Despite rain and flooding, southern Ontario drought worsens

Friday, July 29, 2016, 12:24 PM - Due to one of the driest growing seasons so far on record, drought conditions are spreading through southern Ontario, and the situation is growing worse as we see little rain in the forecast.

Originally published on June 28, 2016, this story has been updated to reflect the most up-to-date watershed conditions.

So far this growing season - which started on April 1 - a patch of unusually dry weather has settled across southern Ontario and southern Quebec.

As of July 26, in an update from the earlier conditions, Agriculture and Agri-Food Canada's Drought Watch website now records extremely dry conditions stretching from Cornwall to the Niagara Peninsula, with some splotches along the shores of Lake Erie towards Windsor, and north through the Simcoe area to the shores of Georgian Bay. Although conditions have improved through the Algonquin Park area, and further north, the drought has been slowly spreading into central and southwestern Ontario. 

Embedded within that swath, especially along the north shores of central Lake Ontario and now through central Ontario, parts of the GTA and down into the Niagara peninsula, are patches of record dry conditions.

Ontario Drought Watch maps for the 2016 growing season so far, for April 1 to June 26 (top) and April 1 to July 26 (bottom). Credit: Agriculture and Agri-Food Canada/S. Sutherland

In Ottawa, counting both snow and rainfall for the growing season so far, the area has received only a little over half the normal amount seen there from April through July. Based on Environment Canada weather records, Ottawa International Airport recording its 2nd lowest precipitation total for the growing season so far (April 1 to July 28), since record keeping began there in 1938, second only to to the same period in 1955.

In Kingston, weather stations in and around the city had never recorded an April and May as dry as they've seen this year, going back to at least 1960. The rain that fell over the city during those two months of 2016 was less than a quarter of the normal amount. Rainfall for June was slightly higher than normal, however it did not make up for the deficit experienced in the previous two months, and the rainfall so far in July - less than one-third the average amount - has only made the situation worse.

As of July 29, 2016, of the 31 watersheds throughout southern Ontario, over two thirds are reporting some level of drought conditions. Eleven are currently at Level 1 (minor drought), mainly through central and southwestern regions. At this stage, authorities typically ask residents for voluntary reductions in water use, to relieve some burden on the water supply. Another 10 watersheds have advanced to Level 2 (moderate drought), including most watersheds in eastern Ontario, plus the Hamilton and Grand River watersheds. At this level, local residents are asked to voluntarily lower their water usage by 20 per cent.

Currently, the Toronto Region Conservation Authority is reporting normal water levels, despite Pearson International Airport recording only 156 mm of precipitation so far this growing season. That's just over half the normal amount the station sees during April-July, and is the fourth lowest total for April-July, going back to 1938 (1949, 1958 and 1959 were lower).

While some rain has passed through southern Ontario, a few times each week, at the most, it has mainly been from scattered showers and thunderstorms. This has not delivered the needed levels of rainfall and has left far too much time between rain events. A large span of the southern Ontario already accumulated a rainfall deficit of greater than 120 millimetres, and as the two maps below indicate, this area is growing.

Ontario Drought Watch maps showing the rain deficit, for April 1 to June 27 (top) and April 1 to July 26, 2016 (bottom). Credit: Agriculture and Agri-Food Canada/S. Sutherland

For some context, 120 millimetres may not seem like very much, but the July 2013 Toronto floods - which caused so much trouble for residents and an estimated cost of around $850 million - was from one storm that delivered a downpour of 126 mm.

Such a downpour under these conditions would actually be disastrous, though, as even dry ground can only absorb so much rain at once.

Toronto just had a small taste of this over the past week, as downpours caused flooding along the lake shore and in parts of the downtown core. This is influenced by the amount of artificial surface the city has, compared to natural ground or greenspace, however the parched ground still has difficulty absorbing large amounts of water all at once.

Based on what the radar was showing, though - as Weather Network Chief Meteorologist Chris Scott pointed out on Twitter - it could have been far worse.

Rather than these intermittent downpours, where a good portion of the water simply runs overground or through storm drains, to swell waterways and ultimately end up in the lakes, what the province needs is a few periods where we have several days of light, steady rainfall, to soak the ground and refill reservoirs and waterways. 

Based on what the forecast is showing, however, with only a few brief episodes of showers indicated, the drought conditions are likely to only get worse.

Come back for further updates as this story progresses.

Sources: Agriculture and Agri-Food Canada | Environment and Climate Change Canada | Rideau Valley Conservation Authority (pdf) | Hamilton Conservation Authority | Grand River Conservation Authority

Watch Below: Has the new era of the 'megafire' begun?