益西卓玛1 冉光辉1 白宇轩2

利用林芝国家基准气侯站冬季(2018年12月-2019年2月),CHP1型太阳直接辐射传感器、DFC2型光电式数字日照计、暗筒式日照计在不同天气模式下的测量值分类进行对比分析。结果表明：三种仪器两两测量值对比绝对偏差和相对偏差,直接辐射传感器测量值在“阴云”、“多云”、“云晴”比暗筒式日照计低,从大到小的顺序为“晴天”＞“阴云”＞“多云”。DFC2型光电式数字日照计仅“晴天”测量值比暗筒式日照计高,其余则低。从大到小顺序为“晴天”＞“多云”＞“阴云”;三种设备测量值可以相互替代,取消人工观测设备后,日照资料可以合并使用。     

Reconstructed Temperature And Precipitation On A Millennial Timescale From Tree-Rings In The Southern Colorado Plateau,U.S.A.

Two independent calibrated and verified climate reconstructions from ecologically contrasting tree-ring sites in the southern Colorado Plateau, U.S.A. reveal decadal-scale climatic trends during the past two millennia. Combining precisely dated annual mean-maximum temperature and October through July precipitation reconstructions yields an unparalleled record of climatic variability. The approach allows for the identification of thirty extreme wet periods and thirty-five extreme dry periods in the 1,425-year precipitation reconstruction and 30 extreme cool periods and 26 extreme warm periods in 2,262-year temperature reconstruction. In addition, the reconstructions were integrated to identify intervals when conditions were extreme in both climatic variables (cool/dry, cool/wet, warm/dry, warm/wet). Noteworthy in the reconstructions are the post-1976 warm/wet period, unprecedented in the 1,425-year record both in amplitude and duration, anomalous and prolonged late 20th century warmth, that while never exceeded, was nearly equaled in magnitude for brief intervals in the past, and substantial decadal-scale variability within the Medieval Warm Period and Little Ice Age intervals.     

Reconstruction of Summer Temperatures in Interior Alaska from Tree-Ring Proxies: Evidence for Changing Synoptic Climate Regimes

Maximum latewood density and δ ¹³C discrimination of Interior Alaska white spruce were used to reconstruct summer (May through August) temperature at Fairbanks for the period 1800–1996, one of the first high-resolution reconstructions for this region. This combination of latewood density and δ ¹³C discrimination explains 59.9% of the variance in summer temperature during the period of record 1906–1996. The 200-yr. reconstruction is characterized by 7 decadal-scale regimes. Regime changes are indicated at 1816, 1834, 1879, 1916, 1937, and 1974, are abrupt, and appear to be the result of synoptic scale climate changes. The mean of summer temperature for the period of reconstruction (1800–1996) was 13.49 °C. During the period of instrument record (1903–1996) the mean of summer temperature was 13.31 °C for both the reconstruction and the recorded data. The coldest interval was 1916–1937 (12.62 ° C) and the warmest was 1974–1996 (14.23 °C) for the recorded data. The reconstruction differs from records of northern hemisphere temperatures over this period, especially because of Interior Alaska warm periods reconstructed from 1834 to 1851 (14.24 °C) and from 1862 to 1879 (14.19 °C) and because of the cool period in the early part of the 20th century (1917–1974). We show additional tree ring data that support our reconstruction of these warm periods. Alternate hypotheses involving autogenic effect of tree growth on the site, altered tree sensitivity, or novel combinations of temperature and precipitation were explored and while they cannot be ruled out as contributors to the anomalously warm 19th century reconstruction, they were not supported by available data. White spruce radial growth is highly correlated with reconstructed summer temperature, and temperature appears to be a reliable index of carbon uptake in this system.     

