Brent M. Lofgren

Evaluation of Potential Impacts on Great Lakes Water Resources Based on Climate Scenarios of Two GCMs

Abstract The results of general circulation model predictions of the effects of climate change from the Canadian Centre for Climate Modeling and Analysis (model CGCM1) and the United Kingdom Meteorological Offices Hadley Centre (model HadCM2) have been used to derive potential impacts on the water resources of the Great Lakes basin. These impacts can influence the levels of the Great Lakes and the volumes of channel flow among them, thus affecting their value for interests such as riparians, shippers, recreational boaters, and natural ecosystems. On one hand, a hydrological modeling suite using input data from the CGCM1 predicts large drops in lake levels, up to a maximum of 1.38 m on Lakes Michigan and Huron by 2090. This is due to a combination of a decrease in precipitation and an increase in air temperature that leads to an increase in evaporation. On the other hand, using input from HadCM2, rises in lake levels are predicted, up to a maximum of 0.35 m on Lakes Michigan and Huron by 2090, due to increased precipitation and a reduced increase in air temperature. An interest satisfaction model shows sharp decreases in the satisfaction of the interests of commercial navigation, recreational boating, riparians, and hydropower due to lake level decreases. Most interest satisfaction scores are also reduced by lake level increases. Drastic reductions in ice cover also result from the temperature increases such that under the CGCM1 predictions, most of Lake Erie has 96% of its winters ice-free by 2090. Assessment is also made of impacts on the groundwater-dependent region of Lansing, Michigan.

Temporal and Spatial Variability of Great Lakes Ice Cover, 1973–2010*

AbstractIn this study, temporal and spatial variability of ice cover in the Great Lakes are investigated using historical satellite measurements from 1973 to 2010. The seasonal cycle of ice cover was constructed for all the lakes, including Lake St. Clair. A unique feature found in the seasonal cycle is that the standard deviations (i.e., variability) of ice cover are larger than the climatological means for each lake. This indicates that Great Lakes ice cover experiences large variability in response to predominant natural climate forcing and has poor predictability. Spectral analysis shows that lake ice has both quasi-decadal and interannual periodicities of ~8 and ~4 yr. There was a significant downward trend in ice coverage from 1973 to the present for all of the lakes, with Lake Ontario having the largest, and Lakes Erie and St. Clair having the smallest. The translated total loss in lake ice over the entire 38-yr record varies from 37% in Lake St. Clair (least) to 88% in Lake Ontario (most). The tot...

Climate Change Impacts on the Hydrology of the Great Lakes-St. Lawrence System

A review of the current state of knowledge on climate change due to an ’enhanced greenhouse effect’ and the response of the climate and hydrologic systems to a changing atmosphere is provided. In particular, the survey presents historic trends in and the impacts of climate change on temperature, precipitation, evapotranspiration, runoff and Great Lakes levels. While much of the impacts research in the Great Lakes-St. Lawrence basin has used equilibrium 2 × CO2 scenarios, the transient scenarios for 2030 and 2050 from the Canadian Centre for Climate Modelling and Analysis and the United Kingdom Hadley Centre coupled atmosphere-ocean global circulation models are also described. If the significant declines in runoff and lakes levels suggested by climate change scenarios are realized, there could be serious supply-demand mismatches and water allocation issues. The issue of climate change reinforces the need for continued cooperative planning and management of the water resources of the Great Lakes-St. Lawrence basin.

Surface Albedo–Climate Feedback Simulated Using Two-Way Coupling

Abstract To simulate the effects of feedback between climate and surface albedo via vegetation, a scheme was developed, based on a generalized life zone scheme, for estimating the land surface albedo as a function of annual mean precipitation and surface temperature. This scheme was applied to the climate of a GCM and made interactive with the GCM. The climate of this run was compared with one in which the land surface albedo was prescribed to a spatially uniform value. Allowing such feedback within the modeling system enhances the atmospheric ascent and heavy precipitation of tropical rainbelts, in comparison with a case with spatially homogeneous surface albedo prescribed. It also intensifies the atmospheric descent and low precipitation rates over subtropical latitudes. That is, a positive feedback occurs at low latitudes. At midlatitudes, thermal forcing due to the spatial distribution of surface albedo has little effect on vertical motion or precipitation. However, in the Central Asian and Gobi Deser...

Simulated Effects of Idealized Laurentian Great Lakes on Regional and Large-Scale Climate*

Comparison is made between general circulation model (GCM) cases with and without the inclusion of idealized Great Lakes, in the form of four rectangular bodies of water, each occupying a single grid cell of the GCM at R30 resolution. The presence of idealized Great Lakes, as opposed to land, results in a phase shift in the annual cycle of latent and sensible heat flux. Very high upward sensible heat flux occurs over these idealized Great Lakes during the early winter. On the average over a region encompassing these idealized Great Lakes, evaporation and precipitation increase during the autumn and winter and decrease during the late spring and summer due to the lakes. Annual average water vapor flux convergence increases. The Great Lakes also alter the meridional air temperature gradient. During the autumn and winter, the meridional temperature gradient is intensified to the north of the Great Lakes and diminished to the south. This intensifies the mean jet stream core and displaces it toward the north. This effect is reduced during the winter compared to the autumn because air temperature changes due to the lakes are unable to penetrate as deeply into the strongly stably stratified winter atmosphere. The increase in jet stream speed seems to increase synoptic wave activity to the northeast of the Great Lakes. As an additional experimental case, a swamp surface (saturated surface with no thermal capacity) is used to represent the Great Lakes. In this case there is little effect on the thermal state of the surface and atmosphere and on the fluxes between them. However, there is increased evaporation during the late summer and early autumn and increased precipitation throughout the summer and autumn. Annual water vapor flux convergence in this experimental case is greater than in the case with no lakes.

