纪后,长江源区春季平均气温在降低,夏、秋季平均气温增高较趋缓,而冬季增温加剧的趋势十分明显;年、夏季降水量变化呈微弱减少趋势,而冬、春和秋季降水量呈现出增加趋势,其中春季增幅较大,冬季增湿趋势明显;长江源区年平均气温在20世纪60年代末70年代初就显现出波动回升的趋势,在1986年前后发生了由冷到暖的突变,冬、春季降水量均在20世纪70年代和80年代出现了由少向多的突变。长江源区气候在波动性变暖变干过程中,自1986年起出现了气候转向暖湿的信号,其主要原因在于全球变暖并由此引起的海洋蒸发和陆地蒸散加强,地气水分循环加快,空中水汽输送加强。     

青藏铁路沿线永冻土区近千年的气候演变特征

利用树木年轮重建了青藏铁路沿线多年冻土区的年平均气温(763—1998年)、年降水序列(1518—1983年)。利用小波分析,发现10年时间尺度上气温可分为14个暖期和13个冷期,在30年时间尺度上中世纪暖期和小冰期表现明显;降水从30年左右时间尺度上看,大致上只有1591—1640年、1671—1730年和1770—1950年降水偏多,其余时间降水都偏少。现今依然处在暖干期。功率谱分析发现,气温主要周期为2．0,2．5,3．6,7．2,22．8和117．7年,降水主要周期为2．1,3．1,4．5,7．7,11．3,20．8,28和62年。     

采用青海两个树木年轮年表重建局地过去降水的初步分析

本文依据青海乌兰、班玛两个经过精确定年的树木年轮年表,通过响应函数计算,求得逐月的气候因素对轮宽生长的贡献。在贡献显著的时区内,经由相关计算确立最佳重建时段,选取预报因子,再用逐步回归方法建立方程来重建过去气候。分析表明在重建时段内的两地降水变化,均有明显的多雨期和少雨期,同时存在显著的周期现象。     

RECENT TRENDS IN TREE-RING RECORDS FROM HIGH ELEVATION SITES IN THE ANDES OF NORTHERN PATAGONIA

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.     

利用树木年轮资料重建新疆东天山300多年来干旱日数的变化

采用东天山6个相邻地点的云杉年轮序列求得该区域平均树木年轮年表（1665～1988年）。通过响应面函数的计算，发现树木生长对温度和降水有明显的非线性响应，表明用该年表序列重建单个温度要素存在一定片面性，利用森林干旱模式计算的树木生长期干旱数，含有温度、降水、土壤性质等诸因子，且与年轮生长明显相关。进而利用树木年轮资料重建了该地区过去300年来干旱日数，与实际旱涝情况吻合较好。     

喜马拉雅山区1951—2010年气候变化事实分析

选择喜马拉雅山南北两侧有代表性的13个气象站1951—2010年的气温、降水资料,分析这些台站气候变化总体趋势、年代际变化及突变特征,结果表明：1961—2010年整个喜马拉雅山区的气温总体呈显著上升趋势,平均升温速率为0.38℃/10a。1970—1990年代升温在加速,2000年代升温速率则有所放缓。中段地区各站在2000年左右发生一次显著的升温突变,而西段和东段虽都出现升温突变,但出现的时间差异较大。1971—2010年喜马拉雅山区的降水在西段呈减少趋势,中段、东段大致呈现出微弱增加趋势,但总体变化趋势不明显。降水的年代际变化也表现为1970—1990年代略有增加,2000年代则有所减少。降水突变在西段以减少为主,在中段和东段以增加为主,但各站发生突变的年代很不一致。     

Observed (1970–1999) climate variability in Central America using a high-resolution meteorological dataset with implication to climate change studies

High spatial resolution of precipitation (P) and average air temperature (Tavg) datasets are ideal for determining the spatial patterns associated with large-scale atmospheric and oceanic indexes, and climate change and variability studies, however such datasets are not usually available. Those datasets are particularly important for Central America because they allow the conception of climate variability and climate change studies in a region of high climatic heterogeneity and at the same time aid the decisionmaking process at the local scale (municipalities and districts). Tavg data from stations and complementary gridded datasets at 50 km resolution were used to generate a high-resolution (5 km grid) dataset for Central America from 1970 to 1999. A highresolution P dataset was used along with the new Tavg dataset to study climate variability and a climate change application. Consistently with other studies, it was found that the 1970-1999 trends in P are generally non-significant, with the exception of a few small locations. In the case of Tavg, there were significant warming trends in most of Central America, and cooling trends in Honduras and northern Panama. When the sea surface temperature anomalies between the Tropical Pacific and the Tropical Atlantic have different (same) sign, they are a good indicator of the sign of P (Tavg) annual anomalies. Even with non-significant trends in precipitation, the significant warming trends in Tavg in most of Central America can have severe consequences in the hydrology and water availability of the region, as the warming would bring increases in evapotranspiration, drier soils and higher aridity.     

Multidecadal oscillatory behaviour of rainfall extremes in Europe

Many studies have observed changes in the frequency and intensity of precipitation extremes and floods during the last decade(s). Natural variability by climate oscillations partly determines the observed evolution of precipitation extremes. Based on a technique for the identification and analysis of changes in extremes, this paper shows that precipitation extremes have oscillatory behaviour at multidecadal time scales. The analysis is based on a unique dataset of 108 years of 10-minute precipitation intensities at Uccle (Brussels), not affected by instrumental changes. We also checked the consistency of the findings with long precipitation records at 724 stations across Europe and the Middle East. The past 100 years show for northwestern Europe, both in winter and summer, larger and more precipitation extremes around the 1910s, 1950–1960s, and more recently during the 1990s–2000s. The oscillations for southwestern Europe are anti-correlated with these of northwestern Europe, thus with oscillation highs in the 1930–1940s and 1970s. The precipitation oscillation peaks are explained by persistence in atmospheric circulation patterns over the North Atlantic during periods of 10 to 15 years.     

Drought reconstruction in the Qilian Mountains over the last two centuries and its implications for large-scale moisture patterns

We present a composite tree-ring chronology from two sites of Qilian Juniper(Sabina przewalskii)in the northwestern Qilian Mountains(QM),Northwestern China.Precipitation in June was found to be the main limiting factor for tree-growth.The tree rings are also significantly and positively correlated with June precipitation over large areas of the northern Tibetan Plateau(TP).The authors thus consider that the tree- ring based drought reconstruction from 1803–2006 is representative of a large area drought hist...