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Assessing hydrological sensitivity of grassland basins in the Canadian Prairies to climate using a basin classification–based virtual modelling approach

18 May 2021-Hydrology and Earth System Sciences Discussions (Copernicus GmbH)-pp 1-39

Abstract: . Significant challenges from changes in climate and land-use face sustainable water use in the Canadian Prairies ecozone. The region has experienced significant warming since the mid 20th Century, and continued warming of an additional 2 °C by 2050 is expected. This paper aims to enhance understanding of climate controls on Prairie basin hydrology through numerical model experiments. It approaches this by developing a basin classification–based virtual modeling framework for a portion of the Prairie region, and applying the modelling framework to investigate the hydrological sensitivity of one Prairie basin class (High Elevation Grasslands) to changes in climate. High Elevation Grasslands dominate much of central and southern Alberta and parts of southwestern Saskatchewan with outliers in eastern Saskatchewan and western Manitoba. The experiments revealed that High Elevation Grasslands snowpacks are highly sensitive to changes in climate, but that this varies geographically. Spring maximum snow water equivalent in grasslands decreases 8% per degree °C of warming. Climate scenario simulations indicated a 2 °C increase in temperature requires at least an increase of 20% in mean annual precipitation for there to be enough additional snowfall to compensate for enhanced melt losses. The sensitivity in runoff is less linear and varies substantially across the study domain; simulations using 6 °C of warming and a 30% increase in mean annual precipitation yields simulated decreases in annual runoff of 40% in climates of the western Prairie but 55% increases in climates of eastern portions. These results can be used to identify those areas of the region that are most sensitive to climate change, and highlight focus areas for monitoring and adaptation. The results also demonstrate how a basin classification–based virtual modeling framework can be applied to evaluate regional scale impacts of climate change with relatively high spatial resolution, in a robust, effective and efficient manner.
Topics: Climate change (56%), Grassland (52%), Precipitation (52%)

Summary (2 min read)

Introduction

  • Hydrological models are essential tools to understand hydrological processes and function at the basin scale, and can also be used to diagnose how specific hydrological processes control catchment responses to change (Rasouli et al., 2014).
  • Modelling a specific basin to evaluate 45 processes or to simulate the effects of change entails large computational and labour costs and requires observations of the basin response with sufficient spatial and temporal coverage.
  • Prairie precipitation trends indicate more rain and less snow in the spring and fall (Shook and Pomeroy, 2012) and runoff generation has been shown to be shifting from snowmelt- to rainfall-driven in eastern Saskatchewan (Dumanski et al., 2015).
  • Recent analysis of hydrometric stations across the 80 region identified sub-regional trends in streamflow associated with drying in the west and south and wetting in the east and north, associated with physical landscape characteristics and climate (Whitfield et al. 2020).
  • This paper aims to demonstrate the utility of a basin classification–based virtual modelling approach for assessing the sensitivity of 110 Canadian Prairie catchments to climate.

Methodology

  • Framework of classification-based virtual basin modeling A basin classification–based virtual modelling platform has three main components: (1) a classification analysis to derive virtual basin characteristics; (2) parameterization and evaluation 120 of a hydrological model of the virtual basin and (3) application of the model to evaluate response to multiple scenarios .

Basin Classification

  • The classification of Canadian Prairie basins was based on the analyses of Wolfe et al. (2019), which divided over 4000 basins, each approximately 100 km2 in area, into seven broad classes, based on a suite of physio-geographic characteristics .
  • This was done because climate is introduced through the long meteorological time series used to drive the virtual basin model and in order to study climate sensitivity any classification that included historical climates could introduce bias.
  • Exclusion of climate had a limited impact on the basin classification, with the seven classes of basins 140 identified closely following the original classification.
  • The High Elevation Grasslands (HEG) class was selected for the development of the virtual basin model.
  • The suffix “- w” in the HRU name indicates HRUs in the wetland catena.

