@misc{Braun2020,
author = {Braun, Jean},
title = {Response to comment by Japsen et al. on "A review of numerical modeling studies of passive margin escarpments leading to a new analytical expression for the rate of escarpment migration velocity"},
series = {Gondwana research : international geoscience journal ; official journal of the International Association for Gondwana Research},
volume = {65},
journal = {Gondwana research : international geoscience journal ; official journal of the International Association for Gondwana Research},
publisher = {Elsevier},
address = {Amsterdam},
issn = {1342-937X},
doi = {10.1016/j.gr.2018.10.003},
pages = {174 -- 176},
year = {2020},
language = {en}
}
@article{BrillPassuniPinedaEspichanCuyaetal.2020,
author = {Brill, Fabio Alexander and Passuni Pineda, Silvia and Espichan Cuya, Bruno and Kreibich, Heidi},
title = {A data-mining approach towards damage modelling for El Nino events in Peru},
series = {Geomatics, natural hazards and risk},
volume = {11},
journal = {Geomatics, natural hazards and risk},
number = {1},
publisher = {Routledge, Taylor \& Francis Group},
address = {Abingdon},
issn = {1947-5705},
doi = {10.1080/19475705.2020.1818636},
pages = {1966 -- 1990},
year = {2020},
abstract = {Compound natural hazards likeEl Ninoevents cause high damage to society, which to manage requires reliable risk assessments. Damage modelling is a prerequisite for quantitative risk estimations, yet many procedures still rely on expert knowledge, and empirical studies investigating damage from compound natural hazards hardly exist. A nationwide building survey in Peru after theEl Ninoevent 2017 - which caused intense rainfall, ponding water, flash floods and landslides - enables us to apply data-mining methods for statistical groundwork, using explanatory features generated from remote sensing products and open data. We separate regions of different dominant characteristics through unsupervised clustering, and investigate feature importance rankings for classifying damage via supervised machine learning. Besides the expected effect of precipitation, the classification algorithms select the topographic wetness index as most important feature, especially in low elevation areas. The slope length and steepness factor ranks high for mountains and canyons. Partial dependence plots further hint at amplified vulnerability in rural areas. An example of an empirical damage probability map, developed with a random forest model, is provided to demonstrate the technical feasibility.},
language = {en}
}
@article{BrunelloAndermannMarcetal.2020,
author = {Brunello, Camilla Francesca and Andermann, Christoff and Marc, Odin and Schneider, Katharina A. and Comiti, Francesco and Achleitner, Stefan and Hovius, Niels},
title = {Annually resolved monsoon onset and withdrawal dates across the Himalayas derived from local precipitation statistics},
series = {Geophysical research letters},
volume = {47},
journal = {Geophysical research letters},
number = {23},
publisher = {American Geophysical Union},
address = {Washington},
issn = {0094-8276},
doi = {10.1029/2020GL088420},
pages = {12},
year = {2020},
abstract = {A local and flexible definition of the monsoon season based on hydrological evidence is important for the understanding and management of Himalayan water resources. Here, we present an objective statistical method to retrieve seasonal hydrometeorological transitions. Applied to daily rainfall data (1951-2015), this method shows an average longitudinal delay of similar to 15 days, with later monsoon onset and earlier withdrawal in the western Himalaya, consistent with the continental progression of wet air masses. This delay leads to seasons of different length along the Himalaya and biased precipitation amounts when using uniform calendric monsoon boundaries. In the Central Himalaya annual precipitation has increased, due primarily to an increase of premonsoon precipitation. These findings highlight issues associated with a static definition of monsoon boundaries and call for a deeper understanding of nonmonsoonal precipitation over the Himalayan water tower.
