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

Abstract

Recent summer water shortages in Metro Vancouver are the result of unanticipated changes in the timing of regional snowmelt and rising summer temperatures. Continuing shortfalls over the next century would pose a significant challenge for water supply management decisions. To understand the magnitude of recent drought events in the context of those that happened in the past, we developed a tree-ring reconstruction of regionalised July–August streamflow to 1711 for Metro Vancouver’s Capilano and Seymour watersheds. We used the annual tree-ring widths of mountain hemlock (Tsuga mertensiana (Bong.) Carr.) and Pacific silver fir (Abies amabilis Douglas ex J. Forbes) trees exhibiting a relationship to the seasonal snowpack as proxies for the nival component of streamflow in a regression model. The model indicates that more multi-year, below-average, streamflow departures occurred during the instrumental record than over the 1711–1992 reconstruction period. The El Niño-Southern Oscillation was significantly (p < 0.05) associated with both reconstructed and measured streamflow for the study region. Similarly, seasonal Pacific Decadal Oscillation demonstrated strong statistical relationships (p < 0.05) with measured streamflow. Over the duration of the reconstruction, significant decadal and multi-decadal periodicities were also observed. The research places the Metro Vancouver water supply in a longer-term context than was previously possible and offers a basis for advancing water supply planning decisions in the context of a rapidly changing climate.