Hurricanes in North America: Impact of Climate Change Insights

__Clausen, Kearston _ Name (Last, First) Module 06, Activity 01 GEOG 104: Principles of Physical Geography Hurricanes in North America Learning Objectives In this activity, you will explore data on the number and intensity of hurricanes in the Atlantic Ocean and try to answer the question of whether the intensity of hurricanes has increased as the ocean temperatures increased over the years. Introduction The Union of Concerned Scientists published a report called “Hurricanes and Climate Change” in July 2008; the report was updated in June 2019. According to the report: While hurricanes are a natural part of our climate system, recent research suggests that there has been an increase in intense hurricane activity in the North Atlantic since the 1970s. In the future, there may not necessarily be more hurricanes, but there will likely be more intense hurricanes that carry higher wind speeds and more precipitation because of global warming. The impacts of this trend are likely to be exacerbated by sea level rise and a growing population along coastlines Warm ocean temperatures are one of the key factors that strengthen hurricane development when overall conditions are conducive to their formation and growth. Hurricanes require high humidity, and relatively constant winds at different altitudes, and can occur when surface ocean temperatures exceed about 79°F (26°C). The rising of warm, moist air from the ocean helps to power the storm. Two other factors may also be contributing to the rising intensities of hurricanes. First, warm air holds more water vapor than cold air—and the rising air temperatures since the 1970s have caused the atmospheric water vapor content to rise as well. This increased moisture provides additional fuel for hurricanes. Climate models project an increase in the average precipitation rate of hurricanes because of global warming. Second, as ocean temperatures rise, there is also less cold, subsurface ocean water to serve as a braking mechanism for hurricanes. When strong storm winds churn up cold subsurface water, the cooler waters can serve to weaken the storm. But if deeper waters become too warm, this natural braking mechanism weakens. For example, Hurricane Katrina intensified significantly when it hit deep pools of warm water in the Gulf of Mexico. 1

Not all changes in climate will fuel hurricanes. For example, when there are large changes in wind speed at different altitudes (also known as "vertical wind shear") above an area of the ocean, those conditions can interfere with hurricane formation. There is evidence that climate change may increase vertical wind shear over some regions in the western tropical Atlantic Ocean. However, when scientists put the pieces together, they project that in general, hurricanes will become more intense in a warming world, with higher wind speeds and greater levels of precipitation. As the climate continues to warm, the average intensity of tropical cyclones (including hurricanes in the North Atlantic) is projected to rise while the overall number of hurricanes globally is expected to either decrease or remain unchanged. Scientists project that, on average, tropical cyclones and hurricanes will have higher wind speeds and higher precipitation rates. There is some evidence that there will be an increase in the frequency of the most intense storms, though there is more evidence of this finding for the eastern North Pacific than there is for the western North Pacific and Atlantic. The projected increase in intense hurricanes is substantial—a doubling or more in the frequency of category 4 and 5 storms by the end of the century—with the western North Atlantic experiencing the largest increase. With continued warming, sea level is likely to rise by one to four feet globally by the end of the century, enabling the powerful surge associated with hurricanes to penetrate further inland than today. https://www.ucsusa.org/resources/hurricanes-and-climate-change Hurricanes are divided into five categories, divided according to the maximum wind speed reached. This is illustrated in the figure on the right. For a storm to be called a hurricane, the maximum sustained wind speed must exceed 74 miles per hour. 2

In order to build up and intensify, hurricanes require warm ocean temperatures, moist air, and low vertical wind shear (i.e. no strong change in wind speed or direction between two different altitudes). The largest Atlantic hurricane on record, Hurricane Sandy reached over 1000 miles in diameter and made landfall in the U.S. on October 29, 2012. Photo: NASA The aftermath of Hurricane Sandy in Mantaloking, New Jersey. Photo: Master Sgt. Mark C. Olsen/US Air Force CC BY (Wikimedia) 3

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During Hurricane Harvey, which struck Southeast Texas on August 25-29, 2017, unprecedented amounts of rainfall were reported, and the National Weather Service had to add two colors to the scale for their precipitation maps. Photo: https://www.weather.gov/hgx/hurricaneharvey 4

Statement of the Research Question Using data from the National Oceanic and Atmospheric Administration, the Union of Concerned Scientists concludes that the total number of Hurricanes reaching North America may not have changed much, but their intensity appears to have strengthened. The graph below shows the intensity of Hurricanes in the North Atlantic. This graph was included in an earlier version of the report by the Union of Concerned Scientists but omitted from the most recent version. Your task for this activity is to evaluate the validity of the claim by the Union of Concerned Scientists that the intensity indeed increased over the last few decades. 5

