Alain Pietroniro

An evaluation of snow accumulation and ablation processes for land surface modelling

This paper discusses the development and testing of snow algorithms with specific reference to their use and application in land surface models. New algorithms, developed by the authors, for estimating snow interception in forest canopies, blowing snow transport and sublimation, snow cover depletion and open environment snowmelt are compared with field measurements. Existing algorithms are discussed and compared with field observations. Recommendations are made with respect to: (a) density of new and aged snow in open and forest environments; (b) interception of snow by evergreen canopies; (c) redistribution and sublimation of snow water equivalent by blowing snow; (d) depletion in snow-covered area during snowmelt; (e) albedo decay during snowmelt; (f) turbulent transfer during snowmelt; and (g) soil heat flux during meltwater infiltration into frozen soils. Preliminary evidence is presented, suggesting that one relatively advanced land surface model, CLASS, significantly underestimates the timing of snowmelt and snowmelt rates in open environments despite overestimating radiation and turbulent contributions to melt. The cause(s) may be due to overestimation of ground heat loss and other factors. It is recommended that further studies of snow energetics and soil heat transfer in frozen soils be undertaken to provide improvements for land surface models such as CLASS, with particular attention paid to establishing the reliability of the models in invoking closure of the energy equation. #1998 John Wiley & Sons, Ltd.

Multisensor Hydrologic Assessment of a Freshwater Wetland

This article evaluates the use of synthetic aperture radar (SAR) and visible/infrared (VIR) satellite imagery for mapping the extent of standing water in the Peace-Athabasca Delta during spring and summer of 1998. SAR images contain data about the geometric and electrical characteristics of the objects, while VIR images contain information about the reflectivity of objects. Radar pulses can also penetrate vegetation to some degree depending on the wavelength and vegetation thickness. It is hypothesized that since Radarsat and SPOT images contain complementary information, flood mapping will be more efficient when the two image types are used in combination. Radarsat SAR and SPOT multispectral imagery from May 1998 and July 1998 were used for the flood mapping. A Radarsat S2 image (27.5° incidence angle) was obtained for May 1998. To evaluate the incidence angle effect on flood mapping, a Radarsat S1 image (27.5° incidence angle) and a Radarsat S7 image (47.0° incidence angle) were obtained for July 1998. The Radarsat scenes were calibrated and filtered, and all imagery were orthorectified to minimize geometric distortion. A Mahalanobis distance algorithm was used to classify the SPOT scenes, the Radarsat scenes, and a combination of the two into open water, flooded vegetation, and nonflooded land. The results indicate that flood mapping in both spring and summer conditions has significantly higher accuracy when Radarsat and SPOT imagery are used in combination, rather than separately. However, it is important to use Radarsat imagery acquired at low incidence angles. Classification of the SPOT scene combined with the Radarsat S1 scene achieved significantly better results than those obtained when the SPOT scene was classified in combination with the Radarsat S7 scene.

Isotope studies in large river basins: A new global research focus

Rivers are an important linkage in the global hydrological cycle, returning about 35%of continental precipitation to the oceans. Rivers are also the most important source of water for human use. Much of the worlds population lives along large rivers, relying on them for trade, transportation, industry, agriculture, and domestic water supplies. The resulting pressure has led to the extreme regulation of some river systems, and often a degradation of water quantity and quality For sustainable management of water supply agriculture, flood-drought cycles, and ecosystem and human health, there is a basic need for improving the scientific understanding of water cycling processes in river basins, and the ability to detect and predict impacts of climate change and water resources development.

Influence of landscape aggregation in modelling snow-cover ablation and snowmelt runoff in a sub-arctic mountainous environment

Abstract Appropriate representation of landscape heterogeneity at small to medium scales is a central issue for hydrological modelling. Two main hydrological modelling approaches, deductive and inductive, are generally applied. Here, snow-cover ablation and basin snowmelt runoff are evaluated using a combined modelling approach that includes the incorporation of detailed process understanding along with information gained from observations of basin-wide streamflow phenomena. The study site is Granger Basin, a small sub-arctic basin in the mountains of the Yukon Territory, Canada. The analysis is based on the comparison between basin-aggregated and distributed landscape representations. Results show that the distributed model based on “hydrological response” landscape units best describes the observed magnitudes of both snow-cover ablation and basin runoff, whereas the aggregated approach fails to represent the differential snowmelt rates and to describe both runoff volumes and dynamics when discontinuous snowmelt events occur.