全天空成像仪云量计算方法的改进

全天空成像仪（total sky imager 440,TSI-440）可以实现白天全天空云量的持续自动监测,时空分辨率较高,得到的云量计算结果更精确.首先介绍了TSI-440的基本原理和资料格式,并基于太湖地区2008年5-10月的TSI-440资料及无锡站地面观测资料,采用统计方法详细地分析了不同天气情况下图像的成像特征及云量的计算误差.结果发现：图像的成像特征与能见度密切相关,红蓝比值随着能见度的减小而增大.另外,仪器在处理阴天图像及复杂天空（多云）图像时,易造成一定的云量计算误差.针对上述问题,本文通过直方图分析,重新选定了红蓝比阈值（晴空点阈值0.62,云点阈值0.66）,基于新阈值计算的云量结果较仪器自带的处理结果更为准确,减小了因天气状况不同而产生的云量计算误差.     

Characteristics of anomalous precipitation events over eastern China during the past five centuries

Characteristics of anomalous precipitation events during the past five centuries in North China (NC) and the middle-lower Yangtze River Valley (MLYRV) were investigated using the data network of dryness/wetness index (DWI) over eastern China. The high occurrence frequency of anomalous precipitation events mainly occurred at periods of high solar forcing, active volcanic eruption, and large anthropogenic forcing (the twentieth century). Coherence and dipole were the two dominant modes in spatial patterns of anomalous precipitation events. Coherent floods dominated the eighteenth and nineteenth centuries, whereas coherent droughts occurred frequently in the seventeenth and twentieth centuries. The dipole patterns of anomalous precipitation events were the most frequent in the twentieth century. NC experienced more floods in the cold periods than warm periods. Both NC and the MLYRV experienced far fewer droughts and more floods in the warm eighteenth century when natural climate forcing dominated, and more droughts in the twentieth century when anthropogenic forcing dominated. Coherent drought was the only spatial pattern of precipitation significantly associated with explosive low-latitude volcanic eruptions. The increased coherent droughts and dipole patterns in the twentieth century support the findings of previous modeling studies that the tropospheric aerosols and human-induced land cover changes play important roles in the changes of summer rainfall over eastern China. Electronic supplementary material  The online version of this article (doi:) contains supplementary material, which is available to authorized users. This paper is a contribution to the AMIP-CMIP Diagnostic Sub-project on General Circulation Model Simulation of the East Asian Climate, coordinated by W.-C. Wang.     

Observed and projected climate change in the European region during the twentieth and twenty-first centuries according to Feddema

Climate change in the European region during the twentieth and twenty-first centuries is analyzed according to Feddema’s method. Precipitation and air temperature data from the twentieth century are taken from the Climatic Research Unit, while data for the twenty-first century are taken from the ENSEMBLES climate change project. The latter were bias-corrected to ensure homogeneity across the twentieth and twenty-first centuries. Climate classes based on monthly and annual values of potential evapotranspiration, precipitation and their ratio, are defined for 30-year averages, from which trend and spatial agreement analysis are calculated. There are separate classes for annual values and for intra-annual variation. The results indicate that the change of annual climate characteristics will be much more intense in the twenty-first than it was in the twentieth century. The dominant process in the projections is warming, mostly via cold to cool (about 45% of grid points) in north Europe and cool to warm (about 8% of grid points) transformations. The second most important process is the drying of moderately moist classes affecting about 10% of the grid points in south Europe. Changes in intra-annual variability classes are more common than changes in the annual ones during the twentieth century. The chance of increase in intra-annual temperature variation from high to extreme is about 5% during the course of the twentieth century, and about 10% in the following century.     

Summer temperatures in the Canadian Rockies during the last millennium: a revised record

We present a significant update to a millennial summer temperature reconstruction (1073–1983) that was originally published in 1997. Utilising new tree-ring data (predominantly Picea engelmannii), the reconstruction is not only better replicated, but has been extended (950–1994) and is now more regionally representative. Calibration and verification statistics were improved, with the new model explaining 53% of May–August maximum temperature variation compared to the original (39% of April–August mean temperatures). The maximum latewood density data, which are weighted more strongly in the regression model than ringwidth, were processed using regional curve standardisation to capture potential centennial to millennial scale variability. The reconstruction shows warm intervals, comparable to twentieth century values, for the first half of the eleventh century, the late 1300s and early 1400s. The bulk of the record, however, is below the 1901–1980 normals, with prolonged cool periods from 1200 to 1350 and from 1450 to the late 19th century. The most extreme cool period is observed to be in the 1690s. These reconstructed cool periods compare well with known regional records of glacier advances between 1150 and the 1300s, possibly in the early 1500s, early 1700s and 1800s. Evidence is also presented of the influence of solar activity and volcanic events on summer temperature in the Canadian Rockies over the last 1,000 years. Although this reconstruction is regional in scope, it compares well at multi-decadal to centennial scales with Northern Hemisphere temperature proxies and at millennial scales with reconstructions that were also processed to capture longer timescale variability. This coherence suggests that this series is globally important for the assessment of natural temperature variability over the last 1,000 years.Authors are listed alphabetically     

