Changes in ice-season characteristics of a European Arctic lake from 1964 to 2008     

Ruibo Lei  Matti Lepp?ranta  Bin Cheng  Petra Heil  Zhijun Li 《Climatic change》2012,115(3-4):725-739

The long-term ice record (from 1964 to 2008) of an Arctic lake in northern Europe (Lake Kilpisj?rvi) reveals the response of lake ice to climate change at local and regional scales. Average freeze-up and ice breakup occurred on 9 November and 19 June, respectively. The freeze-up has been significantly delayed at a rate of 2.3 d per decade from 1964 onward (P?<?0.05). No significant change has taken place in ice breakup. Annual average ice thickness has become smaller since the mid-1980s (P?<?0.05). Air temperature during the early ice season significantly affected the ice thickness. The freeze-up date exhibits the highest correlation with the 2-month average daily minimum air temperature centered at the end of October, while the ice breakup date exhibits the highest correlation with the 2-month average daily maximal air temperature centered in mid May. A 1°C increase in the surface air temperature corresponds to a freeze-up later by 3.4?days and an ice breakup earlier by 3.6?days. Snow cover is a critical factor in lake-ice climatology. For cumulative November to March precipitation of less than 0.13?m, the insulating effect of the snow dominated, while higher rates of precipitation favored thicker ice due to the formation of snow ice. Variations in ice records of Lake Kilpisj?rvi can serve as an indicator of climate variations across the northern Europe. The North Atlantic Oscillation (NAO) does not significantly affect the ice season there, although both the local air temperatures and winter precipitation contain a strong NAO signal.  相似文献   

Floods in the Sahel: an analysis of anomalies, memory, and anticipatory learning     

Petra Tschakert  Regina Sagoe  Gifty Ofori-Darko  Samuel Nii Codjoe 《Climatic change》2010,103(3-4):471-502

This study explores the implications of recent extreme rainfall and flood events in the Sahel and the wider West African region for climate change adaptation. Are these events merely a temporal nuisance as suggested by the lingering desertification discourse or will more climatic extremes characterize the region over the next century? After reviewing incidences of severe rainfall and projected future climate variability, the paper examines local flood knowledge and decision-making, drawing upon a case study in Ghana. The data demonstrate that a variety of response strategies to flooding exist; yet, knowledge of and access to climate forecasts and other learning tools are essentially absent. So far, floods have not triggered mass displacement although cumulative environmental deterioration is likely to cause environmental refugees. The paper recommends to lay to rest the desertification narrative, consider the possibility of both floods and droughts, and mobilize local memory for anticipatory learning and practical adaptation.  相似文献   

Uncertainties in climate change prediction: El Niño-Southern Oscillation and monsoons     

Heiko Paeth  Anja Scholten  Petra Friederichs  Andreas Hense 《Global and Planetary Change》2008,60(3-4):265-288

The sensitivity of climate phenomena in the low latitudes to enhanced greenhouse conditions is a scientific issue of high relevance to billions of people in the poorest countries of the globe. So far, most studies dealt with individual model results. In the present analysis, we refer to 79 coupled ocean–atmosphere simulations from 12 different climate models under 6 different IPCC scenarios. The basic question is as to what extent various state-of-the-art climate models agree in predicting changes in the main features of El Niño-Southern Oscillation (ENSO) and the monsoon climates in South Asia and West Africa. The individual model runs are compared with observational data in order to judge whether the spatio-temporal characteristics of ENSO are well reproduced. The model experiments can be grouped into multi-model ensembles. Thus, climate change signals in the classical index time series, in the principal components and in the time series of interannual variability can be evaluated against the background of internal variability and model uncertainty.There are large differences between the individual model predictions until the end of the 21st century, especially in terms of monsoon rainfall and the Southern Oscillation index (SOI). The majority of the models tends to project La Niña-like anomalies in the SOI and an intensification of the summer monsoon precipitation in India and West Africa. However, the response barely exceeds the level of natural variability and the systematic intermodel variations are larger than the impact of different IPCC scenarios. Nonetheless, there is one prominent climate change signal, which stands out from model variations and internal noise: All forced model experiments agree in predicting a substantial warming in the eastern tropical Pacific. This oceanic heating does not necessarily lead to a modification of ENSO towards more frequent El Niño and/or La Niña events. It simply represents a change in the background state of ENSO. Indeed, we did not find convincing multi-model evidence for a modification of the wavelet spectra in terms of ENSO or the monsoons. Some models suggest an intensification of the annual cycle but this signal is fairly model-dependent. Thus, large model uncertainty still exists with respect to the future behaviour of climate in the low latitudes. This has to be taken into account when addressing climate change signals in individual model experiments and ensembles.  相似文献   

