@article{DriebeBloeckerHerwigetal.1998,
  author    = {Driebe, Thomas and Bl{\"o}cker, Thomas and Herwig, Falk and Sch{\"o}nberner, Detlef},
  title     = {Diffusive overshooting in hot bottom burning AGB models},
  year      = {1998},
  language  = {en}
}
@article{DriebeSchoenbernerBloeckeretal.1998,
  author    = {Driebe, Thomas and Sch{\"o}nberner, Detlef and Bl{\"o}cker, Thomas and Herwig, Falk},
  title     = {The evolution of helium white dwarfs : I. the companion of the millisecond pular PSR J1012+5307},
  year      = {1998},
  language  = {en}
}
@article{DriebeBloeckerSchoenberneretal.1999,
  author    = {Driebe, Thomas and Bl{\"o}cker, Thomas and Sch{\"o}nberner, Detlef and Herwig, Falk},
  title     = {The evolution of helium white dwarfs : II. Thermal instabilities},
  year      = {1999},
  abstract  = {We calculated a grid of evolutionary models for white dwarfs with helium cores (He-WDs) and investigated the occurrence of hydrogen-shell flashes due to unstable hydrogen burning via CNO cycling. Our calculations show that such thermal instabilities are restricted to a certain mass range (M approx 0.21 ... 0.30 Msun), consistent with earlier studies. Models within this mass range undergo the more hydrogen shell flashes the less massive they are. This is caused by the strong dependence of the envelope mass on the white dwarf core mass. The maximum luminosities from hydrogen burning during the flashes are of the order of 105 Lsun. Because of the development of a pulse-driven convection zone whose upper boundary temporarily reaches the surface layers, the envelope's hydrogen content decreases by Delta X approx 0.06 per flash. Our study further shows that an additional high mass-loss episode during a flash-driven Roche lobe overflow to the white dwarf's companion does not affect the final cooling behaviour of the models. Independent of hydrogen shell flashes the evolution along the final white dwarf cooling branch is determined by hydrogen burning via pp-reactions down to effective temperatures as low as approx 8000 K.},
  language  = {en}
}
@article{BloeckerDriebeHerwig1999,
  author    = {Bl{\"o}cker, Thomas and Driebe, Thomas and Herwig, Falk},
  title     = {AGB evolution with overshoot : hot bootom burning vs. dredge-up},
  year      = {1999},
  language  = {en}
}
@article{HerwigBloeckerLangeretal.1999,
  author    = {Herwig, Falk and Bl{\"o}cker, Thomas and Langer, Norbert and Driebe, Thomas},
  title     = {On the formation of hydrogen-deficient post-AGB stars},
  year      = {1999},
  abstract  = {We present an evolutionary sequence of a low mass star from the Asymtotic Giant Branch (AGB) through its post- AGB stage, during which its surface chemical composition changes from hydrogen-rich to strongly hydrogen-deficient as consequence of a very late thermal pulse, following the so-called born-again scenario. The internal structure and abundance changes during this pulse are computed with a \%newly developed numerical method which allows the physically consistent calculation of stellar layers where thermonuclear and mixing time scale are comparable --- a situation which occurs when the helium flash driven convection zone extends to the hydrogen-rich surface layers during the pulse peak. The final surface mass fractions are [He/C/O]=[0.38/0.36/0.22], where the high oxygen abundance is due to diffusive overshoot employed during the AGB evolution. These models are the first to achieve general agreement with the surface abundance pattern observed in hydrogen-deficient post-AGB stars --- e.g. the PG 1159 stars or the WR-type central stars of planetary nebulae ---, confirming the born-again scenario with a physically consistent calculation and supporting the occurrence of convective overshooting in thermally pulsing AGB stars.},
  language  = {en}
}
@article{HeinrichBalanzateguiBensetal.2018,
  author    = {Heinrich, Ingo and Balanzategui, Daniel and Bens, Oliver and Blasch, Gerald and Blume, Theresa and Boettcher, Falk and Borg, Erik and Brademann, Brian and Brauer, Achim and Conrad, Christopher and Dietze, Elisabeth and Dr{\"a}ger, Nadine and Fiener, Peter and Gerke, Horst H. and G{\"u}ntner, Andreas and Heine, Iris and Helle, Gerhard and Herbrich, Marcus and Harfenmeister, Katharina and Heussner, Karl-Uwe and Hohmann, Christian and Itzerott, Sibylle and Jurasinski, Gerald and Kaiser, Knut and Kappler, Christoph and Koebsch, Franziska and Liebner, Susanne and Lischeid, Gunnar and Merz, Bruno and Missling, Klaus Dieter and Morgner, Markus and Pinkerneil, Sylvia and Plessen, Birgit and Raab, Thomas and Ruhtz, Thomas and Sachs, Torsten and Sommer, Michael and Spengler, Daniel and Stender, Vivien and St{\"u}ve, Peter and Wilken, Florian},
