Introduction to wildfires. Assoc. Prof. Dr. Simon Schnabl Assist. Marko Radak

Transcription

1 Introduction to wildfires Assoc. Prof. Dr. Simon Schnabl Assist. Marko Radak 1

2 Outline What is natural disaster? What is fire? What is wildfire? Global wildfire map What causes wildfires? Wildfire spread Behavior of wildfires Effects of wildifres Fighting wildfires Wildfires statistics Wildfire modeling Cellular automata (1D, 2D) Wildfire simulation Conclusions 2

3 What is a natural disaster? A natural disaster is a major adverse event resulting from natural processes of the Earth. A natural disaster can cause loss of life or property damage. Natural disasters Geological disasters Meteorological disasters Hydrological disasters Wildfires Avalanches and landslides Eartquakes Sinkholes Volcanic eruptions Floods Limnic eruptions Tsunames Blizzards Cyclonic storms Droughts Thunderstorms Hailstorms Heat waves Tornadoes Space disasters Impacts Solar storms 3

4 What is a fire? Simple, it is the visible part of a combustion. A combustion is a chemical reaction of three things: Heat, Fuel and Oxygen. These three ingredients must be present before a fire can be made and maintained. This can be best explained in the fire triangle below. For the fire triangle to stand, all three ingredients must be present. If the heat is not enough, or the fuel runs out, or the oxygen runs out, the fire will be out!!! HEAT SOURCE SELF-SUSTAINING COMBUSTION Oxidant: a gas found in air (21%, fire 16%) Fuel: gas, liquid or solids; Solid fuel: wood, dry leaves, dry branches, Heat: spark, lightning, campingfire,. 4

5 What is a wildfire? A wildfire or wildland fire is a fire in an area of combustible vegetation that occurs in the countryside or rural area. Depending on the type of vegetation where it occurs, a wildfire can also be classified more specifically as a: Wilfires Hill fire Brush fire Grass fire Forest fire Bush fire Desert fire Vegetation fire Peat fire 5

6 global wildfire map 6

7 What causes wildfires? Four major natural causes of wildfire ignitions exist: lightning (USA, Canada, Australia, northwest China) sparks from rockfalls spontaneous combustion volcanic eruption Human causes of wildfire ignitions are: arson agriculture, animal husbandry, land-conversion burning, discarded cigarettes (China, Mediterranean Basin) power-line arcs sparks from equipment (e.g. trains) (USA, Australia, ) fireworks, campfires, 7

8 Wildfire spread The spread of wildfires varies based on the flammable material present, its vertical arrangement and moisture content, and weather conditions. Overall, fire types can be generally characterized by their spread as follows: Ground fires burn organic material in the soil. This is a slower burning fire, usually under litter or under vegetation. They burn by glowing combustion. Surface fires burn on the surface of the ground. They burn dry leaves, broken twigs and branches and other materials on the ground. These fires spread quickly. Crown fires burn with huge flames and has intense heat and power. They burn from tree top to tree top and spread very quickly with the wind and heat. It is even worse if they are exposed to steep slopes. 8

9 Behaviour of wildfires Major factors that make wildfires burn more and quicker: Wind Wind directs or changes direction of fire to new areas with new fuels. Additionally, it provides fresh supply of oxygen, a key ingredient of fire, to the situation. Slope Wild fires usually move faster uphill than downhill. The steeper the slope, the faster they burn. This is because steeper slopes tend to have lots of fuels in close proximity and the wind action if much more aggressive uphill. Temperature Conditions with higher temperature tend to absorb moisture from fuels and make them conducive to catch fire. This is why areas with lots of sun and higher temperatures tend to be dry and has more fire events. 9

10 Behaviour of wildfires Humidity Fuels in locations with high humidity and rainfall tend to be damp and moist. Humidity is the amount of water vapor in the air. The higher it is, the higher the moisture in the fuels there and the less likely they are to catch fire. Fuels and space between fuels The ease at which wildfires spread also depends on the fuel composition. Trees and vegetation with lots of moisture tend to slow down fires than dry vegetation such as dry grass, dead leaves, tree needles, brush and small trees. Additionally, some vegetation with high oils and resins aid combustion and makes fires burn with more ease. Wildfires burn more and spread faster if there are more fuels in close proximity Times and seasons In many places, the seasons tell a story. In the US, the summer stretch registers lots of fires. That is because the summer heat makes fuels drier and provides richer oxygen than the winter seasons. In many places in West Africa, the onset of the dry Harmattan Winds from the Sahara desert in the dry seasons make fires burn more. 10

