Spatio‐temporal controls of snowmelt and runoff generation during rain‐on‐snow events in a mid‐latitude mountain catchment

A network of 30 standalone snow monitoring stations was used to investigate the snow cover distribution, snowmelt dynamics, and runoff generation during two rain‐on‐snow (ROS) events in a 40 km² montane catchment in the Black Forest region of southwestern Germany. A multiple linear regression analysis using elevation, aspect, and land cover as predictors for the snow water equivalent (SWE) distribution within the catchment was applied on an hourly basis for two significant ROS flood events that occurred in December 2012. The available snowmelt water, liquid precipitation, as well as the total retention storage of the snow cover were considered in order to estimate the amount of water potentially available for the runoff generation. The study provides a spatially and temporally distributed picture of how the two observed ROS floods developed in the catchment. It became evident that the retention capacity of the snow cover is a crucial mechanism during ROS. It took several hours before water was released from the snowpack during the first ROS event, while retention storage was exceeded within 1 h from the start of the second event. Elevation was the most important terrain feature. South‐facing terrain contributed more water for runoff than north‐facing slopes, and only slightly more runoff was generated at open compared to forested areas. The results highlight the importance of snowmelt together with liquid precipitation for the generation of flood runoff during ROS and the large temporal and spatial variability of the relevant processes. Copyright © 2015 John Wiley & Sons, Ltd.     

Variability and alterations of water temperatures across the Elbe and Danube River Basins

Climate change is predicted to be a major threat to river ecosystems in the 21st century, but long-term records of water temperature in streams and rivers are rare. This study uses long-term water temperature series from the Elbe and the Danube River Basin to quantify the variability, magnitude, and extent of temperature alterations at different time scales. The observed patterns in monthly and daily water temperatures have been successfully described through statistical models based on air temperature, river discharge and the North Atlantic Oscillation Index. These models reveal that air temperature variability describes more than 80 % of the total water-temperature variability, linking anticipated changes in water temperature mainly to those in air temperature. The North Atlantic Oscillation effect deteriorates with decreasing latitude, while the discharge effect becomes more important and increases with the increase in discharge amount. The detected water temperature alterations include a phase shift in spring warming of almost 2 weeks, an increase in the number of days with temperatures above 25 °C and an increase in the duration of summer heat stress. These findings underline a significant risk for fundamental changes in river ecosystems, specifically in disruption of established patterns in food-web synchrony, and may lead to significant distortions in community structure and composition.     

The simulation of European heat waves from an ensemble of regional climate models within the EURO-CORDEX project

The ability of a large ensemble of regional climate models to accurately simulate heat waves at the regional scale of Europe was evaluated. Within the EURO-CORDEX project, several state-of-the art models, including non-hydrostatic meso-scale models, were run for an extended time period (20 years) at high resolution (12 km), over a large domain allowing for the first time the simultaneous representation of atmospheric phenomena over a large range of spatial scales. Eight models were run in this configuration, and thirteen models were run at a classical resolution of 50 km. The models were driven with the same boundary conditions, the ERA-Interim re-analysis, and except for one simulation, no observations were assimilated in the inner domain. Results, which are compared with daily temperature and precipitation observations (ECA&D and E-OBS data sets) show that, even forced by the same re-analysis, the ensemble exhibits a large spread. A preliminary analysis of the sources of spread, using in particular simulations of the same model with different parameterizations, shows that the simulation of hot temperature is primarily sensitive to the convection and the microphysics schemes, which affect incoming energy and the Bowen ratio. Further, most models exhibit an overestimation of summertime temperature extremes in Mediterranean regions and an underestimation over Scandinavia. Even after bias removal, the simulated heat wave events were found to be too persistent, but a higher resolution reduced this deficiency. The amplitude of events as well as the variability beyond the 90th percentile threshold were found to be too strong in almost all simulations and increasing resolution did not generally improve this deficiency. Resolution increase was also shown to induce large-scale 90th percentile warming or cooling for some models, with beneficial or detrimental effects on the overall biases. Even though full causality cannot be established on the basis of this evaluation work, the drivers of such regional differences were shown to be linked to changes in precipitation due to resolution changes, affecting the energy partitioning. Finally, the inter-annual sequence of hot summers over central/southern Europe was found to be fairly well simulated in most experiments despite an overestimation of the number of hot days and of the variability. The accurate simulation of inter-annual variability for a few models is independent of the model bias. This indicates that internal variability of high summer temperatures should not play a major role in controlling inter-annual variability. Despite some improvements, especially along coastlines, the analyses conducted here did not allow us to generally conclude that a higher resolution is clearly beneficial for a correct representation of heat waves by regional climate models. Even though local-scale feedbacks should be better represented at high resolution, combinations of parameterizations have to be improved or adapted accordingly.     

