European climate of the past 500 years: new challenges for historical climatology

Temperature reconstructions from Europe for the past 500 years based on documentary and instrumental data are analysed. First, the basic documentary data sources, including information about climate and weather-related extremes, are described. Then, the standard palaeoclimatological reconstruction method adopted here is discussed with a particular application to temperature reconstructions from documentary-based proxy data. The focus is on two new reconstructions; January–April mean temperatures for Stockholm (1502–2008), based on a combination of data for the sailing season in the Stockholm harbour and instrumental temperature measurements, and monthly Central European temperature (CEuT) series (1500–2007) based on documentary-derived temperature indices of the Czech Republic, Germany and Switzerland combined with instrumental records from the same countries. The two series, both of which are individually discussed in greater detail in subsequent papers in this special edition, are here compared and analysed using running correlations and wavelet analysis. While the Stockholm series shows a pronounced low-frequency component, the CEuT series indicates much weaker low-frequency variations. Both series are analysed with respect to three different long-period reconstructions of the North Atlantic Oscillation (NAO) and are compared with other European temperature reconstructions based on tree-rings, wine-harvest data and various climate multiproxies. Correlation coefficients between individual proxy-based series show weaker correlations compared to the instrumental data. There are also indications of temporally varying temperature cross-correlations between different areas of Europe. The two temperature reconstructions have also been compared to geographically corresponding temperature output from simulations with global and regional climate models for the past few centuries. The findings are twofold: on the one hand, the analysis reinforces the hypothesis that the index-data based CEuT reconstruction may not appropriately reflect the centennial scale variations. On the other hand, it is possible that climate models may underestimate regional decadal variability. By way of a conclusion, the results are discussed from a broader point of view and attention is drawn to some new challenges for future investigations in the historical climatology in Europe.     

Spatiotemporal change in China’s climatic growing season: 1955–2000

The timing, length, and thermal intensity of the climatic growing season in China show statistically significant changes over the period of 1955 to 2000. Nationally, the average start of the growing season has shifted 4.6–5.5 days earlier while the average end has moved 1.8–3.7 days later, increasing the length of the growing season by 6.9–8.7 days depending on the base temperature chosen. The thermal intensity of the growing season has increased by 74.9–196.8 growing degree-days, depending on the base temperature selected. The spatial characteristics of the change in the timing and length of the growing season differ from the geographical pattern of change in temperatures over this period; but the spatial characteristics of change in growing degree-days does resemble the pattern for temperatures, with higher rates in northern regions. Nationally, two distinct regimes are evident over time: an initial period where growing season indicators fluctuate near a base period average, and a second period of rapidly increasing growing season length and thermal intensity. Growing degree-days are highly correlated with March-to-November mean air temperatures in all climatic regions of China; the length of the growing season is likewise highly correlated with March-to-November mean air temperatures except in east, southeast and southwest China at base temperature of 0°C and southeast China at base temperature of 5°C. The growing season start date appears to have the greater influence on the length of the growing season. In China, warmer growing seasons are also likely to be longer growing seasons.     

Changes in climatic elements in the Pan-Hexi region during 1960–2014 and responses to global climatic changes

Theoretical and Applied Climatology - In this paper, robust statistical methods (including the climatic tendency ratio, inverse distance weight (IDW), and Mann-Kendall’s non-parametric...     

Soil erosion in the West African Sahel: a review and an application of a “local political ecology” approach in South West Niger

A review of soil erosion research in the West African Sahel finds that there are insufficient data on which to base policy. This is largely because of the difficulties of measuring erosion and the other components of “soil life”, and because of the highly spatially and temporarily variable natural and social environment of the Sahel. However, a “local political ecology” of soil erosion and new methodologies offer some hope of overcoming these problems. Nonetheless, a major knowledge gap will remain, about how rates of erosion are accommodated and appraised within very variable social and economic conditions. An example from recent field work in Niger shows that erosion is correlated with factors such as male migration, suggesting, in this case, that households with access to non-farm income adopt a risk-avoidance strategy in which soil erosion is accelerated incidentally. It is concluded that there needs to be more research into the relations between erosion and socio-economic factors, and clearer thinking about the meaning of sustainability as it refers to soil erosion in the Sahel.     

