the Creative Commons Attribution 4.0 License.
the Creative Commons Attribution 4.0 License.
Multi-decadal Floodplain Classification and Trend Analysis in the Upper Columbia River Valley, British Columbia
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.
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RC1: 'Comment on hess-2023-211', Anonymous Referee #1, 07 Dec 2023
This work is focused on changes in floodplain wetlands and hydro-climatological variables over a relatively small area (188 km2) in the Upper Columbia River Valley, over the period 1984-2022. The analysis mainly relies on the temporal and spatial variability of land cover observation, and the main results show a reduction of wetlands areas with increasing in shrub and woody areas over the last 40 years.
I found the paper well written and well organized. I think it could be a significant scientific contribution for understanding the hydrological changes of this area. Furthermore, I appreciate the analysis on a seasonal scale, which provides detailed information about changes over different periods.
However, I think that it is very dense of information, and, personally, I mostly struggled in following the key message and results. Please consider abbreviating or shortening some part of the text, in order to provide a clear scientific message. For instance, I would condense lines 22-28 in one sentence, providing only the key message.
Introduction
I would include at the end of the Introduction Section a brief description of the sections of the paper. In this way it would be easier for the reader to follow the work.
Section 2.7
Why do you analyze the peak flow separately from the base flow? And then, why do you look at the hydrograph (Fig. 11) without considering the base-flow contribution?
Section 3.2
(line 267) Here, you assume that the reduction in precipitation, as observed locally at the gauge station, is a possible cause of the decrease in open water. I believe that the hydrological processes of the area can be significantly influenced by the upstream area (6,660 km2), and local rainfall measurements may not represent significant drivers of these changes. Therefore, I would suggest relating these changes solely to discharge observations, which involve all the processes of the upstream area. What do you think about it?
Same point at lines 408-409.
Section 3.3
(line 345) What I see in Figure 10 is not that ‘higher peaks appeared more frequently’. Indeed, as you said at lines 407-408, the highest peaks was observed during 1903-1978. I would rephrase sentence at line 345.
Section 4.3
I appreciate Figure 12, which provides clearly the seasonal variability of the main hydrological processes. I would include in that figure the percentages of increasing/decreasing of the mentioned variables.
Overall, I suggest a minor revision of this work. I hope authors will find these comments useful for their research.
Typos
(line 17) ‘land cover trends’ instead of ‘landcover trends’
(Line 236) ‘it was used’ instead of ‘was used’ (am I right?)
Citation: https://doi.org/10.5194/hess-2023-211-RC1 - AC1: 'Reply on RC1', Italo Rodrigues, 22 Dec 2023
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RC2: 'Comment on hess-2023-211', Anonymous Referee #2, 14 Dec 2023
The authors present a detailed analysis of the evolving landscape of the Upper Columbia River Wetlands (UCRW) in British Columbia, Canada. Through the application of a Random Forest algorithm to Landsat image archives from 1984 to 2022, this paper methodically examines the impact of changing hydro-climatological variables, including air temperature, river discharge, and water levels, on the wetland's landcover. The study's findings are significant, revealing pronounced changes in regional hydrology and vegetation communities, primarily attributed to climate change. This research provides critical insights into the consequences of climate change on wetland ecosystems and underscores the importance of implementing effective management strategies for their preservation. The study concludes by highlighting the increased vulnerability of these wetland habitats to future climatic and hydrological shifts, which may further diminish their extent.
The authors have applied appropriate methods and their approach is grounded in a comprehensive and well-documented review of the relevant literature. The explanation of the methods is detailed and clear. The figures are clear and well-produced. The manuscript is well-written with very minor typos that I was able to catch e.g., whether in line 431.
A lot of important information is included in the supplemental materials regarding the RF model evaluation. If possible including more information about the performance of the model and the effect of the different sample sizes on the performance would be great instead of needing to review the supplemental materials.
If the authors can document and release their GEE notebook and data that would be greatly appreciated.
