Jökull


Jökull - 01.01.2019, Page 117

Jökull - 01.01.2019, Page 117
Tussetschläger et al. Figure 7. Photos of snow patches in the head of Úlfsdalir (H. Tussetschläger) and satellite images for 2016 and 2017 used for comparison. The hillshade is derived from the DEM (25 m resolution) provided by LMI. – Samanburður á notagildi ljósmynda af vettvangi og gervitunglamynda í Úlfsdölum. ble A3 – appendix). For our study especially, the winter period is of interest. We calculated the total precipitation from October until May, when precip- itation is expected to be mostly snow in the moun- tain areas. The mean winter precipitation over the last 19 years in Ólafsfjörður is about 750 mm, the highest amount of winter precipitation was measured in 1998/1999 (1016 mm) and the lowest amount in 2002/2003 (481 mm). In all study areas the pattern of the snow cover is smallest in the period from the earliest available image until 2017. In Brimnesdalur and Kerling the largest spatial extent of snow patches is identified in the time period 1999–2002 during which the mean winter precipitation is 808 mm, which is higher than the overall mean winter precipitation. Similar results are obtained from other weather sta- tions (Akureyri and Skeiðsfoss). Thus, the periods with the largest snow patches coincide with the pe- riods of highest winter precipitation. Similarly, years with significantly decreased size of snow patches such as 2016 and 2017 coincide with relatively low win- ter precipitation (662 mm and 664 mm respectively which is about 33% less than the 2013–2015 average), and relatively high mean annual temperature. Interest- ingly the warmest year is 2014, which also is one of the years when the snow patches are largest. This pat- tern in the year 2014 is considered to emphasise the relative importance of the winter precipitation for the extent of the snow patches. Furthermore, mass bal- ance data collected by the Icelandic Institute of Natu- ral History seem to correlate well with the area distri- bution of the snow fields in recent years. The cirque glaciers, Búrfellsjökull, Deildardalsjökull and Teigar- jökull in Svarfaðardalur displayed positive mass bal- ance in the years 2013, 2014 and 2015, but negative mass balance in the years 2016 and 2017 (Brynjólfs- son, 2018 and 2019). For an overall estimate of main wind direction, frequency and speed we used data from the automatic weather station located on the island of Grímsey. There, the wind direction is not affected by the moun- tainous landscape of Tröllaskagi and is considered to 116 JÖKULL No. 69, 2019
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