Climate Centre General Circulation Model Research Articles

Global modeling of multicomponent aerosol species: Aerosol optical parameters

Canadian Aerosol Module (CAM) has been developed to simulate the atmospheric cycling of principal aerosol species, with the Third Generation Canadian Climate Center General Circulation Model (CCC GCM III) as its climatological driver. Adding an aerosol optical module to this modeling framework, the optical parameters of aerosols are simulated and compared to Sun photometer (AERONET) and satellite (MODIS) observations, as well as lidar observations of aerosol vertical profiles. The model captures well the global distribution and seasonal variation of aerosol optical parameters, showing seasonal maxima of optical depth and absorption over desert and biomass‐burning regions. For most sites and months, the modeled optical depths are within MODIS and AERONET means and standard deviations, and modeled single‐scattering albedo (SSA) and asymmetry factor are within 10% of AERONET retrievals. Fairly good agreement is found between modeled and observed optical depths over tropical oceans, where most models show significant underestimation. The model's overestimation of observed optical depths over parts of Europe by about 0.1 is most likely due to overestimates by older emission inventories. Modeled optical depths and SSA above observed means and standard deviations over areas and at sites within Central Africa and Central and South America suggest overprediction of organic carbon contribution by the model. Common to other models, however, our simulations underestimate the strength of the tropical biomass burning season. Modeled aerosol vertical profiles show better agreement with lidar observations at European sites than at an East Asian site, and more so at upper than at lower altitudes.

Sensitivity of Local Daily Temperature Change Estimates to the Selection of Downscaling Models and Predictors

Abstract A number of statistical downscaling models are applied to the Canadian Climate Centre general circulation model (CCCM) outputs to provide climate change estimates for local daily surface temperature at a network of 39 stations in central and western Europe. Several different linear downscaling methods (multiple linear regression of gridded values, multiple linear regression of principal components, canonical correlation analysis) are applied to a number of sets of predictors (500- and 1000-hPa heights, 850-hPa temperature, 1000–500-hPa thickness, and their combinations) defined on a grid over the Euro–Atlantic domain. The temperature change estimates are shown to vary widely among the methods as well as among the predictors, both in their areal mean, spatial pattern, and elevation dependence in the Alpine region. The most counterintuitive result is the dependence of the estimated warming on the number of principal components (PCs) of predictors: the larger the number of PCs, the higher the warmin...

Simulation of thermal/dissolved oxygen habitat for fishes in lakes under different climate scenarios: Part 1. Cool-water fish in the contiguous US

Fish habitat is strongly constrained by water temperature and available dissolved oxygen (DO). Thermal/DO habitat for cool-water fish in small lakes was therefore determined from simulated daily water temperature and DO profiles. Twenty-seven types of lakes were simulated with past (1961–1979) climate conditions observed at 209 weather stations in the contiguous USA as input, and with a 2×CO 2 climate scenario that is projected to occur at the same locations. The output of the Canadian Climate Centre General Circulation Model (CCC GCM) was used to determine the climate data increments for a doubling of atmospheric CO 2. A verified, process-oriented, unsteady and one-dimensional (vertical) lake water quality model (MINLAKE96) was used for the year-round temperature and DO simulations, which were run in a continuous mode over a 19-year simulation period. Water temperature and DO criteria for survival and good-growth of cool-water fish were provided by the United States Environmental Protection Agency. Cool-water fish in this study comprise seven species, northern pike, white sucker, black crappie, white crappie, yellow perch, sauger, and walleye. Nine fish habitat parameters were developed to quantify thermal habitat of cool-water fish and were extracted for the 27 lake types at 209 locations of the contiguous US. Fish habitat parameters were found to depend more strongly on lake geometry (surface area and maximum depth) and less on trophic state. Winterkill which occurs in eutrophic and mesotrophic, shallow lakes of the north-central and northeastern states of the contiguous US under present climate conditions, is projected to disappear under the 2×CO 2 climate scenario due to a shortening of the ice cover period. Climate warming is projected to increase the good-growth period of cool-water fish by up to 137 days in lakes in the north-central and northeastern states and to decrease it by up to 103 days in lakes at several south-central and southeastern states of the contiguous US. Due to climate warming, the good-growth period, the good-growth habitat areas and the good-growth habitat volumes of cool-water fish are projected to increase by 20, 10, and 8% from the past values, respectively, in medium-depth lakes of the contiguous US. Climate warming is projected to reduce the number of locations, where lakes have suitable cool-water fish habitat, by up to 62 out of 209 (30%). Average reductions are 56, 42, and 7 locations (27, 20, and 3%) for shallow (4 m), medium-depth (13 m), and deep (24 m) lakes, respectively. Summerkill under the projected 2×CO 2 CCC climate scenario is a projected significant negative impact on cool-water fish in southern lakes of the contiguous US, where suitable habitat existed under past conditions.