A new approach to identify the sensitivity and importance of physical parameters combination within numerical models using the Lund–Potsdam–Jena (LPJ) model as an example

Daily global solar irradiation (R _s) is one of the main inputs in environmental modeling. Because of the lack of its measuring facilities, high-quality and long-term data are limited. In this research, R _s values were estimated based on measured sunshine duration and cloud cover of our synoptic meteorological stations in central and southern Iran during 2008, 2009, and 2011. Clear sky solar irradiation was estimated from linear regression using extraterrestrial solar irradiation as the independent variable with normalized root mean square error (NRMSE) of 4.69 %. Daily R _s was calibrated using measured sunshine duration and cloud cover data under different sky conditions during 2008 and 2009. The 2011 data were used for model validation. According to the results, in the presence of clouds, the R _s model using sunshine duration data was more accurate when compared with the model using cloud cover data (NRMSE = 11. 69 %). In both models, with increasing sky cloudiness, the accuracy decreased. In the study region, more than 92 % of sunshine durations were clear or partly cloudy, which received close to 95 % of total solar irradiation. Hence, it was possible to estimate solar irradiation with a good accuracy in most days with the measurements of sunshine duration.     

Ice Age mystery: a proposed theory for the cause of long term climate change

Summary ?Analysis of available data shows that the duration of the glacial/interglacial cycle is determined by the time for the ocean to go through one major temperature cycle. At the start of an interglacial period, clear skies with consequent release of CO₂ from the ocean, warms the atmosphere, which in turn eventually warms the ocean to its maximum. Cloudy skies then cause the climate (land and air temperature) to cool and the CO₂ to be reabsorbed to start glaciation preliminaries. The albedo feedback effect of the glacial ice, a relatively warm ocean, which produces enhanced cloud cover, and the increased solubility of CO₂ in cold seawater ensure a long period of glaciation. Glacial periods end when pack ice spreads out on the ocean cooling it until reduced cloud cover once again allows the Sun’s heat, unreflected by cloud cover, to melt the ice and release CO₂ back into the atmosphere. Received May 22, 2002; accepted June 20, 2002     

A 520 year record of summer sunshine for the eastern European Alps based on stable carbon isotopes in larch tree rings

A 520-year stable carbon isotope chronology from tree ring cellulose in high altitude larch trees (Larix decidua Mill.), from the eastern European Alps, correlates more strongly with summer temperature than with summer sunshine hours. However, when instrumental records of temperature and sunshine diverge after AD1980, the tree ring time series does not follow warming summer temperatures but more closely tracks summer sunshine trends. When the tree ring stable carbon isotope record is used to reconstruct summer temperature the reconstruction is not robust. Reconstructed temperatures prior to the twentieth century are higher than regional instrumental records, and the evolution of temperature conflicts with other regional temperature reconstructions. It is concluded that sunshine is the dominant control on carbon isotope fractionation in these trees, via the influence of photosynthetic rate on the internal partial pressure of CO₂, and that high summer (July–August) sunshine hours is a suitable target for climate reconstruction. We thus present the first reconstruction of summer sunshine for the eastern Alps and compare it with the regional temperature evolution.     

