New article on compound events online in NHESS Discussions

Atmospheric rivers (ARs), long filaments of high water vapour concentration, play an important role in the occurrence of compound events (CEs) in the form of coinciding heavy precipitation and high water levels along the Dutch coast. Over the past 37 years around 70% of all CEs of this type can be associated to the presence of an AR over the Netherlands. This has been shown in a study published in NHESS Discussions last week. The study, which was performed at the Royal Dutch Meteorological Institute in course of the ICOWEX project, assesses modelled coastal water levels, information from an AR database (both derived from reanalysis data) and observed precipitation over the period from 1979 - 2015 to identify the driving mechanisms behind CEs. It presents a first classification of CEs into two categories: (1) CEs associated to an AR over the Netherlands and (2) CEs without such an association. This classification can be used to coordinate future research and function as a guideline for subsequent classification efforts. Additionally, the study provides information on the specific conditions that drive the two different CE classes, with (i) CEs associated to an AR occurring under sea level pressure conditions resembling the positive phase of the North Atlantic Oscillation, and (ii) CEs without the presence of an AR arising under East-Atlantic-pattern-like conditions. These typical sea level pressure patterns and the with it associated changes in moisture transport and sea surface temperature in the North Atlantic, evolve and are clearly visible throughout the week before an event. Thus, the information provided in the study could be used in the early prediction of CEs and thus facilitate the development of an early warning system for the Dutch coastal region. The study is publicly available and open for discussion until the beginning of September. We invite interested researchers to read the manuscript, leave constructive comments or contact the authors for any questions related to the study or compound events in general. Ridder, N., de Vries, H., and Drijfhout, S.: The Role of Atmospheric Rivers in compound events consisting of heavy precipitation and high storm surges along the Dutch coast, Nat. Hazards Earth Syst. Sci. Discuss.,, in review, 2018. [link]