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Friday, 4 November 2016

Not enough rain is also a problem...

(Geoff Coulson, Warning Preparedness Meteorologist, Environment and Climate Change Canada)

Significant rainfall, and the flooding that can result, has been top-of-mind for many of the clients I have talked to that are involved in flood forecasting and emergency management and response. Canada’s insurers are now saying that water is the number one cause of insurance payouts over the last few years. Short duration, high intensity bursts of rainfall have been responsible for significant infrastructure damage in locations across the province over the last 10 or 15 years. Large storm systems, some fed by the remnants of tropical storms, have also caused widespread flooding. Lastly, seasonal spring flooding has also been a concern in parts of the province during periods of rapid warm-up and rain that can combine with snowmelt to cause rivers to overflow. These events have not played favourites with respect to where they have occurred...Windsor, London, Burlington, Toronto, Bracebridge, Peterborough, Ottawa, Timmins, Thunder Bay and Dryden have been but a few of the communities required to deal with the impacts of flooding for a variety of reasons. 

This past summer was no exception as significant rains fell on the Windsor area between September 28 and 30. The bulk of the rain fell during the first part of the event with some locations receiving in excess of 160 mm of rain with the first intense bands that moved over the area. Normal rainfall for the whole month of September in the Windsor area is around 94 mm. Thousands of residents felt the impacts from this event.

And yet, in the same summer that gave us another example of flood damage, other parts of southern and eastern Ontario were dealing with one of the driest spring and summers they had seen in years. Drier than normal conditions have been reported starting in April in some areas of southern and eastern Ontario as the favoured storm tracks, month after month, avoided these areas in favour of other parts of the Great Lakes basin. This extended dryness has led to a variety of impacts in these regions. Low reservoir levels and stream flows, wells drying up, reduced crop yields and the increased need for irrigation on the part of local farmers are but a few of the issues that have occurred. The map below provides the low water condition information gathered by the Ontario Ministry of Natural Resources and Forestry’s (OMNRF’s) Surface Water Monitoring Centre in Peterborough as of October 20, 2016. The map brings together information from a variety of Conservation Authorities and OMNRF’s district offices. 

Low water condition level III is the most severe and is denoted by the red areas on the map. Low water condition level III implies that the water supply is failing to meet the demand and must be managed through the use of water conservation and restrictions and regulation of water use.

Unfortunately, a few rainfalls here and there in the coming weeks are not going to make any notable changes in the overall situation. In fact, the latest precipitation forecasts for November hint that conditions could remain somewhat drier than normal. The situation will also not be improved by the fact that as the weather gets colder, the ground will get harder and precipitation will be more in the form of snow. This will keep needed moisture from getting into the watersheds in the most affected areas and will likely mean the situation will continue into the spring of next year.

So while it is important to acknowledge the significant infrastructure and financial impacts that flooding can cause, this summer has also provided a reminder of the impacts that extreme dryness can create. Climate experts have expressed concerns about both extreme rainfalls and drought in the coming decades. This past summer has provided us some insights into what we could be dealing with in the years to come as some areas deal with flooding rains while others look for rain of any amount.

This blog post has been written by Geoff Coulson, who has been a Meteorologist with Environment and Climate Change Canada for 33 years. For the past 12 years, Geoff has been a Warning Preparedness Meteorologist providing weather information to clients at all levels of government, the media, and the private sector. He also sits on the Provincial Flood Forecasting and Warning Committee and manages the CANWARN volunteer storm spotter program in Ontario.

Geoff Coulson is a panelist at CatIQ’s Canadian Catastrophe Conference (C4 2017) on the Lessons Learned from Ice, Flood & Hail session during the conference.

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