Holocene climatic change in Morocco: a quantitative reconstruction from pollen data

 Annual precipitation, July and January temperatures were reconstructed from a continuous Holocene pollen sequence from the Middle Atlas, Morocco, using the best modern analogues method. The reconstructions show a clear difference between the early and late Holocene: from ∼10 ka to ∼6.5 ka the climate was drier and warmer than during the period since 6.5 ka. The average value of annual precipitation was ∼870 mm until 6.5 ka, then rose to ∼940 mm. Between 10 ka and 6.5 ka January and July temperatures were about 4 °C higher than the present. Both temperatures show a marked decrease between 7 ka and 6 ka. After 6.5 ka July and January temperatures fluctuated between 21 and 23 °C, and 2.5 and 5 °C respectively. January temperatures show a period of intermediate values (∼3.5 °C) between 4 ka and 5.5 ka. The reconstructed climate values generally match palaeolimnological data from the same core, which show five intervals of low lake level during the Holocene. They are also consistent with regional-scale COHMAP simulated palaeoclimate that shows contrasting patterns of rainfall variation between the northwesternmost part of Africa and the intertropical band. Received: 7 July 1997 / Accepted: 28 May 1998     

An assessment of the effects of climatic change on agriculture

This paper summarizes some of the results and conclusions of an international project funded by IIASA and UNEP on the effects of climatic variations on agriculture. An overall goal of the project was to improve our understanding both of first-order effects of climatic variations on agricultural productivity and of higher-order effects on regional and national economies. Two broad types of experiments are described: (i) impact experiments, which provide estimates of first-order and higher-order effects of climatic variations on farming systems, and which assume that no adjustments are put in place, and (ii) adjustment experiments, which evaluate a number of adjustments available at the farm or government level to offset or mitigate these effects.The results from case studies in cool temperate and cold regions in Saskatchewan (Canada), Iceland, Finland, northern European U.S.S.R. and Japan] are described here. Findings from a parallel set of IIASA/UNEP case studies in semiarid regions, which examine the effects of a different set of climatic scenarios, are reported elsewhere (Parry et al., 1988b).     

Three inflow pathways of the Indonesian throughflow as seen from the simple ocean data assimilation

The SODA product is used to investigate three Indonesian throughflow (ITF) branches: the flow through the Makassar Strait; through the South China Sea; and through the eastern Indonesian basins. The results reveal strong interannual variation in the Makassar Strait and the eastern Indonesian basins throughflow. Inspection of vertically integrated dynamic height (0–1000 db), a proxy of transport function, suggests that this interannual variation can be traced to the New Guinea Coastal Current, indicative of a strong influence of the South Pacific. The vertically integrated dynamic height along the south Java coast is related to variation in the North Pacific and in particular near the east coast of Mindanao Island, whereas the vertically integrated dynamic height along the coast of West Australia is related to variation in the South Pacific, and in particular near the coast of New Guinea. The integrated dynamic height difference between the Java and New Guinea coast appears to be a good proxy of ITF transport on the interannual time scale. Regression analysis shows a phase dependence of the three ITF pathways on the Nino3.4 index. Decoupling of current anomalies between the surface and subsurface layers is identified in the developing and mature phase of El Nino, reflecting different effects of local and remote forcing through oceanic pathways at the Makassar Strait and eastern Indonesian basins.     

Evaluation of radar and automatic weather station data assimilation for a heavy rainfall event in southern China

To improve the accuracy of short-term(0–12 h) forecasts of severe weather in southern China, a real-time storm-scale forecasting system, the Hourly Assimilation and Prediction System(HAPS), has been implemented in Shenzhen, China. The forecasting system is characterized by combining the Advanced Research Weather Research and Forecasting(WRF-ARW)model and the Advanced Regional Prediction System(ARPS) three-dimensional variational data assimilation(3DVAR) package. It is capable of assimilating radar reflectivity and radial velocity data from multiple Doppler radars as well as surface automatic weather station(AWS) data. Experiments are designed to evaluate the impacts of data assimilation on quantitative precipitation forecasting(QPF) by studying a heavy rainfall event in southern China. The forecasts from these experiments are verified against radar, surface, and precipitation observations. Comparison of echo structure and accumulated precipitation suggests that radar data assimilation is useful in improving the short-term forecast by capturing the location and orientation of the band of accumulated rainfall. The assimilation of radar data improves the short-term precipitation forecast skill by up to9 hours by producing more convection. The slight but generally positive impact that surface AWS data has on the forecast of near-surface variables can last up to 6–9 hours. The assimilation of AWS observations alone has some benefit for improving the Fractions Skill Score(FSS) and bias scores; when radar data are assimilated, the additional AWS data may increase the degree of rainfall overprediction.     

