Synoptic‐scale flow structures associated with extreme precipitation events in northern Switzerland

Abstract

This article presents a climatological analysis of upper-level synoptic-scale flow structures and low-level moisture signatures associated with extreme precipitation events in north-eastern (NE) and north-western (NW) Switzerland. Extreme daily precipitation events between 1961 and 2010 are identified using a gridded observation-based precipitation data set. ERA-Interim and ERA-40 fields are used to characterize the flow. Large-scale flow configurations over Europe that are common to extreme precipitation events are identified by a K-means clustering approach. For each area, five large-scale flow classes are defined. These flow classes include zonally oriented flows over western Europe accompanied by a ridge over the east Atlantic, amplified upper-level troughs over western Europe, strong westerly or south-westerly flows, wave-breaking events and a broad trough over the Mediterranean. For each class, the main forcing mechanism behind the ascent of moist air, the magnitude of the total precipitable water and the seasonal distribution are presented. The way in which the location and structure of the defined upper-level classes affect the local distribution of precipitation is analysed. Moreover, we analyse the directions of the moisture flux that interacts with the topography and results in extreme precipitation events. The flow conditions range from advective situations in which large amounts of moisture are transported towards the orographic obstacle to flow situations in which heavy precipitation occurs on the lee side of the Alps and ascent is mostly driven by large-scale forcing. The co-occurrence of events between NE and NW Switzerland is presented. Approximately 30% of the events occurred in both areas on the same day or differed in timing by 1 day.

Estimating Trends and Return Periods of Daily Extreme Precipitation Associated with Tropical Cyclones in the Core North American Monsoon

“…The result is indicative of the presence of strong climate gradients that are not usually identified or are difficult to capture with precise measurements from the weather stations. Moreover, this bias is attributed to the fact that in the stations in high mountain areas, the density of the monitoring network is usually low, mainly due to difficult access to these areas [30][31].…”

“…The percentage contribution of P95 in coastal stations was insignificant, mainly because the coastal areas are commonly affected by the passage of easterly waves and of TCs in mountain sites [11,31]. For example, in the 1990s mountain sites received less intense precipitation associated with the monsoon; however, in this same area there were heavy precipitation events associated with TCs that resulted in large water contributions to the mountain area in the early 1990s, which was captured in the 10 large existing dams for agricultural activity.…”

Exceptional integrated vapour transport toward orography: an important precursor to severe floods in Switzerland

“…Dynamically forced ascent includes forced quasi‐geostrophic lifting as well as convergence of moist air masses (Doswell et al . ; Giannakaki and Martius, ).…”

Temporal continuity of extreme precipitation events using sub‐daily precipitation: application to floods in the Ebro basin, northeastern Spain

“…Extremely heavy precipitation may not be recorded in just 1 day, but the total of both days may pose substantial risk. In practice, many studies have used databases at daily scale (Brunetti et al, 2001;Bocheva et al, 2009;Zolina, 2012;Serreze et al, 2015;Giannakaki and Martius, 2016), owing to the difficulty in obtaining long data series at shorter scales. Using these daily databases may introduce uncertainty when identifying events with potential hydrologic risk.…”