Citation: https://doi.org/10.5194/hess-2023-211-RC2 - AC2: 'Reply on RC2', Italo Rodrigues, 22 Dec 2023
Status: closed
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RC1: 'Comment on hess-2023-211', Anonymous Referee #1, 07 Dec 2023
This work is focused on changes in floodplain wetlands and hydro-climatological variables over a relatively small area (188 km2) in the Upper Columbia River Valley, over the period 1984-2022. The analysis mainly relies on the temporal and spatial variability of land cover observation, and the main results show a reduction of wetlands areas with increasing in shrub and woody areas over the last 40 years.
I found the paper well written and well organized. I think it could be a significant scientific contribution for understanding the hydrological changes of this area. Furthermore, I appreciate the analysis on a seasonal scale, which provides detailed information about changes over different periods.
However, I think that it is very dense of information, and, personally, I mostly struggled in following the key message and results. Please consider abbreviating or shortening some part of the text, in order to provide a clear scientific message. For instance, I would condense lines 22-28 in one sentence, providing only the key message.
Introduction
I would include at the end of the Introduction Section a brief description of the sections of the paper. In this way it would be easier for the reader to follow the work.
Section 2.7
Why do you analyze the peak flow separately from the base flow? And then, why do you look at the hydrograph (Fig. 11) without considering the base-flow contribution?
Section 3.2
(line 267) Here, you assume that the reduction in precipitation, as observed locally at the gauge station, is a possible cause of the decrease in open water. I believe that the hydrological processes of the area can be significantly influenced by the upstream area (6,660 km2), and local rainfall measurements may not represent significant drivers of these changes. Therefore, I would suggest relating these changes solely to discharge observations, which involve all the processes of the upstream area. What do you think about it?
Same point at lines 408-409.
Section 3.3
(line 345) What I see in Figure 10 is not that ‘higher peaks appeared more frequently’. Indeed, as you said at lines 407-408, the highest peaks was observed during 1903-1978. I would rephrase sentence at line 345.
Section 4.3
I appreciate Figure 12, which provides clearly the seasonal variability of the main hydrological processes. I would include in that figure the percentages of increasing/decreasing of the mentioned variables.
Overall, I suggest a minor revision of this work. I hope authors will find these comments useful for their research.
Typos
(line 17) ‘land cover trends’ instead of ‘landcover trends’
(Line 236) ‘it was used’ instead of ‘was used’ (am I right?)
Citation: https://doi.org/10.5194/hess-2023-211-RC1 - AC1: 'Reply on RC1', Italo Rodrigues, 22 Dec 2023
-
RC2: 'Comment on hess-2023-211', Anonymous Referee #2, 14 Dec 2023
The authors present a detailed analysis of the evolving landscape of the Upper Columbia River Wetlands (UCRW) in British Columbia, Canada. Through the application of a Random Forest algorithm to Landsat image archives from 1984 to 2022, this paper methodically examines the impact of changing hydro-climatological variables, including air temperature, river discharge, and water levels, on the wetland's landcover. The study's findings are significant, revealing pronounced changes in regional hydrology and vegetation communities, primarily attributed to climate change. This research provides critical insights into the consequences of climate change on wetland ecosystems and underscores the importance of implementing effective management strategies for their preservation. The study concludes by highlighting the increased vulnerability of these wetland habitats to future climatic and hydrological shifts, which may further diminish their extent.
The authors have applied appropriate methods and their approach is grounded in a comprehensive and well-documented review of the relevant literature. The explanation of the methods is detailed and clear. The figures are clear and well-produced. The manuscript is well-written with very minor typos that I was able to catch e.g., whether in line 431.
A lot of important information is included in the supplemental materials regarding the RF model evaluation. If possible including more information about the performance of the model and the effect of the different sample sizes on the performance would be great instead of needing to review the supplemental materials.
If the authors can document and release their GEE notebook and data that would be greatly appreciated.
Citation: https://doi.org/10.5194/hess-2023-211-RC2 - AC2: 'Reply on RC2', Italo Rodrigues, 22 Dec 2023
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