Rain Summers

Warm, wet summers are historically unusual and could bring unexpected disruptions to ecosystems and society, according to new research from the University of British Columbia. googletag.cmd.push(function() googletag.display('div-gpt-ad-1449240174198-2'); ); As climate change raises summer temperatures around the world, increases in precipitation could offset drought risk in some regions. However, a paper published in Nature Communications this month shows that wetter summers may bring other problems in a warming climate.

rain summers

"Terrestrial climates around the world tend to alternate between cool, wet summers in some years and warm, dry summers in other years," said UBC forestry PhD candidate Colin Mahony, lead author of the study. "But climate change is driving many climates towards warmer and wetter conditions. We found that where temperature and precipitation are increasing together, climates are changing faster than the temperature trend alone would suggest."

"Some fungal outbreaks over the past couple of decades, such as Dothistroma needle blight, could likely have been anticipated by tracking how temperature and precipitation were changing together," said Mahony, who has worked as a forester in British Columbia for 10 years and has witnessed the impacts of climate change on the ground. "In order to respond to global warming, we need to understand how the climates of the future will be different than the familiar, historical climates that we are adapted to." More information:Colin R. Mahony et al, Wetter summers can intensify departures from natural variability in a warming climate, Nature Communications (2018). DOI: 10.1038/s41467-018-03132-zJournal information:Nature Communications

According to new research at the University of Reading published in Nature Geoscience, the North Atlantic warming in the 1990s coincided with a shift to wetter summers in the UK and northern Europe and hotter, drier summers around the Mediterranean. The patterns identified match those experienced this summer (2012), when the UK had the wettest summer in 100 years, while the Mediterranean suffered with temperatures as high as 40 degrees centigrade or more.

The temperature of the North Atlantic swings slowly between warmer and cooler conditions, and the present warm phase has a similar pattern to warm conditions that persisted throughout the 1930s, 40s and 50s. During the 1960s, 70s and 80s cooler conditions occurred over the North Atlantic. Computer simulations suggest that these changes in ocean temperature affect the atmosphere above. Warmth in the North Atlantic causes a trough of low pressure over western Europe in summer and steers rain-bearing weather systems slap-bang into the UK.

The previous North Atlantic warm phase also saw a run of wet summers over the UK with notable events including the August 1952 Lynmouth floods and severe flooding during August 1948 which closed the east coast mainline railway for three months.

He said: "The North Atlantic ocean has alternated slowly between warmer and cooler conditions over the last 100 years. We saw a rapid switch to a warmer North Atlantic in the 1990s and we think this is increasing the chances of wet summers over the UK and hot, dry summers around the Mediterranean - a situation that is likely to persist for as long as the North Atlantic remains in a warm phase.

"A transition back to a cooler North Atlantic, favouring drier summers in the UK and northern Europe, is likely and could occur rapidly. Exactly when this will happen is difficult to predict, but we're working on it."

The North Atlantic warming and cooling cycles are known as the Atlantic Multi-Decadal Oscillation (AMO) and they affect temperature, rainfall and wind patterns over Europe, Africa and North and South America. Previous research has suggested the warm and cold swings are related to changes in ocean circulation. Other research at Reading has suggested that it may be possible to predict the warming and cooling cycles some years ahead.

Between 1930 and 1959, the summers with the highest annual rainfall were 1930, 1931, 1932, 1946, 1950, 1954 and 1958. More recently, the summers of 2000, 2007, 2008 and 2012 have also been characterised by above-average rainfall. (Source Dr Roger Brugge, Department of Meteorology, University of Reading). This assessment is based on the extended April-September summer season. Note that the evidence presented in this paper relates to seasonal rainfall averages rather than individual rainfall events.

The map above shows the pattern of changes in summer rainfall that occurred in the 1990s when the North Atlantic Ocean warmed rapidly. The figure shows June-July-August rainfall changes expressed as a percentage of the long term average rainfall for the season. Blue indicates more rain since the 1990s and orange/red less rain. More images are available - contact the University of Reading press office, details as above.

The new study, from the joint Met Office and NERC funded CONVEX project which is led by Newcastle University's Professor Hayley Fowler, uses a state-of-the-art climate model providing the first evidence that hourly summer rainfall rates could increase.

As the atmosphere warms it can hold more moisture and this is expected to intensify rainfall. However, research is needed to understand what this might mean for extremes and how this might affect the UK.

Climate models, which generally work at coarse resolutions, have been able to accurately simulate winter rainfall and have suggested generally wetter winters with the potential for higher daily rainfall rates in the future. 041b061a72