Climate change and hydrology at the prairie margin: Historic and prospective future flows of Canada's Red Deer and other Rocky Mountain rivers

Abstract

The South Saskatchewan River Basin of southern Alberta drains the transboundary central Rocky Mountains region and provides the focus for irrigation agriculture in Canada. Following extensive development, two tributaries, the Oldman and Bow rivers, were closed for further water allocations, whereas the Red Deer River (RDR) remains open. The RDR basin is at the northern limit of the North American Great Plains and may be suitable for agricultural expansion with a warming climate. To consider irrigation development and ecological impacts, it is important to understand the regional hydrologic consequences of climate change. To analyse historic trends that could extend into the future, we developed century‐long discharge records for the RDR, by coordinating data across hydrometric gauges, estimating annual flows from seasonal records, and undertaking flow naturalization to compensate for river regulation. Analyses indicated some coordination with the Pacific decadal oscillation and slight decline in summer and annual flows from 1912 to 2016 (−0.13%/year, Sen's slope). Another forecasting approach involved regional downscaling from the global circulation models, CGCMI‐A, ECHAM4, HadCM3, and NCAR‐CCM3. These projected slight flow decreases from the mountain headwaters versus increases from the foothills and boreal regions, resulting in a slight increase in overall river flows (+0.1%/year). Prior projections from these and other global circulation models ranged from slight decrease to slight increase, and the average projection of −0.05%/year approached the empirical trend. Assessments of other rivers draining the central and northern Rocky Mountains revealed a geographic transition in flow patterns over the past century. Flows from the rivers in Southern Alberta declined (around −0.15%/year), in contrast to increasing flows in north‐eastern British Columbia and the Yukon. The RDR watershed approaches this transition, and this study thus revealed regional differentiation in the hydrological consequences from climate change.

Floodplain forest dynamics: Half‐century floods enable pulses of geomorphic disturbance and cottonwood colonization along a prairie river

“…Flows of the RDR were highly variable across years (Figure 3a),with clusters of high or low flow years, partially coordinated with the Pacific Decadal Oscillation (Philipsen, Gill, et al, 2018). Our study explored river and riparian patterns in eight intervals between the aerial photographs, preceded by a high flow period before 1935 (Figure 3).…”

“…The record suggests a decline in Q through the past century (correlation between Q and year: Pearson r : −0.205, p = .035; but Kendall τ: −0.077 m, p = .244). The trend analysis was influenced by the early, high flow of 1915, and no trend was apparent through the latter part of the twentieth century, when anthropogenic climate change could have been more substantial (Philipsen, Gill, et al, 2018).…”

“…Flows of the RDR through Dinosaur Provincial Park are largely snowmelt and rainfall run-off from upstream regions in the Rocky Mountains and foothills (Philipsen, Gill, et al, 2018). Only about 400 mm of precipitation falls annually in Dinosaur Provincial Park, primarily as rain in late spring and summer, including summer storms that can be intense but localized (Bryan & Campbell, 1980).…”

“…Only about 400 mm of precipitation falls annually in Dinosaur Provincial Park, primarily as rain in late spring and summer, including summer storms that can be intense but localized (Bryan & Campbell, 1980). Flows of the RDR were highly variable across years (Figure 3a), with clusters of high or low flow years, partially coordinated with the Pacific Decadal Oscillation (Philipsen, Gill, et al, 2018). Our study explored river and riparian patterns in eight intervals between the (Philipsen, Gill, et al, 2018).…”

“…This study was undertaken to explore the associations between river floods, fluvial geomorphic disturbance, and floodplain forest patterns along a relatively natural dryland river system. We sought to analyse the longer‐term river and floodplain forest chronology, building upon prior analyses of the historical climate, hydrology and floodplain ecology of the Red Deer River (RDR; Marken, 1993; Cordes, Hughes, & Getty, 1997; Philipsen, Gill, Shepherd, & Rood, 2018; Philipsen, Pearce, & Rood, 2018). At the study onset we expected positive correspondences between floods, geomorphic disturbance and cottonwood colonization, and expected this to reveal the longer‐term chronology for floodplain dynamics along a dryland river (Cordes et al, 1997; Philipsen, Pearce, & Rood, 2018; Schook et al, 2017).…”