Using isotopes to understand landscape-scale connectivity in a groundwater-dominated,lowland catchment under drought conditions     

Lukas Kleine  Doerthe Tetzlaff  Aaron Smith  Tobias Goldhammer  Chris Soulsby 《水文研究》2021,35(5):e14197

The Demnitzer Millcreek catchment (DMC), is a 66 km² long-term experimental catchment located 50 km SE of Berlin. Monitoring over the past 30 years has focused on hydrological and biogeochemical changes associated with de-intensification of farming and riparian restoration in the low-lying landscape dominated by rain-fed farming and forestry. However, the hydrological function of the catchment, which is closely linked to nutrient fluxes and highly sensitive to climatic variability, is still poorly understood. In the last 3 years, a prolonged drought period with below-average rainfall and above-average temperatures has resulted in marked hydrological change. This caused low soil moisture storage in the growing season, agricultural yield losses, reduced groundwater recharge, and intermittent streamflows in parts of an increasingly disconnected channel network. This paper focuses on a two-year long isotope study that sought to understand how different parts of the catchment affect ecohydrological partitioning, hydrological connectivity and streamflow generation during drought conditions. The work has shown the critical importance of groundwater storage in sustaining flows, basic in-stream ecosystem services and the dominant influence of vegetation on groundwater recharge. Recharge was much lower and occurred during a shorter window of time in winter under forests compared to grasslands. Conversely, groundwater recharge was locally enhanced by the restoration of riparian wetlands and storage-dependent water losses from the stream to the subsurface. The isotopic variability displayed complex emerging spatio-temporal patterns of stream connectivity and flow duration during droughts that may have implications for in-stream solute transport and future ecohydrological interactions between landscapes and riverscapes. Given climate projections for drier and warmer summers, reduced and increasingly intermittent streamflows are very likely not just in the study region, but in similar lowland areas across Europe. An integrated land and water management strategy will be essential to sustaining catchment ecosystem services in such catchment systems in future.  相似文献   

Erratum to: Winter storm- and summer thunderstorm-related loss events with regard to climate change in Germany     

Friedrich-Wilhelm Gerstengarbe  Peter C. Werner  Hermann Österle  Tobias Pardowitz  Olaf Burghoff 《Theoretical and Applied Climatology》2013,114(3-4):729-729

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Civil society lobbying and countries’ climate change policies: a matching approach     

Tobias Böhmelt 《Climate Policy》2013,13(6):698-717

Does civil society lobbying affect states’ policies on climate change? Does it facilitate or hamper cooperation towards ‘greener’ policies? Environmental non-governmental organizations (ENGOs) and business lobbying groups alike are increasingly seeking to access states’ negotiation delegations at the United Nations Framework Convention on Climate Change (UNFCCC) in order to affect or even change official delegates’ policies. Previous studies have failed to control for the fact that the set of states that have granted civil society access to their delegations is unlikely to be a random sample. Moreover, the fact that a delegation's policy outputs may converge with the preferences of a civil society group cannot be taken as evidence that it was caused by civil society lobbying. A matching approach that addresses both problems is proposed, which corrects for the non-random assignment of civil society organizations to state delegations and forms quasi-experimental contrasts by sampling a set of ‘most similar’ cases that only differ in their treatment; i.e. civil society lobbying. This approach facilitates a causal interpretation of lobbying efforts. The results indicate that only business groups are likely to exert a causal influence on states’ climate delegations. However, contrary to expectations, these groups appear to have enhanced states’ efforts towards environmentally friendly policies.

Policy relevance

What impact can non-governmental actors have in influencing states’ policies at the climate change negotiations? This question is addressed empirically using a matching approach, which corrects potential challenges in the research on interest group influence. It is shown that business groups are likely to influence states’ policies at the UNFCCC – unlike green interest groups or civil society in general. In light of these findings, three policy implications are derived that might be of importance for states and non-governmental decision makers alike. Most importantly, ENGOs should refocus their efforts for exerting their influence. ENGOs could make their lobbying more effective by first identifying the states that may be more receptive to their preferences and positions.  相似文献   

Alpine snow cover in a changing climate: a regional climate model perspective     

Christian Steger  Sven Kotlarski  Tobias Jonas  Christoph Schär 《Climate Dynamics》2013,41(3-4):735-754

