Claude R. Duguay

The response and role of ice cover in lake-climate interactions:

This paper reviews the current state of knowledge pertaining to the interactions of lake ice and climate. Lake ice has been shown to be sensitive to climate variability through observations and modelling, and both long-term and short-term trends have been identified from ice records. Ice phenology trends have typically been associated with variations in air temperatures while ice thickness trends tend to be associated more to changes in snow cover. The role of ice cover in the regional climate is less documented and with longer ice-free seasons possible as a result of changing climate conditions, especially at higher latitudes, the effects of lakes on their surrounding climate (such as increased evaporation, lake-effect snow and thermal moderation of surrounding areas, for example) can be expected to become more prominent. The inclusion of lakes and lake ice in climate modelling is an area of increased attention in recent studies. An important step in improving predictions of ice conditions in models is the assimilation of remote sensing data in areas where in-situ data is lacking, or non-representative of the lake conditions. The ability to accurately represent ice cover on lakes will be an important step in the improvement of global circulation models, regional climate models and numerical weather forecasting.

Cold Regions Hydrology High-Resolution Observatory for Snow and Cold Land Processes

Snow is a critical component of the global water cycle and climate system, and a major source of water supply in many parts of the world. There is a lack of spatially distributed information on the accumulation of snow on land surfaces, glaciers, lake ice, and sea ice. Satellite missions for systematic and global snow observations will be essential to improve the representation of the cryosphere in climate models and to advance the knowledge and prediction of the water cycle variability and changes that depend on snow and ice resources. This paper describes the scientific drivers and technical approach of the proposed Cold Regions Hydrology High-Resolution Observatory (CoReH2O) satellite mission for snow and cold land processes. The sensor is a synthetic aperture radar operating at 17.2 and 9.6 GHz, VV and VH polarizations. The dual-frequency and dual-polarization design enables the decomposition of the scattering signal for retrieving snow mass and other physical properties of snow and ice.

The Role of Northern Lakes in a Regional Energy Balance

There are many lakes of widely varying morphometry in northern latitudes. For this study region, in the central Mackenzie River valley of western Canada, lakes make up 37% of the landscape. The nonlake components of the landscape are divided into uplands (55%) and wetlands (8%). With such abundance, lakes are important features that can influence the regional climate. This paper examines the role of lakes in the regional surface energy and water balance and evaluates the links to the frequency–size distribution of lakes. The primary purpose is to examine how the surface energy balance may influence regional climate and weather. Lakes are characterized by both the magnitude and temporal behavior of their surface energy balances during the ice-free period. The impacts of combinations of various-size lakes and land–lake distributions on regional energy balances and evaporation cycles are presented. Net radiation is substantially greater over all water-dominated surfaces compared with uplands. The seasonal heat storage increases with lake size. Medium and large lakes are slow to warm in summer. Their large cumulative heat storage, near summer’s end, fuels large convective heat fluxes in fall and early winter. The evaporation season for upland, wetland, and small, medium, and large lakes lasts for 19, 21, 22, 24, and 30 weeks, respectively. The regional effects of combinations of surface types are derived. The region is initially treated as comprising uplands only. The influences of wetland, small, medium, and large lakes are added sequentially, to build up to the energy budget of the actual landscape. The addition of lakes increases the regional net radiation, the maximum regional subsurface heat storage, and evaporation substantially. Evaporation decreases slightly in the first half of the season but experiences a large enhancement in the second half. The sensible heat flux is reduced substantially in the first half of the season, but changes little in the second half. For energy budget modeling the representation of lake size is important. Net radiation is fairly independent of size. An equal area of medium and large lakes, compared with small lakes, yields substantially larger latent heat fluxes and lesser sensible heat fluxes. Lake size also creates large differences in regional flux magnitudes, especially in the spring and fall periods.

Effects of Changes in Arctic Lake and River Ice

Climatic changes to freshwater ice in the Arctic are projected to produce a variety of effects on hydrologic, ecological, and socio-economic systems. Key hydrologic impacts include changes to low flows, lake evaporation regimes and water levels, and river-ice break-up severity and timing. The latter are of particular concern because of their effect on river geomorphology, vegetation, sediment and nutrient fluxes, and sustainment of riparian aquatic habitats. Changes in ice phenology will affect a wide range of related biological aspects of seasonality. Some changes are likely to be gradual, but others could be more abrupt as systems cross critical ecological thresholds. Transportation and hydroelectric production are two of the socio-economic sectors most vulnerable to change in freshwater-ice regimes. Ice roads will require expensive on-land replacements while hydroelectric operations will both benefit and be challenged. The ability to undertake some traditional harvesting methods will also be affected.

The effect of soil and crop residue characteristics on polarimetric radar response

Abstract Although the interaction between linear polarized microwaves and agricultural targets has been studied extensively, far less is understood about the added information provided from polarimetric Synthetic Aperture Radars (SARs). Using 1994 Spaceborne Imaging Radar-C (SIR-C) data, this study examines the sensitivity of linear polarizations and polarimetric parameters to conditions present on agricultural fields during the period of preplanting and postharvest. The polarimetric parameters investigated include circular polarized backscatter, pedestal height, and co-polarized phase differences (PPD). The co-polarizations signature plots are also discussed. Results indicate that the dominant scattering mechanism from these fields varies depending on the type and amount of residue cover, and whether the crop had been harvested. Radar parameters most sensitive to volume and multiple scattering perform best at characterizing these surface conditions. These parameters are the pedestal height, as well as the linear cross-polarization (HV) and the circular co-polarizations (RR). The co-polarizations signature plots and the standard deviation associated with the PPD are also useful in categorizing these cover types. However, the field average PPD provides little information on residue and soil characteristics.

