Underpinning all hydrological simulations is an estimate of the catchment area upstream of a point of interest. Locally, the delineation of a catchment and estimation of its area is usually done using fine scale maps and local knowledge, but for large-scale hydrological modelling, particularly continental and global scale modelling, this level of detailed data analysis is not practical. For large-scale hydrological modelling, remotely sensed and hydrologically conditioned river routing networks, such as HYDROlk and HydroSHEDS, are often used. This study evaluates the accuracy of the accumulated upstream area in each gridpoint given by the networks. This is useful for evaluating the ability of these data sets to delineate catchments of varying scale for use in hydrological models. It is shown that the higher resolution HydroSHEDS data set gives better results than the HYDROlk data set and that accuracy decreases with decreasing basin scale. In ungauged basins, or where other local catchment area data are not available, the validation made in this study can be used to indicate the likelihood of correctly delineating catchments of different scales using these river routing networks.

Assessing hydrological effects of global climate change at local scales is important for evaluating future hazards to society. However, applying climate model projections to local impact models can be difficult as outcomes can vary considerably between different climate models, and including results from many models is demanding. This study combines multiple climate model outputs with hydrological impact modelling through the use of response surfaces. Response surfaces represent the sensitivity of the impact model to incremental changes in climate variables and show probabilies for reaching a priori determined thresholds. Response surfaces were calculated using the HBV hydrological model for three basins in Sweden. An ensemble of future climate projections was then superimposed onto each response surface, producing a probability estimate for exceeding the threshold being evaluated. Site specific impacts thresholds were used where applicable. Probabilistic trends for future change in hazards or potential can be shown and evaluated. It is particularly useful for visualising the range of probable outcomes from climate models and can easily be updated with new results as they are made available.

The HYPE model is a hydrological model for small-scale and large-scale assessments of water resources and water quality, developed at the Swedish Meteorological and Hydrological Institute during 2005-2007. In the model, the landscape is divided into classes according to soil type, land use and altitude. In agricultural lands the soil is divided into three layers, each with individual computations of soil wetness and nutrient processes. The model simulates water flow and transport and turnover of nitrogen and phosphorus. Nutrients follow the same pathways as water in the model: surface runoff, macropore flow, tile drainage and outflow from individual soil layers. Rivers and lakes are described separately with routines for turnover of nutrients in each environment. Model parameters are global, or coupled to soil type or land use. The model was evaluated both by local calibrations to internal variables from different test basins and to data on discharge and nutrients from a large number of small basins. In addition, the estimated parameters were transferred to two larger basins in southern Sweden: River Ronnea and River Vindan. The resulting simulations were generally in good agreement with observations.

As climate change could have considerable influence on hydrology and corresponding water management, appropriate climate change inputs should be used for assessing future impacts. Although the performance of regional climate models (RCMs) has improved over time, systematic model biases still constrain the direct use of RCM output for hydrological impact studies. To address this, a distribution-based scaling (DBS) approach was developed that adjusts precipitation and temperature from RCMs to better reflect observations. Statistical properties, such as daily mean, standard deviation, distribution and frequency of precipitation days, were much improved for control periods compared to direct RCM output. DBS-adjusted precipitation and temperature from two IPCC Special Report on Emissions Scenarios (SRESA1B) transient climate projections were used as inputs to the HBV hydrological model for several river basins in Sweden for the period 1961-2100. Hydrological results using DBS were compared to results with the widely-used delta change (DC) approach for impact studies. The general signal of a warmer and wetter climate was obtained using both approaches, but use of DBS identified differences between the two projections that were not seen with DC. The DBS approach is thought to better preserve the future variability produced by the RCM, improving usability for climate change impact studies.

The aim of this study was to reconstruct river flow to the Baltic Sea using data from different periods during the past thousand years. A hydrological model coupled to simulations from climate models was used to estimate river flow. A "millennium" simulation of past climate from the ECHO-G coupled atmosphere-ocean global climate model provided climatological inputs. Results from this global model were downscaled with the RCA3 regional climate model over northern Europe. Temperature and precipitation from the downscaled simulation results were then used in the HBV hydrological model to simulate river flows to the Baltic Sea for the periods 1000-1199 and 1551-1929. These were compared with observations for the period 1921-2002. A general conclusion from this work is that although climate has varied during the past millennium, variability in annual river flow to the Baltic Sea does not appear more pronounced in recent years than during the previous millennium, or vice versa.

