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ERDS: a satellite-based approach in the extreme rainfall detection field

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Abstract

Many studies have shown a growing trend, in terms of number, frequency and severity of extreme events. As never before, having tools capable to monitor the amount of rain that reaches the Earth’s surface has become a focal point for the identification of areas potentially affected by floods. In order to guarantee an almost global spatial coverage, a precipitation evaluation provided by satellite products proved to be the most appropriate source of information. NASA GPM (Global Precipitation Measurement) mission provides since March 2014 different IMERG (Integrated Multi-satellite Retrievals for GPM) products with a spatial coverage of 60°N - 60°S and a spatial resolution of 0,1° x 0,1°. The first part of our study is aimed to compare at the global scale satellite IMERG early and late data and rain gauge precipitation data, in order to evaluate their relative accuracy. The outcomes demonstrate that satellite data guarantees good result when rainfall aggregation interval is equal or greater than 12 hours. More specifically a 24-hours aggregation interval ensures a probability of detection (defined as the number of hits events divided by the total number of observed events) greater than 80% and a bias of -0,1 mm/h. With an aggregation interval of 72 hours a probability of detection greater than 90% is reached. The outcomes of this analysis supported the development of the updated version of the ITHACA Extreme Rainfall Detection System (ERDS - erds.ithacaweb.org). This system is now able to provide hourly near-real time alerts about extreme rainfall events. ERDS is a strategic tool, capable to provide, during the preparedness and response phases of the emergency cycle, immediate and intuitive information about potential flood events. The information is accessible through a WebGIS application, developed in a complete Open Source environment. Results are published on ERDS website by means of standard WMS services. Specifically, this system automatically downloads the most recent GPM IMERG early run half-hourly data and cumulates it according to specific periods (12hr, 24hr, 48hr, 72hr, 96hr). ERDS generates precipitation alerts where and when the precipitation amount is higher than a specific set of thresholds. This set of thresholds has been calculated for every aggregation interval on the basis of the average annual precipitation values evaluated on a 0,1° x 0,1° grid cell basis.
AIT2018 Firenze 4-6 July 2018
137
Session Application of remote sensing for floods monitoring and hydraulic risk assessment
Friday, 6 July 2018 (15:00 -16:30)
Congress Hall - Chairman: Maria Teresa Melis
Paola Mazzoglio¹, Piero Boccardo², Francesco Laio², Simone Balbo¹, Franca Disabato¹
ERDS: a satellite-based approach in the extreme rainfall detection field
Many studies have shown a growing trend, in terms of number, frequency and severity of extreme events. As never
before, having tools capable to monitor the amount of rain that reaches the Earth’s surface has become a focal point
for the identification of areas potentially affected by floods. In order to guarantee an almost global spatial coverage,
a precipitation evaluation provided by satellite products proved to be the most appropriate source of information.
NASA GPM (Global Precipitation Measurement) mission provides since March 2014 different IMERG (Integrated
Multi-satellite Retrievals for GPM) products with a spatial coverage of 60°N - 60°S and a spatial resolution of 0,1°
x 0,1°. The first part of our study is aimed to compare at the global scale satellite IMERG early and late data and
rain gauge precipitation data, in order to evaluate their relative accuracy. The outcomes demonstrate that satellite
data guarantees good result when rainfall aggregation interval is equal or greater than 12 hours. More specifically
a 24-hours aggregation interval ensures a probability of detection (defined as the number of hits events divided
by the total number of observed events) greater than 80% and a bias of -0,1 mm/h. With an aggregation interval
of 72 hours a probability of detection greater than 90% is reached. The outcomes of this analysis supported the
development of the updated version of the ITHACA Extreme Rainfall Detection System (ERDS - erds.ithacaweb.org).
This system is now able to provide hourly near-real time alerts about extreme rainfall events. ERDS is a strategic
tool, capable to provide, during the preparedness and response phases of the emergency cycle, immediate and
intuitive information about potential flood events. The information is accessible through a WebGIS application,
developed in a complete Open Source environment. Results are published on ERDS website by means of standard
WMS services. Specifically, this system automatically downloads the most recent GPM IMERG early run half-hourly
data and cumulates it according to specific periods (12hr, 24hr, 48hr, 72hr, 96hr). ERDS generates precipitation
alerts where and when the precipitation amount is higher than a specific set of thresholds. This set of thresholds
has been calculated for every aggregation interval on the basis of the average annual precipitation values evaluated
on a 0,1° x 0,1° grid cell basis.
¹ ITHACA - Information Technology for Humanitarian Assistance, Cooperation and Action, Italy
² Politecnico di Torino, Italy
Article
Full-text available
Many studies have shown a growing trend in terms of frequency and severity of extreme events. As never before, having tools capable to monitor the amount of rain that reaches the Earth’s surface has become a key point for the identification of areas potentially affected by floods. In order to guarantee an almost global spatial coverage, NASA Global Precipitation Measurement (GPM) IMERG products proved to be the most appropriate source of information for precipitation retrievement by satellite. This study is aimed at defining the IMERG accuracy in representing extreme rainfall events for varying time aggregation intervals. This is performed by comparing the IMERG data with the rain gauge ones. The outcomes demonstrate that precipitation satellite data guarantee good results when the rainfall aggregation interval is equal to or greater than 12 h. More specifically, a 24-h aggregation interval ensures a probability of detection (defined as the number of hits divided by the total number of observed events) greater than 80%. The outcomes of this analysis supported the development of the updated version of the ITHACA Extreme Rainfall Detection System (ERDS: erds.ithacaweb.org). This system is now able to provide near real-time alerts about extreme rainfall events using a threshold methodology based on the mean annual precipitation.
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