Simulation of thermal/dissolved oxygen habitat for fishes in lakes under different climate scenarios: Part 2. Cold-water fish in the contiguous US

Fish habitat is strongly constrained by water temperature and available dissolved oxygen (DO). Thermal/dissolved oxygen habitat for cold-water fish in small lakes was therefore determined from simulated daily water temperature and dissolved oxygen profiles. Twenty-seven types of lakes were simulated with past (1961–1979) climate conditions observed at 209 weather stations in the USA, and with a 2×CO 2 climate scenario that is projected to occur at the same locations. The output of the Canadian Climate Centre (CCC) General Circulation Model for a doubling of atmospheric CO 2 was used to determine the climate data increments for a doubling of atmospheric CO 2. The methodology was described in Part 1 of this paper. Highlights of the results are as follows: winterkill that occurred due to dissolved oxygen deficiency in eutrophic and mesotrophic, shallow lakes of the north-central and northeastern US under past climate conditions, is projected to be replaced by summerkill due to elevated water temperatures in mesotrophic lakes, or by suitable fish habitat in eutrophic lakes under the 2×CO 2 climate scenario. Shallow lakes at 205 of 209 locations investigated are projected to experience summerkill of cold-water fish under the projected 2×CO 2 climate scenario. Climate warming is also projected to reduce by up to 38% of the past values the length of the good-growth period and the good-growth area/volume for cold-water fish in lakes at most locations in the contiguous US. Average reductions in the number of locations where lakes presently have suitable year-round cold-water fish habitat are 28, 90, and 65 locations for shallow, medium-depth, and deep lakes, respectively. Loss of fish habitat during the summer period (summerkill) under the projected 2×CO 2 climate scenario is a significant negative impact of climate warming on cold-water fish in lakes of the contiguous US. Geographic regions in which lakes cannot support cold-water fish are projected to extend significantly further north under a 2×CO 2 climate scenario.

Simulation of thermal/dissolved oxygen habitat for fishes in lakes under different climate scenarios: Part 3. Warm-water fish in the contiguous US

Fish habitat is strongly constrained by water temperature and dissolved oxygen. Thermal/dissolved oxygen habitat for warm-water fish in small lakes was therefore determined from simulated daily water temperature and dissolved oxygen profiles. Twenty-seven types of lakes were simulated with past (1961–1979) climate conditions observed at 209 weather stations in the contiguous USA as input, and with a 2×CO 2 climate scenario that is projected to occur at the same locations. The output of the Canadian Climate Centre (CCC) General Circulation Model was used to determine the climate data increments for a doubling of atmospheric CO 2. The methodology was described in Part 1 of this paper. The simulation results project the absence of summerkill of warm-water fish in any lake and at any location of the contiguous US under both climate scenarios. Summerkill would occur due to elevated water temperatures or dissolved oxygen deficiency. Under the 2×CO 2 climate scenario, the good-growth period is projected to extend from about 75 days at northern latitudes to an entire year (365 days) at southern latitudes. Climate warming to the 2×CO 2 climate scenario is projected to have several enhancing effects on warm-water fish habitat in lakes of the contiguous US: (1) Winterkill which occurs in eutrophic and mesotrophic, shallow lakes of the north-central and northeastern US under present climate conditions, is projected to disappear. (2) The good-growth period is projected to be lengthened on average by 30–40 days in lakes at all locations investigated, more in deeper than in shallow lakes and more in northern than in southern latitudes. (3) The highest increase of habitat measured in terms of bottom areas or volumes is projected to be over 200% and to occur at northern latitudes. In several southeastern states good-growth habitat areas and volumes are projected to decrease by up to 30% from the past values, which is the only detrimental impact of climate warming on warm-water fish habitat found in this study.

