Impacts of Long-term Climate Cycles on Alberta A Summary by Suzan Lapp and Stefan Kienzle Large Scale Climate Drivers The Pacific Decadal Oscillation (PDO) [Mantua et al., 1997] is the dominant mode of sea surface temperature (SST) variability in the North Pacific Ocean and is one of the main drivers of winter temperature and precipitation in the Pacific Northwest (Figure 1). During a negative (positive) PDO phase winters are typically cooler (warmer) and wetter (drier) in this region. The low-frequency PDO shifts phases on an inter-decadal time scale, usually at about 20 to 35 years [Minobe, 1997; Mantua and Hare, 2002] from warm to cool phases in 1890 and 1947 and from cool to warm in 1925 and 1977 [Minobe, 1997; Deser et al., 2004]. A strong negative relationship exists between the PDO and streamflow in south and central Alberta; therefore, these regions are wetter when the PDO is in its negative phase and drier when the PDO is positive. The influence is particularly strong in southern Alberta and weakens towards central and northern Alberta, but the impact is still evident. The higher frequency El Nino-Southern Oscillation (ENSO) also affects the hydroclimatology of southern and central Alberta (Figure 2). Precipitation and streamflow are decreased during El Niño events and increased during La Niña events [Shabbar and Skinner, 2004; Bonsal and Shabbar, 2008]. The negative (positive) phase of the PDO and El Niño (La Niña) produce similar winter climate conditions in the region. The Arctic Oscillation (AO) is a measure of the intensity of the polar vortex and is closely related to (if not the same as) the North Atlantic Oscillation (NAO) [Wallace and Gutzler, 1981]. A negative relationship exists between southern Prairie winter precipitation (Figure 3) and the NAO, as the positive NAO (and AO) allows more frequent outbreaks of cold (Figure 4), dry Arctic air to the southern Canadian prairies [Bonsal and Shabbar, 2008]. Choice of GCMs to derive future PDO, ENSO and NAO scenarios Overland and Wang [2007], Stoner et al. [2009], and Wang et al. [2010] computed Pacific and Atlantic atmosphere-ocean climate indices from 20 th century simulated GCM SST and surface level pressure (SLP) data and compared their spatial and temporal patterns of
variability to those derived from the observed 20 th century climate indices. From the 23 GCMs with archived data, Lapp et al. [in review] chose the ones best able to simulate the PDO, ENSO, and NAO, using similar comparisons among the 20 th century observed records and the 20 th century simulations. As well, they specifically examined the GCM s capacity to simulate low-frequency variability using the multi-century pre-industrial control runs. They concluded the final set of ten GCMs was CGCM3.1 (T47), CGCM3.1 (T63), ECHAM5/MPI-OM, GDFL-CM2.1, MIROC3.2 (hires), MIROC3.2 (medres), MRI-CGCM2.3.2, NCAR-CCSM3, NCAR-PCM and UKMO-HadCM3. Model runs under the low B1, moderate A1B and high A2 emissions scenarios were selected to derive early 21 st century PDO, ENSO and NAO/AO projections. In conclusion, this study projects a weak mean North Pacific Ocean shift towards more negative PDO-like conditions for the early half of the 21 st century. As long as the PDO s present tele-connection patterns (link to southern Alberta climate) hold, this shift would be expected to increase precipitation occurrence in the Pacific Northwest. These projections of increased winter precipitation do correspond to previous results of climate change scenarios for this region. However, the GCMs split between those showing a shift, often significant, towards more negative PDO-like conditions for all three scenarios, and those showing a contrary shift, also often significant, towards more positive PDO-like conditions for all runs and all three scenarios. The shift towards more occurrences of El Niño-like conditions, however, may counteract the predicted increase in occurrences of negative PDO. This study did not take into account increased temperature projections and the impact to the rain/snow ratio of winter precipitation. GLS river discharge modelling Five actual stream discharge records and three naturalized discharge records in southern Alberta and its environs were analyzed by St. Jacques et al. [2010] through a series of generalized least squares regression equations (GLS) using ENSO, PDO and NAO/AO as predictor variables. Two of the gauges, on the Waterton and the Marias Rivers, are on unregulated or slightly regulated river runs. Three of the gauges measure regulated flows, on the Oldman, St. Mary and Belly Rivers, and in these cases, both the observed actual flows and the reconstructed naturalized flows compiled by Alberta Environment were separately analyzed, providing an additional 6 records [Alberta Environmental Protection, 1998]. Four of the gauges are located in southern Alberta, with one, on the Marias River, in adjacent Montana. All records span at least 90 years; the recommended shortest period to