Den här rapporten sammanfattar det hydrologiska kartmaterial över förändring i medelavrinning, höga flöden och vattenkraftspotential som har levererats till den statliga Klimat- och sårbarhetsutredningen.Beräkningarna som ligger till grund för kartmaterialet har utförts med modellsystemet HBV Sverige. Dagens klimat har baserats på observerad temperatur och nederbörd för perioden 1961-1990. Beräkningar av hydrologiska förhållanden i framtidens klimat har baserats på resultat från regional klimatmodellering vid Rossby Centre på SMHI. Sammantaget har hydrologiska beräkningar genomförts för fem olika framtidsscenarier, fyra beräkningar för perioden 2071-2100 och en beräkning för hela perioden 1961-2100. I detta arbete har två olika metoder för att omsätta klimatmodellresultaten till hydrologiska effekter använts, delta-metoden och scaling-metoden.Medelavrinningen kommer enligt scenarierna att öka för större delen av Sverige, med undantag för de sydöstra delarna av landet. Vad det gäller höga flöden är bilden mer komplex, men i sydvästra Sverige och fjällen blir, enligt scenarierna, höga flöden betydligt vanligare. Vattenkraftspotentialen förväntas enligt scenarierna att öka avsevärt för Sverige som helhet. Alla resultat från HBV Sverige ska i första hand användas för en översiktlig tolkning och identifiering av var fördjupade studier kan vara av särskilt behov. Beräkningarna baserade på den s.k. scaling-metoden är mer preliminära än de övriga beräkningarna eftersom metoden fortfarande är under utveckling.AbstractThis report summarizes the water resource maps of changes in mean annual runoff, large floods and hydropower potential that have been delivered to the Swedish Commission on Climate and Vulnerability.The hydrological model simulations that have been used to produce the maps were done using the HBV Sweden modelling system. Simulations for present climate used observed input of precipitation and temperature from 1961-1990. Calculations of future hydrological conditions were based on results from regional climate modelling at the Rossby Centre, SMHI. Five different regional scenarios of future climate have been used, four representing the future period 2071-2100 and one for the whole period 1961-2100. Two different approaches to interface the hydrological model and the climate models have been used, the delta method and the scaling method.The mean annual runoff will, according to the scenarios, increase for most parts of Sweden except for the south-east parts of the country. The picture becomes more complex when it comes to changes in large floods, but they are expected to increase substantially in the south-west parts and in the Swedish mountains according to the scenarios. The total Swedish hydropower potential is expected to increase substantially according to the scenarios.All results from HBV Sweden should only be used for a general interpretation of where more in depth analyses might be of interest. The simulations based on the so-called scaling method are more preliminarythan the other simulations, since the method is still under development.

This report summarizes the water resource maps of changes in mean annual runoff, large floods and hydropower potential that have been delivered to the Swedish Commission on Climate and Vulnerability. The hydrological model simulations that have been used to produce the maps were done using the HBV Sweden modelling system. Simulations for present climate used observed input of precipitation and temperature from 1961-1990. Calculations of future hydrological conditions were based on results from regional climate modelling at the Rossby Centre, SMHI. Five different regional scenarios of future climate have been used, four representing the future period 2071-2100 and one for the whole period 1961-2100. Two different approaches to interface the hydrological model and the climate models have been used, the delta method and the scaling method. The mean annual runoff will, according to the scenarios, increase for most parts of Sweden except for the south-east parts of the country. The picture becomes more complex when it comes to changes in large floods, but they are expected to increase substantially in the south-west parts and in the Swedish mountains according to the scenarios. The total Swedish hydropower potential is expected to increase substantially according to the scenarios. All results from HBV Sweden should only be used for a general interpretation of where more in depth analyses might be of interest. The simulations based on the so-called scaling method are more preliminary than the other simulations, since the method is still under development.