Possible thunderstorm modifications caused by the Athabasca oil sands development and the Canadian Shield

  • Author / Creator
    Brown, Daniel M.
  • Thunderstorms are common in boreal forest regions and can cause dangerous hazards such as lightning, forest fires, hail, wind, and flooding. Significant research has been conducted to help predict thunderstorms to mitigate or avoid the hazards and damage. The development of thunderstorms depends on many factors, including land cover variations. In this thesis, the Athabasca oil sands development (an anthropogenic land cover modification), and the Canadian Shield (a natural land cover variation), will be examined. The oil sands development creates a massive almost 1000 km2 land disturbance, changing boreal forest to barren land, tailings ponds, and bitumen upgrading facilities. The Canadian Shield is a drastic land cover change from lusher boreal forest on soil to sparser boreal forest on exposed Precambrian bedrock interspersed with intermittent deep, cold lakes. The effect of land disturbances in the boreal forest is relatively unexplored, and cooler, drier climatic conditions and land cover could result in unexpected effects on thunderstorms. The first results chapter in this thesis compares temperature, humidity, precipitation, and lightning near and away from the oil sands development, searching for temporal trends as the oil sands development increases in size. Comparing how weather near the oil sands development changes over time, with respect to weather away from it, eliminates differences due to local effects and general climate variation. The precipitation and lightning did not change over time, thus, the oil sands development does not appear to affect thunderstorm climatology. However, a strengthening heat island and dry island were detected within the oil sands development. In particular, the overnight temperatures have increased about 1.2°C relative to the surroundings. These phenomena are thought to be caused by clearing the land, causing a higher Bowen ratio, and emissions of waste heat from oil upgrading, which might be able to trigger thunderstorms in rare situations. The second results chapter in this thesis used the Weather Research and Forecasting (WRF) model to perform sensitivity experiments. Factor separation was used to quantify the effect of adding/removing two major environmental factors caused by the oil sands development: the land cover disturbance, and the emissions of waste heat. The effect of the oil sands development on thunderstorm intensity was insignificant on all ten days investigated. However, on two of the case study days, the oil sands development appeared to cause thunderstorms to occur one to two hours earlier. The analysis indicates that the oil sands likely triggered storms earlier in these cases, but they appear to be rare. Aircraft measurements indicated that the oil sands development affects thunderstorms mostly when the vertical totals index is greater than 30°C. However, there are probably not enough of these cases to measurably affect climatology. The third results chapter in this thesis analyzed the variation of detected cloud-to-ground lightning density near the Canadian Shield boundary. The results show that significantly less lightning occurs inside the Canadian Shield than just outside, and a strong cloud-to-ground lightning density gradient exists along the boundary. Various statistical analyses suggest that the lightning density gradient is statistically significantly higher near the Canadian Shield boundary than away from it. However, the signal was not detected in regions with large lakes or more complex topography, which seemed to dominate over the Canadian Shield effect. In one region, the Lightning density decreased from 10 strikes per square km down to 6 over less than 100 km. This effect may be caused by a lower detection efficiency in the Canadian Shield. However, it also could be caused by the sudden change in land cover from more lush, moist, higher transpiring broadleaf forest to sparser, lower transpiring needle-leaf forests on bare bedrock. This thesis shows that two unique land cover variations in the boreal forest can affect thunderstorms. However, the magnitude of the effect was not always what was expected. The Athabasca oil sands were expected to enhance thunderstorms significantly, but their effect was much weaker than expected. The Canadian Shield was not anticipated to have much effect at all; however, it significantly diminished thunderstorms. It seems that because thunderstorms occur less in a shorter season and are generally weaker in the boreal forest, that land cover variations could cause thunderstorms to be more difficult to enhance, and easier to diminish.

  • Subjects / Keywords
  • Graduation date
    Fall 2017
  • Type of Item
  • Degree
    Doctor of Philosophy
  • DOI
  • License
    This thesis is made available by the University of Alberta Libraries with permission of the copyright owner solely for non-commercial purposes. This thesis, or any portion thereof, may not otherwise be copied or reproduced without the written consent of the copyright owner, except to the extent permitted by Canadian copyright law.