Plain Language Summary Precipitation in the Himalayas determines water availability for the Indian foreland with large socioeconomic implications. Despite its importance, spatial and temporal patterns of precipitation are poorly understood. Here, we estimate the long-term average and trends of seasonal precipitation at the scale of individual catchments draining the Himalayas. We apply a statistical method to detect the timing of hydrometeorological seasons from local precipitation measurements, focusing on monsoon onset and withdrawal. We identify longitudinal and latitudinal delays, resulting in seasons of different length along and across the Himalayas. These spatial patterns and the annual variability of the monsoon boundaries mean that oft-used, fixed calendric dates, for example, 1 June to 30 September, may be inadequate for retrieving monsoon rainfall totals. Moreover, we find that, despite its prominent contribution to annual rainfall totals, the Indian summer monsoon cannot explain the increase of the annual precipitation over the Central Himalayas. Instead, this appears to be mostly driven by changes in premonsoon and winter rainfall. So far, little attention has been paid to premonsoon precipitation, but governed by evaporative processes and surface water availability, it may be enhanced by irrigation and changed land use in the Gangetic foreland.},
language = {en}
}
@article{CalitriSommervanderMeijetal.2020,
author = {Calitri, Francesca and Sommer, Michael and van der Meij, Marijn W. and Egli, Markus},
title = {Soil erosion along a transect in a forested catchment: recent or ancient processes?},
series = {Catena : an interdisciplinary journal of soil science, hydrology, geomorphology focusing on geoecology and landscape evolution},
volume = {194},
journal = {Catena : an interdisciplinary journal of soil science, hydrology, geomorphology focusing on geoecology and landscape evolution},
publisher = {Elsevier},
address = {Amsterdam},
issn = {0341-8162},
doi = {10.1016/j.catena.2020.104683},
pages = {11},
year = {2020},
abstract = {Forested areas are assumed not to be influenced by erosion processes. However, forest soils of Northern Germany in a hummocky ground moraine landscape can sometimes exhibit a very shallow thickness on crest positions and buried soils on slope positions. The question consequently is: Are these on-going or ancient erosional and depositional processes? Plutonium isotopes act as soil erosion/deposition tracers for recent (last few decades) processes. Here, we quantified the 239+240PU inventories in a small, forested catchment (ancient forest "Melzower Forst", deciduous trees), which is characterised by a hummocky terrain including a kettle hole. Soil development depths (depth to C horizon) and 239+240PU inventories along a catena of sixteen different profiles were determined and correlated to relief parameters. Moreover, we compared different modelling approaches to derive erosion rates from Pu data.
We find a strong relationship between soil development depths, distance-to-sink and topography along the catena. Fully developed Retisols (thicknesses > 1 m) in the colluvium overlay old land surfaces as documented by fossil Ah horizons. However, we found no relationship of Pu-based erosion rates to any relief parameter. Instead, 239+240PU inventories showed a very high local, spatial variability (36-70 Bq m(-2)). Low annual rainfall, spatially distributed interception and stem flow might explain the high variability of the 239+240PU inventories, giving rise to a patchy input pattern. Different models resulted in quite similar erosion and deposition rates (max: -5 t ha(-1) yr(-1) to +7.3 t ha(-1) yr(-1)). Although some rates are rather high, the magnitude of soil erosion and deposition - in terms of soil thickness change - is negligible during the last 55 years. The partially high values are an effect of the patchy Pu deposition on the forest floor. This forest has been protected for at least 240 years. Therefore rather natural events and anthropogenic activities during medieval times or even earlier must have caused the observed soil pattern, which documents strong erosion and deposition processes.},
language = {en}
}
@article{CastinoBookhagenDelaTorre2020,
author = {Castino, Fabiana and Bookhagen, Bodo and De la Torre, Alejandro},
title = {Atmospheric dynamics of extreme discharge events from 1979 to 2016 in the southern Central Andes},
series = {Climate dynamics : observational, theoretical and computational research on the climate system},
volume = {55},
journal = {Climate dynamics : observational, theoretical and computational research on the climate system},
number = {11-12},
publisher = {Springer},
address = {Berlin ; Heidelberg [u.a.]},
issn = {0930-7575},
doi = {10.1007/s00382-020-05458-1},
pages = {3485 -- 3505},
year = {2020},
abstract = {During the South-American Monsoon season, deep convective systems occur at the eastern flank of the Central Andes leading to heavy rainfall and flooding. We investigate the large- and meso-scale atmospheric dynamics associated with extreme discharge events (> 99.9th percentile) observed in two major river catchments meridionally stretching from humid to semi-arid conditions in the southern Central Andes. Based on daily gauge time series and ERA-Interim reanalysis, we made the following three key observations: (1) for the period 1940-2016 daily discharge exhibits more pronounced variability in the southern, semi-arid than in the northern, humid catchments. This is due to a smaller ratio of discharge magnitudes between intermediate (0.2 year return period) and rare events (20 year return period) in the semi-arid compared to the humid areas; (2) The climatological composites of the 40 largest discharge events showed characteristic atmospheric features of cold surges based on 5-day time-lagged sequences of geopotential height at different levels in the troposphere; (3) A subjective classification revealed that 80\% of the 40 largest discharge events are mainly associated with the north-northeastward migration of frontal systems and 2/3 of these are cold fronts, i.e. cold surges. This work highlights the importance of cold surges and their related atmospheric processes for the generation of heavy rainfall events and floods in the southern Central Andes.},