Effects of flow regulation on hydrologic patterns of a large, inland delta

The Peace–Athabasca River Delta (PAD) is one of the largest freshwater deltas and most biologically productive in the world. Because regional evaporation is greater than precipitation, the thousands of lakes and wetlands dotting this area rely on periodic flooding from the Peace and Athabasca rivers to be replenished. Flood frequency significantly declined beginning in the mid-1970s, several years after the initiation of flow regulation of the Peace River. However, the drying trend was interrupted in 1996 when the PAD experienced extensive inland inundation on two separate occasions, one in the spring and one in the summer. A one-dimensional numerical hydrodynamic model was used to evaluate the role of flow regulation and hydroclimatic conditions on the water levels of major lakes found in the PAD. Three Peace River flow scenarios were analysed: the observed flows, the flow regime without the ‘precautionary drawdown’ spill which was required because of the discovery of a sinkhole at the crest of the dam, and the naturalized flow regime, which assumed no dam regulation. Modelling results indicated that the effect of the spill on the flow regime within the PAD was approximately equivalent in magnitude, although different in timing, to what would have resulted from the prevailing hydroclimatic conditions in an unregulated system. Furthermore, even in the absence of the precautionary drawdown spill, the lake levels would have risen well above the maximum daily average, suggesting that 1996 was one of the wettest years on record. Finally, the hydrodynamic regime observed at the end of the summer 1996 was very similar to that modelled under unregulated flow conditions, suggesting that flow regulation could be used to alter the hydrodynamic regime of a large delta to at least partially restore natural conditions and potentially improve ecosystem health. Copyright

Hydrologic assessment of an inland freshwater delta using multi‐temporal satellite remote sensing

The Peace-Athabasca Delta (PAD) is located in the northern extreme of Alberta, Canada and is one of the worlds largest freshwater inland deltas. This complex and dynamic ecosystem has undergone substantial change over the last 25 years, primarily as a result of alterations to the hydrologic regime. The remoteness of the region, along with a shortage of hydrologic and ecological information, has necessitated the development of innovative methods, based on the use of satellite imagery, to assess these changes. Specialized image classification schemes were employed to derive a sixteen-year historical database of changes in water area on large lakes and isolated small basins within the delta. The time series for the large lakes has been used to quantify their hypsometric characteristics, information crucial to defining storage terms for hydraulic flow models of the delta, particularly at high stage conditions that involve over-bank flooding. Analysis of the perched basins has proven that, even with the relatively coarse resolution of LANDSAT images, satellite remote sensing of water conditions in the myriad of PAD riparian basins is a viable technique for hydrologic and ecological monitoring. The satellite derived time-series record of water levels on Jemis Lake has also permitted the first independent validation of the perched-basin water-balance model recently developed for use in assessing water-management options for the PAD. Recommendations for future research using RADARSAT are also noted.

Energy and water cycles in a high-latitude, north-flowing river system: Summary of results from the Mackenzie GEWEX Study-phase I

Abstract The MacKenzie Global Energy and Water Cycle Experiment (GEWEX) Study, Phase 1, seeks to improve understanding of energy and water cycling in the Mackenzie River basin (MRB) and to initiate and test atmospheric, hydrologic, and coupled models that will project the sensitivity of these cycles to climate change and to human activities. Major findings from the study are outlined in this paper. Absorbed solar radiation is a primary driving force of energy and water, and shows dramatic temporal and spatial variability. Cloud amounts feature large diurnal, seasonal, and interannual fluctuations. Seasonality in moisture inputs and outputs is pronounced. Winter in the northern MRB features deep thermal inversions. Snow hydrological processes are very significant in this high-latitude environment and are being successfully modeled for various landscapes. Runoff processes are distinctive in the major terrain units, which is important to overall water cycling. Lakes and wetlands compose much of MRB and are p...

