ALBERT

Description: [1]  Timber harvesting by clear cutting is known to impose environmental impacts, including severe disturbance of the soil-hydraulic properties which intensify the frequency and magnitude of surface runoff and soil erosion. However, it remains unanswered if harvest areas act as sources or sinks for runoff and soil erosion and whether such behavior operates in a steady state or evolves through time. For this purpose, 92 small scale rainfall simulations of different intensities were carried out under pine plantation conditions and on two clear-cut harvest areas of different age. Non-parametrical Random Forest statistical models were set up to quantify the impact of environmental variables on the hydrological and erosion response. Regardless of the applied rainfall intensity, runoff always initiated first and yielded most under plantation cover. Counter to expectations, infiltration rates increased after logging activities. Once a threshold rainfall intensity of 20 mm/h was exceeded, the younger harvest area started to act as a source for both runoff and erosion after connectivity was established whereas it remained a sink under lower applied rainfall intensities. The results suggest that the impact of microtopography on surface runoff connectivity and water repellent properties of the topsoil act as first order controls for the hydrological and erosion processes in such environments. Fast rainfall-runoff response, sediment-discharge-hystereses and enhanced post-logging groundwater recharge at catchment scale support our interpretation. At the end, we show the need to account for non-stationary hydrological and erosional behavior of harvest areas, a fact previously unappreciated in predictive models.

Description: Scarcity of hydrological data, especially streamflow discharge and groundwater level series, restricts the understanding of channel transmission losses (TL) in drylands. Furthermore, the lack of information on spatial river dynamics encompasses high uncertainty on TL analysis in large rivers. The objective of this study was to combine the information from streamflow and groundwater level series with multi-temporal satellite data to derive a hydrological concept of TL for a reach of the Middle Jaguaribe River (MJR) in semi-arid north-eastern Brazil. Based on this analysis, we proposed strategies for its modelling and simulation. TL take place in an alluvium, where river and groundwater can be considered to be hydraulically connected. Most losses certainly infiltrated only through streambed and levees and not through the flood plains, as could be shown by satellite image analysis. TL events whose input river flows were smaller than a threshold did not reach the outlet of the MJR. TL events whose input flows were higher than this threshold reached the outlet losing on average 30% of their input. During the dry seasons (DS) and at the beginning of rainy seasons (DS/BRS), no river flow is expected for pre-events, and events have vertical infiltration into the alluvium. At the middle and the end of the rainy seasons (MRS/ERS), river flow sustained by base flow occurs before/after events, and lateral infiltration into the alluvium plays a major role. Thus, the MJR shifts from being a losing river at DS/BRS to become a losing/gaining (mostly losing) river at MRS/ERS. A model of this system has to include the coupling of river and groundwater flow processes linked by a leakage approach. Copyright © 2012 John Wiley & Sons, Ltd.

Description: Hydrological response to earthquakes has long been observed, yet the mechanisms responsible still remain unclear and likely vary in space and time. This study explores the base flow response in small upland catchments of the Coastal Range of south-central Chile after the MW 8.8 Maule earthquake of 27 February 2010. An initial decline in streamflow followed by an increase of up to 400% of the discharge measured immediately before the earthquake occurred, and diurnal streamflow oscillations intensified after the earthquake. Neither response time, nor time to maximum streamflow discharge showed any relationship with catchment topography or size, suggesting non-uniform release of water across the catchments. The fast response, unaffected stream water temperatures and a simple diffusion model point to the sandy saprolite as the source of the excess water. Base flow recession analysis reveals no evidence for substantial enhancement of lateral hydraulic conductivity in the saprolite after the earthquake. Seismic energy density reached ∼170 J/m3 for the main shock and ∼0.9 J/m3 for the aftershock, exceeding the threshold for liquefaction by undrained consolidation only during the main shock. Although increased hydraulic gradient due to ground acceleration-triggered, undrained consolidation is consistent with empirical magnitude-distance relationships for liquefaction, the lack of independent evidence for liquefaction means that enhanced vertical permeability (probably in combination with co-seismic near-surface dilatancy) cannot be excluded as a potential mechanism. Undrained consolidation may have released additional water from the saturated saprolite into the overlying soil, temporarily reducing water transfer to the creeks but enlarging the cross-section of the saturated zone, which in turn enhanced streamflow after establishment of a new hydraulic equilibrium. The enlarged saturated zone facilitated water uptake by roots and intensified evapotranspiration.

Description: Scarcity of hydrological data, especially streamflow discharge and groundwater level series, restricts the understanding of channel transmission losses (TL) in drylands. Furthermore, the lack of information on spatial river dynamics encompasses high uncertainty on TL’ analysis in large rivers. The objective of this study was to combine the information from streamflow and groundwater level series with multi-temporal satellite data to derive a hydrological concept of TL for a reach of the Middle Jaguaribe River (MJR) in semiarid northeastern Brazil. Based on this analysis, we proposed strategies for its modelling and simulation. TL take place in an alluvium, where river and groundwater can be considered to be hydraulically connected. Most losses certainly infiltrated only through streambed and levees and not through the flood plains, as could be shown by satellite image analysis. TL events, whose input river flows were smaller than a threshold, did not reach the outlet of the MJR. TL events, whose input flows were higher than this threshold, reached the outlet losing on average 30% of their input. During the dry seasons (DS) and at the beginning of rainy seasons (DS/BRS), no river flow is expected for pre-events and events have vertical infiltration into the alluvium. At the middle and the end of the rainy seasons (MRS/ERS), river flow sustained by base flow occurs before/after events and lateral infiltration into the alluvium plays a major role. Thus, the MJR shifts from being a losing river at DS/BRS to become a losing/gaining (mostly losing) river at MRS/ERS. A model of this system has to include the coupling of river and groundwater flow processes linked by a leakage approach. Copyright © 2012 John Wiley & Sons, Ltd.