East African food security as influenced by future climate change and land use change at local to regional scales

Climate change impacts food production systems, particularly in locations with large, vulnerable populations. Elevated greenhouse gases (GHG), as well as land cover/land use change (LCLUC), can influence regional climate dynamics. Biophysical factors such as topography, soil type, and seasonal rainfall can strongly affect crop yields. We used a regional climate model derived from the Regional Atmospheric Modeling System (RAMS) to compare the effects of projected future GHG and future LCLUC on spatial variability of crop yields in East Africa. Crop yields were estimated with a process-based simulation model. The results suggest that: (1) GHG-influenced and LCLUC-influenced yield changes are highly heterogeneous across this region; (2) LCLUC effects are significant drivers of yield change; and (3) high spatial variability in yield is indicated for several key agricultural sub-regions of East Africa. Food production risk when considered at the household scale is largely dependent on the occurrence of extremes, so mean yield in some cases may be an incomplete predictor of risk. The broad range of projected crop yields reflects enormous variability in key parameters that underlie regional food security; hence, donor institutions’ strategies and investments might benefit from considering the spatial distribution around mean impacts for a given region. Ultimately, global assessments of food security risk would benefit from including regional and local assessments of climate impacts on food production. This may be less of a consideration in other regions. This study supports the concept that LCLUC is a first-order factor in assessing food production risk.

Surface Energy Fluxes on the Great Lakes Based on Satellite-Observed Surface Temperatures 1992 to 1995

Abstract Accurate estimates of surface energy exchange components are critical for understanding many physical processes of large lakes and their atmospheric environment. In this paper, the seasonal cycle of latent, sensible, and total heat flux from the surface of the Great Lakes is estimated. Lake surface temperatures derived from the NOAA/AVHRR satellite, along with meteorological data from surface station observations are incorporated in order to estimate spatial distributions of fluxes. Several well-known features are evident. Among these are the very high outgoing fluxes of latent and sensible heat during the late fall and early winter, which drive strong cooling of the lake surface and consequent convective mixing within the lake column. Another is greater seasonal variation of surface temperature and fluxes in shallower waters than in deeper waters. Due to strong static stability of the overlying atmospheric boundary layer during the spring, both the magnitude and the spatial variations of latent and sensible heat fluxes are small during the spring and, to a lesser degree, during the summer. The annual cycles of latent and sensible heat flux over the Great Lakes are roughly opposite in phase to the same fluxes over land, indicating a large exchange of energy via atmospheric advection between the lake and land surfaces. A major weakness of the method used here is that heat fluxes are calculated on the basis of an ice-free surface, making the derived fluxes for January through March roughly estimated.

Sensitivity of Land–Ocean Circulations, Precipitation, and Soil Moisture to Perturbed Land Surface Albedo

Abstract Using general circulation model experiments, it was found that thermally induced overturning circulations that flow between oceans and land at low latitudes can be affected by perturbations to the land surface albedo. When surface albedo is reduced over land at low latitudes, radiative heating of the surface is increased and additional heat is transferred from the surface to the atmosphere, which is largely offset by adiabatic cooling associated with upward motion. This enhanced upward motion is associated with greater low-level convergence of air over the continents, compensated by divergence over the oceans. The enhanced flux of water vapor onto the continents due to this pattern further enhances the thermal forcing through the release of latent heat. In these low-latitude regions with reduced surface albedo, precipitation and soil moisture are increased. Qualitatively opposite effects are obtained by increasing surface albedo. In midlatitude regions, circulation and precipitation are not signi...

Severe Ice Cover on Great Lakes During Winter 2008–2009

The North American Great Lakes contain about 95% of the fresh surface water supply for the United States and 20% for the world. Nearly one eighth of the population of the United States and one third of the population of Canada live within their drainage basins. Because of this concentration of population, the ice cover that forms on the Great Lakes each winter and its year-to-year variability affect the regional economy [Niimi, 1982]. Ice cover also affects the lakes abiotic environment and ecosystems [Vanderploeg et al., 1992] in addition to influencing summer hypoxia, lake effect snow inland, water level variability, and the overall hydrologic cycle of the region [Assel et al., 2004].

Impacts of extreme 2013–2014 winter conditions on Lake Michigan's fall heat content, surface temperature, and evaporation

Since the late 1990s, the Laurentian Great Lakes have experienced persistent low water levels and above average over-lake evaporation rates. During the winter of 2013–2014, the lakes endured the most persistent, lowest temperatures and highest ice cover in recent history, fostering speculation that over-lake evaporation rates might decrease and that water levels might rise. To address this speculation, we examined interseasonal relationships in Lake Michigans thermal regime. We find pronounced relationships between winter conditions and subsequent fall heat content, modest relationships with fall surface temperature, but essentially no correlation with fall evaporation rates. Our findings suggest that the extreme winter conditions of 2013–2014 may have induced a shift in Lake Michigans thermal regime and that this shift coincides with a recent (and ongoing) rise in Great Lakes water levels. If the shift persists, it could (assuming precipitation rates remain relatively constant) represent a return to thermal and hydrologic conditions not observed on Lake Michigan in over 15 years.