This paper provides a reply to a comment from Peters (2014) on our recent effort focused on evaluating changes in streamflow input to Lake Athabasca, Canada. Lake Athabasca experienced a 21.2 % decline in streamflow input between 1960 and 2010 that has led to a marked decline in its water levels in recent decades. A reassessment of trends in naturalized Lake Athabasca water levels shows insignificant changes from our previous findings reported in Rasouli et al. (2013), and hence our previous conclusions remain unchanged. The reply closes with recommendations for future research to minimize uncertainties in historical assessments of trends in Lake Athabasca water levels and to better project its future water levels driven by climate change and anthropogenic activities in the Athabasca Lake basin.
We thank Peters (2014; hereafter P14) for his comment on our recent article focusing on streamflow input to Canada's Lake Athabasca (Rasouli et al., 2013; hereafter R13). This reply provides us with an opportunity to respond to the concerns raised in P14, to clarify the objectives of R13, to update and reaffirm our previously published results, to elaborate on their possible implications on Lake Athabasca water levels, and to propose recommendations for future work. To frame our response, we first outline briefly the two main issues of concern expressed in P14. Issue 1: P14 raises uncertainties on R13's reported trend in the (partially) naturalized levels of Lake Athabasca that omitted its hydraulic connectivity to the Peace–Athabasca Delta (PAD), a 6 % streamflow diversion from the Athabasca River towards Mamawi Lake downstream of the McMurray hydrometric gauge, a geodetic reference change in 2010 for the hydrometric station near Crackingstone Point, the filling of the Williston Reservoir on the upper Peace River from 1968 to 1971, regulation of the Peace River for hydroelectricity operation between 1972 and 1975, and the occurrence of ice-jam floods in 1974, 1996 and 1997 that obstructed the northward drainage from Lake Athabasca. Issue 2: the simple linear extrapolation of the 1960–2010 Lake Athabasca levels to 2100 provides misleading information on their potential future fate. We address these points after revisiting the principal objective and conclusions of R13.
First, we emphasize that the primary objective of R13 was to “assess the
changes in streamflow input to Lake Athabasca and to compare these results
with recent sediment core studies in the area.” This goal was achieved using
an observation-based streamflow data set for eight rivers draining into Lake
Athabasca over 1960–2010. The results of that study reveal a 7.22 km
The first main point of concern expressed in P14 is the potential impact of streamflow changes on Lake Athabasca water levels. We agree that an accurate analysis of observed trends in Lake Athabasca levels requires consideration of three factors neglected in R13: (1) hydrological interactions between the PAD and Lake Athabasca; (2) the geodetic reference change at the hydrometric gauge near Crackingstone Point in 2010; and (3) the filling of the Williston Reservoir behind the WAC Bennett Dam from 1968 to 1971. We update here the analyses presented in R13 to further naturalize the Lake Athabasca levels in consideration of these issues, but demonstrate that this leads to insignificant changes to our previously published results and conclusions. Prior to that, however, we emphasize that R13 addresses this topic as a point of discussion, rather than as a part of their results, and that it is not a primary objective of that study. As such, the lake level changes over 1960–2010 owing to streamflow input declines reported by R13 are of first order only. A comprehensive assessment of changes in the levels of Lake Athabasca clearly requires a more rigorous approach, including an analysis of vertical (e.g., precipitation, evaporation, infiltration, etc.) and horizontal (e.g., total streamflow input and output, groundwater exchanges, etc.) water fluxes to the lake in addition to anthropogenic influences (e.g., bitumen extraction). This should also include consideration of flows (i.e., 6 %) diverted from the Athabasca River towards Mamawi Lake (which would strengthen the declining trends of streamflow input to Lake Athabasca) and the hydraulic connectivity of Lake Claire, Mamawi Lake, and the remainder of the PAD with Lake Athabasca (P14). Such an analysis was clearly beyond the scope and objectives of R13's study. Nevertheless, we note that our (partially naturalized) lake level trend analysis closely matches the corresponding value obtained through streamflow input changes, providing confidence in the reliability of those initial results (consult R13).