Model set-up and parameterization

  • The Cold Regions Hydrological Modelling platform (CRHM) was selected to develop the virtual 165 basin model, as CRHM is particularly suited for simulating the hydrology of the Canadian Prairies.
  • With the correct suite of modules, each representing a key hydrological process, CRHM has proven very capable of representing prairie 170 hydrological processes and accurately emulating water fluxes in this landscape (Fang and Pomeroy, 2009; Fang et al., 2010).
  • Runoff from the ‘wetland’ catena portion of the virtual basin (~33% of area) features a wetland complex HRU 190 within a landscape catena following a sequence from cultivated, to grassland, shrubland, and woodland HRUs .
  • For other HRUs, a minimum value of 0.001 was set to simulate the canopy effects of Prairie vegetation (crop residue, grass) on radiation for snowmelt.
  • For other HRUs, a 300 m fetch was selected.

Model application

  • To ensure that the role of climate variability across HEG was captured in streamflow simulations the model was run over a 46-year baseline period (1960–2006) driven using data from seven 255 locations.
  • The locations were within and nearby the geographical extent of the HEG classification, and represented the variation in climate across the region .
  • For this 290 reason, spring snow water equivalent (SWE) values from snow courses and mean annual hydrographs from hydrometric gauges at multiple sites within the HEG class were compared to virtual basin model outputs to establish that the virtual basin model was capturing the correct timing and magnitudes of important states and fluxes.
  • This method has the advantages of being 325 computationally inexpensive, while avoiding bias, and preserving the covariances among variables, which are important in modeling cold-regions processes (Shook and Pomeroy, 2010).
  • These scenarios were used with the model to quantify sensitivity of snow accumulation and annual runoff to climate change.

Results

  • The HEG class occupies much of the western portion of the Canadian Prairies, and includes the 340 majority of southern Alberta and several isolated patches in both Saskatchewan and Manitoba .
  • Circles represent values beyond these percentiles.
  • The date of annual peak SWE advances as annual air temperature warms .the authors.
  • Under a warmer and wetter climate (6°C 495 warming and 30% increase in annual precipitation) runoff in western portions still experience decreases, but runoff in climates such as Brandon’s increase and remain the same in climates such as Saskatchewan’s .
  • The consequence for streamflow is a 44% decline in annual volume in a drier HEG climate such as Medicine Hat’s (Table 4).

Conclusions

  • Virtual experiments have proven to be suitable to diagnose the hydrological response of basins in 595 this landscape.
  • Where previous studies have focussed on the sensitivity of individual basins in cold regions, and conclusions about wider applicability were made by assuming the basins to be representative, this approach is meant to provide a methodology to assess how regional hydrology may respond 600 to change by modelling a prototypical virtual basin that represents one type of basin in a region.
  • The region is expected to warm 2°C above the 1976 – 2005 climate normal (6.1°C) to 8.1°C by 2040 (Zhang et al., 2019).
  • The virtual basin model outputs are available from the authors by request.
  • CS and CJW conceived the study, also known as Author contributions.

