Drought propagation in high-latitude catchments: Insights from a 60-Year Analysis Using Standardized Indices

Abstract. Droughts, traditionally less associated with high-latitude regions, are emerging as significant challenges due to changing climatic conditions. Recent severe droughts in Europe have exposed the vulnerability of these northern catchments, where shifts in temperature and precipitation patterns may intensify drought impacts. This study investigates the dynamics of drought propagation in high-latitude regions, focusing on four key aspects: (1) the typical lag time for drought conditions to propagate from initial precipitation deficits to impacts on soil moisture, streamflow, and groundwater systems, (2) the probability of precipitation deficits leading to these droughts, (3) the key factors influencing drought propagation, and (4) how drought propagation has evolved under changing climate conditions. By analyzing long-term observational records from 50 Swedish catchments, the study reveals that drought propagation is highly variable and influenced by a complex interplay of catchment characteristics, hydroclimatic conditions, and soil properties. Soil moisture exhibits the shortest propagation times, often responding within a month to precipitation deficits, while groundwater shows the longest and most variable response times, sometimes exceeding several months. The probability of precipitation deficits propagating into soil moisture droughts is highest, followed by streamflow and groundwater, with these probabilities increasing over time. Across all drought types, annual precipitation and streamflow are the strongest governing factors, driving both propagation time and probability. Despite ongoing changing climate, drought propagation times or probabilities have not significantly changed over the past 60 years. However, while most catchments are becoming wetter across all seasons, southern catchments become more vulnerable to spring drought due to increased evaporative demand. These findings highlight the need for tailored, region-specific water management strategies to address seasonal and regional variations in drought risks, particularly as climate change continues to evolve.