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Influence of catchment spatial subdivision on the accuracy of the snow accumulation and snowmelt model Abstract This thesis is focused on influence of catchment spatial subdivision on the accuracy of rainfall-runoff model simulations. A hydrological model HEC-HMS developed by U.S. Army Corps of Engineers was applied in the thesis. Study area includes two experimental catchments; Bystřice River basin and Zlatý Brook basin. Both catchments are located in the Krušné Mountains. The research in catchments has been carried out by the Department of Physical Geography and Geoecology since 2008. The influence of four different horizontal and vertical catchments delineation on runoff simulations was analyzed. The simulations were performed in two two-year periods 11/2008-10/2010 and 11/2010-10/2012. The attention was mainly aimed to snowmelt component of the model, for which temperature index method was chosen. The results of simulations were compared with water stages data measured in catchments outlets and with data from winter field measurements (snow depth and snow water equivalent). The results from both catchments showed that higher accuracy of simulation of the snow water equivalent was reached by dividing the catchments into more elevation zones. However, each of the catchments behaved in different way. The...

En stor del av Sveriges energiproduktion kommer från vattenkraftverken. Dessa kraftverk använder sig av vattenmagasin för att hålla kvar vattenmassa och dammar för att reglera det vattenflöde som ger upphov till energiproduktionen. Efter vinterperioderna uppstår vårfloder, tillfälligt stora mängder vatten från snösmältningen, som kraftigt påverkar vattenmängden i kraftverkens vattenmagasin. Därför behöver regleringar av vattenmängden göras för att kunna ta emot den nya mängd vatten som tros tillkomma under vårfloden. Att göra korrekta prognoser för den rätta regleringen är idag svårt då de tillhörande avrinningsområdena är  tusentals kvadratkilometer stora och endast ett fåtal mätstationer finns tillgängliga. Syftet med detta projekt är att utveckla en metod för att bestämma fördelningen av snömängden i ojämn terräng, med vindriktningen som den största faktorn, för att kunna förutse avrinningens förändring under smältsäsongen.  De huvudsakliga arbetsverktyg som har använts är ArcGIS, Matlab, Excel och geostatiska metoder i kombination. Projektet är kopplat till ett nytt forskningsprojekt (SNODDAS, 2018) finansierat av Energimyndigheten som syftar till att ta fram bättre prognosmodeller för snökapaciteteten i avrinningsområden till vattenkraftsdammar. Det är ett samarbete mellan Uppsala universitet, SMHI och Vattenregleringsföretagen. Var snön kommer att hamna beror på terrängen och den dominerande vindriktningen. Därför kommer denna modell att definiera den del av terrängen som ligger upp-vind mot den dominerande vindriktningen som Sx. Modellens syfte är att beräkna snödistributionen och dess ackumulering i ett områdes höjddata med hjälp av 8 framtagna filer med olika Sx-värden för olika vindriktningar, också kallat Sheltering Index, med vindriktningar från 0º-360º med steg om 45º och sammanställda mätdata för vinterperioden 2017/2018 (19 oktober till 14 april). Det slutliga resultatet blev 61%, 63% och 90% jämfört med beräknad snövattenekvivalent av SeNorge (Norwegian Water Resources and Energy Directorate, 2019). / A large part of Sweden's energy production comes from hydroelectric power plants. These power plants use water reservoirs to retain water mass and dams to regulate the water flow that generates energy production. After the winter periods the large spring rivers, water from the snow melt, greatly affect the amount of water in the power plants' water reservoirs which makes it necessary to make regulations in order to be able to receive the amount of water that is believed to be added during the spring flows. Making accurate forecasts for the right regulations is difficult today as the associated river basins are several thousand square kilometers large and only a few measuring stations are available. This project aims to develop a method for determining the distribution of snow in uneven terrain, with the wind direction being the largest factor, in order to be able to foresee the change of runoff during the melting season. Main work tools are ArcGIS, Matlab, Excel and geostatic methods in combination. The project is linked to a new research project (SNODDAS, 2018) funded by the Swedish Energy Agency, which aims to develop better forecast models for the snow capacity in river basins to hydroelectric power dams. It is a collaboration between Uppsala University, SMHI and water regulation companies. Where the snow will end up depends on the terrain and the dominant wind direction. Therefore, this model will define the part of the terrain that lies up against the dominant wind direction as Sx. The purpose of the model is to calculate the snow distribution and its accumulation in the height data of an area with the aid of 8 files produced with different Sx values for different wind directions, also called the Sheltering Index, with wind directions from 0º-360º with steps of 45º and aggregated measurement data for the winter period 2017/2018 (19 October to 14 April). The results after calculations were 61%, 63% and 90% compared to the snow water equivalent from SeNorge (Norwegian Water Resources and Energy Directorate, 2019).