RESEARCH: Projected Climate Change Effects on Winterkill in Shallow Lakes in the Northern United States.

/ Each winter, hundreds of ice-covered, shallow lakes in the northern United States are aerated to prevent winterkill, the death of fish due to oxygen depletion under the ice. How will the projected climate warming influence winterkill and the need to artificially aerate lakes? To answer this question, a deterministic, one-dimensional year-round water quality model, which simulates daily dissolved oxygen (DO) profiles and associated water temperatures as well as ice/snow covers on lakes, was applied. Past and projected climate scenarios were investigated. The lake parameters required as model input are surface area, maximum depth, and Secchi depth as a measure of radiation attenuation and trophic state. The model is driven by daily weather data. Weather records from 209 stations in the contiguous United States for the period 1961-1979 were used to represent past climate conditions. The projected climate change due to a doubling of atmospheric CO(2) was obtained from the output of the Canadian Climate Center General Circulation Model. To illustrate the effect of projected climate change on lake DO characteristics, we present herein DO information simulated, respectively, with inputs of past climate conditions (1961-1979) and with a projected 2 x CO(2) climate scenario, as well as differences of those values. Specific parameters obtained were minimum under-ice and lake bottom DO concentration in winter, duration of under-ice anoxic conditions (<0.1 mg/liter) and low DO conditions (<3 mg/liter), and percentage of anoxic and low DO lake volumes during the ice cover period. Under current climate conditions winterkill occurs typically in shallow eutrophic lakes of the northern contiguous United States. Climate warming is projected to eliminate winterkill in these lakes. This would be a positive effect of climate warming. Fish species under ice may still experience periods of stress and zero growth due to low DO (<3 mg/liter) conditions under projected climate warming.

Simulation and validation of fish thermal DO habitat in north-central US lakes under different climate scenarios

Fish habitat in lakes is strongly constrained by water temperature and available dissolved oxygen (DO). Suitable fish habitat for three fish assemblages (cold-, cool-, and warm-water) in Minnesota (US) lakes was therefore determined from simulated daily water temperature and dissolved oxygen profiles. A total of 27 types of lakes were simulated under past (1961–1979) and a projected 2×CO 2 climate scenarios. The projected climate scenario was derived from the output of the Canadian Climate Center General Circulation Model for a doubling of atmospheric CO 2. A verified, process-oriented, unsteady and one-dimensional (vertical) year-round lake water quality model ( minlake96) was used for the temperature and DO simulations, which were run in a continuous mode over 19 years. Water temperature and DO criteria for survival and good-growth of each fish guild were provided by the United States Environmental Protection Agency. Simulated suitable fish habitats were compared with fish observations in 3002 Minnesota lakes. Winterkill was simulated to occur in shallow eutrophic and mesotrophic lakes under past climate conditions, and predicted to disappear under the projected 2×CO 2 climate scenario due to a shortening of the ice cover period. Sensitivity of the simulated winterkill to three DO survival limits was analyzed. A lower DO (less than 0.5 mg/1) limit for winterkill produced better agreement with a fish observation database than higher limits. Dependence of the simulated good-growth habitat areas (GGHA) and volumes (GGHV) on the geometry (surface area and maximum depth) and trophic state of a lake was also examined. Fish habitat parameters were found to depend more strongly on geometry and less on trophic state. Climate change is projected to increase GGHA in seasonaly stratified (medium-depth and deep) lakes on the average by 50 and 115% for cool-water and warm-water fish guilds, respectively. It is also projected that cold-water fish species will have a small percentage loss in weakly stratified (medium-depth) lakes, but a small percentage gain of GGHA in deep, strongly stratified lakes.