Tectonic control on the distribution of Palaeocene marine syn‐rift deposits in the Fenris Graben,northwestern Vøring Basin,offshore Norway

The location, shape and stacking pattern of deep‐marine clastic sediments on drifting stage passive continental margins are strongly influenced by the slope and basin floor topography. The tectonic control on sediment routes and dispersal patterns, however, is less understood on rift margins, particularly the impact of subaqueous transfer zones or relay ramps. In this study, an area of the Palaeocene marine syn‐rift succession in the Vøring Basin is mapped in detail to unravel the relationship between fault geometries and sedimentary infill patterns. Using root‐mean‐square (RMS) amplitudes and deposit thicknesses interpreted from seismic data, sedimentary elements in the Fenris Graben and the Gjallar Ridge are related to the fault patterns and the overall basin geometry. Older deposits are found to be aligned parallel to the basin axis, with the greatest sediment thicknesses on the hanging walls and adjacent to rotated faults. The main sediment supply is interpreted to be sourced from the Vøring Marginal High and Greenland, presumably containing a significant proportion of coarser grained material and comprising numerous local depocentres. With continued rifting and decreased fault activity, finer grained deposition draped the previous basin infill and smoothed the basin floor topography. Deposits close to the foot of relay ramps along the Gjallar Ridge, however, suggest that the high may have acted as a local sediment source leading to local depocentres. Transfer zones played a significant role in sediment transport during the early rifting phase, and were able to maintain some influence into the late rifting and early drifting stage. Identification of early‐ and late‐stage transfer zones may therefore help in locating coarser grained depocentres and potential hydrocarbon reservoirs.     

Decarbonization and regulation of Germany's electricity system after Fukushima

Germany's current efforts to decarbonize its electricity system are analysed. As nuclear power and fossil power plants equipped with carbon capture and storage were ruled out in 2011, renewable electricity generation (RES) together with electricity savings are the primary focus for achieving decarbonization. Germany aims to have RES account for at least 80% of its electricity by 2050. Achieving renewable generation needs strong political support and regulatory provisions for its market integration. Four main technical and regulatory challenges are the maintenance of a steady and efficient expansion of RES, the provision of balancing capacities, the realization of the targeted electricity savings, and the smart adaptation of the transport and distribution grid. An overview of the existing and planned regulatory provisions for decarbonization are described, and some gaps identified, particularly with regard to the overall management of the process, the inclusion of electricity savings and the interference of Germany's decarbonization strategies with neighbouring countries. Policies that both accelerate grid expansion and direct RES expansion should immediately be put in place and can be supported by a targeted mobilization of balancing capacities. Electricity savings are a significant and cost-efficient strategy for low-carbon electricity.

Policy relevance

Germany is actively converting its national electricity system towards a fully renewable one. As renewable electricity has reached about a quarter of total consumption, a number of technical and regulatory challenges arise. Current discussions and plans are described for the four main challenges: maintaining and optimizing high investment rates into RES generation technologies, providing balancing capacities, reducing demand, and adapting the grid to the changing needs. Policy recommendations for these four tasks highlight the need to intensify electricity demand reduction and also consider the potential interactions between the German electricity system and its neighbouring countries.     

