Impact of Climate Change on Extreme Events: Insights from Asia and Scandinavia

Sammanfattning: As climate has warmed significantly over past decades, numerous studies have confirmed a pattern of more frequent and more intense hydro-climate events across the globe, such as floods, heatwaves, and droughts. Analyzing the variability of climate events with reliable historical data records is one of the most direct approaches for understanding its patterns of change. The development of climate models provides us with the opportunity to explore the changing trends of climate conditions for different future scenarios. This study presents an exploration of climate variability and extreme weather events at multiple spatial-temporal scales over Asia and Scandinavia, including the analysis for historical period and future projections. This study offers a multifaceted look at precipitation extremes and droughts, and their consequential effects on disaster risk and water management.The first study, based in Gansu Province, China, analyses of four indices of precipitation extremes with regard to both wet and dry spells over the period 1961-2017. A critical climate shift was recorded between 1980-81, leading to subsequent variations in extremes. Comparison of mean extreme indices for preshift (1961-1980) and aftshift (1981-2017) periods was performed to explore possible increasing/decreasing patterns. Findings indicate a transition to a more extreme climate in recent years, with notable differences in precipitation extremes in the northern and southern regions. The Generalized extreme value (GEV) distribution was applied spatially to fit extreme indices with return periods up to 100 years, showing that precipitation extremes in the north have increased that can result in more serious floods and droughts in the future. The study also investigated influences of large-scale atmospheric circulations, showing a complex pattern of correlation between precipitation extremes and indices of large-scale atmospheric circulation. The second study zoomed out to an Asia-Pacific scale, examining 11 precipitation indices across 465 locations in eight countries from 1990-2019. The analysis shows a general decline in extreme precipitation indices, particularly in central-eastern China, Bangladesh, eastern India, Peninsular Malaysia, and Indonesia. The seasonal variability of the amount of wet-day precipitation in most locations in China and India are dominated by precipitation intensity in June-August (JJA), and by precipitation frequency in December-February (DJF). Locations in Malaysia and Indonesia are mostly dominated by precipitation intensity in March-May (MAM) and DJF. We further investigated how these extreme precipitation indices are influenced by El Niño-Southern Oscillation (ENSO) at a seasonal scale. During the ENSO positive phase, significant negative anomalies in seasonal precipitation indices (amount of wet-day precipitation, number of wet days and intensity of wet-day precipitation) were observed in Indonesia, while opposite results were observed for ENSO negative phase. In the third study, drought characteristics in China were analyzed based on the Standardized Precipitation Evapotranspiration Index (SPEI) at both short-term (1-month) and long-term (12-month) scales. The study delineates two distinct subperiods based on the climate shift occurring in 1980s. The findings show geographically diverse changes in drought occurrences, durations, and intensities between the pre- and post-climate-shift subperiods. Notably, an intensifying of drought conditions in northern China and a relative relief from drought in the Tibet Plateau were identified. Furthermore, the impacts of two ENSO phenomena, canonical ENSO and ENSO Modoki, on drought conditions were investigated using singular vector decomposition (SVD). Results suggested that long-term droughts at 12-month scale are more strongly influenced by ENSO phenomena.As a methodological case study focusing on the domain of southern Sweden – eastern Denmark, the fourth study explores the capabilities of high-resolution convection-permitting models (CPMs) in accurately capturing extreme weather events compared with non-convection permitting models. In total, the performance of five Regional Climate Models (RCMs) at various resolutions in representing wet and dry spells compared with observation datasets was evaluated at six locations in Scania, southern Sweden. Additionally, the study projects future changes over whole domain based on wet and dry events under the RCP 8.5 emission scenario for three different periods in 21st century. It was found that high-resolution convection-permitting models significantly outperform coarser models in capturing the characteristics of wet and dry spells. Future climate projections under the RCP 8.5 scenario indicate an increase in the frequency and intensity of wet events, and a decrease in the duration of dry spells. This study offered a future-oriented dimension to the overall research.The research offers a comprehensive view of climate extremes and the impact of climate change across diverse geographical settings, from Asia to Europe. Spatial-temporal patterns of extreme precipitation and drought condition are conducted to provide valuable insights into both historical shifts and future projections. This work establishes its significance in identifying areas at increased risk for natural disasters like high-intensity rainfall, floods, and droughts, thereby informing climate adaptation and disaster risk reduction strategies. The study also serves as a resource in preparing for a more severe changing climate in the future.