Changes in European precipitation seasonality and in drought frequencies revealed by a four-century-long tree-ring isotopic record from Brittany, western France

A new paleoclimatic reconstruction for western France is obtained from tree-ring cellulose stable isotopes. Living trees from Rennes Forest and beams from two ancient buildings in Rennes city have been combined to cover the past four centuries with a gap from 1730 to 1750. The cellulose ¹³C reflects the progressive changes in atmospheric CO₂ isotopic composition. The combined ¹³C and ¹⁸O measurements are used to propose a reconstruction of interannual fluctuations in local summer temperature and water stress. At the decadal time scale, the reconstructed water stress profile exhibits a significant similarity with the historical wine harvest dates, an indicator of warm and dry growth seasons, as well as with the summer central England and central Alps instrumental temperature records and climate model results. Combined with instrumental precipitation records from Paris, these reconstructions suggest a dramatic and widespread change in the seasonality of the precipitation at the beginning of the nineteenth century, with drier winters and wetter summers, which may have contributed to the Alpine glacier decline at the end of the Little Ice Age. The tree-ring isotope records also show a relationship with large-scale North Atlantic circulation changes and the interannual variability is modified between the nineteenth and twentieth centuries (7–8 year periodicities) and the seventeenth century (11–14 year periodicities). By classifying 20-year-long subsets of the reconstructed climatic parameters, we estimate that a decadal mean summer warming of 0.8±0.1°C induced extreme dry years to be 2.2±0.7 times more frequent.     

The 20th century cooling trend over the southeastern United States

Portions of the southern and southeastern United States, primarily Mississippi, Alabama, and Georgia, have experienced century-long (1895–2007) downward air temperature trends that occur in all seasons. Superimposed on them are shifts in mean temperatures on decadal scales characterized by alternating warm (1930s–1940s, 1990s) and cold (1900s; 1960s–1970s) regimes. Regional atmospheric circulation and SST teleconnection indices, station-based cloud cover and soil moisture (Palmer drought severity index) data are used in stepwise multiple linear regression models. These models identify predictors linked to observed winter, summer, and annual Southeastern air temperature variability, the observed variance (r²) they explain, and the resulting prediction and residual time series. Long-term variations and trends in tropical Pacific sea temperatures, cloud cover, soil moisture and the North Atlantic and Arctic oscillations account for much of the air temperature downtrends. Soil moisture and cloud cover are the primary predictors of 59.6 % of the observed summer temperature variance. While the teleconnections, cloud cover and moisture data account for some of the annual and summer Southeastern cooling trend, large significant downward trending residuals remain in winter and summer. Comparison is made to the northeastern United States where large twentieth century upward air temperature trends are driven by cloud cover increases and Atlantic Multidecadal Oscillation (AMO) variability. Differences between the Northeastern warming and the Southeastern cooling trends in summer are attributable in part to the differing roles of cloud cover, soil moisture, the Arctic Oscillation and the AMO on air temperatures of the 2 regions.     

Unprecedented low twentieth century winter sea ice extent in the Western Nordic Seas since A.D. 1200

We reconstructed decadal to centennial variability of maximum sea ice extent in the Western Nordic Seas for A.D. 1200–1997 using a combination of a regional tree-ring chronology from the timberline area in Fennoscandia and δ¹⁸O from the Lomonosovfonna ice core in Svalbard. The reconstruction successfully explained 59% of the variance in sea ice extent based on the calibration period 1864–1997. The significance of the reconstruction statistics (reduction of error, coefficient of efficiency) is computed for the first time against a realistic noise background. The twentieth century sustained the lowest sea ice extent values since A.D. 1200: low sea ice extent also occurred before (mid-seventeenth and mid-eighteenth centuries, early fifteenth and late thirteenth centuries), but these periods were in no case as persistent as in the twentieth century. Largest sea ice extent values occurred from the seventeenth to the nineteenth centuries, during the Little Ice Age (LIA), with relatively smaller sea ice-covered area during the sixteenth century. Moderate sea ice extent occurred during thirteenth–fifteenth centuries. Reconstructed sea ice extent variability is dominated by decadal oscillations, frequently associated with decadal components of the North Atlantic Oscillation/Arctic Oscillation (NAO/AO), and multi-decadal lower frequency oscillations operating at ~50–120 year. Sea ice extent and NAO showed a non-stationary relationship during the observational period. The present low sea ice extent is unique over the last 800 years, and results from a decline started in late-nineteenth century after the LIA.     