Past and Future Changes in Arctic Lake and River Ice

Paleolimnological evidence from some Arctic lakes suggests that longer ice-free seasons have been experienced since the beginning of the nineteenth century. It has been inferred from some additional records that many Arctic lakes may have crossed an important ecological threshold as a result of recent warming. In the instrumental record, long-term trends exhibit increasingly later freeze-ups and earlier break-ups, closely corresponding to increasing air temperature trends, but with greater sensitivity at the more temperate latitudes. Broad spatial patterns in these trends are also related to major atmospheric circulation patterns. Future projections of lake ice indicate increasingly later freeze-ups and earlier break-ups, decreasing ice thickness, and changes in cover composition, particularly white-ice. For rivers, projected future decreases in south to north air-temperature gradients suggest that the severity of ice-jam flooding may be reduced but this could be mitigated by changes in the magnitude of spring snowmelt.

Canadian cryospheric response to an anomalous warm summer: A synthesis of the climate change action fund project “the state of the arctic cryosphere during the extreme warm summer of 1998”

Abstract As of 2003, the warmest year on record in Canada (and globally) was 1998. Extensive warming was observed over the Canadian Arctic during the summer of 1998. A collaborative, interdisciplinary project involving government, universities, and the private sector examined the effect of this unusual warmth on cryospheric conditions and documented the responses, placing them in a 30–40 year context. This paper represents a synthesis of these results. 1998 was characterized by a melt season of exceptional length, having both an unusually early start and late finish. Extremes were noted for cryospheric variables that included ground thaw penetration, snow‐free season, lake‐ice‐free season, glacier melt, and the duration and extent of marine open water. The warm conditions contributed to the break‐up of two long‐term, multi‐year ice plugs in the north‐west Canadian Arctic Archipelago, which allowed floe ice into the Northwest Passage. Synoptic events and preconditioning were observed to play an important role in governing the response of some variables to the warming. It was also noted that response was not uniform in all regions. This study provided an opportunity to examine possible cryospheric response to future, warmer conditions. It also provided a chance to assess the capability of current cryospheric monitoring networks in the Canadian Arctic. This study has suggested the manner of cryospheric response to low frequency, high magnitude events occurring within the broader milieu of large‐scale forcing.

Simulation of surface temperature and ice cover of large northern lakes with 1-D models: a comparison with MODIS satellite data and in situ measurements

ABSTRACT Lake surface temperature (LST) and ice phenology were simulated for various points differing in depth on Great Slave Lake and Great Bear Lake, two large lakes located in the Mackenzie River Basin in Canadas Northwest Territories, using the 1-D Freshwater Lake model (FLake) and the Canadian Lake Ice Model (CLIMo) over the 2002–2010 period, forced with data from three weather stations (Yellowknife, Hay River and Deline). LST model results were compared to those derived from the Moderate Resolution Imaging Spectroradiometer (MODIS) aboard the Earth Observing System Terra and Aqua satellite platforms. Simulated ice thickness and freeze-up/break-up dates were also compared to in situ observations. Both models showed a good agreement with daily average MODIS LSTs on an annual basis (0.935  ≤  relative index of agreement  ≤  0.984 and 0.94  ≤  mean bias error  ≤  4.83). The absence of consideration of snow on lake ice in FLake was found to have a large impact on estimated ice thicknesses (25 cm thicker on average by the end of winter compared to in situ measurements; 9 cm thicker for CLIMo) and break-up dates (6 d earlier in comparison with in situ measurements; 3 d later for CLIMo). The overall agreement between the two models and MODIS LST products during both the open water and ice seasons was good. Remotely sensed data are a promising data source for assimilation into numerical weather prediction models, as they provide the spatial coverage that is not captured by in situ data.

Arctic Freshwater Ice and Its Climatic Role

Freshwater ice dominates the Arctic terrestrial environment and significantly impacts bio-physical and socio-economic systems. Unlike other major cryospheric components that either blanket large expanses (e.g., snow, permafrost, sea ice) or are concentrated in specific locations, lake and river ice are interwoven into the terrestrial landscape through major flow and storage networks. For instance, the headwaters of large ice-covered rivers extend well beyond the Arctic while many northern lakes owe their genesis to broader cryospheric changes. The effects of freshwater ice on climate mostly occur at the local/regional scale, with the degree of influence dependent on the magnitude, timing, location, and duration of ice cover, and the size of the water body. Freshwater-ice formation, growth, decay, and break-up are influenced by climatic variables that control surface heat fluxes, but these differ markedly between lakes and rivers. Despite the importance of freshwater ice, there has been a recent reduction in observational recordings.

River-ice break-up/freeze-up: a review of climatic drivers, historical trends and future predictions

Abstract River ice plays a fundamental role in biological, chemical and physical processes that control freshwater regimes of the cold regions. Moreover, it can have enormous economic implications for river-based developments. All such activities and processes can be modified significantly by any changes to river-ice thickness, composition or event timing and severity. This paper briefly reviews some of the major hydraulic, mechanical and thermodynamic processes controlling river-ice events and how these are influenced by variations in climate. A regional and temporal synthesis is also made of the observed historical trends in river-ice break-up/freeze-up occurrence from the Eurasian and North American cold regions. This involves assessment of several hydroclimatic variables that have influenced past trends and variability in river-ice break-up/freeze-up dates including air-temperature indicators (e.g. seasonal temperature, 0˚C isotherm dates and various degree-days) and large-scale atmospheric circulation patterns or teleconnections. Implications of future climate change on the timing and severity of river-ice events are presented and discussed in relation to the historical trends. Attention is drawn to the increasing trends towards the occurrence of mid-winter break-up events that can produce especially severe flood conditions but prove to be the most difficult type of event to model and predict.