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1
Assessing hydrological sensitivity of grassland basins in the Canadian Prairies to climate using a
basin classificationbased virtual modelling approach
Christopher Spence
1*
, Zhihua He
2
, Kevin R. Shook
2
, Balew A. Mekonnen
3
, JohnW. Pomeroy
2
,
Colin J. Whitfield
4
, Jared D. Wolfe
5
5
* Corresponding author: Christopher Spence (chris.spence@canada.ca)
1
Environment and Climate Change Canada, Saskatoon, Saskatchewan, Canada
2
Centre for Hydrology, University of Saskatchewan, Saskatoon, Saskatchewan, Canada
3
Golder Associates, Calgary, Alberta, Canada
4
School of Environment and Sustainability, University of Saskatchewan, Saskatoon,
10
Saskatchewan, Canada
5
Saskatchewan Ministry of Environment, Regina, Saskatchewan, Canada
*corresponding author: chris.spence@canada.ca
Abstract
15
Significant challenges from changes in climate and land-use face sustainable water use in the
Canadian Prairies ecozone. The region has experienced significant warming since the mid 20th
Century, and continued warming of an additional 2°C by 2050 is expected. This paper aims to
enhance understanding of climate controls on Prairie basin hydrology through numerical model
experiments. It approaches this by developing a basin classificationbased virtual modeling
20
framework for a portion of the Prairie region, and applying the modelling framework to
investigate the hydrological sensitivity of one Prairie basin class (High Elevation Grasslands) to
changes in climate. High Elevation Grasslands dominate much of central and southern Alberta
and parts of southwestern Saskatchewan with outliers in eastern Saskatchewan and western
Manitoba. The experiments revealed that High Elevation Grasslands snowpacks are highly
25
sensitive to changes in climate, but that this varies geographically. Spring maximum snow water
equivalent in grasslands decreases 8% per degree °C of warming. Climate scenario simulations
indicated a 2°C increase in temperature requires at least an increase of 20% in mean annual
precipitation for there to be enough additional snowfall to compensate for enhanced melt losses.
The sensitivity in runoff is less linear and varies substantially across the study domain;
30
simulations using 6°C of warming and a 30% increase in mean annual precipitation yields
simulated decreases in annual runoff of 40% in climates of the western Prairie but 55% increases
in climates of eastern portions. These results can be used to identify those areas of the region that
are most sensitive to climate change, and highlight focus areas for monitoring and adaptation.
The results also demonstrate how a basin classificationbased virtual modeling framework can
35
be applied to evaluate regional scale impacts of climate change with relatively high spatial
resolution, in a robust, effective and efficient manner.
Key words: Prairie, basin classification, virtual experiments, climate change, snow, runoff
40
https://doi.org/10.5194/hess-2021-186
Preprint. Discussion started: 18 May 2021
c
Author(s) 2021. CC BY 4.0 License.

2
Introduction
Hydrological models are essential tools to understand hydrological processes and function at the
basin scale, and can also be used to diagnose how specific hydrological processes control
catchment responses to change (Rasouli et al., 2014). Modelling a specific basin to evaluate
45
processes or to simulate the effects of change entails large computational and labour costs and
requires observations of the basin response with sufficient spatial and temporal coverage.
Modelling of many individual basins is not efficient when attempting to predict regional
responses to changes in climate and/or land-use. Basin classification can regionalize
hydrological model outputs, based on the assumption that basins can be classified by their
50
characteristics and that basins of the same class respond similarly to changes in climate inputs or
their landscapes (e.g., McDonnell and Woods, 2004; Wagener et al., 2007). Parameterizing a
model based upon a representative or stylized basin of a given class allows the output to be
considered representative of all basins of that class. This assumption facilitates regionalization
as it does not necessarily require simulating the distinctive characteristics of every basin,
55
reducing cost and time required for large domain studies. Such a regionalization approach can
be used to assess the sensitivity of large diverse areas to stressors, such as land-use and climate
change.
One such region is the Canadian Prairie ecozone, that portion of the Great Plains of North
60
America that includes southern parts of the provinces of Alberta, Saskatchewan, and Manitoba
and Treaties 1, 2, 4, 6 and 7 in Western Canada (Spence et al., 2019), as mapped in Figure 2.
This region has a cold sub-humid to semi-arid climate and was covered by grassland and sparse
woodlands until the widespread adoption of cultivated agriculture in the late 19
th
and early 20
th
https://doi.org/10.5194/hess-2021-186
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Author(s) 2021. CC BY 4.0 License.

