Franziska Koch

Measuring Snow Liquid Water Content with Low-Cost GPS Receivers

The amount of liquid water in snow characterizes the wetness of a snowpack. Its temporal evolution plays an important role for wet-snow avalanche prediction, as well as the onset of meltwater release and water availability estimations within a river basin. However, it is still a challenge and a not yet satisfyingly solved issue to measure the liquid water content (LWC) in snow with conventional in situ and remote sensing techniques. We propose a new approach based on the attenuation of microwave radiation in the L-band emitted by the satellites of the Global Positioning System (GPS). For this purpose, we performed a continuous low-cost GPS measurement experiment at the Weissfluhjoch test site in Switzerland, during the snow melt period in 2013. As a measure of signal strength, we analyzed the carrier-to-noise power density ratio (C/N0) and developed a procedure to normalize these data. The bulk volumetric LWC was determined based on assumptions for attenuation, reflection and refraction of radiation in wet snow. The onset of melt, as well as daily melt-freeze cycles were clearly detected. The temporal evolution of the LWC was closely related to the meteorological and snow-hydrological data. Due to its non-destructive setup, its cost-efficiency and global availability, this approach has the potential to be implemented in distributed sensor networks for avalanche prediction or basin-wide melt onset measurements.

A novel sensor combination (upGPR‐GPS) to continuously and nondestructively derive snow cover properties

Monitoring seasonal snow cover properties is critical for properly managing natural hazards such as snow avalanches or snowmelt floods. However, measurements often cannot be conducted in difficult terrain or lack the high temporal resolution needed to account for rapid changes in the snowpack, e.g., liquid water content (LWC). To monitor essential snowpack properties, we installed an upward looking ground-penetrating radar (upGPR) and a low-cost GPS system below the snow cover and observed in parallel its evolution during two winter seasons. Applying external snow height (HS) information, both systems provided consistent LWC estimates in snow, based on independent approaches, namely measurements of travel time and attenuation of electromagnetic waves. By combining upGPR and GPS, we now obtain a self-contained approach instead of having to rely on external information such as HS. This allows for the first time determining LWC, HS, and snow water equivalent (SWE) nondestructively and continuously potentially also in avalanche-prone slopes.

Snow Water Equivalent of Dry Snow Derived From GNSS Carrier Phases

Snow water equivalent (SWE) is a key variable for various hydrological applications. It is defined as the depth of water that would result upon complete melting of a mass of snow. However, until now, continuous measurements of the SWE are either scarce, expensive, labor-intense, or lack temporal or spatial resolution especially in mountainous and remote regions. We derive the SWE for dry-snow conditions using carrier phase measurements from the Global Navigation Satellite System (GNSS) receivers. Two static GNSS receivers are used, whereby one antenna is placed below the snow and the other antenna is placed above the snow. The carrier phase measurements of both receivers are combined in double differences (DDs) to eliminate clock offsets and phase biases and to mitigate atmospheric errors. Each DD carrier phase measurement depends on the relative position between both antennas, an integer ambiguity due to the periodic nature of the carrier phase signal, and the SWE projected into the direction of incidence. The relative positions of the antennas are determined under snow-free conditions with millimeter accuracy using real-time kinematic positioning. Subsequently, the SWE and carrier phase integer ambiguities are jointly estimated with an integer least-squares estimator. We tested our method at an Alpine test site in Switzerland during the dry-snow season 2015–2016. The SWE derived solely by the GNSS shows very high correlation with conventionally measured snow pillow (root mean square error: 11 mm) and manual snow pit data. This method can be applied to dense low-cost GNSS receiver networks to improve the spatial and temporal information on snow.

Effects of Climate Change on Hydropower Generation and Reservoir Management

Due to an increase in power demand and renewable energy, Bavaria and Tyrol plan to increase hydroelectric power generation. However, climate change may lead to a decrease in discharge and water availability and thereafter a decrease in hydroelectric power generation without further constructions considering only the current facilities. The change in the simulated annual output of the hydropower plants in the Upper Danube basin divided in the six subbasins Inn, Salzach, Isar, Lech, Iller and the remaining area of the Danube basin are shown for the two periods 2011–20135 and 2036–2060 under the GLOWA-Danube REMO regional-Baseline climate scenario. For the first period, a slight decrease was simulated, whereas for the second period, a significant decrease leads to a reduction in hydroelectric power generation of 9–16 % in the subbasins. Moreover, the trends in mean monthly inflow, outflow and reservoir fill volume are shown for the two periods for the example of the Gepatsch reservoir. Without changing the monthly based operation plan in the future, the change in the pattern of the inflow would have an impact on the reservoir filling volume and the pattern of the discharge at the reservoir outlet which would lead to a more balanced power generation over the year.

Energy: Simulation of Hydropower Generation and Reservoir Management

Within the hydropower module of DANUBIA, all large run-of-the-river and storage power plants in the Upper Danube basin are included. Potential and kinetic energy are used for the generation of hydroelectric power which depends mainly on discharge and drop height. For each hydropower plant, the discharge and the power output were simulated depending on a discharge-power output function for each modelled time step of 1 h. For annual comparability, the annual output was calculated whereof the hydraulicity was derived for the years 1960–2006. Moreover, a monthly based reservoir operation plan was included for each reservoir power plant considering basic reservoir operation rules. A validation was carried out for all hydropower plants, which are, with a coefficient of determination of 0.99, very well reproduced in DANUBIA. The mean simulated annual output of the run-of-the-river and reservoir power plants from 1971 to 2000 is shown, divided in the six subbasins Inn, Salzach, Isar, Lech, Iller and the remaining area of the Danube basin.