language = {en}
}
@article{ChengMilsch2020,
author = {Cheng, Chaojie and Milsch, Harald},
title = {Permeability variations in illite-bearing sandstone},
series = {Journal of geophysical research : Solid earth},
volume = {125},
journal = {Journal of geophysical research : Solid earth},
number = {9},
publisher = {American Geophysical Union},
address = {Washington},
issn = {2169-9313},
doi = {10.1029/2020JB020122},
pages = {21},
year = {2020},
abstract = {Temperature changes and variations in pore fluid salinity may negatively affect the permeability of clay-bearing sandstones with implications for natural fluid flow and geotechnical applications alike. In this study these factors are investigated for a sandstone dominated by illite as the clay phase. Systematic long-term flow-through experiments were conducted and complemented with comprehensive microstructural investigations and the application of Derjaguin-Landau-Verwey-Overbeek (DLVO) theory to explain mechanistically the observed permeability changes. Initially, sample permeability was not affected by low pore fluid salinity indicating strong attraction of the illite particles to the pore walls as supported by electron microprobe analysis (EMPA). Increasing temperature up to 145 degrees C resulted in an irreversible permeability decrease by 1.5 orders of magnitude regardless of the pore fluid composition (i.e., deionized water and 2 M NaCl solution). Subsequently diluting the high salinity pore fluid to below 0.5 M yielded an additional permeability decline by 1.5 orders of magnitude, both at 145 degrees C and after cooling to room temperature. By applying scanning electron microscopy (SEM) and mercury intrusion porosimetry (MIP) thermo-mechanical pore throat closure and illite particle migration were identified as independently operating mechanisms responsible for observed permeability changes during heating and dilution, respectively. These observations indicate that permeability of illite-bearing sandstones will be impaired by heating and exposure to low salinity pore fluids. In addition, chemically induced permeability variations proved to be path dependent with respect to the applied succession of fluid salinity changes.},
language = {en}
}
@article{ChengMilsch2020,
author = {Cheng, Chaojie and Milsch, Harald},
title = {Evolution of fracture aperture in quartz sandstone under hydrothermal conditions},
series = {Minerals},
volume = {10},
journal = {Minerals},
number = {8},
publisher = {MDPI},
address = {Basel},
issn = {2075-163X},
doi = {10.3390/min10080657},
pages = {18},
year = {2020},
abstract = {Fractures efficiently affect fluid flow in geological formations, and thereby determine mass and energy transport in reservoirs, which are not least exploited for economic resources. In this context, their response to mechanical and thermal changes, as well as fluid-rock interactions, is of paramount importance. In this study, a two-stage flow-through experiment was conducted on a pure quartz sandstone core of low matrix permeability, containing one single macroscopic tensile fracture. In the first short-term stage, the effects of mechanical and hydraulic aperture on pressure and temperature cycles were investigated. The purpose of the subsequent intermittent-flow long-term (140 days) stage was to constrain the evolution of the geometrical and hydraulic fracture properties resulting from pressure solution. Deionized water was used as the pore fluid, and permeability, as well as the effluent Si concentrations, were systematically measured. Overall, hydraulic aperture was shown to be significantly less affected by pressure, temperature and time, in comparison to mechanical aperture. During the long-term part of the experiment at 140 degrees C, the effluent Si concentrations likely reached a chemical equilibrium state within less than 8 days of stagnant flow, and exceeded the corresponding hydrostatic quartz solubility at this temperature. This implies that the pressure solution was active at the contacting fracture asperities, both at 140 degrees C and after cooling to 33 degrees C. The higher temperature yielded a higher dissolution rate and, consequently, a faster attainment of chemical equilibrium within the contact fluid. X-ray mu CT observations evidenced a noticeable increase in fracture contact area ratio, which, in combination with theoretical considerations, implies a significant decrease in mechanical aperture. In contrast, the sample permeability, and thus the hydraulic fracture aperture, virtually did not vary. In conclusion, pressure solution-induced fracture aperture changes are affected by the degree of time-dependent variations in pore fluid composition. In contrast to the present case of a quasi-closed system with mostly stagnant flow, in an open system with continuous once-through fluid flow, the activity of the pressure solution may be amplified due to the persistent fluid-chemical nonequilibrium state, thus possibly enhancing aperture and fracture permeability changes.},
language = {en}