Following P14's suggestion, and for completeness, we update and reassess our trend estimates of the 1960–2010 levels of Lake Athabasca near Crackingstone Point (station ID 07MC003) using the Mann–Kendall test (MKT; Mann, 1945; Kendall, 1975; Déry et al., 2005). Here, the lake levels are naturalized to consider the 2010 shift in the Crackingstone Point benchmark elevation and artificial modifications during the filling of the Williston Reservoir in British Columbia and regulation of the Peace River for hydropower development and generation, in addition to the obstruction of Lake Athabasca drainage northward caused by occasional ice-jam flood events in the lower Peace River and construction of weirs on the channels controlling the lake outflow (as already considered in R13). High stage on the lower Peace River can affect the levels of Lake Athabasca through hydraulic damming that can reverse the direction of lake outflows (P14). As such, the construction of the WAC Bennett Dam on the upper Peace River and the ensuing water retention behind it in the Williston Reservoir over 1968–1971 requires special attention owing to its possible impacts on Lake Athabasca levels. This is therefore considered in our updated analyses, in addition to the construction of weirs in 1975 and 1976 on the outflow channels draining Lake Athabasca and the 2010 benchmark elevation change of 0.709 m at Crackingstone Point.
P14 expresses concerns on the impacts of the chosen time periods for R13's
trend analyses that included high flows in the early 1960s. R13 selected
three common study periods each, ending in 2010, with the longest period
starting in 1960, the year after which most of the hydrometric gauges in this
system became active. These time series are selected to conduct systematic
trend analyses based largely on observed data with only limited use of
reconstructed data and to avoid the biases that might be introduced by high
or low flows at the beginning of the time series. Adding data from a few
years prior to 1960 and after 2010 changes slightly the trend magnitudes;
however, these results do not alter the conclusions of R13, as the MKT is
insensitive to outliers in the lake level time series (Wilks, 2011). For
instance, the 1958–2013 mean annual lake level near Crackingstone Point
exhibits a statistically significant decreasing trend of 0.014 m yr
Time series and linear trends of naturalized, mean annual level of
Lake Athabasca observed (Obs)
Linear trends (m yr
Next, the Lake Athabasca level data at Fort Chipewyan (station ID 07MD001)
are added for supplemental analyses of annual, seasonal, and July trends in
lake levels for comparison with the results near Crackingstone Point over
1960–2010 (Fig. 1). The two stations exhibit similar and statistically significant
(
P14 also has reservations about R13's linear extrapolation of the 1960–2010
trend in the (partially naturalized) Lake Athabasca levels to 2100 in the
context of past hydrological variability. R13's extrapolation yields a
possible decline of 2–3 m in Lake Athabasca water levels by 2100, values
within the range observed in the mid-Holocene period as inferred from a
sediment core retrieved within a pond in close proximity to the lake (Wolfe
et al., 2011). We believe that lake levels were higher during the Little Ice
Age (LIA) period when water was abundant and western Canada was developed
(Wolfe et al., 2011) as a result of the prior glacier expansion period.
However, unlike the LIA period when water was plentiful, we argue that much
drier times are ahead, and that future water availability is likely to
resemble that of the mid-Holocene period due to the following reasons:
(1) global air temperatures are expected to continue increasing
significantly, especially at northern latitudes (i.e., over 5
We concur that a detailed analysis of future climatic conditions and hydraulic controls would allow better projections of twenty-first century Lake Athabasca levels, but argue that forthcoming anthropogenic activities in the basin must also be taken into consideration. Thus, a more rigourous approach to better constrain estimates of potential future levels of Lake Athabasca is to employ global climate models (GCMs) or regional climate models (RCMs) driven by future greenhouse gas emissions scenarios. For instance, Kerkhoven and Gan (2011) apply seven GCMs forced by Special Report on Emissions Scenarios (SRES) A1FI, A2, B1, and B2 to investigate the twenty-first century sensitivity of the hydrology of two major watersheds of western Canada, the Fraser and Athabasca River basins. Across all four scenarios and seven GCMs, they find a 21.1 % decline in the mean annual flows of the Athabasca River from 2070 to 2099 with respect to the baseline period 1961–1990. Such a decline, if realized, would double the reduction in Lake Athabasca levels observed over 1960–2010 from changes in streamflow input only.
The impacts of future climate change on streamflow input to Lake Athabasca
assessed with climate models do not consider anthropogenic activities such as
water withdrawals for human consumption, irrigation, and bitumen extraction.