3
centuries. The region’s geomorphology was formed by glacial and post-glacial processes which
65
left numerous internally drained depressions and poorly defined drainage networks. Most of the
Canadian Prairies is in the Saskatchewan-Nelson River Basin, but relatively little runoff is
provided to the major rivers that traverse the region downstream of their mountain headwaters.
Local streams and prairie-derived rivers often have intermittent and highly variable streamflow.
These streams are important local sources of freshwater and are often managed to provide farm,
70
agricultural and municipal water supply and support natural lakes and reservoirs (Pomeroy et al.,
2005). Because they connect to larger systems only intermittently, a small headwaterbasin scale
approach is necessary to generate information about how their behaviour might be impacted by
the aforementioned stressors.
75
Western Canada, including the Canadian Prairies, has been subject to substantial climate
warming since the mid 20
th
century (DeBeer et al., 2016; Bush and Lemmen, 2019). Prairie
precipitation trends indicate more rain and less snow in the spring and fall (Shook and Pomeroy,
2012) and runoff generation has been shown to be shifting from snowmelt- to rainfall-driven in
eastern Saskatchewan (Dumanski et al., 2015). Recent analysis of hydrometric stations across the
80
region identified sub-regional trends in streamflow associated with drying in the west and south
and wetting in the east and north, associated with physical landscape characteristics and climate
(Whitfield et al. 2020). However, it is difficult to attribute streamflow response solely to climate
change because of impoundment of streams, widespread changes in agricultural practices and
wetland drainage since the 1950s (Ehsanzadeh, 2016). Wetland drainage has become
85
widespread in portions of the region (van Meter and Basu, 2015) and the loss of depressional
storage capacity associated with drainage enhances streamflow volumes (Tiner, 2003; Fang et
https://doi.org/10.5194/hess-2021-186
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Author(s) 2021. CC BY 4.0 License.

4
al., 2010; Wilson et al., 2019) and may alter the frequency, timing, and duration of regional
streamflow (Ehsanzadeh et al., 2012; Spence and Mengistu, 2019). Extrapolating intensive
studies of wetland drainage impact in individual basins (Wilson et al., 2019) can be challenging,
90
because basin response is a function of wetland distributions that control contributing area
dynamics (Stichling and Blackwell, 1957; Shaw et al., 2012; Shook and Pomeroy, 2011; Haque
et al. 2017, Spence and Mengistu, 2019). It is uncertain how hydrological fluxes and states in
Canadian Prairie basins will respond to continued climate change and wetland drainage. The
statistical modelling and small basin modelling studies cited here have provided an excellent
95
foundation, but an improved approach is needed to evaluate how changes in climate and
agricultural practices impact hydrological regimes more broadly across the region.
Here, a classification-based virtual modeling framework is proposed as a means to examine
hydrological sensitivity to different climate, land-use and wetland drainage. In this approach,
100
each basin class is modelled in a virtual manner (Weiler and McDonnell, 2004; Armstrong et al.,
2015); as a synthetic or generic basin with characteristics defined by the average or typical
condition of all basins from the same class. In this way, the basin characteristics can be
manipulated to determine how a typical basin may respond to change. There is evidence that
such an approach is viable, as virtual experiments have been used to evaluate hydrological
105
response to different conditions (Di Giammarco et al., 1996; Horn et al., 2005; Dunn et al., 2007;
Mallard et al., 2014; Seo and Schmidt, 2013, Lopez-Moreno et al., 2020), identify factors
influencing hydrological processes (e.g., Weiler and McDonnell, 2004), and study hydrological
controls on water chemistry (Weiler and McDonnell, 2006). This paper aims to demonstrate the
utility of a basin classificationbased virtual modelling approach for assessing the sensitivity of
110
https://doi.org/10.5194/hess-2021-186
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Author(s) 2021. CC BY 4.0 License.

5
Canadian Prairie catchments to climate. Two steps were taken to achieve this objective: (1)
development of a robust class-based virtual basin model for a portion of the Canadian Prairie
and; (2) exploration of virtual basin sensitivity of hydrological response to climate. This work
provides a foundation to extend the virtual basin modelling approach more broadly across the
Canadian Prairie to assess response to climate and land management scenarios.
115
Methodology
Framework of classification-based virtual basin modeling
A basin classificationbased virtual modelling platform has three main components: (1) a
classification analysis to derive virtual basin characteristics; (2) parameterization and evaluation
120
of a hydrological model of the virtual basin and (3) application of the model to evaluate response
to multiple scenarios (Figure 1).
Figure 1: Components of the classification-based virtual basin modeling platform.
125
https://doi.org/10.5194/hess-2021-186
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01 Jan 2000
Abstract: Scientific evidence about global climate change and its consequences began to accumulate during the 1980s. In 1988, the United Nations Environment Programme and the World Meteorological Organization jointly established the Intergovernmental Panel on Climate Change (IPCC). The IPCC concluded in its Second Assessment Report (1996) that Earth has already warmed about 0.6 ˚C over the last century, and projected further increases of 1 to 3.5 ˚C by the year 2100. This projection is based on simulation of atmospheric circulation, the energy exchanges, and other important land/ocean/atmosphere interactions by General Circulation Models (GCMs). These models project climate (10-year or longer averages of weather conditions) over several decades, and give only large-scale predictions because grid spacing in most GCMs is between 2 and 5 degrees of longitude or latitude (about 150 to 360 km). Prediction on small time and space scale, needed for design and planning, are not possible at present. However, results from GCMs simulations suggest that the present mid-latitude rain belt would shift northward; snowmelt and spring runoff would occur earlier than at present; evapotranspiration would be greater; the greatest increases in temperatures will occur in the high latitudes, in winter, and over land; extreme weather events (droughts, storms, floods, ice jams, etc.) will be more frequent and more severe. Climate and hydrologic changes may result in important ecological and socioeconomic consequences. The impacts will vary from beneficial to catastrophic depending upon the magnitude and rate of change, the sensitivity of watersheds and ecosystems to change and the ability of natural or man-made systems to adapt to or mitigate that change.