“Climate-smart agriculture and food security: Cross-country evidence from West Africa”

In the face of climate change and extreme weather events which continue to have significant impacts on agricultural production, climate-smart agriculture (CSA) has emerged as one important entry point in reducing the emission of greenhouse gases and building climate resilience while ensuring increases in agricultural productivity with ensuing implications on food and nutrition security. We examine the relationship between CSA, land productivity (yields), and food security using a survey of farm households in Ghana, Mali, and Nigeria. To understand the correlates of the adoption of these CSA practices as well as the association between CSA, yields, and food security, we use switching regressions that account for multiple endogenous treatments. We find a positive association between the adoption of CSA practices and yields. This increase in yields translate to food security as we observe a positive association between CSA and food consumption scores. Although we show modest associations between the independent use of CSA practices such as adopting climate-smart groundnut varieties, cereal-groundnut intercropping, and the use of organic fertilizers, we find that bundling these practices may lead to greater yield and food security gains. Under the different combinations, the use of climate-smart groundnut varieties exhibit the strongest association with yields and food security. We also estimate actual-counterfactual relationships where we show that the adoption of CSA practices is not only beneficial to CSA adopters but could potentially be beneficial to non-CSA adopters should they adopt. These results have implications for reaching some of the sustainable development targets, especially the twin goals of increasing agricultural productivity and maintaining environmental sustainability.     

Spatiotemporal change in the climatic growing season in Northeast China during 1960–2009

Daily mean air temperatures from 81 meteorological stations in Northeast China were analyzed for the spatiotemporal change of the climatic growing season during the period 1960–2009. Our results showed that latitude strongly influenced the spatial patterns of the mean start (GSS), end (GSE), and length (GSL) of the growing season. For the area studied, a significant increasing trend in GSL during 1960–2009 was detected at a significance level of 0.01, especially after the early 1980s. The area-average GSL has extended 13.3 days during the last 50 years, mainly due to the advanced GSS evident in the spring (7.9 days). The variations of GSS and GSE were closely correlated with the monthly mean temperature (T _mean) of April and October, respectively, while GSL was closely related to the monthly minimum temperatures (T _min) of spring (March to April) and autumn (September to October). The distributions of the trends in growing season parameters (GSS, GSE, and GSL) showed great spatial variability over Northeast China. Significant relationships between altitude and the trend rates of the GSS and GSL were detected, while geographic parameters had little direct effect on the change in GSE. This extended growing season may provide favorable conditions for agriculture and forest, and improve their potential production.     

Modeling the climatic effects of urbanization in the Beijing–Tianjin–Hebei metropolitan area

In this analysis, the weather research and forecasting model coupled with a single-layer urban canopy model is used to simulate the climatic impacts of urbanization in the Beijing–Tianjin–Hebei metropolitan area, which has experienced significant expansion in its urban areas. Two cases examining current landscapes and the sensitivity test of urban areas replaced by cropland have been carried out to explore the changes in the surface air and atmospheric boundary structure. The impact of urbanization on annual mean surface air temperature has been found to be more than 1 °C in urban areas, and the maximum difference is almost 2 °C. The change in near-surface level temperature is most pronounced in winter, but the area influenced by urbanization is slightly larger in summer. The annual mean water vapor mixing ratio and wind speed are both reduced in the urban area. The effect of urbanization can only heat the temperature inside the urban boundary layer, below 850 hPa. The modeling results also indicate that the underlying surface thermal forces induced by the “urban heat island” effect enhance vertical air movement and engenders a convergence zone over urban areas. The convergence at low level together with the moisture increases in the layer between 850 and 700 hPa triggered the increase of convective precipitation.     

Factor Analysis of some climatological elements in Athens, 1931–1992: covariability and climatic change

Summary The climatological parameters of a station are, in general, intercorrelated to various degrees (e.g. cloudiness with sunshine duration or possibly rainfall with temperature). In this work, 15 climatological parameters of the National Observatory of Athens are distributed in groups where the contained parameters are highly covariant. This classification is achieved using P-mode Factor Analysis, based on the monthly values for the period 1931–1992. Using several known criteria, we found up to four significant factors. The first two are the most important ones including the temperature and the precipitation parameters, respectively, with loading values above 0.85. The other two are weaker and variable, depending on the month. Finally, climatic trends of the grouped parameters (factors) are examined and the result compared with those of studies using classical methods.With 2 Figures     

Mixed nonlinear regression for modelling historical temperatures in Central–Southern Italy

This paper has exploited, for Central and Southern Italy (Mediterranean Sub-regional Area), an unprecedented historical dataset as an attempt to model seasonal (winter and summer) air temperatures in pre-instrumental time (back to 1500). Combining information derived from proxy–documentary data and large-scale simulation, a statistical downscaling approach in the form of mixed regression model was developed to adapt larger-scale estimations (regional component) to the sub-regional temperature pattern (local component). It interprets local temperature anomalies by means of monthly based Temperature Anomaly Scaled Index in the range ?5 (very cold conditions in June) to 2 (very warm conditions). The modelled response agrees well with the independent data from the validation sample (Nash–Sutcliffe efficiency coefficient, >0.60). The advantage of the approach is not merely increased accuracy in estimation. Rather, it relies on the ability to extract (and exploit) the right information to replicate coherent temperature series in historical times.     