Vattenkraft är en stor källa till energi i Sverige, främst i de norra delarna av landet. För att få ut maximal potential från vattenkraftverken behövs information om hur mycket vatten eller snö det finns uppströms från kraftverken. Genom att få fram tillförlitliga värden av snömängd är det möjligt att minska osäkerheten i uppskattningarna.Eftersom det är svårt att kartera större avrinningsområden via markbundna observationer, både praktiskt och ekonomiskt, har drönarobservationer utvecklats. För att använda sig av drönare krävs det vetskap om var de ska flygas i för område för att hela avrinningsområdet ska representeras. I projektet tas en modell fram i ArcGIS för att hitta mindre områden inom avrinningsområden som ska vara representativa inom utvalda parametrar. I projektet berörs parametrarna vegetation, höjd, lutningsgrad samt dess riktning.Arbetet för att ta fram en modell som ska underlätta framtida arbete inom och utanför forskningsprojektet DRONES är uppdelat i två delar. Den första delen är att ta fram och granska vilka parametrar som påverkar snödjupet i avrinningsområdet. Den andra delen innefattar arbetet med att skapa en modell i ArcGIS som ska analysera ett avrinningsområde med framtagna parametrar för att hitta mindre områden som representerar det hela.Resultatet från de framtagna modellerna kan tillämpas för att underlätta kartläggningen och snödjupsmätningar i avrinningsområden, vilket kan utnyttjas vid effektivisering av vattenreglering. / Hydropower is a major source of energy in Sweden mainly in the northern parts of the country. To get the maximum potential from the hydropower plants, information is required on how much water or snow there is upstream from the power plants. By obtaining reliable values of the amount of snow, it is possible to reduce the uncertainty in forecasts on spring flood.Due to difficulties in mapping larger catchment areas via ground-level observations, drone observations have been developed. In order to use drone observations, knowledge of where they are to be flown to represent the entire catchment area is required. In this project, a model was developed in ArcGIS to find smaller areas within catchments that are to be representative within selected parameters. The project touches upon the parameters vegetation, height, slope and aspect.The work to develop a model that will facilitate future work within and outside the DRONES research project is divided into two parts. The first part is to analyze which parameters affect the snow depth in the catchment area. The second part consists of creating a model in ArcGIS that will find a smaller area inside a catchment that represents the snow depth for the whole catchment.The results from the developed model can be applied to facilitate the mapping and snow depth measurements in catchment areas, which can be used to streamline water regulation.

The aim of this thesis was to investigate the processes behind an unexpected runoff behaviour after a clear-cut in a boreal forest in northern Sweden (Balsjö). The risks of increased flooding, erosion, nutrient leakage and changes in the local ecosystems are some reasons why it is important to fully understand the effect of clear-cuts on the water balance. In northern boreal forests the snow is of great importance as it results in the main hydrological event of the year, the spring flood. In general, open areas accumulate more snow, have a lower evapotranspiration and therefore maintain a higher runoff than a forest. In a recent paired catchment study at Balsjö the expected pattern after a clear-cut was only shown in three out of five years (2007-2011). The expected increase in runoff did not occur in 2010 and 2011. Two hypothesized alternatives were year-to-year variation of ET or changes in soil water storage. In order to investigate this further the rainfall-runoff model HBV was used. First, the model was calibrated for the forest catchment (Ref) and the clear-cut catchment (CC), using observed data from Balsjö. To account for parameter uncertainty the calibration was performed using parameter optimization, resulting in 100 different parameter sets. Model results were evaluated using observed snow data from Balsjö and ET from Flakaliden, a nearby forest. Both the simulated snow and ET were quite consistent with the observed values. Finally the annual and the spring water balance were studied, using the simulated data. The simulated results did not detect the unexpected runoff behavior for the two years as clearly as the observations. The reason for this was that the model was calibrated for all five years, which meant that annual variations were not taken into account. The hypothesis, that higher ET could be the reason for the unexpected runoff behavior, could neither be dismissed nor confirmed by this thesis. This was because there were no observed data for the clear-cut area and limitations within the HBV model, which meant that sublimation and interception processes could not be analyzed separately. The model results indicated that the change in soil water storage was a more likely explanation for the unexpected runoff behavior. The simulation result showed that the meltwater was stored in the soil water storage. However, this theory does not seem likely since a clear-cut is normally wetter than a forest. The results of this thesis are consistent with other studies as they indicate that clear-cut effects should be studied seasonally as well as annually. The special feature of this thesis was the opportunity to study observed ET and investigate its influence on the water balance.

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From the Proceedings of the 1974 Meetings of the Arizona Section - American Water Resources Assn. and the Hydrology Section - Arizona Academy of Science - April 19-20, 1974, Flagstaff, Arizona / Profiles of snowpack build-up in openings in forest overstories have been widely observed; however, a quantitative characterization of such a snowpack profile would aid in developing empirical guidelines for improving water yields from snowpacks. A technique is outlined that illustrates (a) evaluating snowpack profiles in and adjacent to individual forest openings in terms of increase or decrease in water equivalent, and (b) defining trade-offs between the estimated increase or decrease in snowpack water equivalent and the forest resource removed. Snowpack water equivalent during peak seasonal accumulation was measured in and adjacent to a clearcut strip in a ponderosa pine stand in north-central Arizona. A 4-degree polynomial, which defines the snowpack profile in terms of deposition, redistribution, and ablation characteristics, was empirically selected to describe snowpack water equivalent data points. An increase of 60 percent in snowpack water equivalent was realized by removing 46 percent of the ponderosa pine in the zone of influence, using a strip equal to one and one-half the height of the adjacent overstory.