A 1052-year tree-ring proxy for Alpine summer temperatures

A June–August Alpine temperature proxy series is developed back to AD 951 using 1,527 ring-width measurements from living trees and relict wood. The reconstruction is composed of larch data from four Alpine valleys in Switzerland and pine data from the western Austrian Alps. These regions are situated in high elevation Alpine environments where a spatially homogenous summer temperature signal exists. In an attempt to capture the full frequency range of summer temperatures over the past millennium, from inter-annual to multi-centennial scales, the regional curve standardization technique is applied to the ring width measurements. Correlations of 0.65 and 0.86 after decadal smoothing, with high elevation meteorological stations since 1864 indicate an optimal response of the RCS chronology to June–August mean temperatures. The proxy record reveals warm conditions from before AD 1000 into the thirteenth century, followed by a prolonged cool period, reaching minimum values in the 1820s, and a warming trend into the twentieth century. This latter trend and the higher frequency variations compare well with the actual high elevation temperature record. The new central Alpine proxy suggests that summer temperatures during the last decade are unprecedented over the past millennium. It also reveals significant similarities at inter-decadal to multi-centennial frequencies with large-scale temperature reconstructions, however, deviating during certain periods from H.H. Lamb‘s European/North Atlantic temperature history.     

Multiproxy summer and winter surface air temperature field reconstructions for southern South America covering the past centuries

We statistically reconstruct austral summer (winter) surface air temperature fields back to ad 900 (1706) using 22 (20) annually resolved predictors from natural and human archives from southern South America (SSA). This represents the first regional-scale climate field reconstruction for parts of the Southern Hemisphere at this high temporal resolution. We apply three different reconstruction techniques: multivariate principal component regression, composite plus scaling, and regularized expectation maximization. There is generally good agreement between the results of the three methods on interannual and decadal timescales. The field reconstructions allow us to describe differences and similarities in the temperature evolution of different sub-regions of SSA. The reconstructed SSA mean summer temperatures between 900 and 1350 are mostly above the 1901?C1995 climatology. After 1350, we reconstruct a sharp transition to colder conditions, which last until approximately 1700. The summers in the eighteenth century are relatively warm with a subsequent cold relapse peaking around 1850. In the twentieth century, summer temperatures reach conditions similar to earlier warm periods. The winter temperatures in the eighteenth and nineteenth centuries were mostly below the twentieth century average. The uncertainties of our reconstructions are generally largest in the eastern lowlands of SSA, where the coverage with proxy data is poorest. Verifications with independent summer temperature proxies and instrumental measurements suggest that the interannual and multi-decadal variations of SSA temperatures are well captured by our reconstructions. This new dataset can be used for data/model comparison and data assimilation as well as for detection and attribution studies at sub-continental scales.     

不同天气现象下毕节高温特征及预报回归检验分析

利用毕节2010-2019年观测资料,分析不同天气现象下日最高气温特征,建立高温模型,并对近5 a 24 h高温进行检验,得出如下结论:(1)毕节高温日变化在夏季最稳定,春季波动最大。气温日较差晴天最大,阴天最小,多云时略大于阴间多云。(2)毕节8~10成云出现频率高达65.7%,夏季晴天频率波动大,春、夏季多云频率较高,且按天气现象分类统计月平均高温时,其峰值均出现在7月。(3) 24 h高温预报准确率月、季变化特征明显,夏季准确率最高,较最低的冬季高出21.4%,在区别天气现象的情况下,阴雨天时预报准确率最高,多云时最低,其中12月多云时最低为25%。(4)回归模型分析发现不同季节同种天气现象24 h高温预报影响因子权重差异明显,日照时数和平均本站气压对模型影响程度较高。不同季节晴天影响因子差异最大,拟合效果最好时段在夏季,平均估计误差为1.2℃,估计误差最大在冬季,平均估计误差为1.7℃。     

Influence of the total atmospheric optical depth and cloud cover on solar irradiance components