Intraseasonal variability in the equatorial Atlantic-West Africa during March–June

Intraseasonal (30–80 days) variability in the equatorial Atlantic-West African sector during March–June is investigated using various recently-archived satellite measurements and the NCEP/DOE AMIP-II reanalysis daily data. The global connections of regional intraseasonal signals are first examined for the period of 1979–2006 through lag-regression analyses of convection (OLR) and other dynamic components against a regional intraseasonal convective (OLR) index. The eastward-propagating features of convection can readily be seen, accompanied by coherent circulation anomalies, similar to those for the global tropical intraseasonal mode, i.e., the Madden–Julian oscillation (MJO). The regressed TRMM rainfall (3B42) anomalies during the TRMM period (1998–2006) manifest similar propagating features as for the regressed OLR anomalies during 1979–2006. These coherent features hence tend to suggest that the regional intraseasonal convective signals might be mostly a regional response to, or closely associated with the MJO, and probably contribute to the MJO’s global propagation. Atmospheric and surface intraseasonal variability during March–June of 1998–2006 are further examined using the high-quality TRMM Microwave Imager (TMI) sea surface temperature (SST), columnar water vapor, and cloud liquid water, and the QuikSCAT oceanic winds (2000–2006). Enhanced (suppressed) convection or positive (negative) rainfall anomalies approximately cover the entire basin (0°–10°N, 30°W–10°E) during the passage of intraseasonal convective signals, accompanied by anomalous surface westerly (easterly) flow. Furthermore, a unique propagating feature seems to exist within the tropical Atlantic basin. Rainfall anomalies always appear first in the northwestern basin right off the coast of South America, and gradually extend eastward to cover the entire basin. A dipolar structure of rainfall anomalies with cross-equatorial surface wind anomalies can thus be observed during this evolution, similar to the anomaly patterns on the interannual time scale discovered in past studies. Coherent intraseasonal variations and patterns can also be found in other physical components.

A return to wet conditions over Africa: 1995–2010

Climatic trends over sub-Saharan Africa are described using major river flows, European Community Medium-Range Weather Forecasts, Coupled Forecast System, global land surface data assimilation and National Center for Environmental Prediction reanalysis, Global Precipitation Climate Center gauge data, and satellite observations in the period 1995–2010. The Niger and Zambezi rivers reached flow levels last seen in the 1950s (2,000 and 5,000 m³ s^?1, respectively), and rainfall across the Congo Basin increased steadily ~+0.16 mm day^?1 year^?1. Weather events that contributed to flooding are studied and include the Zambezi tropical trough of 4 January 2008 and the Sahelian easterly wave of 19 July 2010. Diurnal summer rainfall increased threefold over the 1995–2010 period in conjunction with a strengthened land–sea temperature contrast, onshore flow, and afternoon uplift. 700 mb zonal winds over East Africa became easterly after 2001, so clean Indian Ocean air was entrained to the Congo, improving convective efficiency. Relationships between the African monsoon circulation and global teleconnections are explored. Zonal wind convergence around the Congo appears related with the tropical multi-decadal oscillation and signals in the Atlantic during the study period.     

‘Telling a different tale’: literary, historical and meteorological readings of a Norfolk heatwave

Articulated initially by physical scientists, the idea of anthropogenic global climate change has been subject to increasingly diverse examinations in recent years. The idea has been appropriated by economists, worked with by engineers and, more recently, scrutinised by social scientists and humanities scholars. Underlying these examinations are different, yet rarely exposed, presumptions about what kind of ??thing?? climate is: a physical abstraction, a statistical construct, an imaginative idea. If the ontological status of climate is rarely made explicit it becomes difficult to know whether the different epistemologies used to reveal climates ?? and their changing properties ?? are appropriate. This study offers one way in which the different worlds inhabited by the idea of climate may be revealed. It does so by examining a heatwave: a powerful meteorological phenomenon one would think and one which scientific accounts of climate change tell us will become more frequent in the future. The heatwave in question occurred in July 1900 in the county of Norfolk, England. This heatwave inhabits three very different worlds: the imaginative world of L P Hartley in his novel The Go Between; the historical world of late Victorian Norfolk; and the digital world of the climate sciences. The traces of the heatwave left in these different worlds are varied and access to them is uneven. Constructing an adequate interpretation of this singular climatic event and its meaning is challenging. The study suggests that grasping the idea of climate may be harder than we think. Climates may be ineffable. Yet the approach to the study of climate illustrated here opens up new ways of thinking about the meaning and significance of climate change.     

