Impacts of future climate on the hydrology of a northern headwaters basin and its implications for a downstream deltaic ecosystem

Abstract

Anthropogenic and climatic‐induced changes to flow regimes pose significant risks to river systems. Northern rivers and their deltas are particularly vulnerable due to the disproportionate warming of the Northern Hemisphere compared with the Southern Hemisphere. Of special interest is the Peace–Athabasca Delta (PAD) in western Canada, a productive deltaic lake and wetland ecosystem, which has been recognized as a Ramsar site. Both climate‐ and regulation‐induced changes to the hydrological regime of the Peace River have raised concerns over the delta's ecological health. With the damming of the headwaters, the role of downstream unregulated tributaries has become more important in maintaining, to a certain degree, a natural flow regime, particularly during open‐water conditions. However, their flow contributions to the mainstem river under future climatic conditions remain largely uncertain. In this study, we first evaluated the ability of a land‐surface hydrological model to simulate hydro‐ecological relevant indicators, highlighting the model's strengths and weaknesses. Then, we investigated the streamflow conditions in the Smoky River, the largest unregulated tributary of the Peace River, in the 2071–2100 versus the 1981–2010 periods. Our modelling results revealed significant changes in the hydrological regime of the Smoky River, such as increased discharge in winter (+190%) and spring (+130%) but reduced summer flows (−33%) in the 2071–2100 period compared with the baseline period, which will have implications for the sustainability of the downstream PAD. In particular, the projected reductions in 30‐day and 90‐day maximum flows in the Smoky River will affect open‐water flooding, which is important in maintaining lake levels and connectivity to perimeter delta wetlands in the Peace sector of the PAD. The evaluation of breakup and freeze‐up flows for the 2071–2100 period showed mixed implications for the ice‐jam flooding, which is essential for recharging high‐elevation deltaic basins. Thus, despite projected increase in annual and spring runoff in the 2071–2100 period from the Smoky sub‐basin, the sustainability of the PAD still remains uncertain.

Western Canadian freshwater availability: current and future vulnerabilities

“…Furthermore, higher river freeze-up ice levels in combination with generally declining spring snowpack have contributed to reduced frequency of ice-jam flooding in the PAD (Beltaos et al 2006a). This reduction is projected to continue (Beltaos et al 2006b;Rokaya et al 2019) and peak flow magnitudes to increase under a warmer climate (Eum et al 2017;Dibike et al 2019;Rokaya et al 2020).…”

Advances in modelling large river basins in cold regions with Modélisation Environmentale Communautaire—Surface and Hydrology (MESH), the Canadian hydrological land surface scheme

“…Modelling the MRB has proven to be demanding, not least because the large computational requirements and the complexities around permafrost simulation, and only preliminary simulations of future change are currently available for the basin. However, Rokaya et al (2020a, 2020b) assessed the impacts of climate change on the Smoky River, a major sub‐basin of the Peace tributary of the MRB, using a bias‐corrected 15‐member ensemble from the Canadian Regional Climate Model version 4 (CanRCM4) (Asong et al, 2020). The results indicate significant changes to the flow regime with increased winter and spring flows and lower summer flows for the end of the 21st century compared to the baseline period (1981–2010), with earlier peaks for open water flooding (see fig.…”

“…The river basin model (RBM), a semi‐Lagrangian, one dimensional, process‐based stream water temperature model (Yearsley, 2012) has been combined with MESH. MESH‐RBM can be used to simulate and forecast ice‐cover durations (Morales‐Marín et al, 2019b), and has also been applied in operational forecasting of river ice breakup (Rokaya et al, 2020a; Rokaya et al, 2020b). The model provides a practical tool for ice‐jam flood forecasting and warning, and simulates breakup progression for the entire catchment, providing an advantage over existing site‐specific prediction methods.…”

A stochastic modelling approach to forecast real-time ice jam flood severity along the transborder (New Brunswick/Maine) Saint John River of North America

“…MESH is a physically-based hydrological land-surface model from Environment and Climate Change Canada (ECCC) (Pietroniro et al, 2007) and has been widely used in different parts of Canada, from small to large catchments (Mengistu & Spence, 2016;Haghnegahdar et al, 2017;Yassin et al, 2017;Lindenschmidt et al, 2019;Budhathoki et al, 2020;Rokaya et al, 2020). MESH uses a grouped response unit (GRU) approach to capture basin heterogeneity.…”