Broadband solar irradiance data obtained in the spectral range 400–940 nm at Kwangju, South Korea from 1999–2000 have been analyzed to investigate the effects of cloud cover and atmospheric optical depth on solar radiation components. Results from measurements indicate that the percentage of direct and diffuse horizontal components of solar irradiance depend largely on total optical depth (TOD) and cloud cover. During summer and spring, the percentages of diffuse solar irradiance relative to the global irradiance were 5.0% and 4.9% as compared to 2.2% and 3.0% during winter and autumn. The diffuse solar irradiance is higher than the direct in spring and summer by 24.2%, and 40.6%, respectively, which may largely be attributed to the attenuation (scattering) of radiation by heavy dust pollution and large cloud amount. In cloud-free conditions with cloud cover ≤2/10, the fraction of the direct and diffuse components were 66.0% and 34.0%, respectively, with a mean daily global irradiance value of 7.92±2.91 MJ m⁻² day⁻¹. However, under cloudy conditions (with cloud cover ≥8/10), the diffuse and direct fractions were 97.9% and 2.2% of the global component, respectively. The annual mean TOD under cloudless conditions (cloud cover≤2/10) yields 0.74±0.33 and increased to as much as 3.15±0.67 under cloudy conditions with cloud amount ≥8/10. An empirical formula is derived for estimating the diffuse and direct components of horizontal solar irradiance by considering the total atmospheric optical depth (TOD). Results from statistical models are shown for the estimation of solar irradiance components as a function of TOD with sufficient accuracy as indicated by low standard error for each solar zenith angle (SZA).     

Observation of new particle formation and growth under cloudy conditions at Gosan Climate Observatory,Korea

Under cloudy conditions at the Gosan Climate Observatory (GCO), Korea, we observed distinct new particle formation and growth (NPF) events from simultaneous co-located measurements of aerosol and cloud profiles, cloud cover, shortwave radiation, and the number concentration and size distribution of aerosols. The high frequency of NPF was observed at GCO under decreased downwelling solar radiation caused by clouds. Although we observed about 15 and 40 % decreases in downwelling surface shortwave radiations, in the presence of thick mid-level (low-level) clouds, on January 28 and 30, 2012, respectively, distinct NPFs with a growth rate of 3.3 (3.9) nm h^?1 were observed. We examined a 4-year series (May 2008 to April 2012) of continuous measurements of the size distribution of aerosol numbers and visually observed cloud cover. We found that approximately 13 % (i.e., 35 days out of 280 days) of total NPF events were observed under cloud-free conditions (i.e., cloud cover of 0/10). About 20 % (i.e., 57 days out of 280 days) of total NPF events occurred under mostly overcast conditions (i.e., cloud cover of 9/10–10/10). Although NPF events occurring under cloudy conditions were also found elsewhere, the frequency of NPF occurring at GCO seems much higher. The average value of relative humidity for the strong-NPF event days is lower than that of the weak and non-NPF event days for all cloud categories. No significant difference in the condensation sink was found among strong-, weak-, and non-NPF days, but the condensation sink showed a slight decreasing tendency with increasing cloudiness. Further investigations on precursor gases and preexisting aerosols under cloudy conditions are needed.     

Changing Gradients of Climate Change in Southern Africa during the Past Millennium: Implications for Population Movements

Climates of equatorial East Africa and subtropical Southern Africa have varied inversely over long periods of time. The high-resolution ¹⁸O stalagmite record from Cold Air Cave in the Makapansgat valley in South Africa and a similar resolution lake-level record for Lake Naivasha in Kenya have been in anti-phase for much of the last thousand years. A similar relationship is evident in the twentieth century meteorological record. The changes in rainfall in the two regions on multi-decadal to centennial scales have influenced both settlement patterns and livelihoods of Iron Age agriculturalists. The resulting latitudinal gradient of change may have been a significant factor in promoting southward migration of Sotho-Tswana speaking people from equatorial East Africa during the first few centuries of the last millennium and earlier. This would have occurred at times when environments in the north were deteriorating and those to the south were ameliorating.     

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.