The hydrometric gauge on the main stem Athabasca River at McMurray remains
upstream of the major Alberta oil sands deposits and does not reflect water
withdrawals related to bitumen extraction. Pavelsky and Smith (2008) report
that current water extraction related to oil production in the Alberta oil
sands will rise and triple from 0.54 km
This reply to a comment from P14 confirms our previous findings and
conclusions on the magnitude of streamflow input declines in the Lake
Athabasca drainage with potential impacts on its level over 1960–2010. R13
reported a 7.22 km
The proliferation of recent work on the hydrology of the Lake Athabasca
drainage demonstrates the keen interest that exists in better understanding
this economically and ecologically important basin. We therefore end this
reply with the following recommendations for future research efforts:
A comprehensive water budget for Lake Athabasca with consideration of all
major freshwater fluxes over a historical period remains a priority for
future research. This could include a combination of observed and simulated
water fluxes to develop a century-scale water budget for Lake Athabasca with
impacts on its water levels. Remote sensing products could also supplement
observational and modelling data sets, either through optical data to
estimate changes in surface water area (e.g., Pavelsky and Smith, 2008) or
gravimetric data for total volumetric changes in basin-scale water storage
(e.g., Sheffield et al., 2009). The construction of the large Site C dam by BC Hydro on the Peace River near Fort
St. John, BC, was recently approved in December 2014, which may lead to
further alterations on the hydrology of the Lake Athabasca system. Future
work should therefore assess the possible hydrological impacts of the planned
Site C dam, in addition to the possible consequences imposed on this system
(e.g., recharge of the PAD). Augmenting the network of hydrometric gauges along rivers draining into
Lake Athabasca, especially on the main stem Athabasca River downstream from
the Alberta oil sands operations, is of great priority and should be implemented
immediately. This is particularly important to assess the rapidly intensifying
demands for freshwater (sourced mainly from the Athabasca River itself) used
in the extraction of bitumen from the oil sands operations in the region. To extend back in time the instrumental-era records of the Lake Athabasca
basin hydrology, additional proxy data throughout the basin should be
collected, compared, and synthesized. This could include samples of sediment
cores (e.g., Wolfe et al., 2008, 2011) and tree rings (Sauchyn et al., 2011).
This will put into perspective the historical variability in the hydrological
regime of this drainage basin and provide insights into its current state and
future fate. In addition, trend analysis of historical hydroclimatic records
can only provide near-future hydrological prospects of the Lake Athabasca
system, and thus climate models are needed for long-term projections. Projecting future inflows to Lake Athabasca with potential impacts to its
levels necessitates high-resolution output from GCMs or RCMs to drive
state-of-the-art hydrological models (e.g., the Variable Infiltration
Capacity model; Liang et al., 1994; Kang et al., 2014). These climate model
simulations require full consideration of anthropogenic influences
(i.e., land cover/use changes, flow regulation and retention, and water
extraction), climate variability (i.e., impacts of the phase change of
large-scale teleconnections such as El Niño–Southern Oscillation (ENSO)
and Pacific Decadal Oscillation (PDO) on lake inflows), in addition to a
range of climate change scenarios, to assess the potential future freshwater
supply in the Lake Athabasca drainage. These climate simulations should also
assess the diminishing contribution of glacier melt to runoff generation in
the headwaters of the Athabasca River (Marshall et al., 2011). This will lead
to improved knowledge of the potential future variability and extremes in Lake Athabasca levels, allowing
for better management of freshwater resources, policy development and
adaptation strategies in northern Canada. Exchanges of information from holders of traditional knowledge and that
derived from western science should be undertaken to obtain a broader
perspective on observed changes in the Lake Athabasca drainage. Merging these
two lines of knowledge has been shown to provide corroborating evidence on
the impacts of climate change on the environment, including water resources
(e.g., Sanderson et al., 2015). We thus encourage a continued dialogue
between First Nations communities living in and near the watersheds flowing
into Lake Athabasca and western scientists to expand our knowledge of this
important system in a period of accelerating environmental and climate
changes.
Funding provided by the government of Canada's Canada Research Chair (CRC) program and an NSERC Discovery Grant awarded to S. J. Déry. Sincere thanks also to Stewart Rood (University of Lethbridge) and David Sauchyn (University of Regina) for their constructive comments that led to an improved paper. Edited by: A. Ghadouani