Unlocking the full potential of Earth observation during the 2015 Texas flood disaster

Abstract

Intense rainfall during late April and early May 2015 in Texas and Oklahoma led to widespread and sustained flooding in several river basins. Texas state agencies relevant to emergency response were activated when severe weather then ensued for 6 weeks from 8 May until 19 June following Tropical Storm Bill. An international team of scientists and flood response experts assembled and collaborated with decision-making authorities for user-driven high-resolution satellite acquisitions over the most critical areas; while experimental automated flood mapping techniques provided daily ongoing monitoring. This allowed mapping of flood inundation from an unprecedented number of spaceborne and airborne images. In fact, a total of 27,174 images have been ingested to the USGS Hazards Data Distribution System (HDDS) Explorer, except for the SAR images used. Based on the Texas flood use case, we describe the success of this effort as well as the limitations in fulfilling the needs of the decision-makers, and reflect upon these. In order to unlock the full potential for Earth observation data in flood disaster response, we suggest in a call for action (i) stronger collaboration from the onset between agencies, product developers, and decision-makers; (ii) quantification of uncertainties when combining data from different sources in order to augment information content; (iii) include a default role for the end-user in satellite acquisition planning; and (iv) proactive assimilation of methodologies and tools into the mandated agencies.1. Challenges Delivering Actionable InformationAn increasing abundance of remotely sensed data, from satellite and airborne sensors, as well as other types of geospatial data can describe and quantify major flood events. New and ongoing Earth-observing missions are now providing a large, near-real time quantity of valuable, globally consistent and coherent geospatial data that can potentially deliver accurate information at the appropriate temporal and spatial resolution for disaster management and emergency response. Such data span most of the natural life-cycle of a flood event, from initiation though to peak inundation, and then eventual waning and drying to states resembling preflood conditions. Time scales vary from a few days to a few months.The recently launched GPM, SMAP, GCOM-w, and SMOS missions provide useful information concerning precipitation and soil moisture and also surface water conditions. Satellites and sensors such as MODIS, Landsat, EO-1, Sentinel, TerraSAR-X, and COSMO-SkyMed can document regional floodplain inundation, and commercially operated very high resolution sensors from the air and space (e.g., WorldView and GeoEye satellites operated by DigitalGlobe) provide cadastral-level data including damage assessment capability; note that the latter has also been demonstrated with high-resolution satellite SAR sensors (http://www.jpl.nasa. gov/spaceimages/details.php?id5PIA17687), such as COSMO-SkyMed, TerraSAR-X, and Radarsat-2. Figure 1

Global Estimates of River Flow Wave Travel Times and Implications for Low‐Latency Satellite Data

“…Satellite‐based early flood warning systems likely have the greatest utility for cities that are located far downstream from basin headwaters and do not have well‐developed gauge networks in place. This being said, we note that low‐latency remote sensing observations can still greatly benefit cities located in relatively small basins with well‐developed infrastructure (e.g., Schumann et al, ). Similar to cities, areas containing fewer dams or dams with larger contributing areas will potentially benefit the most from NRT satellite products, at least when considering data latency alone.…”

The need for scientific rigour and accountability in flood mapping to better support disaster response

“…This situation is, of course, frustrating to both the decision maker and the product developer, whose flood maps may not be used as intended or indeed may not be used at all. Schumann et al () outlined several reasons for this apparent underutilization by decision makers: (a) limited time and capacity to understand, process, and handle the datasets; (b) limited near real‐time data accessibility, bandwidth, and sharing capacity; (c) incompatibility between user platforms and geospatial data formats; (d) data availability may be simply unknown and/or data latency (lag from acquisition to delivery) may be inadequate; and (e) limited understanding by scientists and engineers about end‐user product and timing needs.…”

“…However, it is this contemporary push towards big and novel concepts that may be partly responsible for the notable lack of rigorous local let‐alone global‐scale validation (i.e., accuracy assessment) of satellite products. Consequently, scientific accountability is missing, particularly in the case of satellite flood maps that need to be delivered in a timely manner and often under conditions of very limited resources during disasters to assist response operations in any location (as outlined by Schumann, Frye, et al, , in a detailed account of the Texas 2015 flood disaster).…”

Contributions of Operational Satellites in Monitoring the Catastrophic Floodwaters Due to Hurricane Harvey

“…Compared with high spatial resolution sensors, such as optical sensors like the Landsat and radar sensors, which usually offer a 6-16 day repeat cycle, operational satellites usually have relatively high temporal resolution, of twice per day for polar orbiting satellites and 5-30 min for operational geostationary satellites. As a flood is usually a short term event, operational satellites with large area coverage and frequent revisit, either used alone or in combination with other high spatial resolution sensors, or complemented by numerical model simulations, have played significant roles in the detection and monitoring of large floods [18][19][20][21]. For example, Schumann et al [18] demonstrated an application for the May-June 2015 Texas flood disaster using only satellite observations.…”

“…As a flood is usually a short term event, operational satellites with large area coverage and frequent revisit, either used alone or in combination with other high spatial resolution sensors, or complemented by numerical model simulations, have played significant roles in the detection and monitoring of large floods [18][19][20][21]. For example, Schumann et al [18] demonstrated an application for the May-June 2015 Texas flood disaster using only satellite observations. In that case, MODIS flood maps at a 250 m resolution were composited with many images from other high resolution sensors like the Landsat 7/8 at 30 m resolution and Sentinel-1 at various resolution, and so on.…”