Response of Freezing/Thawing Indexes to the Wetting Trend under Warming Climate Conditions over the Qinghai–Tibetan Plateau during 1961–2010: A Numerical Simulation

Since the 1990s, the Qinghai–Tibetan Plateau(QTP) has experienced a strikingly warming and wetter climate that alters the thermal and hydrological properties of frozen ground. A positive correlation between the warming and thermal degradation in permafrost or seasonally frozen ground(SFG) has long been recognized. Still, a predictive relationship between historical wetting under warming climate conditions and frozen ground has not yet been well demonstrated,despite the expectation that it will b...     

When timing matters-considering changing temporal structures in runoff response surfaces

Scenario-neutral response surfaces illustrate the sensitivity of a simulated natural system, represented by a specific impact variable, to systematic perturbations of climatic parameters. This type of approach has recently been developed as an alternative to top-down approaches for the assessment of climate change impacts. A major limitation of this approach is the underrepresentation of changes in the temporal structure of the climate input data (i.e., the seasonal and day-to-day variability) since this is not altered by the perturbation. This paper presents a framework that aims to examine this limitation by perturbing both observed and projected climate data time series for a future period, which both serve as input into a hydrological model (the HBV model). The resulting multiple response surfaces are compared at a common domain, the standardized runoff response surface (SRRS). We apply this approach in a case study catchment in Norway to (i) analyze possible changes in mean and extreme runoff and (ii) quantify the influence of changes in the temporal structure represented by 17 different climate input sets using linear mixed-effect models. Results suggest that climate change induced increases in mean and peak flow runoff and only small changes in low flow. They further suggest that the effect of the different temporal structures of the climate input data considerably affects low flows and floods (at least 21% influence), while it is negligible for mean runoff.     

The Weierbach experimental catchment in Luxembourg: A decade of critical zone monitoring in a temperate forest - from hydrological investigations to ecohydrological perspectives

The Weierbach experimental catchment (0.45 km²) is the most instrumented and studied sub-catchment in the Alzette River basin in Luxembourg. Within the last decade, it has matured towards an interdisciplinary critical zone observatory focusing on a better understanding of hydrological and hydro-geochemical processes. The Weierbach catchment is embedded in an elevated sub-horizontal plateau, characterized by slate bedrock and representative of the Ardennes Massif. Its climate is semi-marine, with precipitation being rather evenly distributed throughout the year. Base flow is lowest from July to September, essentially due to higher losses through evapotranspiration in summer. The regolith is composed of Devonian slates, overlaid by Pleistocene slope deposits and entirely covered by forest with 70% deciduous and 30% coniferous trees. Since 2009, the Weierbach has been extensively equipped for continuously monitoring water fluxes and physico-chemical parameters within different compartments of the critical zone. Additionally, these compartments are sampled fortnightly at several locations to analyze δ¹⁸O and δ²H isotopic composition of water including rainfall, throughfall, soil water, groundwater and streamwater. This ongoing monitoring and sampling programme is used for answering pressing questions related to fundamental catchment functions of water infiltration, storage, mixing and release in forest ecosystems. A recently started research line aims at investigating interactions between forest eco-hydrosystems with the atmosphere and understanding how catchments will respond to a non-stationary climate.     

Daily streamflow trends in Western versus Eastern Norway and their attribution to hydro-meteorological drivers

Regional warming and modifications in precipitation regimes has large impacts on streamflow in Norway, where both rainfall and snowmelt are important runoff generating processes. Hydrological impacts of recent changes in climate are usually investigated by trend analyses applied on annual, seasonal, or monthly time series. None of these detect sub-seasonal changes and their underlying causes. This study investigated sub-seasonal changes in streamflow, rainfall, and snowmelt in 61 and 51 catchments respectively in Western (Vestlandet) and Eastern (Østlandet) Norway by applying the Mann–Kendall test and Theil–Sen estimator on 10-day moving averaged daily time series over a 30-year period (1983–2012). The relative contribution of rainfall versus snowmelt to daily streamflow and the changes therein have also been estimated to identify the changing relevance of these driving processes over the same period. Detected changes in 10-day moving averaged daily streamflow were finally attributed to changes in the most important hydro-meteorological drivers using multiple-regression models with increasing complexity. Earlier spring flow timing in both regions occur due to earlier snowmelt. Østlandet shows increased summer streamflow in catchments up to 1100 m a.s.l. and slightly increased winter streamflow in about 50% of the catchments. Trend patterns in Vestlandet are less coherent. The importance of rainfall has increased in both regions. Attribution of trends reveals that changes in rainfall and snowmelt can explain some streamflow changes where they are dominant processes (e.g., spring snowmelt in Østlandet and autumn rainfall in Vestlandet). Overall, the detected streamflow changes can be best explained by adding temperature trends as an additional predictor, indicating the relevance of additional driving processes such as increased glacier melt and evapotranspiration.     

STELLA: Two New Robotic Telescopes for Binary-Star Research

Several new robotic telescopes had or will see first light in 2005/2006 and are designed for either wide-field imaging, high-precision photometry or even for high-resolution echelle spectroscopy. These telescopes are in the 1–2 m class and therefore will focus on very specific tasks. Here, I present an update of the robotic STELLA facility currently under construction in Tenerife and emphasize its science capabilities for binary-star research. Among the many science applications of STELLA is the monitoring of magnetic activity in single and binary stars and their relation to age, rotation rate, metallicity and binarity per se.The AIP STELLA team members are T. Granzer, M. Weber, M. Woche, M. I. Andersen, J. Bartus, S.-M. Bauer, F. Dionies, T. Fechner, H. Korhonen, J. Paschke, E. Popow, A. Ritter, A. Schwope, A. Staude, A. Washuettl