Impact of drought on wildland fires in Greece: implications of climatic change?

An increasing trend and a statistically significant positive correlation between wildfire occurrence, area burned and drought (as expressed by the Standardized Precipitation Index, SPI) have been observed all over Greece, during the period 1961?C1997. In the more humid and colder regions (Northern and Western Greece) the number of fires and area burned were positively correlated to both summer (SPI6_October) and annual drought (SPI12_September), whereas in the relatively more dry and hot regions (Southern and Central Greece) the number of fires and area burned were correlated only to summer drought. In 1978, Greece entered a period of prolonged drought, possibly as a result of the global climatic change. Data analysis of the period 1978?C1997 revealed a statistically significant increase in the mean annual number of fires, the area burned and the summer and annual drought episodes in the relatively more humid and colder regions (Northern and Western) of Greece (which in the past were characterized by less fires and area burned) compared to the more dry and hot regions (Southern and Eastern Greece), which always presented high fire activity. Additionally, analyzing the two sub-periods (1961?C1977, 1978?C1997) separately, drought was significantly correlated only to fire occurrence during the years 1961?C1977, whereas during 1978?C1997 drought was significantly correlated mainly to area burned. It became obvious that drought episodes, although they are not solely responsible for fire occurrence and area burned, they exert an increasingly significant impact on wildfire activity in Greece.     

Torneträsk tree-ring width and density ad 500–2004: a test of climatic sensitivity and a new 1500-year reconstruction of north Fennoscandian summers

This paper presents updated tree-ring width (TRW) and maximum density (MXD) from Torneträsk in northern Sweden, now covering the period ad 500–2004. By including data from relatively young trees for the most recent period, a previously noted decline in recent MXD is eliminated. Non-climatological growth trends in the data are removed using Regional Curve Standardization (RCS), thus producing TRW and MXD chronologies with preserved low-frequency variability. The chronologies are calibrated using local and regional instrumental climate records. A bootstrapped response function analysis using regional climate data shows that tree growth is forced by April–August temperatures and that the regression weights for MXD are much stronger than for TRW. The robustness of the reconstruction equation is verified by independent temperature data and shows that 63–64% of the instrumental inter-annual variation is captured by the tree-ring data. This is a significant improvement compared to previously published reconstructions based on tree-ring data from Torneträsk. A divergence phenomenon around ad 1800, expressed as an increase in TRW that is not paralleled by temperature and MXD, is most likely an effect of major changes in the density of the pine population at this northern tree-line site. The bias introduced by this TRW phenomenon is assessed by producing a summer temperature reconstruction based on MXD exclusively. The new data show generally higher temperature estimates than previous reconstructions based on Torneträsk tree-ring data. The late-twentieth century, however, is not exceptionally warm in the new record: On decadal-to-centennial timescales, periods around ad 750, 1000, 1400, and 1750 were equally warm, or warmer. The 200-year long warm period centered on ad 1000 was significantly warmer than the late-twentieth century (p < 0.05) and is supported by other local and regional paleoclimate data. The new tree-ring evidence from Torneträsk suggests that this “Medieval Warm Period” in northern Fennoscandia was much warmer than previously recognized.     

Impacts of future climatic change (2070–2099) on the potential occurrence of debris flows: a case study in the Massif des Ecrins (French Alps)

In this paper we investigate the impacts of future climatic change on the occurrence of debris flows in the Massif des Ecrins (French Alps). Two distinct aspects are discussed: the impact of future climatic change on the evolution of the process, and changes in the spatial distribution. Three climate simulations are presented for the current period (1970–1999) and for future periods (2070–2099) using GCM ARPEGE CLIMAT model developed by Météo-France. Simulated data are then statistically downscaled to obtain a higher spatial resolution. In the first step, we compare occurrence probabilities in the current period and in the next century. In the second step, we estimate which zones would be affected by the process in the future at the scale of the Massif des Ecrins. For the current period, the best model was obtained between debris flows and the number of days between June 15th and October 15th with more than 20 mm calculated either from observed meteorological or simulated data. Results of the ARPEGE model considering the A2 hypothesis (IPCC 2007) showed that the most significant climatic trends for the end of the century will be a decrease in intense rainy events and an increase in temperature. These trends are expected to reduce the occurrence of hill slope debris flows in the Massif des Ecrins. From a spatial point of view, the increase in temperature should result in a shift of the 0°C isotherm to a higher elevation which, in turn, should result in a 20% reduction of the number of slopes affected by the process.