}
@article{CoesfeldKuesterKuechlyetal.2020,
author = {Coesfeld, Jacqueline and Kuester, Theres and Kuechly, Helga U. and Kyba, Christopher C. M.},
title = {Reducing variability and removing natural light from nighttime satellite imagery: A case study using the VIIRS DNB},
series = {Sensors},
volume = {20},
journal = {Sensors},
publisher = {MDPI},
address = {Basel},
pages = {13},
year = {2020},
abstract = {Temporal variation of natural light sources such as airglow limits the ability of night light sensors to detect changes in small sources of artificial light (such as villages). This study presents a method for correcting for this effect globally, using the satellite radiance detected from regions without artificial light emissions. We developed a routine to define an approximate grid of locations worldwide that do not have regular light emission. We apply this method with a 5 degree equally spaced global grid (total of 2016 individual locations), using data from the Visible Infrared Imaging Radiometer Suite (VIIRS) Day-Night Band (DNB). This code could easily be adapted for other future global sensors. The correction reduces the standard deviation of data in the Earth Observation Group monthly DNB composites by almost a factor of two. The code and datasets presented here are available under an open license by GFZ Data Services, and are implemented in the Radiance Light Trends web application.},
language = {en}
}
@misc{CoesfeldKuesterKuechlyetal.2020,
author = {Coesfeld, Jacqueline and Kuester, Theres and Kuechly, Helga U. and Kyba, Christopher C. M.},
title = {Reducing variability and removing natural light from nighttime satellite imagery: A case study using the VIIRS DNB},
series = {Postprints der Universit{\"a}t Potsdam : Mathematisch-Naturwissenschaftliche Reihe},
journal = {Postprints der Universit{\"a}t Potsdam : Mathematisch-Naturwissenschaftliche Reihe},
number = {11},
issn = {1866-8372},
doi = {10.25932/publishup-52439},
url = {http://nbn-resolving.de/urn:nbn:de:kobv:517-opus4-524397},
pages = {15},
year = {2020},
abstract = {Temporal variation of natural light sources such as airglow limits the ability of night light sensors to detect changes in small sources of artificial light (such as villages). This study presents a method for correcting for this effect globally, using the satellite radiance detected from regions without artificial light emissions. We developed a routine to define an approximate grid of locations worldwide that do not have regular light emission. We apply this method with a 5 degree equally spaced global grid (total of 2016 individual locations), using data from the Visible Infrared Imaging Radiometer Suite (VIIRS) Day-Night Band (DNB). This code could easily be adapted for other future global sensors. The correction reduces the standard deviation of data in the Earth Observation Group monthly DNB composites by almost a factor of two. The code and datasets presented here are available under an open license by GFZ Data Services, and are implemented in the Radiance Light Trends web application.},
language = {en}
}
@article{CookTurowskiHovius2020,
author = {Cook, Kristen L. and Turowski, Jens M. and Hovius, Niels},
title = {Width control on event-scale deposition and evacuation of sediment in bedrock-confined channels},
series = {Earth surface processes and landforms : the journal of the British Geomorphological Research Group},
volume = {45},
journal = {Earth surface processes and landforms : the journal of the British Geomorphological Research Group},
number = {14},
publisher = {Wiley},
address = {Hoboken},
issn = {0197-9337},
doi = {10.1002/esp.4993},
pages = {3702 -- 3713},
year = {2020},
abstract = {In mixed bedrock-alluvial rivers, the response of the system to a flood event can be affected by a number of factors, including coarse sediment availability in the channel, sediment supply from the hillslopes and upstream, flood sequencing and coarse sediment grain size distribution. However, the impact of along-stream changes in channel width on bedload transport dynamics remains largely unexplored. We combine field data, theory and numerical modelling to address this gap. First, we present observations from the Daan River gorge in western Taiwan, where the river flows through a 1 km long 20-50 m wide bedrock gorge bounded upstream and downstream by wide braidplains. We documented two flood events during which coarse sediment evacuation and redeposition appear to cause changes of up to several metres in channel bed elevation. Motivated by this case study, we examined the relationships between discharge, channel width and bedload transport capacity, and show that for a given slope narrow channels transport bedload more efficiently than wide ones at low discharges, whereas wider channels are more efficient at high discharges. We used the model sedFlow to explore this effect, running a random sequence of floods through a channel with a narrow gorge section bounded upstream and downstream by wider reaches. Channel response to imposed floods is complex, as high and low discharges drive different spatial patterns of erosion and deposition, and the channel may experience both of these regimes during the peak and recession periods of each flood. Our modelling suggests that width differences alone can drive substantial variations in sediment flux and bed response, without the need for variations in sediment supply or mobility. The fluctuations in sediment transport rates that result from width variations can lead to intermittent bed exposure, driving incision in different segments of the channel during different portions of the hydrograph.},
language = {en}
}