Long-term variations of river ice breakup timing across Canada and its response to climate change

https://doi.org/10.1016/j.coldregions.2020.103091Get rights and content

Highlights

  • An overall earlier river ice breakup trend was observed across Canada.

  • The earlier breakup trend is not as strong as expected under climate change.

  • Spring warming trend was found to be not as pronounced as winter warming.

  • River ice breakup in lower latitude regions are more sensitive to climatic warming.

  • Rainfall and flow regulation can both advance and delay river ice breakup.

Abstract

River ice breakup has extensive implications on cold-region hydrological, ecological and river morphological systems. However, spatial and temporal breakup patterns under the changing climate are not well explored on large scale. This study discusses the spatial-temporal variations of breakup timing over terrestrial ecozones and five selected river basins of Canada based on long-term (1950–2016) data record. The link between the discovered patterns and climatic drivers (including air temperature, snowfall and rainfall), as well as elevation and anthropogenic activities are analyzed. An overall earlier breakup trend is observed across Canada and the spring air temperature is found to be the main driver behind it. However, the most pronounced warming trends across Canada is observed in winter. Spring warming trend is not as strong as winter warming and even becomes weak as period changes from 1950–2016 to 1970–2016, resulting in more stations showing later and significant later breakup during 1970–2016. Breakup pattern also displays evident spatial differences. Significant earlier breakup trends are mainly seen in western Canada (e.g. the Nelson River basin) and Arctic where spring warming trends are evident. Later and mixed breakup trends are generally identified in regions with weak warming or even cooling trends, such as Atlantic Canada and the St. Lawrence River basin. Spring snowfall generally delays breakup. Spring rainfall usually advances breakup dates while winter-rainfall can also delay breakup through refreezing. The increased snowfall in the north and increased rainfall in the south may be the reason why breakup timing is more sensitive to climatic warming in lower latitude regions than in higher latitude regions. Additionally, breakup timing in main streams and large rivers appears to be less sensitive to the warming trend than the headwaters and small tributaries. Elevation and flow regulation are also found to be contributing factors to the changes in breakup timing.

Introduction

The cryosphere is very sensitive to climate variability and can provide some of the most visible signatures of climate change (IPCC, 2013). River ice is one of the main components of the cryosphere, and thus its long-term records can serve as good indicators of climate change and variability in northern regions (Magnuson et al., 2000; Prowse et al., 2011, Prowse et al., 2007). In Canada, ice is present in nearly every river for some period of the year and is an important aspect of winter hydrology. River ice breakup in particular, can greatly affect water quantity and quality of the river system, and can be both harmful and beneficial to human (Beltaos and Prowse, 2009; Hicks, 2009; Prowse et al., 2011; Weyhenmeyer et al., 2011).

Many previous studies have shown that breakup in Canadian rivers had generally become earlier. For example, Jasek and Shen (1999) discovered that breakup of the Yukon River had advanced by approximately 5 days per century from 1896 to 1998. Beltaos (2002) found that the date of breakup of the Saint John River had become 11 days earlier per century for the period of 1927–1997 and the trend had become more noticeable since late 1950s. Earlier breakup was also found in several local regions of Canada, such as southern British Columbia rivers (Doyle and Ball, 2008), the Mackenzie River basin (de Rham et al., 2008; Goulding et al., 2009), northwest rivers (Janowicz, 2010) and south-central Ontario waterbodies (Fu and Yao, 2015). Although historical trends of rive ice breakup at a variety of spatial and temporal scales have been investigated, large-scale spatial and temporal analyses across Canada remain sparse. By far the most comprehensive such studies were conducted by Zhang et al. (2001) and Lacroix et al. (2005) using ice data from approximately the second half of the 20th century, and both studies reported an overall trend towards earlier breakup.