6 citations


Posted ContentDOI
Abstract: While it is well known that the vast majority of the time only a portion of any watershed contributes runoff to the outlet, this extent is rarely documented The power-law form of the streamflow and contributing area (Q-Ac) relationship has been known for a half century, but it is uncommon for it to be quantified or its controls evaluated In this study a semi-distributed hydrological model (MESH-PDMROF) that can simulate contributing area and streamflow was employed to compare contributing area and flood frequency distributions in a southern Manitoba, Canada catchment and test the hypothesis that the relationship between a catchment’s floods and contributing area is a power function that influences the form of regional flood-area relationships The model simulated streamflow reasonably well (Nash Sutcliffe values = 062) Modelled estimates of the area contributing to the mean annual flood were much lower (03) than those derived from independent topographic analysis (09) described in earlier literature, even after bias and error corrections Estimates of the coefficient and exponent of the Q-Ac power law function ranged from 008–014 and 09–112, respectively Lower exponent values of regional flood frequency curves suggest they are a construct of Q-Ac curves from individual basins The non-linear nature of this relationship implies any contributing area change will have a profound impact on flood magnitude The mean annual flood of the major river in this region, the Red, has increased 33 % since 1987 Applying the coefficient and exponent ranges above suggests this is associated with an expansion in contributing areas of 29–38 % There are implications for the attribution of causes and mitigation of nutrient transport from regional watersheds However, how physiography and land and water management could change Q-Ac power law exponents is poorly known and MESH-PDMROF does not provide explicit estimates of the spatial distribution of contributing area These are areas encouraged for future research

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"Assessing hydrological sensitivity ..." refers methods in this paper

  • ...Actual evapotranspiration was simulated using the Penman– Monteith equation (Monteith, 1965), and evaporation from typically saturated surfaces subject to advection, such as wetlands and stream channels, was calculated using the Priestley and Taylor equation (Priestley and Taylor, 1972)....

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Abstract: Hydrology does not yet possess a generally agreed upon catchment classification system. Such a classification framework should provide a mapping of landscape form and hydro-climatic conditions on catchment function (including partition, storage, and release of water), while explicitly accounting for uncertainty and for variability at multiple temporal and spatial scales. This framework would provide an organizing principle, create a common language, guide modeling and measurement efforts, and provide constraints on predictions in ungauged basins, as well as on estimates of environmental change impacts. In this article, we (i) review existing approaches to define hydrologic similarity and to catchment classification; (ii) discuss outstanding components or characteristics that should be included in a classification scheme; and (iii) provide a basic framework for catchment classification as a starting point for further analysis. Possible metrics to describe form, hydro-climate, and function are suggested and discussed. We close the discussion with a list of requirements for the classification framework and open questions that require addressing in order to fully implement it. Open questions include: How can we best represent characteristics of form and hydro-climatic conditions? How does this representation change with spatial and temporal scale? What functions (partition, storage, and release) are relevant at what spatial and temporal scale? At what scale do internal structure and heterogeneity become important and need to be considered?