The decline of Late Bronze Age civilization as a possible response to climatic change

The disintegration of Eastern Mediterranean civilization at the end of the late Bronze Age (late thirteenth and twelfth centuries B.C.) has traditionally been attributed to the irruption of new peoples into this area. However, the nearly contemporaneous decline of highly organized and powerful states in Greece, Anatolia, Egypt, and Mesopotamia warrants consideration of possible environmental causes likely to operate over sizable areas, especially since archaeological research has not succeeded in establishing the presence of newcomers at the onset of the Bronze Age disturbances.Climatic change is a particularly attractive candidate since temperature and precipitation variations persisting over relatively short times can adversely affect agricultural output. Carpenter (1966) argued that the Mycenaean decline and migrations in and from Greece in the late thirteenth century were caused by prolonged drought and not the incursion of less civilized Dorian tribes. Donley (1971) and Bryson et al. (1974) have presented evidence of a spatial drought pattern which occurred in January 1955 that might be invoked to support this thesis. Population movements in Anatolia at the same time, though not as well established, can be delimited to some degree by the distribution of Hitto-Luwian peoples in the late ninth century B.C. It is hypothesized here that a drought induced migration of Luwian peoples from Western Antolia occurred early in the twelfth century B.C., that it was associated in some fashion with the invasion of Egypt by the Sea Peoples in the reign of Ramesses III, and that the defeated remnants of these peoples settled along the Levantine coast and filtered into North Syria and the upper Euphrates valley.It has been suggested that past climatic patterns recur in the present epoch but with a possibly different frequency. To establish that a spatial drought analogue to the above hypothesized migration can occur, temperature and precipitation records from 35 Greek, Turkish, Cypriot, and Syrian weather stations for the period 1951–1976 were examined. The Palmer drought index, an empirical method of measuring drought severity, was computed for each of these stations for the period of record. Since wheat yields tend to be highly correlated with winter precipitation for the area in question, the drought indices for the winter months were subjected to an empirical eigenvector analysis. An eigenvector (drought pattern) consistent with the postulated population movements in Anatolia occurred within the modern climatological record and was found to have been the dominant pattern in January 1972. The potential problems of eigenvector analysis in investigating problems of this type are discussed.     

Rapid climatic change and the deep ocean

A simple transient two-dimensional (latitude-depth) upwelling-diffusion ocean model coupled with an energy balance climate model is used to determine the surface temperature response to changes in the deep water formation rate. The changes in surface temperature are large and rapid with a large magnification at high latitudes, suggesting that rapid climate changes during the Glacial-Holocene transition could have been the result of variations in the rate of deep water formation. If this is true, the mechanism is essentially transient in nature and cannot be predicted using steady state models.     

Evidence of climatic change in Nigeria based on annual series of rainfall of different daily amounts, 1919–1985

Annual series of light rainfall, moderate rainfall and heavy rainfall are computed for 4 zones arranged from south to north in Nigeria: Coastal, Guinea-Savanna, Midland and Sahelian zones. Daily rainfall data for the period 1919–85 are utilized. Each series is examined for evidence of change in structure in terms of pattern of decrease and increase in dry and wet years, the overall trend, and the occurrence of runs of dry and wet years. The northern Nigeria (Midland and Sahel) heavy rainfall series and the Sahel moderate rainfall series are found to depict evidence of climatic change as defined by Landsberg (1975) that climatic conditions must change to a new equilibrium position with the values of climatic elements changed significantly. On the other hand Landsberg's definition of climatic fluctuations as involving temporary deflection which can revert to earlier conditions is found to fit the 4 regional light rainfall series and the Midland area moderate rainfall series. The southern Nigeria moderate and heavy rainfall series are found to depict only evidence of high frequency oscillations about a stable long-term mean. The recent drought in Nigeria north of about 9° N is shown to be associated with a large decline in moderate and heavy rainfalls over this part of the country.     

对县局雷达雨量标校站建设的具体做法和体会

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浅谈桂平气象站环境变化对气象观测资料的影响

通过对桂平市1954～2011年的气温、相对湿度、日照和雾天气现象日数等观测资料的显著性变化原因分析,说明桂平城市化造成了气象站观测环境的变化,影响了气象观测资料的“三性”.     

Estimating crop top microclimates from weather station data

Abstract

A mathematical model (Microsim) was developed to estimate the microclimate at the top of nearby crops using inputs of weather station data and some knowledge about crop characteristics, such as height, albedo, and leaf area index. The model was tested using data measured simultaneously over a weather station and over each of two crops ‐ corn and soybean. Temperatures at the top of unstressed, uniform crops on level terrain within 1600 m of a recording weather station were estimated within 1.0° C 96% of the time for a corn crop and 92% of the time for a soybean crop. Winds at crop top were estimated within 0.4 m s^?1 92% of the time for corn and 100% of the time for soybean. Energy balance flux density estimates for the corn crop resulted in correlation coefficients of r > 0.89 for each of R_n, LE, H and G. microsim worked well under atmospheric conditions that ranged from very stable to unstable.

An enhancement was made to the model to describe wind and temperature profiles based on the complete fetch characteristics of the sites. This resulted in significantly better wind estimates, but had the disadvantage of requiring more information about the crop and weather station surroundings.     

