WET Hydrology & Hydrogeology

Surface water is critical for meeting water needs in British Columbia’s Okanagan Basin, but the timing and magnitude of its availability is being altered through climate and land use changes and growing water demand. WEAP, an integrated water management model, was used to consider future scenarios for water supply and demand in an unregulated and a reservoir-supported stream that supply the District of Peachland. Potential changes to the magnitude and timing of streamflow were evaluated in response to the following scenarios: (i) climate change (derived from the HadCM3 and CGCM2 GCMs for the 2020s and 2050s), (ii) a simulated prolonged drought, (iii) land cover change resulting from a Mountain Pine Beetle (MPB) outbreak, and (iv) combinations of these conditions. These changes, in combination with likely demand increases and reservoir operating rules were evaluated in terms of stress on water availability for human use and aquatic life. Results demonstrate that anticipated future climate conditions will critically reduce streamflow relative to demand (societal and ecological) in at least a few months of “normal” and “dry” years. On the unregulated creek, an earlier recession of peak spring snowmelt, accompanied by higher demands at the beginning of the summer outdoor watering season as early as the 2020s, reduced the ability to meet downstream needs. On the regulated stream, two “very dry” years under a climate change scenario resulted in deficits for municipal water users under a higher reservoir release scenario. In all scenarios, even with the higher flows expected under the MPB scenario, some combinations of demand, reservoir operations and climate variability resulted in less than optimal conditions for instream ecological flow needs. Beyond the implications for the District of Peachland, this work demonstrates a method of using an accessible modeling tool for integrating knowledge from the fields of climate science, forest hydrology, water systems management and stream ecology to aid in water and land management decision-making.

Representation of the impacts of irrigation in agricultural systems is often simplified in life cycle assessment (LCA) to consider only water and energy consumption. This research aimed to understand the importance of irrigation as a contributor to a more comprehensive suite of environmental outcomes of Okanagan cherry orchard production and to elucidate whether employing more efficient irrigation technologies on orchards propagated relevant reductions to environmental impacts. However, how human consumption of freshwater use impacts terrestrial ecosystems is not well understood in life cycle impact assessment and presents a challenge for accurately modelling these pathways. A regionalized life cycle inventory of Okanagan water delivery systems was developed and an LCA was performed to determine the share and distribution of environmental burdens associated with irrigation water, inclusive of processes within the water supply network. To improve our capacity to understand of the impacts of human consumption of freshwater use, a methodological framework was also developed using a literature analysis to model the impacts of freshwater use on terrestrial dryland and semi-arid ecosystems, as applicable to the semi-arid Okanagan. Irrigation contributed a significant portion to most life cycle environmental impacts of cherry production. The highest impact contributions from irrigation were found in the categories water scarcity, human toxicity, freshwater ecotoxicity, and mineral resource use. Employment of more efficient irrigation technologies than the most common irrigation system used on cherry orchards decreased impacts to these categories by 10-16%. Increased carbon dioxide emissions from bicarbonate deposited in orchard soils from irrigation did not make substantial relative impacts to the overall emissions of Okanagan cherry production. When the increased nitrous oxide emissions associated with drip irrigation were considered in the model of cherry orchard production, drip irrigation still outperformed microsprinkler in every impact category except climate change, where higher impacts due to nitrous oxide emissions from drip irrigation were counteracted by the decreased efficiency of microsprinkler systems. Biotic mechanisms for inclusion in the development of a mechanistic impact pathway linking freshwater use to consequent impacts to semi-arid biomes through the use of the “water- web” concept were identified. Mechanistic factors along this impact pathway included invertebrate primary and secondary consumers and phreatophytic plants that propagate water through the biome.