The Effect of Climate Change on Floods in British Columbia

A hydrological modelling of the flood response of two watersheds to climate change are presented. The two study watersheds are the Upper Campbell and the Illecillewaet watersheds located in British Columbia. The first watershed is a maritime watershed located on the east slopes of the Vancouver Island mountains whereas the second watershed is located in the Selkirk Mountains in Eastern British Columbia. The Canadian Climate Centre General Circulation Model (CCC GCM) has been used for the estimation of the effect of the climate change on meteorological parameters. The CCC GCM is a steady state model and the output of the 1991 run has been used. In addition to the changes in the amounts of precipitation and temperature usually assumed in hydrological climate change studies, other meteorological and climatic parameters are also considered; specifically, the effect of climate on the spatial distribution of precipitation with elevation, and also on cloud cover, glaciers, vegetation distribution, vegetation biomass production, and plant physiology. The results showed that the mean annual temperature in the two watersheds could increase by more than 3°C and the annual basin-wide precipitation could increase by 7.5% in Upper Campbell watershed and by about 17% in the Illecillewaet watershed. As a result, the mean annual runoff will increase by 7.5% in the Upper Campbell watershed and 21% in the Illecillewaet basin. For the study of floods, nine flood parameters have been investigated, the total number of flood episodes, the flood days per year, the duration of flood events, the annual flood volume, the mean flood flow, the mean flood peak, the annual maximum flood peak, the day of occurrence of the centroid of flood volume, and the day of occurrence of annual maximum flood peak. These nine parameters were extracted from the hydrographs of the two study watersheds using the double long-term mean daily flow. The study showed that, under the climate change scenario, the floods in the maritime Upper Campbell watershed would increase, on average, in magnitude by 14%, in volume by 94%, in frequency by 11%, and duration by 44%. The timing of the floods would remain almost unchanged, and the centroid of flood volume would shift earlier by only 2 days. In contrast, in the interior mountain Illecillewaet watershed, the floods would decrease, on average, in magnitude by 7%, in volume by 38%, and frequency by 23%. The duration of flood events, under the altered climate scenario, would remain, essentially, unchanged increasing by only 2.6%. Also, the study showed that in the Illecillewaet watershed the largest change between the altered climate and the present climate scenarios would be the timing of floods since the centroid of flood volume would occur 20 days earlier. The above changes in the flood response of the two study watersheds can be explained by the changes in the distribution and form of annual precipitation. These results indicate that different management procedures will be needed to minimize the effects of climate change on the flooding of the two climatically different watersheds and the regions that they represent.

Projections of Climate Change Effects on Water Temperature Characteristics of Small Lakes in the Contiguous U.S.

