Lecture 9 + 10: fire and climate change

Question 1

difference between climate and weather

Answer 1

• climate - long term variations (30 years or more)
• weather - short term variations (a few days to a few years)

Question 2

Global energy budget

Answer 2

• powered by the sun
• energy received by the sun is 4000 times greater than the energy that is within the earth’s interior

Question 3

greenhouse effect

Answer 3

• where gases in the lower atmosphere absorb and reradiate the energy to the earth
• water vapor = the most abundant gas
• CO2
• methane

Question 4

Hydrologic cycle

Answer 4

• 24% of solar energy is used to evaporate water in the hydrologic cycle
• water is uniquely qualified to be a medium for energy transfer

Question 5

Coriolis effect

Answer 5

• forces imposed on the earth by the earth’s rotation
• sets cold and warm air into motion
• influences ocean surface water motion which in turn influences the motion of deep ocean water
• the force responsible for transporting the energy stored in water around the world

Question 6

ice age

Answer 6

• icehouse: an ice age where glaciers are created
• requirements (1) large continental masses near the poles to collect snowfall and build ice sheets and (2) ocean circulation that favors north-south directions

Question 7

mitigation strategies for climate change

Answer 7

• reduce greenhouse gas
• Paris agreement
• who pays for it? it’s hard to get all countries to agree

Question 8

benefits of fire

Answer 8

• the boreal frosts is a fire-dependent ecosystem
• certain plants need smoke and or fire to germinate their seeds
• control parasite
• percent overaccumulation of organic debris

Question 9

lightning caused fires

Answer 9

• occur in remote locations
• burn undetected longer
• tend to merge into large fires

Question 10

duff

Answer 10

• mat or organic debris on the ground
• lightning on moist duff does not start fires
• lighting on dry duff starts fired

Question 11

pyrolysis

Answer 11

• receding combustion is pyrolysis
• chemical decomposition by the action of heat
• input: wood material heated above initiation temperature
• output: flammable hydrocarbon vapors; water vapor; tar; mineral residue

Question 12

combustion

Answer 12

• the act of burning

Question 13

three stages of combustion of wood

Answer 13

• preheating: resting T degrees expels water from wood
• flaming combustion: stage if greatest energy release; if heat and oxygen are present, hydrocarbon vapors from pyrolysis ignite. moves slowly into wood through cracks
• smoldering and glowing combustion: flames gradually die off; slowing combustion: heat slowly reaches the interior of the log

Question 14

heat transfer mechanisms

Answer 14

• conduction: transfer through a material or between materials in contact
• convection: transfer through fluid
• radiation: heat transfer via radiation (like warming coffee in microwave)

Question 15

heat transfer in a log-tree

Answer 15

• heat moves inward (conduction: particles in pyrolyzed gases in cracks)
• heat moves outward (conduction from collisions of particles from hot to cold areas)

Question 16

how do forests fires kill trees

Answer 16

• damage to trunk (localized cell death)
  - controlling factors: bark thickness; stem diameter; stem water content
• damage to crown
  - thick foliage provides some shielding to branches
  - injury to branches, leaves and buds
  - controlling factors: thermal properties of crown (mass, water content) and temperatures and residence time of hot air plume
• damage to roots
  - smoldering particularly harmful
  - causes: heat transfer to roots by conduction
  controlling factor: duration of soil heating

Question 17

the spread of fire

Answer 17

• fuel (duff, plant)
• topography (fire burns faster upslope like holding a match downward)
• weather (wind) (brings O2 and pushes flame or transports embers
• fire behavior

Question 18

firestorm

Answer 18

• fire powerful enough to create own winds - hot air is less dense and rises into a convection column creating a low-pressure area on the ground
• danger to firefighters
• occasional fire whirls
• jets of air flowing downwards the ground

Question 19

fire danger rating system

Answer 19

• looking at moisture, drought, wind and buildup

Question 20

prescribed burning

Answer 20

• planned and controlled burns
• removes built-up fuel loads- reduces the risk of large uncontrollable fire

Question 21

air tanker

Answer 21

• canada is a world leader
• minimum depth: 2m
• minimum length of water body: 1500m
• can carry water and or fire retardant
• drop form a height of 30-35m
• only summers in canada

Question 22

fighting fire with fire

Answer 22

• back fire
• fire deliberately set to consume fuel in front of an ascending fire in order to stop it