Extraction and motion estimation of vehicles in single-pass airborne LiDAR data towards urban traffic analysis

Airborne LiDAR data are characterized by involving not only rich spatial but also temporal information. It is possible to extract vehicles with motion artifacts from single-pass airborne LiDAR data, based on which the motion state and velocity of vehicles can be identified and derived. In this paper, a complete strategy for urban traffic analysis using airborne LiDAR data is presented. An adaptive 3D segmentation method is presented to facilitate the task of vehicle extraction. The method features an ability to detect local arbitrary modes at multi scales, thereby making it particularly appropriate for partitioning complex point cloud data. Vehicle objects are then extracted by a binary classification using object-based features. Furthermore, the motion analysis for extracted vehicles is performed to distinguish between moving and stationary ones. Finally, the velocity is estimated for moving vehicles. The applicability and efficiency of the presented strategy is demonstrated and evaluated on three ALS datasets acquired for the propose of city mapping, where up to 87% of vehicles have been extracted and up to 83% of moving traffic can be recovered together with reasonable velocity estimates. It can be concluded that airborne LiDAR data can provide value-added products for traffic monitoring applications, including vehicle counts, location and velocity, along with traditional products such as building models, DEMs and vegetation models.     

Assessment of ZTD derived from ECMWF/NCEP data with GPS ZTD over China

The accuracy and feasibility of computing the zenith tropospheric delays (ZTDs) from data of the European Center for Medium-Range Weather Forecasts (ECMWF) and the United States National Centers for Environmental Prediction (NCEP) are studied. The ZTDs are calculated from ECMWF/NCEP pressure-level data by integration and from the surface data with the Saastamoinen model method and then compared with the solutions measured from 28 global positioning system (GPS) stations of the Crustal Movement Observation Network of China (CMONOC) for 1 year. The results are as follows: (1) the error of the integration method is 1–3 cm less than that of the Saastamoinen model method. The agreement between the ECMWF ZTD and GPS ZTD is better than that between NCEP ZTD and GPS ZTD; (2) the bias and root mean square difference (RMSD), especially the latter, have a seasonal variation, and the RMSD decreases with increasing altitude while the variation with latitude is not obvious; and (3) when using the full horizontal resolution of 0.5° × 0.5° of the ECMWF meteorological data in place of a reduced 2.5° × 2.5° grid, the mean RMSD between GPS and ECMWF ZTD decreases by 4.5 mm. These results illuminated the accuracy and feasibility of computing the tropospheric delays and establishing the ZTD prediction model over China for navigation and positioning with ECMWF and NCEP data.     

Decoupled warming and monsoon precipitation in East Asia over the last deglaciation

Our understanding of the continental climate development in East Asia is mainly based on loess–paleosol sequences and summer monsoon precipitation reconstructions based on oxygen isotopes (δ¹⁸O) of stalagmites from several Chinese caves. Based on these records, it is thought that East Asian Summer Monsoon (EASM) precipitation generally follows Northern Hemisphere (NH) summer insolation. However, not much is known about the magnitude and timing of deglacial warming on the East Asian continent. In this study we reconstruct continental air temperatures for central China covering the last 34,000 yr, based on the distribution of fossil branched tetraether membrane lipids of soil bacteria in a loess–paleosol sequence from the Mangshan loess plateau. The results indicate that air temperature varied in phase with NH summer insolation, and that the onset of deglacial warming at ~ 19 kyr BP is parallel in timing with other continental records from e.g. Antarctica, southern Africa and South-America. The air temperature increased from ~ 15 °C at the onset of the warming to a maximum of ~ 27 °C in the early Holocene (~ 12 kyr BP), in agreement with the temperature increase inferred from e.g. pollen and phytolith data, and permafrost limits in central China.Comparison of the tetraether membrane lipid-derived temperature record with loess–paleosol proxy records and stalagmite δ¹⁸O records shows that the strengthening of EASM precipitation lagged that of deglacial warming by ca. 3 kyr. Moreover, intense soil formation in the loess deposits, caused by substantial increases in summer monsoon precipitation, only started around 12 kyr BP (ca. 7 kyr lag). Our results thus show that the intensification of EASM precipitation unambiguously lagged deglacial warming and NH summer insolation, and may contribute to a better understanding of the mechanisms controlling ice age terminations.