Ludwig Braun - Academia.edu (original) (raw)

Papers by Ludwig Braun

IAHS-AISH publication, 1984

This study investigates the influence of snowmelt model structure on the overall performance of r... more This study investigates the influence of snowmelt model structure on the overall performance of runoff modelling in various-sized basins, where the snow cover is typically short-lived and rather thin. The per¬ formance of the following snowmelt models is compared: temperature-index method (Bergstrom, 1976) ; temperature and wind-index method; combination method (Anderson, 1973); extended combination method (using also water vapour pressure as an input variable) energy balance method. The performance is assessed by comparing linear scale plots of measu¬ red and simulated discharge and by applying the numerical efficiency criterion according to Nash and Sutcliffe (1970). For a given catchment, melt rates as calculated by the various snowmelt models are used as input to one and the same runoff model. In the small-scale Rietholzbach basin (3.18 km2), meteorological data as used in this study are measured at a point having a temporal resolu¬ tion of one hour and are considered representa...

This paper is a valuable contribution to the knowledge of glacial hydrology in the Caucasus Area.... more This paper is a valuable contribution to the knowledge of glacial hydrology in the Caucasus Area. It is worth to be published, however, it needs many minor revisions that are directly put into the manuscript. I am attaching the scan of the annotated manuscript and hope that the authos can include them.

Hydrology Research, 1981

During the melt season of 1978, the nature of snow and ice storage, the energy sources and the st... more During the melt season of 1978, the nature of snow and ice storage, the energy sources and the stream flow response were investigated at a site, a small-scale and a meso-scale watershed in the Coast Mountains of British Columbia, Canada. Differences in system internal homogeneity and system response times at each of these scales indicated the usefulness of this empirical classification. It is also demonstrated that different methods of analysis of snowmelt systems are appropriate at the different scales.

… -Publications of the …, 1993

Many conceptual runoff models are well able to simulate daily discharge based on a rather modest ... more Many conceptual runoff models are well able to simulate daily discharge based on a rather modest data input (e.g. daily values of air temperature and precipitation) provided that calibration via discharge is possible. The underlying assumption is that no considerable losses or gains of water take place via subterranean pathways. This study reports on the application of an operationally used conceptual runoff model in a 96 km 2 Swiss alpine watershed known to exhibit a complex karst-related hydrological behaviour. Three additional model parameters are introduced, one taking into account aspect-dependent snow melt, and two parameters controlling karst-related water losses. The values of these additional parameters are derived externally, and optimal values of the remaining parameters are achieved by a manual calibration procedure on the basis of discharge. A plausible complete water balance and satisfactory snow storage simulations are achieved by means of this extended model. It can be concluded that a rather simple conceptual model can be applied in karst basins under the assumption that certain intermediate model results can be optimized and verified with the aid of additional measurements apart from the standard hydrometeorological network.

The water equivalent (SWE) of the seasonal snow cover can be an important component of the water ... more The water equivalent (SWE) of the seasonal snow cover can be an important component of the water cycle in mountainous areas, and the knowledge of this temporary storage term may for example be very valuable for predicting seasonal discharge, for making short-range discharge forecasts and also for assessing water quality aspects. Direct measurements of the SWE usually refer to index points and are seldom part of the standard meteorological networks. Therefore it may be advantageous to simulate this storage term based on the available meteorological data. The choice of the appropriate type of model will largely depend on the purpose of the simulation and the data availability. For operational forecasting and prediction practices, various conceptual models describing snow accumulation, melt and internal processes as well as runoff processes in a rather general way are usually sufficient if a minimal data requirement is met. To answer more complex questions such as the hydrological cons...

The aim of this contribution is to show how snow- and glaciermelt influence runoff today and in t... more The aim of this contribution is to show how snow- and glaciermelt influence runoff today and in the future under the assumption that global warming continues. This assumption will not necessarily come into effect, but according to climatologists, the opposite is rather unlikely in the next few hundred years, for example a drastic cooling due to changes in ocean currents. Mountain regions receive more precipitation than the lowlands around them, and act as a reservoir of this excess water by temporarily storing it in the form of snow and ice. Melt is highest during warm and dry periods and thus runoff increases during times of drought. This release from snow and ice storage ensures a reliable water flow in rivers, and thus is of great value in terms of irrigation and other water uses. Glaciers, therefore, influence the water cycle very favourably by collecting water during times of abundance and releasing it when there is a lack of precipitation. Even in a warmer climate we expect pr...

