Remote Sensing-based Flood Mapping and Flood Hazard Assessment in Haiti

Transcription

1 csdms.colorado.edu Remote Sensing-based Flood Mapping and Flood Hazard Assessment in Haiti Rebuilding for Resilience: How Science and Engineering Can Inform Haiti's Reconstruction, March 22 - March 23, 2010, University of Miami - Coral Gables, FL Prof. G. Robert Brakenridge Dartmouth Flood Observatory, Dartmouth College, and Visiting Scientist, Community Surface Dynamics Modeling System, University of Colorado Dr. Scott D. Peckham (Presenter) Community Surface Dynamics Modeling System, University of Colorado

2 1) Floods commonly produce catastrophic damage in Haiti 2) Not all such floods are from tropical cyclones On May 18-25, 2004, a low-pressure system originating from Central America brought exceptionally heavy showers and thunderstorms to Haiti and the Dominican Republic. Rainfall amounts exceeded 500 mm (19.7 inches) across the border areas of Haiti and the Dominican Republic At the town of Jimani, DR, 250 mm (10 inches) of rain fell in just 24 hours. NASA Tropical Rainfall Measuring Mission (TRMM) data.

3 Lethal Major Floods in the Dominican Republic / Haiti are a Near-Annual Event The Dartmouth Flood Observatory data archive dates back to Between 1986 and early 2004 (prior to Hurricane Jeanne in November), at least, fourteen lethal events impacted the island, including: Year Month Casualties 1986 early June > late October early September - Hurricane Gilbert late May early November Hurricane Gordon > mid November Late August Hurricane Gustaf > late September - Hurricane Georges > late October - Hurricane Jose mid-may late May early December - Tropical Storm Odette mid-november late May >2000

4 NASA s two MODIS sensors, Aqua and Terra, are an important flood mapping tool: Visible and near IR spectral bands provide excellent land/water discrimination over wide areas. Automatic georeferencing data accurate to +/- 50 m. Frequent (more than daily) coverage using both Aqua and Terra. Data provided by NASA free via ftp. MODIS sensors operating since late 1999 (Terra) and mid-2002 (Aqua) Spatial resolution (250 m) is adequate to map many river floods

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6 Other useful sensors include ASTER Small footprint but high spatial resolution (15 m) Can be used after a flood event in upland areas to map debris flows and landslides. Then: preserve such information in GIS data bases. This work by Brakenridge and Gubbels, ASTER before and after images indicate that debris-carrying flows of floodwater on the north flank of the Massif de la Salle originated as confined discharges within steep-walled channels of bedrock inside canyons. As the floodwaters flowed out onto the relatively flatter lands of the alluvial plain below, they spread out, wiping out riverside settlements in Haiti and the adjacent part of the Dominican Republic.

7 The Dartmouth Flood Observatory Just as gauging stations, ideally, record long term history of flood discharges, remote sensing can record, directly, the long term history of floodplain inundation. It must, however, be processed for that purpose. The archive at the Dartmouth Flood Observatory provides a starting point for this task. Following is the map sheet from the Observatory s global archive, for Hispaniola. The GIS data are made available free of charge. The maps are not complete, but a starting point: not all floods have been mapped.

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9 Another detail view, showing in different green and blue colors mapped previous flooding

10 How might remote sensing of flooding inform Haiti s postearthquake reconstruction? 1) Much of Haiti s recent flood history has been recorded by NASA satellite remote sensing. This record of prior events can provide useful information for assessing future flood hazard. 2) Present optical orbital sensors allow sustained (twice daily) surveillance: as damaging flood events occur, their location, duration, and severity can be measured in near-real time. 3) Precipitation measurements from orbit (TRMM and the follow-on GPM sensors) already allow improved flood prediction in nations such as Haiti. This capability will not be useful without much-improved local warning systems.

11 Possible Recommendations: 1) Once obtained, these GIS data should be archived in accessible formats, and be made available to the general and international public. 2) As new floods occur, flood mapping should continue as a routine, not special ad hoc activity. 3) The most efficient and cost-effective way to define future flood hazard in Haiti is to make full use of the ~25 year-long record of orbital remote sensing of Haiti: simply map those floods that have already occurred. Special Thanks to: NASA, the European Commission s Joint Research Centre and the World Bank

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13 Detail of past and current (red, at time this display was prepared) flooding near Gonnaives

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15 The death toll continues to climb from last week s flooding in Haiti and the Dominican Republic. The U.S. Agency for International Development (USAID) reports that at least 1,068 people are dead, 1,600 are missing, and 25,000 are in need of emergency food and non-food assistance. In the Dominican Republic, 414 are dead and 274 are missing (all from the town of Jimani). The flooding took place on May 24-25, The worst flooding occurred along a river system that drains the north flank of the Massif de la Salle and in a poorly drained area along the south flank of the massif

16 More recently, and as described in : Jeffrey Masters, Ph.D. Director of Meteorology, Weather Underground, Inc. During hurricane season of 2008, four storms--fay, Gustav, Hanna, and Ike--dumped heavy rains on Haiti. The rugged hillsides, stripped bare of 98% of their forest cover let flood waters rampage into large areas of the country. Particularly hard-hit was Gonaives, the fourth largest city. According to reliefweb.org, Haiti suffered 793 killed, with 310 missing and another 593 injured. The hurricanes destroyed 22,702 homes and damaged another 84,625. About 800,000 people were affected--8% of Haiti's total population. The flood wiped out 70% of Haiti's crops, resulting in dozens of deaths of children due to malnutrition in the months following the storms. Damage was estimated at over $1 billion, the costliest natural disaster in Haitian history. The damage amounted to over 5% of the country's $17 billion GDP.

17 The years 1998 and 2008, with multiple tropical storms, were not unusual.. An unnamed storm killed over 2000 in 1935 Hurricane Hazel killed over 1000 in Hurricane Flora killed over 8000 people in Hurricane Jeanne of 2004 passed just north of the country as a tropical storm, dumping 13 inches of rains on the nation's northern mountains. The resulting floods killed over 3000 people, mostly in the town of Gonaives. (From: Jeffrey Masters, Ph.D. Director of Meteorology, Weather Underground, Inc.

18 Another ASTER before- and after- pair On the other side of the massif, ponding of water created a series of lakes, one of which submerged the town of Mapou. Note the extensive landslide and mudflow scars, where receding floodwaters left deposits of gravel, indicated in white. At least seven lakes appeared where no lakes existed before. Mapou lies submerged in the southeastern part of the largest lake.

19 Runoff along the southern flank of the Massif de la Salle, generated by torrential rains, formed new lakes in southeastern Haiti and modified the landscape by sweeping tons of debris and gravel downstream. In this image, remote sensing has been transformed into useful GIS map information, showing location of landslides and debris flows, in red, and storm-related flooding, in light blue. If systematized over whole nation, such data can and should inform reconstruction.