California wildfires 2017 - Thomas Fire analysis¶

The Thomas Fire was a massive wildfire that started in early December 2017 in Ventura and Santa Barbara counties and grew into California's largest fire ever.

In [43]:

import arcgis
from arcgis import *
from arcgis.mapping import MapImageLayer

In [44]:

gis = GIS("https://python.playground.esri.com/portal", "arcgis_python", "amazing_arcgis_123")

Visualize the extent of damage¶

In [45]:

from ipywidgets import *

postfire = MapImageLayer('https://tiles.arcgis.com/tiles/DO4gTjwJVIJ7O9Ca/arcgis/rest/services/Digital_Globe_Imagery_Dec_11th/MapServer')

def side_by_side(address):
    location = geocode(address)[0]

    satmap1 = gis.map(location)
    satmap1.basemap = 'satellite'

    satmap2 = gis.map(location)
    satmap2.add_layer(postfire)

    satmap1.layout=Layout(flex='1 1', padding='6px', height='450px')
    satmap2.layout=Layout(flex='1 1', padding='6px', height='450px')

    box = HBox([satmap1, satmap2])
    return box

Nob Hill, Ventura, CA¶

In [84]:

side_by_side('Montclair Dr, Ventura, CA')

Out[84]:

Vista Del Mar Hospital, Ventura, CA¶

In [86]:

side_by_side('801 Seneca St, Ventura, CA 93001')

Out[86]:

Remote Sensing and Image Processing¶

In [48]:

landsat_item = gis.content.search('title:Multispectral Landsat', 'Imagery Layer', outside_org=True)[0]
landsat = landsat_item.layers[0]
landsat_item

Out[48]:

Multispectral Landsat
Landsat 8 OLI, 30m Multispectral 8 band scenes with visual renderings and indices. Updated daily. Based on the Landsat on AWS collections.

Imagery Layer by esri_livingatlas
Last Modified: October 07, 2016
0 comments, 0 views

Select before and after rasters¶

In [49]:

aoi = {'spatialReference': {'latestWkid': 3857, 'wkid': 102100}, 'type': 'extent', 
       'xmax': -13305000, 'xmin': -13315000, 'ymax': 4106000, 'ymin': 4052000}

arcgis.env.analysis_extent = {"xmin":-13337766,"ymin":4061097,"xmax":-13224868,"ymax":4111469,
                              "spatialReference":{"wkid":102100,"latestWkid":3857}}

landsat.extent = aoi

In [50]:

import pandas as pd
from datetime import datetime

selected = landsat.filter_by(where="(Category = 1)",
                             time=[datetime(2017, 11, 15), datetime(2018, 1, 1)],
                             geometry=arcgis.geometry.filters.intersects(aoi))

df = selected.query(out_fields="AcquisitionDate, GroupName, CloudCover, DayOfYear", 
                    order_by_fields="AcquisitionDate").sdf
df['AcquisitionDate'] = pd.to_datetime(df['AcquisitionDate'], unit='ms')
df.tail(5)

Out[50]:

	AcquisitionDate	CloudCover	DayOfYear	GroupName	OBJECTID	SHAPE	Shape_Area	Shape_Length
0	2017-11-23 18:34:42.440000057	0.0441	327	LC80420362017327LGN00_MTL	668630	{"rings": [[[-13208036.3849, 4199102.123899996...	5.131484e+10	906509.716682
1	2017-12-09 18:34:39.503999949	0.2136	343	LC80420362017343LGN00_MTL	681950	{"rings": [[[-13208251.4004, 4199098.6241], [-...	5.127378e+10	906136.246386
2	2017-12-25 18:34:42.003000021	0.6529	359	LC80420362017359LGN00_MTL	692453	{"rings": [[[-13210387.2213, 4199063.157099999...	5.129089e+10	906293.823931

In [72]:

prefire = landsat.filter_by('OBJECTID=668630') # 2017-11-23 
midfire = landsat.filter_by('OBJECTID=681950') # 2017-12-09

Visual Assessment¶

In [90]:

from arcgis.raster.functions import *

apply(midfire, 'Natural Color with DRA')

Out[90]:

Visualize Burn Scars¶

Extract the [6, 4, 1] bands to improve visibility of fire and burn scars. This band combination pushes further into the SWIR range of the electromagnetic spectrum, where there is less susceptibility to smoke and haze generated by a burning fire.