The central volcano Barðarbunga, with a 65 km² large caldera, is located on the northwestern edge... more The central volcano Barðarbunga, with a 65 km² large caldera, is located on the northwestern edge of Vatnajokull ice cap. It is connected with a 190 km long, from southwest to northeast running fissure system within the Neovolcanic Zone of Iceland. The subglacial volcano reaches a height of 2009 m a.s.l. and is covered with an up to 850 m thick ice layer. On 16 August 2014 high seismic activity had started in the area of Barðarbunga and lasted until the end of February 2015. Three geothermal/tectonic events occurred and could be monitored continuously with TerraSAR-X and TanDEM-X radar data within the project IsViews (Iceland subglacial Volcanoes interdisciplinary early warning system). The development of a six months lasting fissure eruption in the Holuhraun glacier forefield, located 40 km northeast of Barðarbunga, was observed with near real-time TerraSAR-X Stripmap data and TanDEM-X RawDEMs. The maximum extend of the lava field was measured to 84.5 km² and the volume to 1.48 km³...

Hydrology Research, 1994

The snow-water equivalent (SWE) of the seasonal snow cover is an important component of the water... more The snow-water equivalent (SWE) of the seasonal snow cover is an important component of the water cycle in the Swiss Alps. It is used for predicting seasonal discharge, for short-range discharge forecasts and also for assessing water quality aspects. The SWE has been measured every two weeks at about 50 stations located between 860 and 2,540 m a.s.l. for more than 30 years. In addition there are special investigation areas with stations located between 600 m and 2,900 m a.s.l. where SWE is measured once per winter. The main characteristics of temporal and spatial SWE distributions are analyzed. The variations of SWE values depend in ranking order on elevation, on the year-to-year variations, on the region and on the exposition. The standardized SWE-values depend mostly on the year-to-year variations and on the region.

Hydrology and Earth System Sciences Discussions, 2006

The paper presents a catchment modeling approach for remote glacierized Himalayan catchments. The... more The paper presents a catchment modeling approach for remote glacierized Himalayan catchments. The distributed catchment model TAC D , which is widely based on the HBV model, was further developed for the application in highly glacierized catchments on a daily timestep and applied to the Nepalese Himalayan headwater Langtang Khola (360 km 2). Low laying reference stations are taken for temperature extrapolation applying a second order polynomial function. Probability based statistical methods enable bridging data gaps in daily precipitation time series and the redistribution of cumulated precipitation sums over the previous days. Snow and ice melt was calculated in a distributed way based on the temperature-index method employing calculated daily potential sunshine durations. Different melting conditions of snow and ice and melting of ice under debris layers were considered. The spatial delineation of hydrological response units was achieved by taking topographic and physiographic information from maps and satellite images into account, and enabled to incorporate process knowledge into the model. Simulation results demonstrated that the model is able to simulate daily discharge for a period of 10 years and point glacier mass balances observed in the research area with an adequate reliability. The simple but robust data pre-processing and modeling approach enables the determination of the components of the water balance of a remote, data scarce catchment with a minimum of input data.

Geophysical Research Letters, 2017

Conventional glacier‐wide mass balances are commonly used to study the effect of climate forcing ... more Conventional glacier‐wide mass balances are commonly used to study the effect of climate forcing on glacier melt. Unfortunately, the glacier‐wide mass balances are also influenced by the glacier's dynamic response. Investigations on the effects of climate forcing on glaciers can be largely improved by analyzing point mass balances. Using a statistical model, we have found that 52% of the year‐to‐year deviations in the point mass balances of six glaciers distributed across the entire European Alps can be attributed to a common variability. Point mass balance changes reveal remarkable regional consistencies reaching 80% for glaciers less than 10 km apart. Compared to the steady state conditions of the 1962–1982 period, the surface mass balance changes are −0.85 m water equivalent (w.e.) a−1 for 1983–2002 and −1.63 m w.e. a−1 for 2003–2013. This indicates a clear and regionally consistent acceleration of mass loss over recent decades over the entire European Alps.

Earth System Science Data Discussions, 2017

A comprehensive hydrometeorological and glaciological data set is presented, originating from a m... more A comprehensive hydrometeorological and glaciological data set is presented, originating from a multitude of recordings at several intensively operated research sites in the Rofental (1891–3772 m a.s.l., Ötztal Alps, Austria). The data sets are spanning a period of 150 years and hence represent a unique, worldwide unprecedented pool of high mountain observations. Their collection has originally been initiated to support the scientific investigation of the glaciers Hintereis-, Kesselwand- and Vernagtferner. Later, additional measurements of meteorological and hydrological variables have been undertaken; data now comprise records of temperature, relative humidity, short- and longwave radiation, wind speed and direction, air pressure, precipitation and water levels. For the glaciers, annual mass balance, glacier front variation and flow velocities as well as photographic images of the glacier status have been recorded. Since 2001, a series of distributed (airborne a...