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  • ...Basin classification can regionalize hydrological model outputs, based on the assumption that basins can be classified by their 50 characteristics and that basins of the same class respond similarly to changes in climate inputs or their landscapes (e.g., McDonnell and Woods, 2004; Wagener et al., 2007)....

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  • ...…that basins can be classified by their characteristics and that basins of the same class respond similarly to changes in climate inputs or their land- Published by Copernicus Publications on behalf of the European Geosciences Union. scapes (e.g. McDonnell and Woods, 2004; Wagener et al., 2007)....

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Abstract: Despite significant recent advancements, global hydrological models and their input databases still show limited capabilities in supporting many spatially detailed research questions and integrated assessments, such as required in freshwater ecology or applied water resources management. In order to address these challenges, the scientific community needs to create improved large-scale datasets and more flexible data structures that enable the integration of information across and within spatial scales; develop new and advanced models that support the assessment of longitudinal and lateral hydrological connectivity; and provide an accessible modeling environment for researchers, decision makers, and practitioners. As a contribution, we here present a new modeling framework that integrates hydrographic baseline data at a global scale (enhanced HydroSHEDS layers and coupled datasets) with new modeling tools, specifically a river network routing model (HydroROUT) that is currently under development. The resulting ‘hydro-spatial fabric’ is designed to provide an avenue for advanced hydro-ecological applications at large scales in a consistent and highly versatile way. Preliminary results from case studies to assess human impacts on water quality and the effects of dams on river fragmentation and downstream flow regulation illustrate the potential of this combined data-and-modeling framework to conduct novel research in the fields of aquatic ecology, biogeochemistry, geo-statistical modeling, or pollution and health risk assessments. The global scale outcomes are at a previously unachieved spatial resolution of 500 m and can thus support local planning and decision making in many of the world's large river basins. Copyright © 2013 John Wiley & Sons, Ltd.

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  • ...The basin delineations used in the study were taken from the HydroSHEDs dataset (Lehner and Grill, 2013), which provides geographically contiguous delineations of basins for the world, including the Prairie ecozone....

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  • ...The basin delineations used in the study were taken from the HydroSHEDs dataset (Lehner and Grill, 2013), which provides geographically contiguous delineations of basins for the world, including the Prairie ecozone....

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John W. Pomeroy1, D. M. Gray1, T. Brown1, N. R. Hedstrom2  +3 moreInstitutions (4)
Abstract: After a programme of integrated field and modelling research, hydrological processes of considerable uncertainty such as snow redistribution by wind, snow interception, sublimation, snowmelt, infiltration into frozen soils, hillslope water movement over permafrost, actual evaporation, and radiation exchange to complex surfaces have been described using physically based algorithms. The cold regions hydrological model (CRHM) platform, a flexible object-oriented modelling system was devised to incorporate these algorithms and others and to connect them for purposes of simulating the cold regions hydrological cycle over small to medium sized basins. Landscape elements in CRHM can be linked episodically in process-specific cascades via blowing snow transport, overland flow, organic layer subsurface flow, mineral interflow, groundwater flow, and streamflow. CRHM has a simple user interface but no provision for calibration; parameters and model structure are selected based on the understanding of the hydrological system; as such the model can be used both for prediction and for diagnosis of the adequacy of hydrological understanding. The model is described and demonstrated in basins from the semi-arid prairie to boreal forest, mountain and muskeg regions of Canada where traditional hydrological models have great difficulty in describing hydrological phenomena. Some success is shown in simulating various elements of the hydrological cycle without calibration; this is encouraging for predicting hydrology in ungauged basins.

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"Assessing hydrological sensitivity ..." refers background or methods in this paper

  • ...CRHM is a modular, process-based, spatially semi-distributed hydrological model, which includes the key cold regions and warm season hydrological processes that operate in western Canada and elsewhere (Pomeroy et al., 2007)....

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  • ...Fetch distances were set using values recommended in Pomeroy et al. (2007)....

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  • ...Fang and Pomeroy (2007) and Pomeroy et al. (2007) attempted to determine the sensitivities of snow accumulation and runoff to drought at Bad Lake, Saskatchewan....

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