An analysis is presented of an ensemble of regional climate model (RCM) experiments from the ENSEMBLES project in terms of mean winter snow water equivalent (SWE), the seasonal evolution of snow cover, and the duration of the continuous snow cover season in the European Alps. Two sets of simulations are considered, one driven by GCMs assuming the SRES A1B greenhouse gas scenario for the period 1951–2099, and the other by the ERA-40 reanalysis for the recent past. The simulated SWE for Switzerland for the winters 1971–2000 is validated against an observational data set derived from daily snow depth measurements. Model validation shows that the RCMs are capable of simulating the general spatial and seasonal variability of Alpine snow cover, but generally underestimate snow at elevations below 1,000 m and overestimate snow above 1,500 m. Model biases in snow cover can partly be related to biases in the atmospheric forcing. The analysis of climate projections for the twenty first century reveals high inter-model agreement on the following points: The strongest relative reduction in winter mean SWE is found below 1,500 m, amounting to 40–80 % by mid century relative to 1971–2000 and depending upon the model considered. At these elevations, mean winter temperatures are close to the melting point. At higher elevations the decrease of mean winter SWE is less pronounced but still a robust feature. For instance, at elevations of 2,000–2,500 m, SWE reductions amount to 10–60 % by mid century and to 30–80 % by the end of the century. The duration of the continuous snow cover season shows an asymmetric reduction with strongest shortening in springtime when ablation is the dominant factor for changes in SWE. We also find a substantial ensemble-mean reduction of snow reliability relevant to winter tourism at elevations below about 1,800 m by mid century, and at elevations below about 2,000 m by the end of the century.  相似文献   

Mapping global land system archetypes   总被引：1，自引：0，他引：1  

Tomáš Václavík  Sven Lautenbach  Tobias Kuemmerle  Ralf Seppelt 《Global Environmental Change》2013,23(6):1637-1647

Land use is a key driver of global environmental change. Unless major shifts in consumptive behaviours occur, land-based production will have to increase drastically to meet future demands for food and other commodities. One approach to better understand the drivers and impacts of agricultural intensification is the identification of global, archetypical patterns of land systems. Current approaches focus on broad-scale representations of dominant land cover with limited consideration of land-use intensity. In this study, we derived a new global representation of land systems based on more than 30 high-resolution datasets on land-use intensity, environmental conditions and socioeconomic indicators. Using a self-organizing map algorithm, we identified and mapped twelve archetypes of land systems for the year 2005. Our analysis reveals similarities in land systems across the globe but the diverse pattern at sub-national scales implies that there are no ‘one-size-fits-all’ solutions to sustainable land management. Our results help to identify generic patterns of land pressures and environmental threats and provide means to target regionalized strategies to cope with the challenges of global change. Mapping global archetypes of land systems represents a first step towards better understanding the global patterns of human–environment interactions and the environmental and social outcomes of land system dynamics.  相似文献   

Analysis of the Slab Ocean El Nino atmospheric feedbacks in observed and simulated ENSO dynamics     

Dietmar Dommenget  Sabine Haase  Tobias Bayr  Claudia Frauen 《Climate Dynamics》2014,42(11-12):3187-3205

In a recent study it was illustrated that the El Nino Southern Oscillation (ENSO) mode can exist in the absence of any ocean dynamics. This oscillating mode exists just due to the interaction between atmospheric heat fluxes and ocean heat capacity. The primary purpose of this study is to further explore these atmospheric Slab Ocean ENSO dynamics and therefore the role of positive atmospheric feedbacks in model simulations and observations. The positive solar radiation feedback to sea surface temperature (SST), due to reduced cloud cover for anomalous warm SSTs, is the main positive feedback in the Slab Ocean El Nino dynamics. The strength of this positive cloud feedback is strongly related to the strength of the equatorial cold tongue. The combination of positive latent and sensible heat fluxes to the west and negative ones to the east of positive anomalies leads to the westward propagation of the SST anomalies, which allows for oscillating behavior with a preferred period of 6–7 years. Several indications are found that parts of these dynamics are indeed observed and simulated in other atmospheric or coupled general circulation models (AGCMs or CGCMs). The CMIP3 AGCM-slab ensemble of 13 different AGCM simulations shows unstable ocean–atmosphere interactions along the equatorial Pacific related to stronger cold tongues. In observations and in the CMIP3 and CMIP5 CGCM model ensemble the strength and sign of the cloud feedback is a function of the strength of the cold tongue. In summary, this indicates that the Slab Ocean El Nino dynamics are indeed a characteristic of the equatorial Pacific climate that is only dominant or significantly contributing to the ENSO dynamics if the SST cold tongue is sufficiently strong. In the observations this is only the case during strong La Nina conditions. The presence of the Slab Ocean ENSO atmospheric feedbacks in observations and CGCM model simulations implies that the family of physical ENSO modes does have another member, which is entirely driven by atmospheric processes and does not need to have the same spatial pattern nor the same time scales as the main ENSO dynamics.  相似文献   

An east–west‐trending Quaternary tunnel valley in the south‐eastern North Sea and its seismic–sedimentological interpretation     