Journal of Glaciology, 2016

ABSTRACTMost Icelandic glaciers show high-accumulation rates during winter and strong surface mel... more ABSTRACTMost Icelandic glaciers show high-accumulation rates during winter and strong surface melting during summer. Although it is difficult to establish and maintain mass-balance programs on these glaciers, mass-balance series do exist for several of the ice caps (Björnsson and others, 2013). We make use of the frequent volcanic eruptions in Iceland, which cause widespread internal tephra layers in the ice caps, to reconstruct the surface mass balance (SMB) in the ablation zone. This method requires information about surface geometry and ice velocity, derived from remote-sensing information. In addition, the emergence angle of the tephra layer needs to be known. As a proof-of-concept, we utilize a prominent tephra layer of the Mýrdalsjökull Ice Cap to infer local SMB estimates in the ablation area back to 1988. Using tephra-layer outcrop locations across the glacier at different points in time it is possible to determine local mass changes (loss and redistribution) for a large par...

Iahs Aish Publication, 1989

Journal of Glaciology, 2015

Observations show that glaciers around the world are in retreat and losing mass. Internationally ... more Observations show that glaciers around the world are in retreat and losing mass. Internationally coordinated for over a century, glacier monitoring activities provide an unprecedented dataset of glacier observations from ground, air and space. Glacier studies generally select specific parts of these datasets to obtain optimal assessments of the mass-balance data relating to the impact that glaciers exercise on global sea-level fluctuations or on regional runoff. In this study we provide an overview and analysis of the main observational datasets compiled by the World Glacier Monitoring Service (WGMS). The dataset on glacier front variations (∼42 000 since 1600) delivers clear evidence that centennial glacier retreat is a global phenomenon. Intermittent readvance periods at regional and decadal scale are normally restricted to a subsample of glaciers and have not come close to achieving the maximum positions of the Little Ice Age (or Holocene). Glaciological and geodetic observations...

Glacierized catchments are important source regions for water, and detailed knowledge of water av... more Glacierized catchments are important source regions for water, and detailed knowledge of water availability is a prerequisite for good resource management strategies. Reliable and physically consistent runoff simulations become even more important if climate change impacts on alpine water resources are to be assessed. However, hydrological modeling of glacierized catchments is challenging ice melt which represents an additional source of water. Thus, adequate calibration strategies are needed especially in data scarce regions. An important question is how powerful a limited amount of data might be for model calibration. Accordingly, we analyzed the calibration power of limited discharge measurements, mass balance observations and the combination of by means of both Monte Carlo analyzes and multi-criteria model performance evaluation. Ensembles of 100 parameter sets were selected by evaluating the simulations based on a limited and discrete number of discharge measurements, glacier m...

Journal of Hydrology, 2007

The arid lowlands of Central Asia are highly dependent on the water supplied by the Tien Shan mou... more The arid lowlands of Central Asia are highly dependent on the water supplied by the Tien Shan mountains. Snow and ice storage make large contributions to current runoff, particularly in summer. Two runoff models with different temporal resolutions, HBV-ETH and OEZ, were applied in three glaciated catchments of the Tien Shan mountains. Scenario runs were produced for a climate change caused by the doubling of atmospheric CO 2 as predicted by the GISS global circulation model and assuming a 50% reduction of glaciation extent, as well as a complete loss of glaciation. Agreement of the results was best for runs based on 50% glaciation loss, where both models predict an increase in spring and summer runoff compared to current levels. Scenarios for complete loss of glaciation predict an increase in spring runoff levels, followed by lower runoff levels for July and August. Model predictions differ concerning the degree of reduction of late summer runoff. These scenarios are sensitive to model simulation of basin precipitation, as well as to reduction of glaciation extent.

Journal of Hydrology, 2013

We modified the well-known HBV-ETH model to develop a partially distributed hydrological model th... more We modified the well-known HBV-ETH model to develop a partially distributed hydrological model that was able to simulate runoff in a highly glacierised basin. By introducing additional calibration criteria (annual and winter glacier mass balance) we reduced the goodness-of-fit for runoff, but improved the description of the accumulation and ablation processes involved. Final adjustment of the model parameters, after choosing the best out of 10,000 random parameter sets, allowed us to find a parameter calibration with acceptable errors for all criteria, which was then confirmed by good model performance during the validation period. The glacier-wide winter mass balance and the annual mass balance in the ablation area were simulated well, while the annual mass balance in the accumulation area showed inaccuracies. Good simulation of the processes during the 2003 heat wave in Europe proved that the model also delivers reliable results for meteorological conditions different from those used during calibration.