Geophysical evidence of the Eastern Marginal Fault of the Cheb Basin (Czech Republic)     

Vratislav Blecha  Tomáš Fischer  Petr Tábořík  Jan Vilhem  Radek Klanica  Jan Valenta  Petra Štěpančíková 《Studia Geophysica et Geodaetica》2018,62(4):660-680

The western part of the Bohemian Massif hosts an intersection of two regional fault zones, the SW-NE trending Oh?e/Eger Graben and the NNW-SSE trending Mariánské Lázně Fault, which has been reactivated several times in the geological history and controlled the formation of the Tertiary Cheb Basin. The broader area of the Cheb Basin is also related to permanent seismic activity of M_L 3+ earthquake swarms. The Eastern Marginal Fault of the Cheb Basin (northern segment of the Mariánské Lázně Fault) separates the basin sediments and underlying granites in the SW from the Kru?né Hory/Erzgebirge Mts. crystalline unit in the NE. We describe a detailed geophysical survey targeted to locating the Eastern Marginal Fault and determining its geometry in the depth. The survey was conducted at the Kopanina site near the Nový Kostel focal zone, which shows the strongest seismic activity of the whole Western Bohemia earthquake swarm region. Complex geophysical survey included gravimetry, electrical resistivity tomography, audiomagnetotellurics and seismic refraction. We found that the rocks within the Eastern Marginal Fault show low resistivity, low seismic velocity and density, which indicates their deep fracturing, weathering and higher water content. The dip of the fault in shallow depths is about 60° towards SW. At greater depths, the slope turns to subvertical with dip angle of about 80°. Results of geoelectrical methods show blocky fabric of the Cheb Basin and deep weathering of the granite bedrock, which is consistent with geologic models based on borehole surveys.  相似文献   

Seismic behaviour of masonry buildings built of low compressive strength units     

Petra Triller  Miha Tomaževič  Matija Gams 《Bulletin of Earthquake Engineering》2018,16(12):6191-6219

Seismic behaviour of masonry buildings, built of low compressive strength units, is discussed. Although such materials have already been tested and approved for use from mechanical and thermal insulation point of view, the knowledge regarding their structural behaviour is still lacking. In order to investigate the resistance and deformation capacity of this particular type of masonry construction in seismic conditions, a series of eight walls and model of a two-storey full scale confined masonry building have been tested by subjecting the specimens to cyclic shear loads. All tests were conducted under a combination of constant vertical load and quasi static, cyclically imposed horizontal load. The behaviour of tested specimens was of typical shear type. Compared with the behaviour of plain masonry walls, the presence of tie-columns resulted into higher resistance and displacement capacity, as well as smaller lateral resistance degradation. The response of the model was determined by storey mechanism with predominant shear behaviour of the walls and failure mechanism of the same type as in the case of individual confined masonry walls. Adequate seismic behaviour of this particular masonry structural type can be expected under the condition that the buildings are built as confined masonry system with limited number of stories.  相似文献   

Insights From a Multi-Method Recharge Estimation Comparison Study     

David Walker  Geoff Parkin  Petra Schmitter  John Gowing  Seifu A. Tilahun  Alemseged T. Haile  Abdu Y. Yimam 《Ground water》2019,57(2):245-258

Although most recharge estimation studies apply multiple methods to identify the possible range in recharge values, many do not distinguish clearly enough between inherent uncertainty of the methods and other factors affecting the results. We investigated the additional value that can be gained from multi-method recharge studies through insights into hydrogeological understanding, in addition to characterizing uncertainty. Nine separate groundwater recharge estimation methods, with a total of 17 variations, were applied at a shallow aquifer in northwest Ethiopia in the context of the potential for shallow groundwater resource development. These gave a wide range of recharge values from 45 to 814 mm/a. Critical assessment indicated that the results depended on what the recharge represents (actual, potential, minimum recharge or change in aquifer storage), and spatial and temporal scales, as well as uncertainties from application of each method. Important insights into the hydrogeological system were gained from this detailed analysis, which also confirmed that the range of values for actual recharge was reduced to around 280-430 mm/a. This study demonstrates that even when assumptions behind methods are violated, as they often are to some degree especially when data are limited, valuable insights into the hydrogeological system can be gained from application of multiple methods.  相似文献   

Natural background levels and threshold values for groundwater in fluvial Pleistocene and Tertiary marine aquifers in Flanders,Belgium     

Marleen Coetsiers  Petra Blaser  Kristine Martens  Kristine Walraevens 《Environmental Geology》2009,57(5):1155-1168