  title     = {Interdisciplinary Geo-ecological Research across Time Scales in the Northeast German Lowland Observatory (TERENO-NE)},
  series = {Vadose zone journal},
  volume    = {17},
  journal   = {Vadose zone journal},
  number    = {1},
  publisher = {Soil Science Society of America},
  address   = {Madison},
  issn      = {1539-1663},
  doi       = {10.2136/vzj2018.06.0116},
  pages     = {25},
  year      = {2018},
  abstract  = {The Northeast German Lowland Observatory (TERENO-NE) was established to investigate the regional impact of climate and land use change. TERENO-NE focuses on the Northeast German lowlands, for which a high vulnerability has been determined due to increasing temperatures and decreasing amounts of precipitation projected for the coming decades. To facilitate in-depth evaluations of the effects of climate and land use changes and to separate the effects of natural and anthropogenic drivers in the region, six sites were chosen for comprehensive monitoring. In addition, at selected sites, geoarchives were used to substantially extend the instrumental records back in time. It is this combination of diverse disciplines working across different time scales that makes the observatory TERENO-NE a unique observation platform. We provide information about the general characteristics of the observatory and its six monitoring sites and present examples of interdisciplinary research activities at some of these sites. We also illustrate how monitoring improves process understanding, how remote sensing techniques are fine-tuned by the most comprehensive ground-truthing site DEMMIN, how soil erosion dynamics have evolved, how greenhouse gas monitoring of rewetted peatlands can reveal unexpected mechanisms, and how proxy data provides a long-term perspective of current ongoing changes.},
  language  = {en}
}
@article{HerwigSchoenbernerBloecker1998,
  author    = {Herwig, Falk and Sch{\"o}nberner, Detlef and Bl{\"o}cker, Thomas},
  title     = {On the validity of the core-mass luminosity relation for TP-AGB stars with efficient dredge-up},
  year      = {1998},
  language  = {en}
}
@article{HerwigBloecker1999,
  author    = {Herwig, Falk and Bl{\"o}cker, Thomas},
  title     = {Overshoot in giant stars},
  year      = {1999},
  language  = {en}
}
@article{HerwigBloeckerSchoenberner1999,
  author    = {Herwig, Falk and Bl{\"o}cker, Thomas and Sch{\"o}nberner, Detlef},
  title     = {The role of convective boundaries},
  year      = {1999},
  language  = {en}
}
@article{HerwigSchoenbernerBloecker1999,
  author    = {Herwig, Falk and Sch{\"o}nberner, Detlef and Bl{\"o}cker, Thomas},
  title     = {Violation of the Core Mass - Luminosity relation for AGB models wich experience the thord dredge-up},
  year      = {1999},
  language  = {en}
}
@article{FalkKirkLohmannetal.2017,
  author    = {Falk, Thomas and Kirk, Michael and Lohmann, Dirk and Kruger, Bertus and H{\"u}ttich, Christian and Kamukuenjandje, Richard},
  title     = {The profits of excludability and transferability in redistributive land reform in central Namibia},
  series = {Development Southern Africa},
  volume    = {34},
  journal   = {Development Southern Africa},
  publisher = {Routledge, Taylor \& Francis Group},
  address   = {Abingdon},
  issn      = {0376-835X},
  doi       = {10.1080/0376835X.2016.1269633},
  pages     = {314 -- 329},
  year      = {2017},
  abstract  = {Policies which redistribute property rights to land can improve the well-being of rural households and can have overall growth effects. In many cases, however, land reforms are driven mainly by politically justified objectives. Under such circumstances, little emphasis is placed on whether and, if so, how property rights can increase productivity. Following 18 years of land reform implementation in Namibia, we evaluated 65 beneficiaries in Namibia. We assess to which degree land rights affects their farm income. The study focuses on Namibia's two main commercial land reform instruments, namely the Farm Unit Resettlement Scheme and the Affirmative Action Loan Scheme. We find evidence that the majority of land reform projects are not profitable. Further, our study confirms the importance of the right to restrict land access compared with the right to transfer. The long-term leasehold contract seemingly provides sufficient incentives to make productive use of the land.},
