Moisture Updates - October 4, 2023

Synopsis

Maps 1 & 2: In the 14-days since the last report (September 20, 2023), most of southern Alberta has finally received much needed rain. Although amounts have been modest through the central (10-15 mm) and northern portions of the region (5-10 mm), it has still been welcome. Lands across the west-half of the region and through the extreme southeastern portions were more fortunate, receiving upwards of 20 mm of rain with the greatest accumulations found along the foothills were some locales received upwards of 40 mm. Elsewhere the Central, Peace and North East Regions were somewhat drier with most lands receiving less than 10 mm along with some large areas that received less than 5 mm. For this time of year, generally speaking most of the dry lands across the Southern Region and eastern portions of the Central Region have been trending to at least near normal during this relatively short window of 14-days (Map 2). In the near term, at the very least this is a promising trend.

30-Day Precipitation Trends as of October 4, 2023

Maps 3 & 4: Looking back over the past 30-days, some of the very dry land across the Southern Region and eastern portions of Central Region have trended closer to normal with respect to rainfall received (Map 3). However, this is historically a relatively dry part of the year. The trend to near normal is good and it will need to continue in order to help rebuild dwindling moisture supplies both in the soil itself and across the landscape in general. In contrast, very dry conditions have prevailed across much of the Central Peace Region with several pockets of once in 50-year lows evident. Similarly most of the North West and large portions of the North East Regions have been relatively dry. However with the exception of parts of the Peace Region, most of these areas are not facing severe deficits like parts of the Central and Southern Regions are.

Over the last 30-days precipitation accumulations have been highly variable, with large areas in each of the four regions receiving less than 15 mm and within these areas some locales have received less than 10 mm (Map 4). October is an important month for soil moisture recharge and there is still about 3-weeks until freeze up, providing an early winter fails to materialize. With the arrival of colder air at this time of year that often collides with lingering warmer air, weather can be very unpredictable and reasonable moisture this late in the year is still possible.

Soil Moisture Reserves as of October 4, 2023

Maps 5 & 6: Recent rains across the western and extreme south-eastern portions of the Southern Region have helped bring soil moisture levels closer to average for this time of year (Map 5). However, bear in mind that at this time of year, average soil moisture levels tend to be quite low, across these areas. For example, on average (1961-2022) most of the Special Areas and the eastern half of the Southern Region, only has 20 to 40 mm of water reserves in 120 cm depth of soil, assuming a spring wheat crop was planted (Map 6). Therefore, at this time of year it does not take much rain to achieve “average soil moisture” levels in these areas.

Elsewhere, much of the Central Region remains below normal with deficits relative to normal increasing towards the foothills (Map 5) where it is normally relatively wetter in the fall (Map 6). Generally for those parts of the province lying north of Wetaskiwin and extending well up into the Peace Region, many areas are now near normal. However, some exceptions do exist in the western and northern Peace Region were significant deficits remain. However, this far north, overwinter snowpacks tend to be deeper (contain more water) and this gives more hope for a rebound in the spring.

Perspective

Map 7: Despite recent modest gains in soil moisture, along with a 30-day trend in many areas towards “normal” rainfall for this time of year there remains a serious moisture deficit across many lands. Looking back across the previous 3-years, most of Alberta remains in a deficit situation (map 7) with respect to moisture. This is undoubtedly reflected in the reduced vigor of perennial crops and native vegetation, along with dwindling surface water supplies (lake, rivers, streams, dugouts, marshes, etc.) . Much of the Southern and Central Regions are estimated to see a 3-year period this dry on average, less than once in 50-years. It’s important to realize that these maps only depict current conditions relative to the 1961 to 2022 period and do not include some arguably more severe dry spells that occurred in the late 1800’s and again through the 1910 to 1940 period.

Unfortunately a lack of station density during the first part of the 20th century makes provincial mapping that included these episodes unreliable for many places and we are thus confined, for the purposes of this report, to a window of a perceived normal, staring in the 1960. In fact, from about 1961-1997, Alberta enjoyed a relatively cool and wet spell that was seemingly uncharacteristic of the early parts of both the 20th century and the 21st century.