Impacts of climate and catastrophic forest changes on streamflow and water balance in a mountainous headwater stream in Southern Alberta

V Mahat,A Anderson

doi:10.5194/hess-17-4941-2013

V Mahat, A Anderson

Open Access

https://doi.org/10.5194/hess-17-4941-2013

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Abstract

Abstract. Rivers in Southern Alberta are vulnerable to climate change because much of the river water originates as snow in the eastern slopes of the Rocky Mountains. Changes in likelihood of forest disturbance (wildfire, insects, logging, etc.) may also have impacts that are compounded by climate change. This study evaluates the impacts of climate and forest changes on streamflow in the upper parts of the Oldman River in Southern Alberta using a conceptual hydrological model, HBV-EC (Hydrologiska Byråns attenbalansavdelning, Environment Canada), in combination with a stochastic weather generator (LARS-WG) driven by GCM (global climate model) output climate data. Three climate change scenarios (A1B, A2 and B1) are selected to cover the range of possible future climate conditions (2020s, 2050s, and 2080s). The GCM projected less than a 10% increase in precipitation in winter and a similar amount of precipitation decrease in summer. These changes in projected precipitation resulted in up to a 200% (9.3 mm) increase in winter streamflow in February and up to a 63% (31.2 mm) decrease in summer flow in June. Flow also decreased in July and August, when irrigation is important; these reduced river flows during this season could impact agriculture production. The amplification in the streamflow is mostly driven by the projected increase in temperature that is predicted to melt winter snow earlier, resulting in lower water availability during the summer. Uncertainty analysis was completed using a guided GLUE (generalized likelihood uncertainty estimation) approach to obtain the best 100 parameter sets and associated ranges of streamflows. The impacts of uncertainty in streamflows were higher in spring and summer than in winter and fall. Forest change compounded the climate change impact by increasing the winter flow; however, it did not reduce the summer flow.

Highlights

The eastern slopes of the Rocky Mountains in Alberta, Canada, have the highest precipitation and runoff ratios
A watershed in the eastern slopes of the Southern Alberta Rocky Mountains was modeled to investigate the potential impacts of climate and forest changes on its hydrology using a simple conceptual hydrological model, HBV-EC
Climate data downscaled to 1 × 1 km grids are disaggregated to daily realizations using a stochastic weather generator, Long Ashton Research Station Weather Generator (LARS-WG)

Summary

Introduction

The eastern slopes of the Rocky Mountains in Alberta, Canada, have the highest precipitation and runoff ratios (annual streamflow as a proportion of annual precipitation). This generates the majority of streamflow for many rivers including the Oldman River, which provides water for domestic and recreational purposes and supports a broad base of regional agriculture and fishery industries in Southern Alberta (Bladon et al, 2008; Emelko et al, 2011; Silins et al, 2009; Stone et al, 2001). Hydrology of mountainous regions are most likely to be affected by climate change as precipitation would change from snow to rain in a warming climate (IPCC, 2007). Given the present near-full allocation of water for human use in this region, along with the possibility of longer-term limitations in water supply, understanding and predicting how climate and forest changes in this region are likely to affect the production/timing of streamflow are increasingly important (Silins et al, 2009)

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