渭河下游一次强降水过程自动站资料分析

应用常规气象观测资料、FY-2C气象卫星资料和自动气象站资料,对2008-08-20发生在渭河下游的对流性强降水天气进行分析,结果表明：副热带高压外围的西南暖湿气流和贝湖冷槽分裂南下冷空气在渭河流域交汇,为暴雨形成提供了有利的条件,低层切变线、低涡、低空急流是暴雨产生的主要影响系统;在卫星云图上有圆形暴雨云团特征,tBB低值中心对应强降水中心;暴雨发生前自动气象站地面要素特征表现明显,地面能量锋区和地面中尺度辐合系统对暴雨的监测预警有较好的指示性。     

Assessing the sensitivity of Canada's ecosystems to climatic change

Global warming due to increased concentrations of atmospheric CO₂ is expected to be amplified in middle and higher latitudes. Consequently, ecosystems in these latitudes will experience more pronounced climatic variations. This investigation attempts to assess the sensitivity of Canada's ecosystems to climatic change. Potential ecological impacts resulting from global warming are outlined. With this background, the effects of a doubled CO₂ climate are applied to a classification model derived from the current ecological setting. Results reveal not only major shifts in ecological boundaries but also changes in the character of these broadly distributed ecosystems.     

Assessing the impact of climatic change on food production

Attempts to assess the impact of a hypothetical climatic change on food production have relied on the use of statistical models which predict crop yields using various climatic variables. It is emphasized that the coefficients of these models are not universal constants, but rather statistical estimates subject to several sources of error. Thus, any statement regarding the estimated impact of climatic change on food production must be qualified appropriately.The National Center for Atmospheric Research is sponsored by the National Science Foundation.     

Variability of rainfall and effective onset and length of the monsoon season over a sub-humid climatic environment

The study has analyzed the variability and trends in monthly, seasonal and annual rainfall and rainy days of four locations over different agro-ecological zones of Bihar, namely Samastipur (zone-I), Madhepura (zone-II), Sabour (zone-IIIA) and Patna (zone-IIIB). The Mann–Kendall nonparametric test was employed for detection of statistical significance and slopes of the trend lines were determined using the method of least square linear fitting. The variability and trends of onset of effective monsoon and length of monsoon period were also analyzed using the same method. The mean annual rainfall varies from 1137 mm at Patna to 1219 mm at Sabour. July is the rainiest month in all the zones followed by August. Maximum increase in annual rainfall was found at Sabour (40.1% of mean/30 years at 95% confidence level) and minimum for Patna (10.1% of mean/30 years). Significant increasing trend of rainfall during July, August and September at rates of 41.9, 83.2, and 112.7% of the mean/30 years, respectively has been noticed at Madhepura. Analysis of rainy days indicates that rainy days increased during winter and annually for all the sites. The mean effective onset of monsoon varies from 18th June at Sabour to 28th June at Patna. The trends in the date of effective onset of monsoon indicate that the date tends to be early in all the sites except Madhepura. But a significant delayed trend in the onset at a rate of 2.8% of the mean/30 years has been observed for Madhepura. The early trend of the effective onset of monsoon and increasing trends of length of monsoon season have been observed for Samastipur, Sabour and Patna.     

气候突变的定义和检测方法

气候突变现象及其理论的研究是近代气候学一个新兴的研究领域.本文是气候突变研究评述的第一部分,着重讨论了突变,主要是气候突变的定义和气候突变信号的各种检测方法.把气候突变归纳为四类,即均值突变、变率突变、转折突变和翘翘板(seasaw)突变.并通过Mann-Kendall法的检测,发现在本世纪20年代经历了一次全球范围的气候突变.     

Signals of climatic change in the Central-Western Mediterranean basin

Summary Climatic scenario models forecast an increase of the air temperature in the next century of 1.5–3.5 °C, because of the anthropogenic enhancement of the concentration greenhouse gases in the atmosphere. The analysis of the trend of long-lasting data series of climatic parameters seems to support such a prediction: indeed due to the increase of greenhouse gases in the atmosphere, a climate modification could be already ongoing. Several papers have been published dealing with the global scale climate, this paper, however, deals with an investigation on the regional scale, referring specifically to the Central-Western Mediterranean basin. We are concerned with the parameters which are more affected by climate changes, such as pressure, temperature and precipitation. The analysis carried out indicates that in the Central-Western Mediterranean basin the climate is evolving in a consistent way; we have found: i) an increase of air pressure at the surface and at the upper levels; ii) a reduction in cloudiness and precipitation amount; iii) an increase by about 1 °C in surface air temperature during the period 1860–1995 and in more recent years a rise of the freezing level and of the tropopause; iv) a reduction of strong cyclogenetic events and an increase of heat waves. These results, although compatible with the scenarios predicted, do not allow a final conclusion to be drawn concerning a man-made influence on climate change in the basin.With 13 Figures     

气候变迁研究现状的几个问题

气候变迁研究在近几年有很大的发展,现在它已不只是一个学术问题,而是一个具有重要现实意义的科学课题了。随着社会生产的发展,编制长期发展规划和设计重大工程都需要参考过去和未来的气候情况。其目的不仅是为了预防气候灾害,而且也要求对今后气候资源有所估计,以便开发利用。我国农业学大寨运动蓬勃开展以来,很多地方迅速