11 Effects of wildfires Economic costs Wildfires can do immediate damage to wildlife and vegetation. Fires also destroy houses and almost anything in its way. Additionally, the city spends millions of money to fight them with chemicals, logistics, aircrafts and trucks, time and personnel. The economic loss can be huge. Soils and organic matter Take forest soils for example. Forest soils are rich in decaying debris and nutrients, and are composed of many natural features that support a myriad of life forms and organic activities. Wildfires raise the temperatures of these soils to over 900 C and this potentially wipes away almost all the organic value of the soil. Watershed The effect on watershed is also key. Burned organic matter in the soil (volatized organic compounds) also affect the natural layering of the soils. This negatively affects infiltration and percolation, making the soil surfaces water repellent. Water therefore is unable to drain into water tables and the run-offs on the surfaces cause erosion. Researchers believe that forest fires are not all that bad, as they have some benefits too. In fact, they believe that even though young animals and birds may die, many animals are able to escape or move away from fires. Many plants easily grow back and there is usually good recovery after a fire. 11 Some plants have their seeds opened up and exposed to ash-enriched soils.

12 Fightning wildifres Different fires are fought differently, but the big idea is usually the same to deprive the fire of its fuel and let it go out by itself. This can be achieved in many ways. Firelines of firebreaks With bull dozers and land equipment, firefighters clear a ring around the fire area and to get rid of all fuel in the fire s path. As the fire gets to the ring, it can no longer spread as there is no fuel in its path. Firing out Fire fighters look for a natural edge or boundary, such as a road, stream or plain field, and they do a controlled burn of all the fuel between the barrier and the fire. Aircrafts Special aircrafts call air tankers fly over the fire and dump water, fire retardant (eg. the pink coloured one is called jelly-o) and chemicals (foam) on the fire. Technology These days, satellites, computers, aircrafts and digital equipment are used to monitor fires, forecast wind directions and create instant and effective maps and information needed to fight fires. Fireman Trained firefighters are key to fighting fires 12

13 wildifres Statistics 13

14 wildifre modelling In computational science, wildfire modeling is concerned with numerical simulation of wildland fires in order to understand and predict fire behavior. Wildfire modeling can ultimately increase safety of firefighters and the public, reduce risk, and minimize damage. Approaches to wildfire modeling Wilfire models have been developed since 1940 to the present, but a lot of chemical and thermodynamic questions related to fire behaviour are still to be resolved. Wildfire models: Theoretical models Empirical models Semi-empirical Simulation models (Cellular automata -CA) A simple wildfire propagation model 14

15 USE OF CELLULAR AUTOMATA (CA) Cellular automata/cellular automaton Discrete dynamical system Modeling complex behavior Dimension 1 n Lattice of cells Cell state 2 k Neighborhood Local transition rules Animating cells at time steps (t = 0, 1, 2...) Visualisation of cell behavior 15

16 CELLULAR AUTOMATA - 1D CA Lattice of cells 1 d < ; d = dimension of lattice, e.g. d=1 is 1D lattice Cell state 2 k ; k = number of cell states, e.g. in binary state, k = 2, (states 0 and 1) Neighborhood (r =radius of neighborhood) Local transition rules (φ) Generation (t =time step, e.g. t = n, n th generation) n th generation (t =n)... C i,j 1 (t) C i,j (t) C i,j+1 (t)... C i+1,j t + 1 = φ[ C i,j 1 t, C i,j t, C i,j+1 t ] e.g. 1D, r = 1, k = 2 2r+1... Cell neighborhood (3 cell unit) k = 2 cell state (binary: 0,1) k 2r = 8 combinations 2 8 =256 transition rules e.g. r = 2, k = = = 4.294,967,296 transition rules e.g. r = 1, k = = =

17 10 generations 1D CA Local transition rules Initial time step t=0 {i, j} {i, j-1}, {i, j+1} ; t = 0 Next time step t=1 {i+1,j} in time step t +1 i + 1, j t+1 depends on { i, j 1, i, j, i, j + 1 } t +transition rules 200 generations 17

18 CELLULAR AUTOMATA - 2D CA C i+1,j C i+1,j-1 C i+1,j C i+1,j+1 C i,j-1 C i,j C i,j+1 C i,j-1 C i,j C i,j+1 C i-1,j C i-1,j-1 C i-1,j C i-1,j+1 von Neumann, r = 1 Moore, r = 1 von Neumann r = 1 k = 2, r =1 k = 2, r =1 Moore r = = = 4,294,967,296 transition rules 2 9 = = 1, transition rules 18

19 Programming principle of binary 1D CA 19

20 Wildfire simulation - 2D ca 20

21 summary Phenomenon Wildfire Socioeconomic influence Wildfire Modeling Cellular automata Homogenity Locality Parallelism 21