be used for this type of analysis should include a full PDO cycle (begin no later than 1950). The GLS regression analysis showed a regional pattern of declining flows in the 20 th century. Six of the eight models revealed significant declining trends, with the exceptions being the naturalized St. Mary and the naturalized Belly discharge records, which showed no trends. Both of the gauge records in relatively undisturbed watersheds, the Marias and Waterton Rivers, showed significant declines, as did the naturalized Oldman River, which indicates that the declines are not purely due to direct human impact, but also to hydroclimatic causes, presumably global warming. The current year PDO or a lead or lag was the explanatory variable that always appeared in the optimum predictor set. New results from St. Jacques et al. (in prep) conclude, using the series of GLS regression equations and ENSO, PDO and NAO/AO as predictor variables, that projections of 21 st century surface water availability will generally decline, resulting from the trend in the GLS equations. Researchers have projected increased summer temperature and decreased precipitation and increases in winter precipitation and temperature for this region. The results of the GLS equations for the rivers suggests that in the competition between these two opposing effects on surface water availability, the former with dominate in this region. Conclusions Based on the wide range of projected PDO, ENSO and NAO indices from the various GCMs for the early 21 st century it is difficult to make any concrete statements about the future hydroclimate of Alberta. These models overall did a poor job and showing the teleconnection between ENSO and PDO (interaction between tropical SSTs and north Pacific SSTs) suggesting that the models are not capturing the large scale interaction between the ocean and atmosphere; however a new suite of models will be available summer 2011 that may provide better insight to future large scale indices. It is interesting to note that the streamflow trend analyses, regardless of projected indices, are generally showing a decline in available surface water for the 21 st century for Alberta that may lead to severe water shortages.
References Alberta Environmental Protection (1998), South Saskatchewan River basin historical weekly natural flows 1912 to 1995. Technical Report Alberta Environment. Bonsal, B., and A. Shabbar (2008), Impacts of large-scale circulation variability on low streamflows over Canada: a review, Can. Water. Res. J., 33, 137-154. Deser, C., A.S. Phillips, and J.W. Hurrell. 2004. Pacific interdecadal climate variability: linkages between the tropics and the North Pacific during boreal winter since 1900. Journal of Climate 17: 3109-3124. Lapp, S., J-M. St. Jacques, E.M. Barrow, and D.J. Sauchyn. (In Review). GCM Projections for the Pacific Decadal Oscillation under Greenhouse Forcing for the Early 21 st Century. Int. J. Climatol. Mantua, N.J., and S.R. Hare (2002), The Pacific Decadal Oscillation, J. Oceanogr., 58, 35-44. Mantua, N.J., S.R. Hare, Y. Zhang, J.M. Wallace, and R.C. Francis (1997), A Pacific interdecadal climate oscillation with impacts on salmon production, Bull. Amer. Meteorol. Soc., 78, 1069-1079. Minobe, S. (1997), A 50-70 year climatic oscillation over the North Pacific and North America, Geophys. Res. Let., 24, 683-686. Overland, J.E., and M. Wang (2007), Future climate of the North Pacific ocean, Eos, 88, 178, 182. Shabbar, A., and W. Skinner (2004), Summer drought patterns in Canada and the relationship to global sea surface temperatures, J. Clim., 17, 2866-2880. St. Jacques, J-M., D.J. Sauchyn, and Y. Zhao. 2010. Northern Rocky Mountain streamflow records: global warming trends, human impacts or natural variability? Geophysical Research Letters 37: L06407, DOI:10.1029/2009GL042045. Stoner, A.M.K., K. Hayhoe, and D.J. Wuebbles. 2009. Assessing general circulation model simulations of atmospheric teleconnection patterns. Journal of Climate 22: 4348-4372.
Wallace, J.M., and D.S. Gutzler (1981), Teleconnections in the geopotential height field during the Northern Hemisphere winter, Mon. Weather Rev., 109, 784-812. Wang, M., J.E. Overland, and N.A. Bond (2010), Climate projections for selected large marine ecosystems, J. Mar. Sys., 79, 258-266.
Figure 1. Correlation map between November-March PDO index and corresponding precipitation. Areas outlined in black are significant (p=0.05). Black triangles represent tree-ring locations used in previous work.
Figure 2. Correlation map between Nino3.4 July-December index and December-February precipitation. Areas outlined in black are significant (p=0.05).
Figure 3. Correlation map between annual AO index and annual precipitation. Areas outlined in black are significant (p=0.05).
Figure 4. Correlation map between annual AO index and annual average temperature. Areas outlined in black are significant (p=0.05).