Description: Temperature trends in Switzerland differ depending on the time of the year, day and elevation. Warming trends are strongest during spring and early summer with enhanced warming of daytime maximum temperatures. Elevation‐based differences in temperature trends show up during autumn and winter with stronger warming at lower elevations. Due to the environmental and socio‐economic importance of mountainous regions, it is crucial to understand causes and consequences of climatic changes in those sensitive landscapes. Daily resolution alpine climate data from Switzerland covering an elevation range of over 3,000 m between 1981 and 2017 have been analysed using highly resolved trends in order to gain a better understanding of features, forcings and feedbacks related to temperature changes in mountainous regions. Particular focus is put on processes related to changes in weather types, incoming solar radiation, cloud cover, air humidity, snow/ice and elevation dependency of temperature trends. Temperature trends in Switzerland differ depending on the time of the year, day and elevation. Warming is strongest during spring and early summer with enhanced warming of daytime maximum temperatures. Elevation‐based differences in temperature trends occur during autumn and winter with stronger warming at lower elevations. We attribute this elevation‐dependent temperature signal mainly to elevation‐based differences in trends of incoming solar radiation and elevation‐sensitive responses to changes in frequencies of weather types. In general, effects of varying frequencies of weather types overlap with trends caused by transmission changes in short‐ and long‐wave radiation. Temperature signals arising from snow/ice albedo feedback mechanisms are probably small and might be hidden by other effects.

Description: Several trend studies have shown that hydrological conditions are changing considerably in the Alpine region. However, the reasons for these changes are only partially understood and trend analyses alone are not able to shed much light. Hydrological modelling is one possible way to identify the trend drivers, i.e., to attribute the detected streamflow trends, given that the model captures all important processes causing the trends. We modelled the hydrological conditions for two alpine catchments in western Austria (a large, mostly lower-altitude catchment with wide valley plains and a nested high-altitude, glaciated headwater catchment) with the distributed, physically-oriented WaSiM-ETH model, which includes a dynamical glacier module. The model was calibrated in a transient mode, i.e., not only on several standard goodness measures and glacier extents, but also in such a way that the simulated streamflow trends fit with the observed ones during the investigation period 1980 to 2007. With this approach, it was possible to separate streamflow components, identify the trends of flow components, and study their relation to trends in atmospheric variables. In addition to trends in annual averages, highly resolved trends for each Julian day were derived, since they proved powerful in an earlier, data-based attribution study. We were able to show that annual and highly resolved trends can be modelled sufficiently well. The results provide a holistic, year-round picture of the drivers of alpine streamflow changes: Higher-altitude catchments are strongly affected by earlier firn melt and snowmelt in spring and increased ice melt throughout the ablation season. Changes in lower-altitude areas are mostly caused by earlier and lower snowmelt volumes. All highly resolved trends in streamflow and its components show an explicit similarity to the local temperature trends. Finally, results indicate that evapotranspiration has been increasing in the lower altitudes during the study period.

Description: The information about climate change impact on river discharge is vitally important for planning adaptation measures. The future changes can affect different water-related sectors. The main goal of this study was to investigate the potential water resource changes in Ukraine, focusing on three mesoscale river catchments (Teteriv, Upper Western Bug, and Samara) characteristic for different geographical zones. The catchment scale watershed model—Soil and Water Integrated Model (SWIM)—was setup, calibrated, and validated for the three catchments under consideration. A set of seven GCM-RCM (General Circulation Model-Regional Climate Model) coupled climate scenarios corresponding to RCPs (Representative Concentration Pathways) 4.5 and 8.5 were used to drive the hydrological catchment model. The climate projections, used in the study, were considered as three combinations of low, intermediate, and high end scenarios. Our results indicate the shifts in the seasonal distribution of runoff in all three catchments. The spring high flow occurs earlier as a result of temperature increases and earlier snowmelt. The fairly robust trend is an increase in river discharge in the winter season, and most of the scenarios show a potential decrease in river discharge in the spring.

Description: Floods and debris flows in small Alpine torrent catchments (〈10 km 2 ) arise from a combination of critical antecedent system state conditions and mostly convective precipitation events with high precipitation intensities. Thus, climate change may influence the magnitude-frequency-relationship of extreme events twofold: by a modification of the occurrence probabilities of critical hydrological system conditions and by a change of event precipitation characteristics. We investigated three small Alpine catchments in different altitudes in Western Austria by both field experiments and process-based simulation. We used rainfall-runoff model runs driven by localized climate scenarios in order to estimate future frequencies of stormflow triggering system state conditions. According to the differing altitudes of the study catchments, two effects of climate change on the hydrological systems can be observed. On the one hand the seasonal system state conditions of medium altitude catchments are most strongly affected by air temperature controlled processes such as the development of the winter snow cover as well as evapotranspiration. On the other hand, the unglaciated high altitude catchment is less sensitive to climate change induced shifts regarding days with critical antecedent soil moisture and desiccated litter layer due to its elevation-related small proportion of sensitive areas. For the period 2071 – 2100, we found that the number of days with critical antecedent soil moisture content will be significantly reduced to about 60% or even less in summer in all catchments. In contrast, the number of days with dried out litter layers causing hydrophobic effects will increase by up to 8 - 11% of the days in the two lower altitude catchments. The intensity analyses of heavy precipitation events indicate a clear increase in rain intensities of up to 10%. This article is protected by copyright. All rights reserved.