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Climate change vulnerability and risk
Published in Jonathan Lautze, Zebediah Phiri, Vladimir Smakhtin, Davison Saruchera, The Zambezi River Basin, 2017
Richard D. Beilfuss, Charles Nhemachena
The importance of environmental flows for restoring the Lower Zambezi Basin below Cahora Bassa Dam was first proposed to the Government of Mozambique by consultants SWECO/SWED POWER (1983). They recommended an environmental flow release (freshet) from Cahora Bassa to coincide with high flows from downstream tributaries, aimed at reducing the impact of soil salinisation on natural vegetation, improving agricultural productivity and the carrying capacity of grasslands, expanding floodplain waterbodies and reducing the growth of invasive aquatic macrophytes in river channels. In 1997, under the auspices of the Zambezi Valley Planning Authority, the operators of Cahora Bassa Dam hosted a Workshop on the Sustainable Management of Cahora Bassa Dam and the Zambezi Valley (Beilfuss 1997). More than 50 participants from government agencies, academic institutions and development NGOs concluded that environmental flow releases from Cahora Bassa Dam were necessary to restore human livelihoods and ecosystems downstream (Davies 1998).
The state of isotope hydrology research in Canada (2007–2022)
Published in Canadian Water Resources Journal / Revue canadienne des ressources hydriques, 2023
Tricia A. Stadnyk, J.J. Gibson, J. Birks, T. L. Holmes
Characterizing the isotopic composition of winter precipitation and snowmelt is also a significant challenge globally (e.g. Koehler 2019). From 2010–2014, Canadian researchers participated in a coordinated effort to examine best practices for snow and snowmelt sample collection in cold regions (Penna et al. 2014). A high latitude Canadian study site was implemented at the University of Manitoba to test various sampling strategies and provide recommendations for effective sample collection techniques across the Prairies. Unlike the European sites where the passive capillary samplers were highly effective (in part due to aging of the snowpack), the flat Prairie sites have a tendency to flood during the spring freshet due to frozen soils and a lack of drainage, contaminating the capillary samplers with soil water and highly enriched melt water. Similarly, the Canadian site snow cores are found to be reasonably representative of snow pack isotopic composition due to less again and better preservation of isotopes in precipitation signals.
Climate change impacts on snow and streamflow drought regimes in four ecoregions of British Columbia
Published in Canadian Water Resources Journal / Revue canadienne des ressources hydriques, 2021
Jennifer R. Dierauer, D. M. Allen, P. H. Whitfield
Annual runoff is projected to increase for all four catchments (Figure 3). Relative (%) increases in runoff are largest for the coldest, driest catchment (Fort Nelson), while absolute (mm/year) increases in runoff are largest for the warmest, wettest catchment (Capilano; Figure 3 and Appendix). In addition to increases in annual runoff, the within-year distribution of runoff changes substantially. The spring freshet starts earlier for all catchments and decreases in magnitude for all but Fort Nelson (Figure 4), which is the northernmost and coldest catchment. In the warmest catchment (Capilano), the spring freshet disappears completely for both future time periods under both RCPs. In all catchments, the slope of the spring freshet rising limb decreases, indicating a longer spring melt season with slower snowmelt (Figure 4). These changes (declined spring freshet peak and a longer melt season) are consistent with the findings of previous observation-based studies (Hamlet and Lettenmaier 2007; Rood et al. 2008).
A multi-century July-August streamflow reconstruction of Metro Vancouver's water supply contribution from the Capilano and Seymour watersheds in southwestern British Columbia, Canada
Published in Canadian Water Resources Journal / Revue canadienne des ressources hydriques, 2021
The high relief and mixed (rain and snow) precipitation regime characterising the watersheds results in high monthly streamflow totals in November to January from rainfall and in April to June from snowmelt, with summer streamflow declining until October (Figure 2A and C). The instrumental record shows that the timing and magnitude of the annual freshet displays considerable year-to-year variability (Moore et al. 2010). Following the spring freshet, a significant proportion of the summer baseflow is associated with the emergence of shallow groundwater sourced to melting snow. Snow-derived summer streamflow is typically lowest in July and August (Figure 2B and C) when it averages 7.5 m3s−1 for the Capilano and Seymour watersheds, with a relatively high variance (16.0 m3s−1) over the length of the common period (1958–2017) (Figure 2B). Over the instrumental period, minimum July–August streamflow occurred in 1944 (2.1 m3s−1) and the maximum recorded streamflow occurred in 1974 (19.7 m3s−1) (Figure 2D). A generally positive trend is observed in the streamflow record until the 1976/77, after which there was a notable shift in the discharge regime (Figure 2D). Comparable shifts are observed in other regional streamflow records and are believed associated with climate oscillations generated from the Pacific Ocean (Rodenhuis et al. 2009). These hydroclimatic conditions indicate that summer streamflow droughts in all three watersheds is directly associated with shallow spring snow and early spring freshets (Moore et al. 2010).