  language  = {en}
}
@article{FalkLohmannAzebaze2016,
  author    = {Falk, Thomas and Lohmann, Dirk and Azebaze, Nadege},
  title     = {Congruence of appropriation and provision in collective water provision in Central Namibia},
  series = {International journal of the commons},
  volume    = {10},
  journal   = {International journal of the commons},
  publisher = {Brill},
  address   = {Urtrecht},
  issn      = {1875-0281},
  doi       = {10.18352/ijc.583},
  pages     = {71 -- 118},
  year      = {2016},
  abstract  = {Achieving cooperation in natural resource management is always a challenge when incentives exist for an individual to maximise her short term benefits at the cost of a group. We study a public good social dilemma in water infrastructure provision on land reform farms in Namibia. In the context of the Namibian land reform, arbitrarily mixed groups of livestock farmers have to share the operation and maintenance of water infrastructure. Typically, water is mainly used for livestock production, and livestock numbers are subject to high fluctuations due to the given environmental conditions. Our paper assesses how alternative payment systems with differing congruence of provision and appropriation support the cooperation in the group given the ever-changing equilibria. In a first step, we conducted an exploratory overview of the social-ecological system of central Namibian land reform projects. The Social Ecological System (SES) Framework served as a guideline for this assessment (Ostrom 2009). Taking the complexity of the cooperation situation into account, in the second step we designed a role-play that is based on a social-ecological simulation model. The role-play simulates the real-life decision situations of land reform beneficiaries wherein equilibria are permanently changing. This approach helped us to not only better understand the cooperation challenges of Namibian land reform beneficiaries, but also supported stakeholders in their decision making and institution building. Our study provides evidence to support that land reform beneficiaries increase their contributions as they own more livestock and as other group members increase their payments. Nevertheless, only groups with relatively homogeneous livestock endowments manage to agree on payment rules. Interestingly, the dominant rule is an "equal payment per farmer" and not a "payment per head of livestock", though the latter would imply a higher congruence of provision and appropriation.},
  language  = {en}
}
@misc{JingHesseKumaretal.2018,
  author    = {Jing, Miao and Heße, Falk and Kumar, Rohini and Wang, Wenqing and Fischer, Thomas and Walther, Marc and Zink, Matthias and Zech, Alraune and Samaniego, Luis and Kolditz, Olaf and Attinger, Sabine},
  title     = {Improved regional-scale groundwater representation by the coupling of the mesoscale Hydrologic Model (mHM v5.7) to the groundwater model OpenGeoSys (OGS)},
  series = {Postprints der Universit{\"a}t Potsdam : Mathematisch Naturwissenschaftliche Reihe},
  journal   = {Postprints der Universit{\"a}t Potsdam : Mathematisch Naturwissenschaftliche Reihe},
  number    = {851},
  issn      = {1866-8372},
  doi       = {10.25932/publishup-42703},
  url       = {http://nbn-resolving.de/urn:nbn:de:kobv:517-opus4-427030},
  pages     = {1989 -- 2007},
  year      = {2018},
  abstract  = {Most large-scale hydrologic models fall short in reproducing groundwater head dynamics and simulating transport process due to their oversimplified representation of groundwater flow. In this study, we aim to extend the applicability of the mesoscale Hydrologic Model (mHM v5.7) to subsurface hydrology by coupling it with the porous media simulator OpenGeoSys (OGS). The two models are one-way coupled through model interfaces GIS2FEM and RIV2FEM, by which the grid-based fluxes of groundwater recharge and the river-groundwater exchange generated by mHM are converted to fixed-flux boundary conditions of the groundwater model OGS. Specifically, the grid-based vertical reservoirs in mHM are completely preserved for the estimation of land-surface fluxes, while OGS acts as a plug-in to the original mHM modeling framework for groundwater flow