Aquifers from the same typology can have strongly different groundwater chemistry. Deducing the groundwater quality of less well-characterized aquifers from well-documented aquifers belonging to the same typology should be done with great reserve, and can only be considered as a preliminary approach. In the EU’s 6th FP BRIDGE project “Background cRiteria for the IDentification of Groundwater thrEsholds”, a methodology for the derivation of threshold values (TV) for groundwater bodies is proposed. This methodology is tested on four aquifers in Flanders of the sand and gravel typology. The methodology works well for all but the Ledo-Paniselian aquifer, where the subdivision into a fresh and saline part is disproved, as a gradual natural transition from fresh to saline conditions in the aquifer is observed. The 90 percentile is proposed as natural background level (NBL) for the unconfined Pleistocene deposits, ascribing the outliers to possible influence of pollution. For the Tertiary aquifers, high values for different parameters have a natural origin and the 97.7 percentile is preferred as NBL. The methodology leads to high TVs for parameters presenting low NBL, when compared to the standard used as a reference. This would allow for substantial anthropogenic inputs of these parameters.  相似文献   

Modelling Freshwater Resources at the Global Scale: Challenges and Prospects     

Petra Döll  Hervé Douville  Andreas Güntner  Hannes Müller Schmied  Yoshihide Wada 《Surveys in Geophysics》2016,37(2):195-221

Quantification of spatially and temporally resolved water flows and water storage variations for all land areas of the globe is required to assess water resources, water scarcity and flood hazards, and to understand the Earth system. This quantification is done with the help of global hydrological models (GHMs). What are the challenges and prospects in the development and application of GHMs? Seven important challenges are presented. (1) Data scarcity makes quantification of human water use difficult even though significant progress has been achieved in the last decade. (2) Uncertainty of meteorological input data strongly affects model outputs. (3) The reaction of vegetation to changing climate and CO₂ concentrations is uncertain and not taken into account in most GHMs that serve to estimate climate change impacts. (4) Reasons for discrepant responses of GHMs to changing climate have yet to be identified. (5) More accurate estimates of monthly time series of water availability and use are needed to provide good indicators of water scarcity. (6) Integration of gradient-based groundwater modelling into GHMs is necessary for a better simulation of groundwater–surface water interactions and capillary rise. (7) Detection and attribution of human interference with freshwater systems by using GHMs are constrained by data of insufficient quality but also GHM uncertainty itself. Regarding prospects for progress, we propose to decrease the uncertainty of GHM output by making better use of in situ and remotely sensed observations of output variables such as river discharge or total water storage variations by multi-criteria validation, calibration or data assimilation. Finally, we present an initiative that works towards the vision of hyperresolution global hydrological modelling where GHM outputs would be provided at a 1-km resolution with reasonable accuracy.  相似文献   

Lake ecosystem responses to catchment disturbance and airborne pollution: an 800-year perspective in southern Sweden     

Petra Bragée  Preetam Choudhary  Joyanto Routh  John F. Boyle  Dan Hammarlund 《Journal of Paleolimnology》2013,50(4):545-560

Sediment sequences spanning the last 800 years from two small lakes in the south Swedish uplands were explored for assessment of effects of changing human population, local land-use practices and airborne pollution on lake-ecosystem functioning and resilience. Variations in nutrient cycling and deposition of lithogenic elements were studied, using a multi-proxy stratigraphic approach. Carbon and nitrogen elemental and isotopic analyses were applied in combination with records of hydrocarbons (n-alkanes) to investigate the sources and depositional conditions of sediment organic matter. Changes in fluvial and airborne delivery of inorganic matter were based on X-ray fluorescence measurements. The results reveal that population growth and related increases in land-use pressure had a major impact on catchment erosion and input of terrestrial organic matter to the lakes from the 1500s to the end of the 1800s. Evidence also exists of a brief period of catchment disturbance at ca. 1200–1300, followed by recovery, likely connected to the Black Death pandemic. At ca. 1900 synchronous shifts in most of the proxy records suggest a marked change in external forcing common to the two lakes related to a major decrease in population density and the introduction of modern forestry following the industrial revolution. Interestingly, the two sediment records exhibit generally coherent trends in C/N ratio, organic C content and δ¹³C, both before and after 1900, indicating broadly similar sensitivities of the lake ecosystems to human impact. In contrast, deviating trends in total N content, δ¹⁵N and lithogenic element concentrations (K, Ti, Rb and Zr) reflect site-specific responses to local disturbances during the last century due to different nutrient conditions and catchment properties. Our companion sediment records highlight the importance of understanding long-term human impact on watersheds and demonstrate how regional versus local forcing of lake ecosystems, as well as site-specific responses related to catchment characteristics can be reconstructed.  相似文献   

Preface: Economics of groundwater management     

Peter Reinelt  Nicholas Brozovi?  M. Ejaz Qureshi  Petra Hellegers 《Hydrogeology Journal》2012,20(5):817-820

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