To simulate effects of projected climate change on water temperature characteristics of small lakes in the contiguous U.S., a deterministic, one-dimensional year-round water temperature model is applied. In cold regions the model simulates ice and snow cover on a lake. The lake parameters required as model input are surface area, maximum depth, and Secchi depth as a measure of radiation attenuation and trophic state. The model is driven by daily weather data. Weather records from 209 stations in the contiguous U.S. for the period 1961–1979 were used to represent present climate conditions. The projected climate change owing to a doubling of atmospheric CO2 was obtained from the output of the Canadian Climate Center General Circulation Model. The simulated water temperature and ice characteristics are related to the geometric and trophic state lake characteristics and to geographic location. By interpolation, the sensitivity of lake water temperature characteristics to latitude, longitude, lake geometry and trophic status can therefore be quantified for small lakes in the contiguous U.S. The 2× CO2 climate scenario is projected to increase maximum and minimum lake surface temperatures by up to 5.2°C. (Maximum surface water temperatures in lakes near the northern and the southern border of the contiguous U.S. currently differ by up to 13°C.) Maximum temperature differences between lake surface and lake bottom are projected to increase in average by only 1 to 2°C after climate warming. The duration of seasonal summer stratification is projected to be up to 66 days longer under a 2×CO2 climate scenario. Water temperatures of less than 8°C are projected to occur on lake bottoms during a period which is on the order of 50 days shorter under a 2×CO2 climate scenario. With water temperature change projected to be as high as 5.2°C, ecological impacts such as shifts in species distributions and in fish habitat are most likely. Ice covers on lakes of northern regions would also be changed strongly.

Changes to the runoff of Canadian ecozones under a doubled CO2 atmosphere

Increases in atmospheric greenhouse gases may change the hydrology of a number of Canada's regions. This will have an impact on aquatic and wetland ecosystems as well as municipal, industrial, and power generation uses. It is thus important to get an estimate of the potential changes to the Canadian hydrological cycle in order to make intelligent decisions concerning mitigation factors that society may be forced to undertake. We divided Canada into ecoclimatologically similar regions called "ecozones." We developed two month-stepped temperature-precipitation-runoff models for the country using an artificial intelligence neural network (ANN) approach. We modified input temperature and precipitation variables in the ANN models to match those predicted by the Canadian Climate Centre General Circulation Model II for a doubled CO2 atmosphere and calculated new monthly equilibrium runoff predictions. Our results predict that much of Canada will experience higher annual runoff than is currently the case. The timing of runoff will change significantly in a number of the ecozones, as we show that in many regions, peak runoff will occur approximately 1 month earlier than is currently the case. The ANN model did not work as well for basins in the Prairie ecozone, as we could not develop a good model with data from regulated rivers.

Changes to the runoff of Canadian ecozones under a doubled CO&lt;sub&gt;2&lt;/sub&gt; atmosphere

Increases in atmospheric greenhouse gases may change the hydrology of a number of Canada's regions. This will have an impact on aquatic and wetland ecosystems as well as municipal, industrial, and power generation uses. It is thus important to get an estimate of the potential changes to the Canadian hydrological cycle in order to make intelligent decisions concerning mitigation factors that society may be forced to undertake. We divided Canada into ecoclimatologically similar regions called "ecozones." We developed two month-stepped temperature-precipitation-runoff models for the country using an artificial intelligence neural network (ANN) approach. We modified input temperature and precipitation variables in the ANN models to match those predicted by the Canadian Climate Centre General Circulation Model II for a doubled CO2 atmosphere and calculated new monthly equilibrium runoff predictions. Our results predict that much of Canada will experience higher annual runoff than is currently the case. The timing of runoff will change significantly in a number of the ecozones, as we show that in many regions, peak runoff will occur approximately 1 month earlier than is currently the case. The ANN model did not work as well for basins in the Prairie ecozone, as we could not develop a good model with data from regulated rivers.

Simulated Climate Change Effects on Year-Round Water Temperatures in Temperate Zone Lakes