Using Excel to Graph and Process Data In this activity, you will use the same data to evaluate these historical records of Hurricane activity in North America. These data can be found at the following website: http://www.aoml.noaa.gov/hrd/hurdat/DataByYearandStorm.htm You do not have to go to this website and download the data – this has already been done and the data are stored in the file Hurricanes.xls (these data were accessed on August 28, 2017). This file contains the number of hurricanes in each category for the years 1851-2016. When you open the Excel file, you should see the following: 6

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For each year, the number of hurricanes in each of the five strength categories is given. Thus, in 1851 (the first year of the record) there was one Category 1 hurricane and one Category 3 hurricane, and so forth. Add columns for the following quantities:  Total numbers of hurricanes.  Average intensity.  Percent of strong hurricanes (category 3 and higher). Adjust the Column width if necessary. Your worksheet should look as follows: For each year, the Total Number is the sum of however many hurricanes there are in each strength category. We can use the SUM function to get this total. Place the cursor in Cell G3 and type the following: =SUM(B3:F3) which results in summation of all the values in cells B3 to F3. Now rather than typing in Cell G4 the formula =SUM(B4:F4) and so forth until we get to the end of the record, we can use an Excel short-cut. Place the cursor over the little square in the lower-right corner of Cell G3, as shown below. The left click and drag the mouse down to the end of the record. This copies and adjusts the formula for all of the cells. You can check by clicking on any of the cells in Column G and reading the formula in the bar. 7

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To calculate the Average Intensity in any given year, we add the number of hurricanes in each category multiplied by the strength of each category and divide by the total number of hurricanes in that year. For some years, such as in 1862-1864, the total number of hurricanes is zero. Since Excel gives an error message when dividing by zero, we add a tiny number to the denominator and type the following formula in Cell H3: = (B3*1 + C3*2 + D3*3 + E3*4 +F3*5) / (G3+1.0E-10) Again, copy the formula to all other cells in column H, and the worksheet should look like this: 9

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Finally, the percent of strong hurricanes equals the number of hurricanes in column D through F, divided by the total number of hurricanes (again, with a small number added to prevent division by zero). So, in cell I3 we type = 100*SUM(D3:F3) / (G3+1.0E-10) After copying this formula to all cells in column I we get the following: The next step is to make graphs of these quantities, showing how they changed over time. To insert a graph, first highlight both column A and column G, by first clicking on the “A” of the first column, holding down the “ctrl” key on a PC and the “Command ⌘” key on a Mac, and click on the “G”. Both co9lumns should now be highlighted. Goto Insert – Recommended Charts and select the line chart. Copy and paste this chart into your answer. Do the same for Average Intensity and Percent Strong Hurricanes. You should now have three graphs pasted in your document. 10

Because there is large interannual variability, looking at the 5-year running mean can reveal any trends. For any function F(t), the 5-yr running mean is defined as F ave = [F(t-4) + F(t-3) + (F(t-2) + F(t-1) + (F(t)] / 5 11

Since the record starts with 1851, the first year for which we can calculate the 5-yr running mean is 1855. In Cell J7 we type the following formula: =SUM(G3:G7)/5 and repeat this formula for all other cells in column J. Doing the same for the other two quantities, the worksheet should look like this: Create another three plots to show these 5-yr running averages and paste these also into your answer sheet. Note: you can create six different graphs, or you can create three graphs that show the annual values plus the 5-yr running mean in one graph. To plot two time series in the same plot highlight column A, G and J all at once and go to Insert and Recommended Chart which should show you the option of two lines in one graph. 12

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Now you can answer the following questions:  Can you observe any long-term trends in any of the three quantities? o Not really, except for the fact that it looks like there may be more strong hurricanes as the graph goes along, but that seems to be it.  Are there unusual time periods in these data? o The early 2000s seemed to have more hurricanes than other years.  Is the data reliable, especially for the earlier period? Why or why not? o The earlier data is much less reliable than the data recorded via machines meant to detect this. This is also due to much of the data being collected via word of mouth rather than actual collection methods.  Any other comments? o Nope! Submission Upload your completed assignment to Canvas before this Friday at 11:59 pm . Note that only the Word or pdf document is required – you DO NOT submit the modified Excel file! 14

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