Paul E. Todhunter

The borehole temperature record of climate warming in the mid-continent of North America

Abstract Ground-surface temperature (GST) histories, determined from a carefully selected set of twenty-nine borehole temperature profiles, show a warming trend over the last century that increases systematically with latitude in the mid-continent of North America. Except one site in north Texas, the borehole locations lie within a 500 × 1000 km transect that extends from the Kansas-Nebraska border into southern Manitoba. Ground-surface warming during the last century increases from +0.4°C at 41.1°N to + 2.0°C at 49.6°N. Surface air temperature (SAT) warming in the transect, determined from Historical Climatology Network stations, increases from + 0.5°C per century at 40°C per century at 48.8°N. These warming trends agree with the regional warming pattern predicted by GCM simulations of global warming. However, the magnitudes of warming determined from the GST and the SAT data agree in regions where seasonal ground freezing does not occur but differ significantly where seasonal ground freezing does occur. Analysis of ground and air temperature coupling suggests that the greater warming observed in the GST histories in seasonally frozen ground is due to a secular increase in soil moisture that corresponds with increased precipitation during the past 50 years.

Remote Detection of Prairie Pothole Ponds in the Devils Lake Basin, North Dakota

A decadal-scale wet spell in the closed Devils Lake basin of North Dakota has resulted in increases in the elevation and extent of the basins terminal lakes—Devils and Stump—as well as increases in the size and number of small prairie pothole ponds. Changes in lake surface area have been studied thoroughly, whereas the fluctuations in pond surface area have been virtually ignored. We use a subpixel classification technique in combination with a Landsat TM and ETM+ Band 5 (middle infrared; 1,550-1,750 nm) density slice to improve estimates of changes in the combined area of ponds in the basin for selected years between 1991 and 2002. The resulting information is a first step toward more accurate assessment of the impact of wetland flooding on the region.

MICROCLIMATIC VARIATIONS ATTRIBUTABLE TO URBAN-CANYON ASYMMETRY AND ORIENTATION

The energetic response of urban canyons to variable urban geometry is investigated using the URBAN3 numerical model. The energy budgets of six typical urban geometry scenarios encompassing a combination of symmetrical and asymmetrical north-south and east-west aligned urban canyons are examined for a warm summer day under which maximum inter-urban system energetic variations would be expected. Significant inter-urban canyon energy total differences are found which are closely linked to patterns of net solar radiation. The net solar radiation, net radiation and turbulent sensible heat flux totals are particularly sensitive to urban geometry. Implications of the study with respect to the magnitude of synoptic vs. geometric sources of urban energetic variation, and microscale and mesoscale urban modelling applications are discussed. [Key words: urban climatology, urban canyon energy budgets, urban geometry.]

Terminal Lake Flooding and Wetland Expansion in Nelson County, North Dakota

The Devils Lake Basin of North Dakota, an interior drainage basin located within a dry, subhumid environment, has experienced pervasive flood conditions since the 1993 onset of a wet spell of unprecedented magnitude and duration. This unique natural-hazard environment has resulted in flooding from both the expansion of the surface area of the basins terminal lakes (Devils Lake and Stump Lake) and increases in the number and size of rural wetlands. To assess the relative extent of both terminal lake and rural wetland flooding, we focused on Nelson County, which contains Stump Lake and is representative of other counties in the basin. Remotely sensed data acquired by Landsat Thematic Mapper was used to map open-water extent in 2001, and results were compared to 1992 land-cover data provided by the United States Geological Survey (USGS). Our analysis indicates a 53% increase in the size of Stump Lake and a 426% increase in the area of rural wetland ponds. Stump Lake flooding is spatially restricted and has had limited impact upon the surrounding lakeshore environment. Rural wetland flooding is pervasive and has a deleterious effect upon the regions agricultural economic base.