In [92]:

extract_band(midfire, [6,4,1])

Out[92]:

In [93]:

extract_band(prefire, [6,4,1])

Out[93]:

For comparison, the same area before the fire started shows no burn scar.

Quantitative Assessment¶

The Normalized Burn Ratio (NBR) can be used to delineate the burnt areas and identify the severity of the fire.

The formula for the NBR is very similar to that of NDVI except that it uses near-infrared band 5 and the short-wave infrared band 7: \begin{align} {\mathbf{NBR}} = \frac{\mathbf{B_5} - \mathbf{B_7}}{\mathbf{B_5} + \mathbf{B_7}} \\ \end{align}

The NBR equation was designed to be calcualted from reflectance, but it can be calculated from radiance and digitalnumber(dn) with changes to the burn severity table below.

For a given area, NBR is calculated from an image just prior to the burn and a second NBR is calculated for an image immediately following the burn. Burn extent and severity is judged by taking the difference between these two index layers:

\begin{align} {\Delta \mathbf{NBR}} = \mathbf{NBR_{prefire}} - \mathbf{NBR_{postfire}} \\ \end{align}

The meaning of the ∆NBR values can vary by scene, and interpretation in specific instances should always be based on some field assessment. However, the following table from the USGS FireMon program can be useful as a first approximation for interpreting the NBR difference:

\begin{align}{\Delta \mathbf{NBR}} \end{align}	Burn Severity
0.1 to 0.27	Low severity burn
0.27 to 0.44	Medium severity burn
0.44 to 0.66	Moderate severity burn
> 0.66	High severity burn

[Source: http://wiki.landscapetoolbox.org/doku.php/remote_sensing_methods:normalized_burn_ratio]

Use Band Arithmetic and Map Algebra¶

In [55]:

nbr_prefire  = band_arithmetic(prefire, "(b5 - b7) / (b5 + b7+1000)")
nbr_postfire = band_arithmetic(midfire, "(b5 - b7) / (b5 + b7+1000)")

nbr_diff = nbr_prefire - nbr_postfire

In [56]:

burnt_areas = colormap(remap(nbr_diff,
                             input_ranges=[0.1,  0.27,  # low severity 
                                           0.27, 0.44,  # medium severity
                                           0.44, 0.66,  # moderate severity
                                           0.66, 1.00], # high severity burn
                             output_values=[1, 2, 3, 4],                    
                             no_data_ranges=[-1, 0.1], astype='u8'), 
                       colormap=[[4, 0xFF, 0xC3, 0], [3, 0xFA, 0x8E, 0], [2, 0xF2, 0x55, 0], [1, 0xE6, 0,    0]])

In [57]:

burnt_areas.draw_graph()

Out[57]:

Area calculation¶

In [58]:

ext = {"xmax": -13246079.10806628, "ymin": 4035733.9433013694, "xmin": -13438700.419344831, "ymax": 4158033.188557592,
       "spatialReference": {"wkid": 102100, "latestWkid": 3857}, "type": "extent"}
pixx = (ext['xmax'] - ext['xmin']) / 1200.0
pixy = (ext['ymax'] - ext['ymin']) / 450.0

res = burnt_areas.compute_histograms(ext, pixel_size={'x':pixx, 'y':pixy})

numpix = 0
histogram = res['histograms'][0]['counts'][1:]
for i in histogram:
    numpix += i

Report burnt area¶

In [59]:

from IPython.display import HTML
sqmarea = numpix * pixx * pixy # in sq. m
acres = 0.00024711 * sqmarea   # in acres

HTML('<h3>Thomas fire has consumed <i>{:,} acres</i>  till {}</h3>.'.format(int(acres), df.iloc[-1]['AcquisitionDate'].date()))

Out[59]:

Thomas fire has consumed 341,676 acres till 2017-12-25

In [60]:

import matplotlib.pyplot as plt
%matplotlib inline

plt.title('Distribution by severity', y=-0.1)
plt.pie(histogram, labels=['Low Severity', 'Medium Severity', 'Moderate Severity', 'High Severity']);
plt.axis('equal');

Visualize burnt areas¶

In [94]:

m = gis.map('Carpinteria, CA')
m

Out[94]:

In [63]:

m.add_layer([midfire, burnt_areas])

Raster to Feature layer conversion¶

Use Raster Analytics and Geoanalytics to convert the burnt area raster to a feature layer. The to_features() method converts the raster to a feature layer and create_buffers() fills holes in the features and dissolves them to output one feature that covers the extent of the Thomas Fire.

In [65]:

from arcgis.geoanalytics.use_proximity import create_buffers

fire_item = burnt_areas.to_features(output_name='ThomasFire_Boundary')

fire_layer = fire_item.layers[0]
fire_layer.filter = 'st_area_sh > 3000000'

fire = create_buffers(lyr, 100, 'Meters', dissolve_option='All', multipart=True, output_name='ThomasFire')

In [67]:

fire = gis.content.search('Thomas_Fire', 'Feature Layer')[0]
fire

Out[67]:

Thomas_Fire_Boundary
Thomas_Fire_Boundary

Feature Layer Collection by arcgis_python
Last Modified: June 22, 2018
0 comments, 0 views

In [98]:

vectormap = gis.map('Carpinteria, CA')
vectormap.basemap = 'dark-gray'
vectormap.add_layer(fire)
vectormap

Impact Assessment¶

Compute infrastructure and human impact¶

In [69]:

from arcgis.geoenrichment import enrich
from arcgis.features import SpatialDataFrame

sdf = SpatialDataFrame.from_layer(fire.layers[0])

fire_geometry = sdf.iloc[0].SHAPE
sa_filter = geometry.filters.intersects(geometry=fire_geometry, sr=4326)

secondary_roads_layer = FeatureLayer("https://tigerweb.geo.census.gov/arcgis/rest/services/TIGERweb/Transportation_LargeScale/MapServer/1")
secondary_roads = secondary_roads_layer.query(geometry_filter=sa_filter, out_sr=4326)

local_roads_layer = FeatureLayer("https://tigerweb.geo.census.gov/arcgis/rest/services/TIGERweb/Transportation_LargeScale/MapServer/2")
local_roads = local_roads_layer.query(geometry_filter=sa_filter, out_sr=4326)

def age_pyramid(df):
    import warnings
    import seaborn as sns
    import matplotlib.pyplot as plt

    %matplotlib inline
    warnings.simplefilter(action='ignore', category=FutureWarning)
    pd.options.mode.chained_assignment = None 
    plt.style.use('ggplot')

    df = df[[x for x in impacted_people.columns if 'MALE' in x or 'FEM' in x]]
    sf = pd.DataFrame(df.sum())
    sf['age'] = sf.index.str.extract('(\d+)').astype('int64')

    f = sf[sf.index.str.startswith('FEM')]
    m = sf[sf.index.str.startswith('MALE')]
    f = f.sort_values(by='age', ascending=False).set_index('age')
    m = m.sort_values(by='age', ascending=False).set_index('age')

    popdf = pd.concat([f, m], axis=1)
    popdf.columns = ['F', 'M']
    popdf['agelabel'] = popdf.index.map(str) + ' - ' + (popdf.index+4).map(str)
    popdf.M = -popdf.M
    
    sns.barplot(x="F", y="agelabel", color="#CC6699", label="Female", data=popdf, edgecolor='none')
    sns.barplot(x="M",  y="agelabel", color="#008AB8", label="Male",   data=popdf,  edgecolor='none')
    plt.ylabel('Age group')
    plt.xlabel('Number of people');
    return plt;

Visualize affected roads on map¶

In [97]:

impactmap = gis.map('Carpinteria, CA')
impactmap.basemap = 'streets'

impactmap

In [71]:

impactmap.draw([local_roads, secondary_roads])

Age Pyramid of affected population¶

In [25]:

impacted_people = enrich(sdf, 'Age')
age_pyramid(impacted_people);

ArcGIS API for Python Sample Notebooks