Investigation and Reconstructions of the Hydroclimatic Variability of the Souris River Basin

Abstract

growing dependence on surface water resources in the Prairie Provinces has resulted in an increasing vulnerability to hydrological drought. A serious risk from recent and projected climate warming in the Canadian Prairies is a shift in the amount and timing of streamflow. The Souris River Basin has, over the years, been plagued with problems associated with either inadequate water supplies and flooding, both of which affect the social and economic well being of the residents of the Souris River Basin. Managing for the greater range of hydrologic variability evident in proxy records versus gauged, hydrometric records can prepare water managers for adaptation to climate change. Fourteen (2 previously collected and 12 new) moisture sensitive tree-ring sites were chosen and 37 chronologies (annual, earlywood, and latewood) were developed and used to create robust multi-proxy reconstructions of annual water year (October – September) and summer (June – August) streamflow for four gauges within the Souris River Basin. Multiple linear regressions were able to account for ~54-76% and ~38-67% of the instrumental variance for water-year and summer flows, respectively, extending the historical record as far back as 1726, for a total of 280 years. Hydrological extremes were quantified and classified as abnormally wet years being in the 75th percentile, while discharge in the lowest 25th percentile were considered as drought years, with the most severe episodes indicated by flows in the lowest 10th percentile. Water year flows indicate that the most severe low flow events took place in the late 1810s, mid 1830s, 1860s, late 1890s to early 1900s, and again in the mid 1950s. Streamflow reconstructions for the Souris Basin capture the low flow events occurring during the late 1880s through the 1890s (the „Great Die-Up‟); as well as another event known as one of the most severe and long lasting reconstructed droughts from 1841 through 1865, the drought of the late 1790s through the early 1800s, and the occurrence of „El Año del Hambre‟ – the year of hunger, during the late 1780s , as well as during the 12 year period from the 1750s to early 1760s. Spectral analyses provide evidence that streamflow variability in the Souris River Basin is driven by a combination of interannual (~2-6 year), interdecadal (~7-11 year), and multidecadal (~20-30 year) ocean-atmosphere oscillations, such as indices of ENSO, solar sunspot cycles, and PDO, respectively. Correlation analyses, cross-wavelet transforms and wavelet transform coherence identify significant periods of high common power and coherence of high, interdecadal, and low frequency oscillation relationships of streamflow with ENSO, solar sunspot cycles, and PDO indices, respectively. When these sea-surface temperatures and atmospheric oscillations are coupled, and in-phase with each other, it may lead to more prolonged and possibly greater in magnitude extremes than when climate anomalies are out of phase, resulting in a relatively modest influence of streamflow variability.