and transport modeling. The applicability of the coupled model (mHM-OGS v1.0) is evaluated by a case study in the central European mesoscale river basin - Nagelstedt. Different time steps, i.e., daily in mHM and monthly in OGS, are used to account for fast surface flow and slow groundwater flow. Model calibration is conducted following a two-step procedure using discharge for mHM and long-term mean of groundwater head measurements for OGS. Based on the model summary statistics, namely the Nash-Sutcliffe model efficiency (NSE), the mean absolute error (MAE), and the interquartile range error (QRE), the coupled model is able to satisfactorily represent the dynamics of discharge and groundwater heads at several locations across the study basin. Our exemplary calculations show that the one-way coupled model can take advantage of the spatially explicit modeling capabilities of surface and groundwater hydrologic models and provide an adequate representation of the spatiotemporal behaviors of groundwater storage and heads, thus making it a valuable tool for addressing water resources and management problems.},
  language  = {en}
}
@article{JingHesseKumaretal.2018,
  author    = {Jing, Miao and Hesse, Falk and Kumar, Rohini and Wang, Wenqing and Fischer, Thomas and Walther, Marc and Zink, Matthias and Zech, Alraune and Samaniego, Luis and Kolditz, Olaf and Attinger, Sabine},
  title     = {Improved regional-scale groundwater representation by the coupling of the mesoscale Hydrologic Model (mHM v5.7) to the groundwater model OpenGeoSys (OGS)},
  series = {Geoscientific model development : an interactive open access journal of the European Geosciences Union},
  volume    = {11},
  journal   = {Geoscientific model development : an interactive open access journal of the European Geosciences Union},
  number    = {5},
  publisher = {Copernicus},
  address   = {G{\"o}ttingen},
  issn      = {1991-959X},
  doi       = {10.5194/gmd-11-1989-2018},
  pages     = {1989 -- 2007},
  year      = {2018},
  abstract  = {Most large-scale hydrologic models fall short in reproducing groundwater head dynamics and simulating transport process due to their oversimplified representation of groundwater flow. In this study, we aim to extend the applicability of the mesoscale Hydrologic Model (mHM v5.7) to subsurface hydrology by coupling it with the porous media simulator OpenGeoSys (OGS). The two models are one-way coupled through model interfaces GIS2FEM and RIV2FEM, by which the grid-based fluxes of groundwater recharge and the river-groundwater exchange generated by mHM are converted to fixed-flux boundary conditions of the groundwater model OGS. Specifically, the grid-based vertical reservoirs in mHM are completely preserved for the estimation of land-surface fluxes, while OGS acts as a plug-in to the original mHM modeling framework for groundwater flow and transport modeling. The applicability of the coupled model (mHM-OGS v1.0) is evaluated by a case study in the central European mesoscale river basin - Nagelstedt. Different time steps, i.e., daily in mHM and monthly in OGS, are used to account for fast surface flow and slow groundwater flow. Model calibration is conducted following a two-step procedure using discharge for mHM and long-term mean of groundwater head measurements for OGS. Based on the model summary statistics, namely the Nash-Sutcliffe model efficiency (NSE), the mean absolute error (MAE), and the interquartile range error (QRE), the coupled model is able to satisfactorily represent the dynamics of discharge and groundwater heads at several locations across the study basin. Our exemplary calculations show that the one-way coupled model can take advantage of the spatially explicit modeling capabilities of surface and groundwater hydrologic models and provide an adequate representation of the spatiotemporal behaviors of groundwater storage and heads, thus making it a valuable tool for addressing water resources and management problems.},
  language  = {en}
}
@article{JingHesseKumaretal.2019,
  author    = {Jing, Miao and Hesse, Falk and Kumar, Rohini and Kolditz, Olaf and Kalbacher, Thomas and Attinger, Sabine},
  title     = {Influence of input and parameter uncertainty on the prediction of catchment-scale groundwater travel time distributions},
  series = {Hydrology and earth system sciences : HESS},
  volume    = {23},
  journal   = {Hydrology and earth system sciences : HESS},