Glacier snow line mapping using ERS-1 SAR imagery

Abstract This article paper evaluates the effectiveness of ERS-1 synthetic aperture radar (SAR) imagery for mapping movement of the transient snow line in a temperate glacier basin during an ablation season. The two primary objectives of this study are to normalize the topographically induced distortions (radiometric and geometric) inherent in SAR imagery of rugged terrain and to delineate the snow line in the normalized imagery. The radiometric distortions are normalized with a cosine correction, and the image texture is enhanced to take advantage of the spatial distribution of tonal variations within each image. To minimize geometric distortions and georeference the imagery, each cosine corrected/texture enhanced SAR image is orthorectified to an error of approximately 60 m using a DEM and satellite orbital and ephemeris data. A supervised classification is performed on the orthorectified imagery to map the spatial distribution of snow and glacial ice within the basin. The visual boundary between the wet snow and glacier ice surfaces on the orthorectified images is within 75 m horizontally of the snow line obtained from field data. The glacier boundary is also discernible to within 75 m of the surveyed glacier outline. Several isolated bare ice areas on the lower glacier give a low return, similar to wet snow, resulting in some confusion between glacier ice and wet snow. It is speculated that the incident wave is lost within the crevasses and surface runoff runnels due to specular reflection within the features. Despite the localised confusion between glacier ice and wet snow, the wet-snow line and can be mapped reasonably well and in a timely manner using ERS-I SAR imagery.

Rationale for Monitoring Discharge on the Ground

AbstractThe hydrological cycle is receiving increasing attention both as an essential natural resource for humans and ecosystems and as a critical component controlling the earth’s climate system. Better understanding of the water cycle and its interaction with changing climate will require improved monitoring of the various water fluxes and storages in hydrological processes. River discharge is a unique component reflecting an integrated hydrological signal over larger regions. Existing in situ monitoring solutions to monitor discharge are often considered too expensive and the difficulties in data sharing are viewed as insurmountable obstacles, which has led to growing interest in finding an alternative. This paper argues that in situ monitoring is far less expensive than claimed and the obstacles are not necessarily as insurmountable as often stated and a conscious effort to revitalize in situ monitoring will be needed. This paper demonstrates that there is no substitute for in situ discharge monitorin...

Dissolved oxygen decline in ice-covered rivers of northern Alberta and its effects on aquatic biota

To determine whether existing dissolved oxygen (DO) regulationswere adequate to protect riverine biota, the Northern River Basins Studyrequired a research and assessment program to establish the effect ofpulp mill and municipal sewage discharges on under-ice DO concentrationsand aquatic biota in the Athabasca, Wapiti and Smoky rivers of northernAlberta, Canada. Analysis of monitoring data collected over >30 yearsshowed that pulp mill and municipal effluents have caused “sags” in DObelow their discharges and contributed to an increased rate of declinein DO over 10s of kilometers in the Wapiti-Smoky rivers or 100s ofkilometers in the Athabasca River. To permit forecasting of DO declinesin response to changes in river discharge or effluent biochemical oxygendemand (BOD), a one-dimensional steady-state river water quality modelwas implemented that successfully (r2 =0.74–0.92) predicted DO concentrations over an 820 km reach of theAthabasca River for the 1990–1994 winters. Experiments on nativefish and benthic macroinvertebrate species showed that exposure to lowDO and low temperatures (2–3°C) caused delays in hatch ofmountain whitefish eggs (at 6.5 mg/L DO), reduced mass of bull troutalevins post-hatch (at 5.0 mg/L DO), extended the spawning period ofburbot (at 6.0 mg/L DO), and depressed feeding rates and loweredsurvival of the mayfly Baetis tricaudatus (at 5 mg/L DO).As a result of recommendations from this integrated program of rivermonitoring, modelling and experimentation, effluent BOD loading has beenreduced to the Athabasca and Wapiti rivers and the provincial DOguideline for protection of aquatic life has been increased from 5.0 to6.5 mg/L.