Numerous studies examined the factors that may have contributed to the changes in the breakup timing. Air temperature during certain winter/spring months is probably the most significant influencing factor of river ice breakup events (Fu and Yao, 2015; Ghanbari et al., 2009; Obyazov and Smakhtin, 2014). However, river ice breakup is not controlled by a simple heat index (e.g., air temperature), other factors such as snowfall and rainfall may also be contributing factors (Beltaos and Prowse, 2009). Snow can impede heat flux into the ice cover and increase the albedo of the ice surface, and thus increased snowfall tends to delay spring breakup (Jensen et al., 2007; Vavrus et al., 1996). Rainfall during ice season may have a negative feedback on breakup timing as the heat released from rain can rapidly melt the ice (Nõges and Nõges, 2014). However, Ariano and Brown (2019) found that mid-winter rain can refreeze to form white ice, leading to increased ice thickness and delayed breakup. In addition, cloud cover and elevation can indirectly affect breakup by altering the solar radiation and air temperature (Jakkila et al., 2009; Jensen et al., 2007; Lopez et al., 2019), but these studies focused on lake ice breakup.

Most previous studies that analyzed breakup trends were based on individual river or rivers in small-scale regions. The two large-scale spatial analyses across Canada (Zhang et al., 2001; Lacroix et al., 2005) analyzed periods before 2000s. Therefore, it is of great necessity to investigate large-scale spatial and temporal patterns of river ice breakup in response to climate change, using long and uniform river ice data. This study focuses on trends and changes in breakup timing for major Canadian rivers over the period of 1950–2016. Periods of 1960–2016 and 1970–2016 are also analyzed to explore how the discovered trends may change with the period of analysis. General trends and changes, as well as spatial and temporal patterns over terrestrial ecozones and selected river basins are discussed. Studies have shown that Canada warms faster than the rest of the world and precipitation is projected to increase in most of Canada (Bush and Lemmen, 2019). Those observed trends in breakup are thus connected to the trends in climatic variables including air temperature, snowfall and rainfall since these factors are the primary drivers of the variability and change in the cryosphere. The potential effects of elevation and flow regulation on breakup timing are also evaluated as these factors further complicate how river ice breakup responds to changes in climatic. Additionally, the impact of missing values in the dataset is discussed.

Section snippets

Data

The dataset of breakup dates used in this study is extracted from the Water Survey of Canada (WSC) HYDAT database. The ‘B’ symbol in the discharge record denotes when the gauge station is affected by ice; thus the last ‘B’ can be considered an indication of breakup. To ensure data quality, breakup dates extracted from HYDAT database were examined by cross-checking with other sources including the National Snow and Ice Data Center (NSIDC) and Alberta Environment and Parks river ice reports (Chen

General trends

Fig. 2 shows the results from the trend analysis of the breakup date datasets. It can be seen that the majority of stations show trend towards earlier breakup (including both significant earlier and non-significant earlier) in all three analyzed periods. During 1950–2016, about 70% or more of the stations show earlier breakup. This is in agreement with previously studies (Lacroix et al., 2005; Vincent et al., 2015) that reported earlier breakup trends at the vast majority of locations across

Influencing factors of river ice breakup

This section assesses the influencing factors on the observed trends in breakup dates. Five parameters, air temperature, snowfall, rainfall, elevation, and flow regulation, were selected based on the literature review. Other factors, such as large-scale atmospheric and oceanic circulation patterns (e.g. NAO, PNA and ENSO), may also contribute to the change of river ice breakup (Bonsal et al., 2006; Schmidt et al., 2019) but are not discussed here.

Conclusion

This study explored large-scale spatial and temporal variations of river ice breakup timing across Canada with more comprehensive and longer dataset. An overall earlier breakup trend was found across Canada, especially for the Pacific and Western Mountains, Central Plains and Arctic. Mixed trends were identified in the Atlantic and Great Lakes – St. Lawrence region while later breakup trends were observed in Boreal Shield and Taiga Shield. Breakup date was found to be mainly correlated with

Declaration of Competing Interest

The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.

Acknowledgement

This research is supported by the Natural Sciences and Engineering Research Council of Canada Discovery Grant. This support is gratefully acknowledged.

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