A deterministic, one-dimensional model is presented to simulate daily water temperature profiles and associated ice and snow covers for dimictic and polymictic lakes of the temperate zone. The lake parameters required as model input are surface area (As), maximum depth (HMAX), and Secchi depth (zs), the latter, used as a measure of light attenuation and trophic state. The model is driven by daily weather data and operates year-round over multiple years. The model has been tested with extensive data (over 5,000 temperature points). Standard error between simulated and measured water temperatures is 1.4°C in the open water season and 0.5°C in the ice cover season. The model is applied to simulate the sensitivity of Minnesota lake water temperature characteristics to climate change. The projected climate changes due to a doubling of atmospheric CO2 are obtained from the output of the Canadian Climate Center General Circulation Model (CCC GCM) and the Goddard Institute of Space Studies General Circulation Model (GISS GCM). Simulated lake temperature characteristics have been plotted in a coordinate system with a lake geometry ratio (A s 0.25 /HMAX) on one axis and Secchi depth on the other. The lake geometry ratio expresses a lake's susceptibility to stratification. By interpolation, the sensitivity of lake temperature characteristics to changes of water depth and Secchi depth under the projected climate scenarios can therefore be obtained. Selected lake temperature characteristics simulated with past climate conditions (1961–1979) and with a projected 2 × CO2 climate scenario as input are presented herein in graphical form. The simulation results show that under the 2 × CO2 climate scenario ice formation is delayed and ice cover period is shortened. These changes cause water temperature modifications throughout the year.

The Utilization of Bryophytes in Bioclimatic Modeling: Predicted Northward Migration of Peatlands in the Mackenzie River Basin, Canada, as a Result of Global Warming

The Utilization of Bryophytes in Bioclimatic Modeling: Predicted Northward Migration of Peatlands in the Mackenzie River Basin, Canada, as a Result of Global Warming

Climate changes in the greater and southern Caribbean

A climate change resulting from recent increases in the atmospheric greenhouse gases (GHGs) is supposed to occur sometime in the middle of the next century. This climate change induced by GHGs would be caused by radiative forcing through the greenhouse effect and would lead to global warming and eventually to sea-level rise. This paper presents a climate change scenario for the greater Caribbean as simulated by the Canadian Climate Centre (CCC) general circulation model (GCM). The CCC GCM projects a GHG induced temperature increase of about 2°C and more extreme rainfall conditions for the greater Caribbean. The climate records of temperature, rainfall and cloudiness for several stations on the island of Trinidad are then examined in an attempt to detect GHG climate change signals. The temperature change to date, close to 1°C, and the fluctuations in rainfall patterns, over the last five decades, seem to be indicative of early greenhouse signals. © 1997 The Royal Meteorological Society.

The effects of climatic change and C0 2 fertilisation on agriculture in Québec

The agricultural sector forms an important part of the economy of Quebec. The risk of global increase of atmospheric CO 2 concentration and associated climatic change and their influence on agriculture need to be assessed. Although many studies have been conducted on the effect of climate change on agriculture in various parts of the world, fewer studies have focused on the combined effects of climatic change and CO 2 fertilisation on agriculture. This study, using the outputs of the Canadian Climate Centre (CCC) general circulation model coupled with the Food and Agricultural Organization (FAO) crop model, attempts to assess the response of agricultural productivity to both direct (or fertilisation) and indirect (or climatic) effects of increased atmospheric CO 2 concentration, for a variety of crops including C 3 and C 4 cereals, legumes, vegetables and special crops grown in Quebec. It appears that Ca cereal (corn and sorghum) crops would benefit by climate change but would be least favoured by CO 2 fertilisation effect.

Optimal Spectral Topography and Its Effect on Model Climate

Gibbs oscillations in the truncated spectral representation of the earth's topography are strongly reduced by determining its spectral coefficients as a minimum of a nonuniformly weighted, nonquadratic cost function. The cost function penalizes the difference between spectral and true topography with weights that are explicit functions of the topographic height and its gradient. The sensitivity of the Canadian Climate Centre general circulation model's climate to the presence of Gibbs oscillations is determined for T32 and T48 resolutions by comparing the climates with optimal spectral topography to those with standard spectral topography. The main effect of Gibbs oscillations in the standard spectral topography is to induce spurious grid-scale ripples in the surface fluxes, which, for the surface energy balance, can be on the order of several tens of watts per square meter. Ripples in the surface fluxes are nearly absent in the model climate with the optimal spectral topography.