Daniel A. Hepp  Dierk Hebbeln  Stefan Kreiter  Hanno Keil  Christian Bathmann  Jürgen Ehlers  Tobias Mörz 《第四纪科学杂志》2012,27(8):844-853

A combination of a dense reflection seismic grid and up to 50‐m‐long records from sediment cores and cone penetration tests was used to study the geometry and infill lithology of an E–W‐trending buried tunnel valley in the south‐eastern North Sea. In relation to previously known primarily N–S‐trending tunnel valleys in this area, the geometry and infill of this 38‐km‐long and up to 3‐km‐wide valley is comparable, but its E–W orientation is exceptional. The vertical cross‐section geometry may result from subglacial sediment erosion of advancing ice streams and secondary incision by large episodic meltwater discharges with high flow rates. The infill is composed of meltwater sands and reworked till remnants on the valley flanks that are overlain by late Elsterian rhythmic, laminated, lacustrine fine‐grained sediments towards the centre of the valley. A depression in the valley centre is filled with sediments most likely from the Holsteinian transgression and a subsequent post‐Holsteinian lacustrine quiet‐water setting. The exceptional axis orientation of this tunnel valley points to a regional N–S‐oriented ice front during the late Elsterian. Copyright © 2012 John Wiley & Sons, Ltd.  相似文献   

Dynamics of snow ablation in a small Alpine catchment observed by repeated terrestrial laser scans     

Luca Egli  Tobias Jonas  Thomas Grünewald  Michael Schirmer  Paolo Burlando 《水文研究》2012,26(10):1574-1585

The spatio‐temporal distribution of snow in a catchment during ablation reflects changes in the total amount of snow water equivalent and is thus a key parameter for the estimation of melt water run‐off. This study explores possible rules behind the spatial variability of snow depth during the ablation season in a small Alpine catchment with complex topography. The snow depth observations are based on more than 160 000 terrestrial laser scanner data points with a spatial resolution of 1 m, which were obtained from 11 scanning campaigns of two consecutive ablation seasons. The analysis suggests that for estimating cumulative snow melt dynamics from the catchment investigated, assessing the initial snow distribution prior to the melt season is more important than addressing spatial differences in the melt behaviour. Snow volume and snow‐covered area could be predicted well using a conceptual melt model assuming spatially uniform melt rates. However, accurate results were only obtained if the model was initialized with a pre‐melt snow distribution that reflected measured mean and standard deviation. Using stratified melt rates on the other hand did not improve the model results. At least for sites with similar meteorological and topographical conditions, the model approach presented here comprises an efficient way to estimate snow depletion dynamics, especially if persistent snow accumulation pattern between years facilitate the characterization of the initial snow distribution prior to the melt. Copyright © 2011 John Wiley & Sons, Ltd.  相似文献   

Origin of the martian dichotomy and Tharsis from a giant impact causing massive magmatism     

Gregor J. Golabek  Tobias Keller  Guizhi Zhu  James A.D. Connolly 《Icarus》2011,215(1):346-357

The origin of the ancient martian crustal dichotomy and the massive magmatic province of Tharsis remains an open problem. Here, we explore numerically a hypothesis for the origin of these two features involving both exogenic and endogenic processes. We propose a giant impact event during the late stage of planetary formation as the source of the southern highland crust. In a second stage, the extraction of excess heat by vigorous mantle convection on the impacted hemisphere leads to massive magmatism, forming a distinct Tharsis-like volcanic region. By coupling short-term and long-term numerical simulations, we are able to investigate both the early formation as well as the 4.5 Gyr evolution of the martian crust. We demonstrate numerically that this exogenic-endogenic hypothesis is in agreement with observational data from Mars.  相似文献   

Land cover mapping in the Upper Shire River catchment in Malawi using Landsat satellite data     

Lobina G. Palamuleni  Harold J. Annegarn  Tobias Landmann 《国际地球制图》2013,28(7):503-523

Land cover mapping forms a reference base for resource managers in their decision-making processes to guide rural/urban growth and management of natural resources. The aim of this study was to map land cover dynamics within the Upper Shire River catchment, Malawi. The article promotes innovation of automated land cover mapping based on remote sensing information to generate data products that are both appropriate to, and usable within different scientific applications in developing countries such as Malawi. To determine land cover dynamics, 1989 and 2002 Landsat images were used. Image bands were combined in transformations and indices with physical meaning; together with spatial data, to enhance classification accuracy. A maximum likelihood classification for each image was computed for identification of land cover variables. The results showed that the combination of spatial and digital data enhanced classification accuracy and the ability to categorise land cover features, which are relatively inhomogeneous.  相似文献