Now do question 3 mark your choice or choices in

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Now do question 3; mark your choice or choices. In question 3, statements 2, 3, and 4 are true. Number 3, you will note, states that level ground receives about the same intense heating as south aspects. We're usually talking about valley bottoms here. Also remember that at night, temperatures on south slopes and valley bottoms may be much different due to-surface inversions and thermal belt effects. On page 10, we see more topographic effects on fuel temperatures. Time of the year influences the amount of solar heating received, thus affecting ground surface and air temperatures. Figure 9 gives the amount of solar heat received at Boise, Idaho, by average day of month. For example, during March, this area receives about 1,250 BTUs per average day per square foot of horizontal surface. July receives the highest amount of solar heating at almost 2500 BTUs per
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average day per square foot. The average day in July receives twice as much solar heat as an average day in March. Now let's look at September. It receives about 1,700 BTUs per square foot on an average day. You may have noted that although solar equinoxes; that is, equal days and nights, occur during the months of March and September, September receives considerably more solar heating than March. Why is this? Well, the reason is that there are more cloudy days at Boise during March than September. Actually, when the sun is shining, March 21 should receive about the same amount of solar heating as September 21. The point that we want to make here is that time of year has considerable influence on fuel temperatures and fuel moisture contents. Latitude, or distance north of the equator, also has some effect on the amount of solar heating received. Although heating values will vary by locality, the shape of the Boise curve is mostly representative of that of the contiguous states. The curve will be considerably different for Alaska and northern Canada. How about elevation? Figure 10 illustrates the accepted "normal" temperature lapse rate of about 3-1/2° decrease per 1,000 feet of elevation rise. Note that as temperature decreases with elevation, the relative humidity increases. We have determined fuel moisture percents for the given temperatures and relative humidities as listed at the right. In this example, with an elevation rise of 5,000 feet, dead fuel moisture contents have increased from 4 percent to 8 percent. Together with later curing dates and higher green to dead fuel ratios at higher elevations, the overall fuel moisture differences can be very significant to fire ignition and spread-rates. On page 11, question 4 is about elevation. Please mark your choice or choices. In question 4, you should have marked statements 1, 3, and 4. Each of these definitely affects fuel moisture contents. Obviously, number 2 should state that snow melt dates are later at higher elevations, which also makes curing dates later in the season.
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  • Spring '04
  • MIchealJenkins
  • fuel moisture

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