• Energy Research

For climate-change impact studies at the catchment scale, meteorological variables are typically extracted from ensemble simulations provided by global and regional climate models, which are then downscaled and bias-adjusted for each study site. For bias adjustment, different statistical methods that re-scale climate model outputs have been suggested in the scientific literature. They range from simple univariate methods that adjust each meteorological variable individually, to more complex and more demanding multivariate methods that take existing relationships between meteorological variables into consideration. Over the past decade, several attempts have been made to evaluate such methods in various regions. There is, however, still no guidance for choosing appropriate bias adjustment methods for a study at hand. In particular, the question whether the benefits of potentially improved adjustments outweigh the cost of increased complexity, remains unanswered. This paper presents a comprehensive evaluation of the performance of two commonly used univariate and two multivariate bias adjustment methods in reproducing numerous univariate, multivariate and temporal features of precipitation and temperature series in different catchments in Sweden. The paper culminates in a discussion on trade-offs between the potential benefits (i.e., skills and added value) and disadvantages (complexity and computational demand) of each method to offer plausible, defensible and actionable insights from the standpoint of climate-change impact studies in high latitudes. We concluded that all selected bias adjustment methods generally improved the raw climate model simulations, but that not a single method consistently outperformed the other methods. There were, however, differences in the methods' performance for particular statistical features, indicating that other practical aspects such as computational time and heavy theoretical requirements should also be taken into consideration when choosing an appropriate bias adjustment method.

Study Region: SwedenStudy focus:Although Sweden has historically been a country abundant with water, observed changes in temperature and precipitation patterns during the past century have perturbed regional hydrologic regimes, including the severity, frequency and duration of streamflow droughts. This study utilizes the standardized streamflow index (SSI) and the threshold-level method to provide an unprecedented overview of spatiotemporal patterns of streamflow droughts in 50 Swedish catchments over the past six decades. The study catchments were categorized into five clusters, of which each was analyzed for changes in various drought characteristics over the period 1961–2020. New hydrological insights for the region: Multiple severe streamflow drought events were detected over the past 60 years. Remarkably, droughts in 1976 and 1996 were identified as the most extreme and wide-spread events, also compared to the latest 2018 drought. Southern catchments were generally more often and more severely affected than northern catchments. Our results suggest a wetting tendency over the past six decades across the entire country. This occurs in conjunction with less severe, shorter and less frequent droughts, especially during colder winter months. Only in the southernmost regions, a slight drying trend in spring and summer was found. Thus, we argue that a better understanding and regional management of streamflow droughts is essential to secure the needs of the environment, society and economy now and in the future.

Complex non-linear relationships exist between air and soil temperature responses to climate change. Despite its influence on hydrological and biogeochemical processes, soil temperature has received less attention in climate impact studies. Here we present and apply an empirical soil temperature model to four forest sites along a climatic gradient of Sweden. Future air and soil temperature were projected using an ensemble of regional climate models. Annual average air and soil temperatures were projected to increase, but complex dynamics were projected on a seasonal scale. Future changes in winter soil temperature were strongly dependent on projected snow cover. At the northernmost site, winter soil temperatures changed very little due to insulating effects of snow cover but southern sites with little or no snow cover showed the largest projected winter soil warming. Projected soil warming was greatest in the spring (up to 4°C) in the north, suggesting earlier snowmelt, extension of growing season length and possible northward shifts in the boreal biome. This showed that the projected effects of climate change on soil temperature in snow dominated regions are complex and general assumptions of future soil temperature responses to climate change based on air temperature alone are inadequate and should be avoided in boreal regions.

The water content of the topsoil is one of the key factors controlling biogeochemical processes, greenhouse gas emissions and biosphere - atmosphere interactions in many ecosystems, particularly in northern peatlands. In these wetland ecosystems, the water content of the photosynthetic active peatmoss layer is crucial for ecosystem functioning and carbon sequestration, and is sensitive to future shifts in rainfall and drought characteristics. Current peatland models differ in the degree in which hydrological feedbacks are included, but how this affects peatmoss drought projections is unknown. The aim of this paper was to systematically test whether the level of hydrological detail in models could bias projections of water content and drought stress for peatmoss in northern peatlands using downscaled projections for rainfall and potential evapotranspiration in the current (1991-2020) and future climate (2061-2090). We considered four model variants that either include or exclude moss (rain)water storage and peat volume change, as these are two central processes in the hydrological self-regulation of peatmoss carpets. Model performance was validated using field data of a peatland in northern Sweden. Including moss water storage as well as peat volume change resulted in a significant improvement of model performance, despite the extra parameters added. The best performance was achieved if both processes were included. Including moss water storage and peat volume change consistently reduced projected peatmoss drought frequency with >50%, relative to the model excluding both processes. Projected peatmoss drought frequency in the growing season was 17% smaller under future climate than current climate, but was unaffected by including the hydrological self-regulating processes. Our results suggest that ignoring these two fine-scale processes important in hydrological self-regulation of northern peatlands will have large consequences for projected climate change impact on ecosystem processes related to topsoil water content, such as greenhouse gas emissions.

