Sometimes spring comes early, and sometimes it’s late – but one thing is always true: it’s wet. Depending on the amount of spring melt we have to contend with and where you live in the province, you might have to slosh your way through melting snow and ice for weeks.
This is the time at which many Albertans become concerned about the risk of summer flooding in their communities, particularly if the winter has been particularly long and snowy. It’s important to remember that in southern Alberta, mountain snowpack is not a major cause of flooding. It plays a part – as do existing water levels and the condition of the soil – but the biggest factor determining summer flood risk is rainfall – how much we get, how much falls in short periods, and where in the province it falls.
But even though it’s not the main cause of flooding, snowpack can impact how severe the flood can be . As you can probably guess, runoff from melting snow contributes to rising water levels. But snowpack can also prevent the rain water from being absorbed by the ground – which can also contribute to flooding.
Because of these factors, our river forecasters have to take snowpack into account when they make their predictions (check out this blog post to learn more about how that’s done). To do this, they have to look at two different types of snowpack – mountain and plains.
Location, location, location
Mountain snow and plains snow behave in different ways. Snow on the plains melts quickly in the spring and disappears rapidly. As it melts, it may cause temporary ‘ponds’ to form or cause minor flooding of small streams. But this melting doesn’t usually have a big impact on larger rivers – which are the source of most major flooding.
In contrast, mountain snowpack typically melts at a slower pace, and keeps melting well into the summer. This is for one simple reason: it’s generally much colder up there than it is down on the plains. As a result of this slow melting, mountain snowpack’s not usually a primary cause of flooding.
Because plains and mountain snowpack are different, it’s important for us to monitor snowpack throughout the province – even in places that are really remote. A lot of data comes to us electronically, from monitoring stations that monitor snow conditions and send their data to us via satellite. But snow surveying by hand often gives us a better estimate, just because it gives us the ability to measure more spots in a given area. All of Alberta’s plains snowpack information – and as much of the mountain snowpack information as possible – is gathered by hand.
Using the data – and keeping up with the results
Once we’ve got the data, it becomes one of many variables river forecasters use to assess potential flood risk. You can see some of the maps and data used by the forecasters here. (There’s different data for river basins,mountain and plains snowpack, and precipitation levels in different parts of the province)
Based on analysis of this data, our river forecasting centre issues:
- river breakup and spring runoff advisories, throughout the spring
- high water level alerts and flood watches, throughout the spring and summer