04 Sep 2023
 | 04 Sep 2023
Status: this preprint is currently under review for the journal HESS.

Multi-decadal Floodplain Classification and Trend Analysis in the Upper Columbia River Valley, British Columbia

Italo Sampaio Rodrigues, Christopher Hopkinson, Laura Chasmer, Ryan MacDonald, Suzanne Bayley, and Brian Brisco

Abstract. Floodplain wetland ecosystems experience significant seasonal water fluctuation over the year, resulting in a dynamic hydroperiod, with a range of vegetation community responses. This paper assesses trends and changes in landcover and hydro-climatological variables, including air temperature, river discharge, and water level in the Upper Columbia River Wetlands (UCRW), British Columbia, Canada. A time series landcover classification from the Landsat image archive was generated using a Random Forest algorithm from 1984 to 2022. Peak river flow timing, duration, and anomalies were examined to evaluate temporal coincidence with observed landcover trends. The land cover classifier used to segment changes in wetland area and open water performed well (Kappa = 0.82). Over the last four decades, observed river discharge and air temperature have increased, precipitation has decreased, the timing of peak flow is earlier, and flow duration has been reduced. The frequency of both high discharge events and dry years have increased, indicating a shift towards more extreme floodplain flow behavior. These hydrometeorological changes are associated with a shift in the timing of snow melt from April to mid-May and are associated with seasonal changes in the vegetative communities over the 39-year period. The area of woody shrub landcover has increased in the spring (April to mid-May), peak flow period (late-May to July) and early fall (August to mid-September) by +6 % to +12 % since 1984. In the spring and early fall, the area of open water has decreased –3 % to –6 % since 1984, while it has increased 3 % during the peak flow period. The area of marsh land cover (mostly bulrush and cattails) has declined in every season by –29 % in spring, –19 % in the peak flow period and –5 % in early fall. These findings suggest that increasing temperatures have already impacted regional hydrology, wetland hydroperiod and floodplain landcover in the Upper Columbia Valley in Canada. Overall, there is substantial variation in seasonal and annual land cover reflecting the dynamic nature of floodplain wetlands, but the results show that the wetlands are drying out with increasing the areas of woody/shrubby habitat and loss of aquatic habitat. The results suggest that floodplain wetlands, particularly marsh and open water habitats are vulnerable to climatic and hydrological changes that could further reduce their areal extent in the future.

Italo Sampaio Rodrigues et al.

Status: open (until 30 Oct 2023)

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Italo Sampaio Rodrigues et al.

Italo Sampaio Rodrigues et al.


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Short summary
The research evaluated the trends and changes in land cover and river discharge in the Upper Columbia River Wetlands using remote sensing and hydroclimatic data. The river discharge increased during the peak flow season, resulting in a positive trend in the open water extent in the same period, while on an annual basis open water area is declining. Furthermore, since 2003 the peak flow has occurred eleven days earlier than 1903–1928, which has led to larger discharges in a shorter time.