Droughts can affect a multitude of public and private sectors, with impacts developing slowly over time. While droughts are traditionally quantified in relation to the hydrological components of the water cycle that they affect, this manuscript demonstrates a novel approach to assess future drought conditions through the lens of the water-energy-food-ecosystem (WEFE) nexus concept. To this end, a set of standardized drought indices specifically designed to represent different nexus sectors across 50 catchments in Sweden was computed based on an ensemble of past and future climate model simulations. Different patterns in the response of the four nexus sectors water, energy, food and ecosystem services to future climate change emerged, with different response times and drought durations across the sectors. These results offer new insights into the propagation of drought through the WEFE nexus in cold climates. They further suggest that future drought projections can be better geared towards decision makers by basing them on standardized drought indices that were specifically tailored to represent particular nexus sectors.

This literature review maps existing research on the security of supply for the food, drinking water, energy, and transport sectors in the context of climate extremes. The study examines how climate-related extreme weather impacts these supply systems, what scientific models and methods have been developed and applied in previous research, and what challenges remain for future studies. This study is conducted as a scoping review based on an analysis of 140 scientific articles. The results show that supply chains in all examined sectors are vulnerable to disruptions directly or indirectly caused by extreme weather events. The study describes how climate extremes trigger such disruptions and outlines their potential short and longterm consequences. Existing interdependencies within and across multiple sectors pose a substantial challenge to the security of supply. Therefore, further research is needed on the cascading effects of climate extremes and their implications for preparedness for supply chain disruptions. As the climate continues to change, the risk for compound events – where two or more crises occur simultaneously or sequentially – is increasing. Addressing this risk requires additional research from a polycrisis perspective. Furthermore, the review highlights the importance of testing and further developing scientific models specifically adapted to Nordic contexts to generate more relevant data and knowledge for this region.

Datamängden består av dagliga observationer av nederbörd, temperatur och avrinning för 50 avrinningsområden i Sverige över en 60-årsperiod (1961-2020). Utöver dessa observationer innehåller datamängden även information om geografiskt läge, marktäckning, jordtyper, hydrologiska signaturer och reglering för varje avrinningsområde. Informationen samlades in från olika källor, inklusive Sveriges meteorologiska och hydrologiska institut (SMHI), Sveriges geologiska undersökning (SGU) samt flera Copernicus-produkter som tillhandahölls av European Environment Agency. De sammanställda, geografiskt matchade och bearbetade uppgifterna är tillgängliga online. Datasetet omfattar två definierade "klimatnormalperioder": 1961-1990 och 1991-2020 och innehåller en bred variation av hydroklimatiska, topografiska och miljömässiga egenskaper, vilket gör det till en ovärderlig resurs för både forskare och praktiker. Det kan ge insikter i hydrologiska processer, möjliggör utforskning av klimatförändringars påverkan samt stödjer utformningen av hållbara strategier för vattenförvaltning. På grund av den långa tidsperioden lämpar sig datasetet för kalibrering av modeller, utbildning, metodutveckling och främjar tvärvetenskaplig forskning över olika discipliner. Det utgör en viktig grund för att förstå och hantera vattenrelaterade utmaningar i en föränderlig miljö. This community-accessible dataset comprises daily hydroclimatic variables (precipitation, temperature, and streamflow) observed across 50 catchments in Sweden. The dataset covers a 60-year period (1961-2020) and includes information on geographical location, landcover, soil types, hydrologic signatures, and regulation for each catchment. Data was collected from various sources, such as the Swedish Meteorological and Hydrological Institute (SMHI), the Swedish Geological Survey (SGU) and several Copernicus products provided by the European Environment Agency. The compiled, spatially-matched, and processed data is publicly available online. The dataset spans two designated 'climate normal periods' (CNPs): 1961-1990 and 1991-2020, and a wide range of hydroclimatic, topographic and environmental catchment properties, making it a valuable resource for researchers and practitioners to gain in-depth insights into hydrological processes, explore climate change impacts, and devise sustainable water management strategies. With its long record period and versatility, the dataset is a great resource for model calibration, education, method development, and fostering transdisciplinary research across various disciplines.