Beth Tellman1, Ken Maits2, Jonathan Giezendanner1, Rohit Mukherjee1, Hannah Friedrich1, Eleonora Demaria2 1 University of Arizona 2 Pima County Regional Flood Control District
Flooding in the desert: Assessing the value of satellite observations of inundation from the North American Monsoon with the Pima County Regional Flood Control District
Extent & Duration Analytics for each Flood Event
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Table 1. Water detection algorithms used for each sensor
@pazjusticiavida |https://beth-tellman.github.io/
Flood Monitoring
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Finding cloud free images at peak- temporal/spatial frequency makes Planetscope more valuable than other sensors
We will help protect 10 million people and seed global resilience by enabling everyone at risk access to the disaster information they need.
btellman@Arizona.edu
Satellite sensors considered
Flood Frequency (years)
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30
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For each flood event, we use a python script to generate a graph showing the available remote sensing images, along with the percentage of overlap with the Region of Interest (RoI) and % of cloudiness.For successful flood mapping in the desert, consecutive cloud free images are needed to map rapid soil moisture change, and only Planetscope can provide that frequency.
Social [Pixel] Lab
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Can satellite observations show floods outside the 100-year floodplain?
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100-year floodplains in Tucson Arizona mapped by FEMA,
the County, and developers
-It floods in the desert! The North American Monsoon brings intense storms and sometimes flash floods each summer. 2021 was the third wettest on record in Tucson (12.79 inches).
-broad, shallow floodplains here have poorly defined distributary flow networks, making flood water hard to model. More extreme precipitation with climate change also broadens floodplains.
-updating flood maps important for insurance access, targeting buyouts, and investing in flood resilience
Flood date, 31st July 2022
Cloud Free PlanetScope next day!
Jul 31, 2022
Aug 1, 2022
Example of two consecutive days covering a flood event, along with the available Planetscope images for the RoI.
Finding peak flood with precipitation in 2021 and 2022
Pima County identified 10 flood events, of which 7 had with likely satellite coverage in the past 2 years. With the help of Earth Engine, spatial and temporal precipitation (NLDAS) time series to understand when and where the peak flood event likely occurred to search for imagery.
PUBLIC EARTH ENGINE APP TO GENERATE HYETOGRAPHS/MAPS: https://jgiezendanner.users.earthengine.app/view/pimacountyrainfallmonitoringnldas
Return Time - MODIS
Multi-approach model validation with road closures and hand labeled PlanetScope data
Pre-Rainfall
31 July 2022
Post-Rainfall
1 August 2022
Random Forest
Wet Soil
Dry Land
Vegetation
Standing Water
Road Closure
The first approach is to assess observable floods using road closure points. Leading up to expected flooding, roads are closed to reduce losses and minimize harm. We use the point data locations and dates of closure on road segments to estimate the percent of flooded roads that satellites classifications identify as flooded.
The second approach is image classification accuracy assessment, where overall accuracy, commission and omission errors will be calculated. To conduct the accuracy assessment of observed flooding, we will visually interpret PlanetScope imagery to create hand labeled annotations of flood and wet soil and compare with the model output. We will use the road closure points to determine locations where labels will be generated, and subsequently used to validate model accuracy.
Of 10 floods examined, only 7 had suitable cloud-free imagery with visible standing water
Monsoon floods occur in late afternoon and evening, but most satellite overpasses occur around 10 am, 12-20 hours after rainfall peaks
Most water has receded before satellite overpass (except in insets, green water), but some standing water remains matching modeled floodplains
Planscope False Color Image Composite (NIR, R, G) Sewailo Golf Club, Pima County, Arizona
Before Rainfall, 31st July
After Rainfall, 1st August
Changing flow paths and flood patterns in construction sites
Changing flow paths and flood water potentially due to new construction can be observed with daily Planetscope imagery. Left shows an example of water retention on an unfinished construction site property after August 1 2022 heavy rain in Northen Tucson in the Catalina foothills.
Standing Water
Can wet soils show us where the water went?
Changes in the Near-Infrared (NIR) band where reflectance decreases the day following floods reveal wet soil in addition to standing water. Threshold NIR change or random forest approaches are promising to differentiate classes of standing water versus wet soils were water flowed.
water
wet
Blue: Possible signatures of water flow paths where NIR drop from the 31st July - 1st Aug (‘22) flood event.
drier
wetter
NIR Threshold change approach
Random Forest approach
PlanetScope False Color Composite
RoI
Planet Scenes
2005 pre earth moving
2022 construction
July 31 2022 pre storm
Aug 1 2022 post storm