Weather conditions were cold in May and June in the eastern parts of Iceland. However, a comparison of measurements from the Bruarjökull Glacier from 2001 and up until the present day showed that this was not unusual. Weather conditions in May were similar to measurements recorded in 2005 and June was similar to measurements recorded in 2001. Conditions were expected to change rapidly towards the end of June as temperatures would rise and ablation and water flow would increase. However, weather conditions in July were affected by dominating northerly winds with cold spells and heavy cloud coverage. Run-off from glaciers increased slightly and temperatures and sunlight levels reached a historical low in July in the lower regions of the Brúarjökull Glacier.
Water flow in the Jökulsár á Dal River has been monitored since 1963. The average flow rate last July was approx. 180 m3/s. This is the lowest recorded level for the same period since monitoring began and only approx. half of the average recorded water flow. Monitoring results show that the average flow rate for the Jökulsá á Dal River in July has not been this poor since 1993 when it measured 210 m3/s. The average temperature in Egilsstaðir and the eastern part of Iceland in July of 1993 was 7.5°C. Temperatures in 2015 were similar, reaching 7.6°C.
The average temperature in Egilsstaðir for the month of July (since 1963) is 10.6°C and conditions have been similar in the Blanda area. Temperatures in the Hveravellir area were the lowest recorded since 1993. Water flow into the Blanda Reservoir reflected the poor weather conditions and the average for July was 49 m3/s or the lowest recorded in the last decade. Conditions in the Þjórsá area were similar to those in the northern and eastern parts of Iceland with low temperatures and low water flow rates. Heavy snow coverage remained until temperatures began to rise in June. The results from the Þjórsá and Tungnaá Rivers for June and July were close to average as compared with continuous flow records from 1988. Despite cold weather in the Þjórsá-Tungnaá area in June and July, snow accumulation from last winter has helped to fill reservoirs. The snow in the area has now melted completely and the flow rate in late summer will be reliant on precipitation and glacial ablation levels.
These conditions have significantly affected the outlook for Landsvirkjun’s reservoir levels. Low ablation levels have affected the Hálslón Reservoir where the water level has only risen by 10 m in July and is now 593 m.a.s.l or only 37% of the reservoir’s full capacity. The reservoir will require over 30 m of water to fill up this autumn and there is only a 50% chance that this will occur.
The Blanda Reservoir is experiencing similar problems as the water supply almost ceased in late July and is now only 55%. The Þjórsá area is mostly unaffected and the Þórisvatn and Hágöngulón Reservoirs are above average for July (78%).
Favourable weather conditions in August and September could significantly affect Landsvirkjun’s water budget. Landsvirkjun will need to evaluate the need for limiting power delivery this coming winter if water inflow remains close to the lowest recorded levels.