TY - JOUR AB - Assessment of water resources from remote mountainous catchments plays a crucial role for the development of rural areas in or in the vicinity of mountain ranges. The scarcity of data, however, prevents the application of standard approaches that are based on data-driven models. The Hindu Kush–Karakoram–Himalaya mountain range is a crucial area in terms of water resources, but our understanding of the response of its high-elevation catchments to a changing climate is hindered by lack of hydro-meteorological and cryospheric data. Hydrological modeling is challenging here because internal inconsistencies—such as an underestimation of precipitation input that can be compensated for by an overestimation of meltwater—might be hidden due to the complexity of feedback mechanisms that govern melt and runoff generation in such basins. Data scarcity adds to this difficulty by preventing the application of systematic calibration procedures that would allow identification of the parameter set that could guarantee internal consistency in the simulation of the single hydrological components. In this work, we use simulations from the Hunza River Basin in the Karakoram region obtained with the hydrological model TOPKAPI to quantify the predictive power of discharge and snow-cover data sets, as well as the combination of both. We also show that short-term measurements of meteorological variables such as radiative fluxes, wind speed, relative humidity, and air temperature from glacio-meteorological experiments are crucial for a correct parameterization of surface melt processes. They enable detailed simulations of the energy fluxes governing glacier–atmosphere interaction and the resulting ablation through energy-balance modeling. These simulations are used to derive calibrated parameters for the simplified snow and glacier routines in TOPKAPI. We demonstrate that such parameters are stable in space and time in similar climatic regions, thus reducing the number of parameters requiring calibration. AU - Pellicciotti, Francesca AU - Buergi, Cyrill AU - Immerzeel, Walter Willem AU - Konz, Markus AU - Shrestha, Arun B. ID - 12646 IS - 1 JF - Mountain Research and Development SN - 0276-4741 TI - Challenges and uncertainties in hydrological modeling of remote Hindu Kush–Karakoram–Himalayan (HKH) basins: Suggestions for calibration strategies VL - 32 ER - TY - JOUR AB - Accurate quantification of the spatial distribution of precipitation in mountain regions is crucial for assessments of water resources and for the understanding of high-altitude hydrology, yet it is one of the largest unknowns due to the lack of high-altitude observations. The Hunza basin in Pakistan contains very large glacier systems, which, given the melt, cannot persist unless precipitation (snow input) is much higher than what is observed at the meteorological stations, mostly located in mountain valleys. Several studies, therefore, suggest strong positive vertical precipitation lapse rates; in the present study, we quantify this lapse rate by using glaciers as a proxy. We assume a neutral mass balance for the glaciers for the period from 2001 to 2003, and we inversely model the precipitation lapse by balancing the total accumulation in the catchment area and the ablation over the glacier area for the 50 largest glacier systems in the Hunza basin in the Karakoram. Our results reveal a vertical precipitation lapse rate that equals 0.21 ± 0.12% m−1, with a maximum precipitation at an elevation of 5500 masl. We showed that the total annual basin precipitation (828 mm) is 260% higher than what is estimated based on interpolated observations (319 mm); this has major consequences for hydrological modeling and water resource assessments in general. Our results were validated by using previously published studies on individual glaciers as well as the water balance of the Hunza basin. The approach is more widely applicable in mountain ranges where precipitation measurements at high altitude are lacking. AU - Immerzeel, Walter Willem AU - Pellicciotti, Francesca AU - Shrestha, Arun B. ID - 12647 IS - 1 JF - Mountain Research and Development KW - General Environmental Science KW - Development KW - Environmental Chemistry SN - 0276-4741 TI - Glaciers as a proxy to quantify the spatial distribution of precipitation in the Hunza basin VL - 32 ER - TY - JOUR AB - Distributed glacier melt models generally assume that the glacier surface consists of bare exposed ice and snow. In reality, many glaciers are wholly or partially covered in layers of debris that tend to suppress ablation rates. In this paper, an existing physically based point model for the ablation of debris-covered ice is incorporated in a distributed melt model and applied to Haut Glacier d'Arolla, Switzerland, which has three large patches of debris cover on its surface. The model is based on a 10 m resolution digital elevation model (DEM) of the area; each glacier pixel in the DEM is defined as either bare or debris-covered ice, and may be covered in snow that must be melted off before ice ablation is assumed to occur. Each debris-covered pixel is assigned a debris thickness value using probability distributions based on over 1000 manual thickness measurements. Locally observed meteorological data are used to run energy balance calculations in every pixel, using an approach suitable for snow, bare ice or debris-covered ice as appropriate. The use of the debris model significantly reduces the total ablation in the debris-covered areas, however the precise reduction is sensitive to the temperature extrapolation used in the model distribution because air near the debris surface tends to be slightly warmer than over bare ice. Overall results suggest that the debris patches, which cover 10% of the glacierized area, reduce total runoff from the glacierized part of the basin by up to 7%. AU - Reid, T. D. AU - Carenzo, M. AU - Pellicciotti, Francesca AU - Brock, B. W. ID - 12648 IS - D18 JF - Journal of Geophysical Research: Atmospheres KW - Paleontology KW - Space and Planetary Science KW - Earth and Planetary Sciences (miscellaneous) KW - Atmospheric Science KW - Earth-Surface Processes KW - Geochemistry and Petrology KW - Soil Science KW - Water Science and Technology KW - Ecology KW - Aquatic Science KW - Forestry KW - Oceanography KW - Geophysics SN - 0148-0227 TI - Including debris cover effects in a distributed model of glacier ablation VL - 117 ER - TY - CONF AB - Software model checking, as an undecidable problem, has three possible outcomes: (1) the program satisfies the specification, (2) the program does not satisfy the specification, and (3) the model checker fails. The third outcome usually manifests itself in a space-out, time-out, or one component of the verification tool giving up; in all of these failing cases, significant computation is performed by the verification tool before the failure, but no result is reported. We propose to reformulate the model-checking problem as follows, in order to have the verification tool report a summary of the performed work even in case of failure: given a program and a specification, the model checker returns a condition Ψ - usually a state predicate - such that the program satisfies the specification under the condition Ψ - that is, as long as the program does not leave the states in which Ψ is satisfied. In our experiments, we investigated as one major application of conditional model checking the sequential combination of model checkers with information passing. We give the condition that one model checker produces, as input to a second conditional model checker, such that the verification problem for the second is restricted to the part of the state space that is not covered by the condition, i.e., the second model checker works on the problems that the first model checker could not solve. Our experiments demonstrate that repeated application of conditional model checkers, passing information from one model checker to the next, can significantly improve the verification results and performance, i.e., we can now verify programs that we could not verify before. AU - Beyer, Dirk AU - Henzinger, Thomas A AU - Keremoglu, Mehmet AU - Wendler, Philipp ID - 1384 T2 - Proceedings of the ACM SIGSOFT 20th International Symposium on the Foundations of Software Engineering TI - Conditional model checking: A technique to pass information between verifiers ER - TY - JOUR AB - For G = GL 2, PGL 2, SL 2 we prove that the perverse filtration associated with the Hitchin map on the rational cohomology of the moduli space of twisted G-Higgs bundles on a compact Riemann surface C agrees with the weight filtration on the rational cohomology of the twisted G character variety of C when the cohomologies are identified via non-Abelian Hodge theory. The proof is accomplished by means of a study of the topology of the Hitchin map over the locus of integral spectral curves. AU - De Cataldo, Mark A AU - Tamas Hausel AU - Migliorini, Luca ID - 1472 IS - 3 JF - Annals of Mathematics TI - Topology of hitchin systems and Hodge theory of character varieties: The case A 1 VL - 175 ER -