  number    = {1},
  publisher = {Copernicus},
  address   = {G{\"o}ttingen},
  issn      = {1027-5606},
  doi       = {10.5194/hess-23-171-2019},
  pages     = {171 -- 190},
  year      = {2019},
  abstract  = {Groundwater travel time distributions (TTDs) provide a robust description of the subsurface mixing behavior and hydrological response of a subsurface system. Lagrangian particle tracking is often used to derive the groundwater TTDs. The reliability of this approach is subjected to the uncertainty of external forcings, internal hydraulic properties, and the interplay between them. Here, we evaluate the uncertainty of catchment groundwater TTDs in an agricultural catchment using a 3-D groundwater model with an overall focus on revealing the relationship between external forcing, internal hydraulic properties, and TTD predictions. Eight recharge realizations are sampled from a high-resolution dataset of land surface fluxes and states. Calibration-constrained hydraulic conductivity fields (Ks fields) are stochastically generated using the null-space Monte Carlo (NSMC) method for each recharge realization. The random walk particle tracking (RWPT) method is used to track the pathways of particles and compute travel times. Moreover, an analytical model under the random sampling (RS) assumption is fit against the numerical solutions, serving as a reference for the mixing behavior of the model domain. The StorAge Selection (SAS) function is used to interpret the results in terms of quantifying the systematic preference for discharging young/old water. The simulation results reveal the primary effect of recharge on the predicted mean travel time (MTT). The different realizations of calibration-constrained Ks fields moderately magnify or attenuate the predicted MTTs. The analytical model does not properly replicate the numerical solution, and it underestimates the mean travel time. Simulated SAS functions indicate an overall preference for young water for all realizations. The spatial pattern of recharge controls the shape and breadth of simulated TTDs and SAS functions by changing the spatial distribution of particles' pathways. In conclusion, overlooking the spatial nonuniformity and uncertainty of input (forcing) will result in biased travel time predictions. We also highlight the worth of reliable observations in reducing predictive uncertainty and the good interpretability of SAS functions in terms of understanding catchment transport processes.},
  language  = {en}
}
@article{LohmannFalkGeissleretal.2014,
  author    = {Lohmann, Dirk and Falk, Thomas and Geissler, Katja and Blaum, Niels and Jeltsch, Florian},
  title     = {Determinants of semi-arid rangeland management in a land reform setting in Namibia},
  series = {Journal of arid environments},
  volume    = {100},
  journal   = {Journal of arid environments},
  publisher = {Elsevier},
  address   = {London},
  issn      = {0140-1963},
  doi       = {10.1016/j.jaridenv.2013.10.005},
  pages     = {23 -- 30},
  year      = {2014},
  abstract  = {To assess the ecological and economic implications of the redistributive land reform in semi-arid Namibia, we investigated to what extent land reform beneficiaries adjust herd size and herd composition according to environmental (rainfall, vegetation) and economic variables (herd size, financial assets, running costs). We performed model-based role-plays with Namibian land reform beneficiaries, simulating 10 years of rangeland management. Our study revealed that the farmers surveyed mainly manage their herds according to their economic situation (herd size and account balance) but do not take environmental variability (rainfall and vegetation) into account. Further, our results indicate that, due to financial pressure, farmers are not able to apply their desired management strategies, and that owners of small farms face a higher risk of economic failure. However, farmers apply rather conservative and constant stocking rates and will thus, given the current economic limitations, likely not contribute to semi-arid savanna degradation. We conclude that land reform beneficiaries need support to be able to apply straightforward and efficient management strategies. This could be achieved by facilitating cooperation between small farming businesses and by supporting initial investment in productive cattle herds at the time of redistribution of the land.},
  language  = {en}
}