Characteristics of Extreme Daily Precipitation Events over the Arctic Region

Abstract:

Most climate models project that precipitation will increase over the Arctic during the 21^st century. This is viewed as a response to both increased atmospheric vapor flux convergence and loss of the sea ice cover which provides for local moisture sources. While observational evidence for increased precipitation is growing, it is difficult to draw firm conclusions, especially given the sparse observational network, and strong impacts of low-frequency atmospheric variability. Here, we use station records from the National Climatic Data Center, The Norwegian Meteorological Institute and other national sources to examine the spatial characteristics of extreme daily precipitation events across the Arctic (the area poleward of 65 degrees N) and recent trends. The focus is on the period 1979-2014. Extreme events at each of the 145 stations selected for analysis are defined as those within the top 1% of their statistical distribution. The spatial distribution of the size of the 1% event broadly follows the spatial pattern of annual precipitation. For stations in Iceland, Svalbard and coastal Norway influenced by Atlantic moisture sources, the 1% event size ranges from 14 to 25 mm; recent work shows that these high-latitude events are often linked to atmospheric rivers. This contrasts sharply with polar desert sites in the Canadian Arctic Archipelago and many locations along the Siberian coast, that, being removed from significant moisture sources, have values from 3-10 mm. When the Arctic region is assessed as a whole, the frequency of extreme events shows a slight positive trend over the study period. However, regional analyses, based on similarities between the size of the top 1% precipitation event, reveals areas of positive and negative trends that vary between region, season and month.