Characterizing the spatial and temporal variability of June–July moisture conditions in the Canadian prairies

Abstract

Palmer's moisture anomaly index (Z-index) was used to characterize the frequency, severity, and spatial extent of June-July moisture anomalies for 43 crop districts across the Canadian prairies during 1920-99. In addition, the main modes of spatial and temporal variability in moisture conditions were identified and used to elucidate the physical mechanisms responsible for causing these moisture anomalies to occur. The crop districts were divided into five relatively homogeneous moisture regions using cluster analysis, and moisture anomaly statistics were analysed for each region.The single most severe June-July drought on the Canadian prairies occurred in 1961. This drought covered more than 86% of the study region and had a mean severity (Z-index) of −5.67. Other severe June-July droughts occurred in the Canadian prairies (in order of severity) in 1988, 1936, 1929, and 1937. The results demonstrated that the severity and spatial extent of moisture anomalies on the Canadian prairies are strongly correlated, indicating that the more severe events tend to affect larger areas. The most drought-prone regions experienced moisture conditions detrimental to crop production in approximately one year out of every six years.The spatial analysis revealed the existence of three preferred spatial patterns of moisture variability on the Canadian prairies and each pattern can be attributed to a unique set of atmospheric and oceanic forcings. The temporal analysis verified the presence of coherent periodicities (in particular quasi-2, -4, and -10-15 year oscillations) in the moisture time series.

Spatial and temporal variability of prairie lake hydrology as revealed using stable isotopes of hydrogen and oxygen

“…5a) suggests that the low degree of isotopic enrichment likely arises because of the uniformly strong influence of water inflow from snowmelt or groundwater that buffers all lakes against short-term inter-annual variation in chemical composition, either by dilution of enriched water with depleted groundwater (Birks and Remenda 1999;Yu et al 2002), or by export of enriched surface waters into shallow aquifers (van der . Similarly, the relatively low sensitivity of lake isotopic values to interannual variations in precipitation is consistent with the long residence time of these lakes (.10 yr when known) and the relatively low amounts of total precipitation in this subhumid to semiarid region (Walker et al 1995;Quiring and Papakyriakou 2005).…”

“…4), although as discussed above, we suggest that groundwater could increase the slope of the observed LEL in small groups of lakes (Yu et al 2002) and that site-specific estimates of d groundwater may be required in future mass-balance models. Finally, we assumed that precipitation received during 2003 and 2004 was characteristic of the long-term fluxes and isotopic signatures of the region, even though we recognize that the climate and hydrology of the northern Great Plains is characterized by very high inter-annual variability (Walker et al 1995;Quiring and Papakyriakou 2005). In this regard, we believe that the inter-annual variation in slope of isotope regressions based on seasonal surveys in 2003 (4.77) and 2004 (5.14) may reflect differences in mean temperature and humidity among years, both of which influence determinations of d* and LEL slope (Gibson et al 2005(Gibson et al , 2008.…”

“…Inputs of energy tend to synchronize the seasonal variability in physical (ice melt, thermal stratification) and chemical (salinity, ionic composition) properties of lakes (Magnuson et al 2000;Bonsal et al 2006), whereas inputs of mass (water, dissolved substances) reduce temporal coherence among lakes (Pham et al 2008), likely because of differences among sites in catchment characteristics that regulate mass flow (soil, geology, vegetation, topography, etc. ;Blenckner 2005) and because the distribution of precipitation is more spatially variable than that of temperature (Walker et al 1995;Whitfield et al 2002;Quiring and Papakyriakou 2005). In the Canadian Prairies, .70% of total annual precipitation falls as summer rain; however, in many basins 80% of runoff is derived from the melting of winter snow packs during spring (Steppuhn 1981;Akinremi et al 1999).…”

Paleolimnological evidence of the effects on lakes of energy and mass transfer from climate and humans

“…Such high spatial synchrony arises because E transfers associated with solar and thermal influx are relatively uniform over broad geographic areas (Whitfield et al 2002;Drö scher et al 2009), whereas m transfer associated with precipitation, runoff, and groundwater is more spatially variable (Walker et al 1995;Quiring and Papakyriakou 2005) and reduces temporal coherence among lakes (Pham et al 2008(Pham et al , 2009Drö scher et al 2009). Similarly, the unit effects of changes in E or m influx (e.g., effects uC 21 , mg P 21 , and so on) appear to be greatest when the lake content or background flux of a given factor is low, as evidenced by the disproportionate limnological effects of water heating during spring (Blenckner et al 2007) or nutrient inputs to oligotrophic lakes (Schindler 2001).…”

Characterizing the Surface Features of the 1999–2005 Canadian Prairie Drought in Relation to Previous Severe Twentieth Century Events

“…A variety of drought indicators at various temporal scales have identified largearea, multi-year dry episodes over the Canadian Prairies during the 1890s, 1910s, 1930s, 1980s and most recently from 1999 to 2005 (with 2001 and 2002 being the worst drought years) (Nkemdirim and Weber, 1999;Wheaton, 2000;Quiring and Papakyriakou, 2005;Chipanshi et al, 2006;Bonsal and Regier, 2007). During this most recent episode, parts of the Canadian Prairies experienced their worst drought for the last 100 years .…”