Effects of climate warming on fish thermal habitat in streams of the United States

The effects of climate warming on the thermal habitat of 57 species of fish of the U.S. were estimated using results for a doubling of atmospheric carbon dioxide that were predicted by the Canadian Climate Center general circulation model. Baseline water temperature conditions were calculated from data collected at 1,700 U.S. Geological Survey stream monitoring stations across the U.S. Water temperatures after predicted climate change were obtained by multiplying air temperature changes by 0.9, a factor based on several field studies, and adding them to baseline water temperatures at stations in corresponding grid cells. Results indicated that habitat for cold and cool water fish would be reduced by ∼50%, and that this effect would be distributed throughout the existing range of these species. Habitat losses were greater among species with smaller initial distributions and in geographic regions with the greatest warming (e.g. the central Midwest). Results for warm water fish habitat were less certain because of the poor state of knowledge regarding their high and low temperature tolerances; however, the habitat of many species of this thermal guild likely will also be substantially reduced by climate warming, whereas the habitat of other species will be increased.

Influence d'un changement climatique dû à une hausse de gaz à effet de serre sur l'agriculture au quebec

Abstract This study, using a climate change scenario generated by the Canadian Climate Centre (CCC) general circulation model (GCM) examines the impacts of such a climate change on agriculture in s...

Effect of Climate Change on Hydrologic Regime of Two Climatically Different Watersheds

Hydrologic modeling of the responses of two study watersheds to climate change is presented. The watersheds are the Upper Campbell and the Illecillewaet watersheds located in British Columbia. The first is a maritime watershed located on the eastern slopes of the Vancouver Island mountains; the second is located in the Selkirk Mountains in Eastern British Columbia. The Canadian Climate Centre General Circulation model has been used for the prediction of potential effects of climate change on meteorological parameters. In addition to the changes in the amounts of precipitation and temperature usually assumed in hydrologic climate change studies, other meteorological and climatic parameters also considered are the effect of climate on the spatial distribution of precipitation with elevation, as well as on cloud cover, glaciers, vegetation distribution, vegetation biomass production, and plant physiology. The results showed that the mean annual temperature in the two watersheds could increase by more than 3°C and the annual basinwide precipitation could increase by 7.5% in the Upper Campbell watershed and by about 17% in the Illecillewaet watershed. The higher temperatures changed some snowfall to rainfall and the extra precipitation was mainly in the form of rain. The increase of the CO 2 concentration caused stomata closure that reduced evapotranspiration. This effect was compensated by increased biomass in the Upper Campbell watershed, but not in the Illecillewaet watershed. These changes produced higher flows in winter and smaller flows in summer. The largest change in the hydrograph shape was in the Illecillewaet watershed where the mean annual maximum daily flow decreased by about 13% and its frequency was reduced. On the other hand, the mean annual runoff increased by 21%. In contrast, although the shape of the simulated annual hydrograph of the Upper Campbell watershed was not affected, magnitude and frequency of the annual maximum precipitation increased. Also, the mean annual runoff in the Upper Campbell watershed increased by 7.5%. These results indicate that different management procedures may be needed to minimize the effects of climate change on the water resources of the two climatically different watersheds and the regions that they represent.

The Potential Vorticity Budget of an Atmospheric General Circulation Model

Abstract The flux form of the potential vorticity (PV) equation in isentropic coordinates is used to examine the effects of advection and the effects of parameterized mechanical and thermal forcing on the PV budget of the second generation Canadian Climate Centre general circulation model (CCC GCM). Model data corresponding to Northern Hemisphere winter are used. The simulated PV flux contains significant nonadvective contributions in the planetary boundary layer, in the gravity wave drag regions of the Northern Hemisphere, and in the tropical midtroposphere in regions of intense latent heat release associated with persistent moist convection. The model advective PV flux is compared to the advective PV flux calculated from a National Centers for Environmental Prediction observational dataset. Large discrepancies are seen where parameterized gravity wave drag dominates the mechanical forcing field in the model. The zonally averaged model PV flux in the upper troposphere and lower stratosphere is characteri...