Cold and Hot Periods Associated with Dry Conditions over the Canadian Prairies

Abstract

Dry conditions and droughts are a normal feature of the Canadian Prairie climate. A common perception is that these periods of below-normal precipitation are always associated with above-average temperatures. Using a core region centred near Edmonton, Alberta, this study incorporates gridded temperature and precipitation information for the period 1900-2009 to quantify how often cold, as well as hot, dry conditions occurred. Shorter-term records of atmospheric circulation, upper-air soundings and surface cloud-related variables are then used to examine some of the factors leading to these conditions. Using drought criteria based on the Standardized Precipitation Index, 15 month-long anomalously cold, dry periods were identified; this is about an order of magnitude less than the number of hot, dry periods. Cold periods generally occurred in the late spring and occurred within some of the major droughts affecting the region. The cold periods were linked with the advection of cold, dry air from the north, whereas hot periods were somewhat attributable to air descending the eastern flank of the Western Cordillera. To understand drought fully, all conditions leading to the persistent lack of precipitation need to be considered including those instances with cold temperatures.RÉSUMÉ [Traduit par la redaction] Les conditions sèches et les sécheresses représentent un phénomène normal dans les Prairies. Il est communément admis qu'au cours de ces périodes caractérisées par des précipitations inférieures à la normale, les températures sont invariablement supérieures à la moyenne. Dans notre étude, qui porte sur une région centrale près d'Edmonton en Alberta, nous intégrons les données maillées sur les températures et les précipitations entre 1900 et 2009 afin de quantifier la fréquence à laquelle les conditions sèches par temps froid autant que par temps chaud se sont présentées. Nous nous servons ensuite des enregistrements à court terme de la circulation atmosphérique, d'observations en altitude et de variables de surface liées aux nuages afin d'examiner quelques facteurs responsables de ces conditions. Au moyen de critères de sécheresse établis en fonction de l'Indice des précipitations normales, nous avons établi qu'il y a eu 15 périodes de sécheresse de durée d'un mois par temps anormalement froid, ce qui est inférieur au nombre de périodes de sécheresse par temps chaud. Les périodes froides ont généralement eu lieu à la fin du printemps, pendant quelques-unes des grandes sécheresses qui ont frappé la région. Ces périodes étaient reliées à l'advection de l'air froid et sec provenant du nord; en revanche, les périodes chaudes étaient dans une certaine mesure attribuables à l'air descendant sur le flanc est de la Cordillère nord-américaine. Pour bien comprendre le phénomène des sécheresses, il faut tenir compte de toutes les conditions qui expliquent l'absence persistante de précipitations, y compris les occurrences avec temps froid.

Summary and synthesis of Changing Cold Regions Network (CCRN) research in the interior of western Canada – Part 1: Projected climate and meteorology

“…5a). This large-scale setting favors the development of cyclones that bring warm-season precipitation to southwestern Canadian regions (Szeto et al, 2011(Szeto et al, , 2015(Szeto et al, , 2016. The intensity of the low can be quantified by the H index as detailed earlier and the development of this feature is shown in Fig.…”

“…In particular, strong upslope rainstorms over southern Alberta, similar to the one that caused the 2013 Calgary flood (Pomeroy et al, 2015;Liu et al, 2016;Kochtubajda et al, 2016;Li et al, 2017), could result from upper lows that are located over the northwestern US, whereas floodproducing extreme rain events over the eastern Prairies (see for example Brimelow et al, 2014;Szeto et al, 2015) could result from upper lows that were centered only slightly to the east. Furthermore, some systems that track slowly across the region could bring extreme precipitation to both the eastern and western regions (e.g., Szeto et al, 2011). When combined with the increased winter precipitation and earlier snowmelt and freshet in a warmed climate, the expected increase in extreme spring precipitation could substantially increase the risk of extreme Prairie spring floods over both the western and eastern Prairies.…”

Hydrological responses to climatic variability in a cold agricultural region

“…For example, large‐scale atmospheric features such as a quasi‐stationary mid‐tropospheric ridge impede atmospheric moisture supply from the major sources and restrict recycling of evapotranspiration (e.g., Bonsal & Lawford, ; Bonsal, Wheaton, Meinert, & Siemens, ; Liu, Stewart, & Szetco, ; Raddatz, ; Shabbar, Bonsal, & Khandekar, ; Shabbar, Bonsal & Szeto, ). Canadian Prairie drought is commonly associated with warmer summers (Roberts, Stewart, & Lin, ), colder winters (Fang & Pomeroy, ; Stewart, Bonsal, Harder, Henson, & Kochtubajda, ), higher near‐surface energy in summer, a smaller percentage of precipitation occurring under overcast conditions, intense precipitation events, lower annual precipitation, and sparse vegetation (Armstrong, Pomeroy, & Martz, ; Roberts et al, ; Stewart, Henson, Carmichael, Hanesiak, & Szetco, ). These extreme climate years exert strong controls on hydrological processes such as snow accumulation, runoff, frozen soil infiltration, and evapotranspiration (e.g., Pomeroy et al, ).…”

Climate Change, Drought and Human Health in Canada

“…Surface air temperatures are often high/elevated during drought, although this is not always the case. For some long duration droughts, there are periods when temperatures are below normal [ 11 ]. Droughts can also be windy or calm.…”