A model of net radiation over suburban snowpacks

Abstract Fieldwork by Xu and Buttle (Proc. East. Snow Conf.43, 173–184, 1987) has identified enhanced net radiation around homes as a contributing factor to the increased snowmelt rates observed in suburban environments relative to rural areas. A simple steady-state building climatology model was developed and linked to a ripe snowpack model to examine the effect of suburban homes on the net radiation balance over the sorrounding snowpacks. An error estimation of simulated hourly net radiation was determined by comparing model-predicted and observed net radiation at two suburban homes in Peterborough, Ontario, during a snowmelt period in March 1985. Results demonstrate that the model effectively simulates the complex mean hourly daytime net radiation inputs over ripe suburban snowpacks under all-sky conditions.

A climatology of airborne dust for the Red River Valley of North Dakota

Abstract The Red River Valley of North Dakota has been identified as one of the highest potential dust production regions in the United States. This paper provides a climatological summary of the airborne dust environment in the region using historical meteorological data for Fargo, North Dakota. Data for the period 1948–1994 were extracted for all 3-hourly weather observations which recorded an obstruction to vision due to dust, blowing dust or dust storms. Data were compiled on the year, month, day and hour of each observation, as well as the horizontal visibility, wind speed, wind direction, and other present weather occurring at the time of each event. Airborne dust events in the Red River Valley of the North normally involve local entrainment of dust, and show a strong peak in the frequency of occurrence during the afternoon and spring seasons, although a secondary winter peak is also present. Dust events have decreased in frequency over the study period, apparently in response to improved farm management practices. Most events fall into two basic categories: winter events generated by passing cold fronts or strong regional pressure gradients, and often accompanied by blowing snow and light snow showers, and spring events triggered by the passage of cyclones and fronts, and normally not accompanied by other prevailing weather at the time of the observation. Results are discussed in relation to the unique soil, meteorological and surface cover conditions of the Red River Valley of North Dakota.

Uncertainty of the Assumptions Required for Estimating the Regulatory Flood: Red River of the North

AbstractFederal guidelines specify the log-Pearson Type III (LP3) distribution as the basis for the estimation of the 100-year peak discharge that serves as the regulatory flood for floodplain management in the United States. The LP3 distribution has been shown to provide a reasonable and flexible model of flood risk. Use of the LP3 distribution involves a number of explicit assumptions about the annual maximum series that are often implicitly assumed but not shown directly to be satisfied in flood frequency analysis studies of individual stations. In this case study, the validity of these assumptions for the Red River of the North at Grand Forks gaging station is examined. None of the four examined assumptions are satisfied completely. The stationarity assumption is not met because the regional climate samples two separate climatic modes, the peak discharge time series is not a random and independent set of events, the precipitation—runoff relationships are not uniform over time, and the flood peaks resu...

The Effect of Low Plant Cover on the Surface Air Layer

Vegetation occupies the space between the earth’s surface and the atmosphere. A plant cover not only takes up space, but forms a transition zone, because the individual plant parts, such as leaves, needles, twigs, and branches, behave like solid ground, absorbing and emitting radiation, evaporating, and playing their part in the exchange of energy with the surrounding air. However, the air is still able to circulate within the plant cover more or less freely. Thus vegetation forms a new component part of the air layer near the ground.

The Influence of Topography on the Microclimate

In Chapter II, the microclimate of a level surface without vegetation was considered. Then in Chapters V and VI, this assumption was abandoned, and the interactions of vegetation and microclimate were studied. Now the assumption that the ground is level will also be abandoned, and the influences exerted on microclimate by the topographic variations of the terrain will be investigated.

Caveant admonitus (“Let the forewarned beware”)

Purpose – This paper aims to review the performance of the flood forecasting, warning, and response system (FFWRS) during the 1997 Red River of the North flood to identify the factors that contributed to FFWRS underperformance during this flood disaster.Design/methodology/approach – The individual components of the FFWRS are reviewed – data collection, flood forecasting, forecast dissemination, decision‐making, and action implementation, as well as the communication linkages between each system category. The unique challenges and breakdowns that occurred at each system category and communication linkage are identified for this catastrophic flood event.Findings – Forecast uncertainty was poorly communicated by flood forecasters, and misunderstood by decision makers. Both forecasters and decision makers were rigidly committed to probability‐thinking based on what they thought was most likely to happen; neither group adequately considered the possibility of a worst‐case scenario.Practical implications – Fore...