Summary report Natural Hazards Risk Analysis Technical Working Group , Cox’s Bazar | Status October 2020
What is this report about?
This report summarizes the current work of the Natural Hazard Risk Analysis Technical Working Group (NatHaz TWG), a specialized sub-group of the Information and Assessment Working Group (IMAWG). More specifically, it presents natural hazards products that are available and have been validated by the Sector Coordinators and the Heads of Sub-Office Group (HOSOG). All agencies involved with camp planning and implementation are advised to use them as part of their toolkits to strengthen informed risk reduction and mitigation activities.
Natural hazards mapping and risk analyses are not static activities. They are subject to change due to the constantly evolving situation, environment and available information. The products under the coordination of NatHaz TWG reflect the current status at the time of creation. Regular updates will be provided, depending on new findings and changing conditions. This report is meant as a living document. All actors are invited to pro- actively ensure they are using the latest information.
The inventory of previously developed products is tabulated in Annex 1. The products are delineated in a set of Info-sheets (Annex 2) and technical notes (Annex 3).
What is currently available?
Hazard maps: Flood1 Landslide2 Wind3 Storm surge4
Each map shows areas that could be affected by the respective hazard. All map products may be downloaded here. The maps are simplified representations derived from more complex data (available on request). The latter requires an appropriate level of GIS proficiency, as well as technical expertise to understand the methodologies and interpret the results. The maps have indicative value; they are not ground-proofed products and entail limitations. The identified zones do not necessarily imply exposure and, similarly, the remaining zones are not necessarily free from any danger. These maps provide general overview of the hazards distribution in the camp area, and support camp scale site development and preparedness activities. They are NOT designed for detailed site planning and should therefore not be used as a decision making tool at this level. Site planning decisions need specific on-site evaluations and appropriate technical expertise.
Other products: 2019 Hydrometeorological- SMSD Incident Database: Data from a variety of rain, weather, and hydrological field instrumentation was merged with the SMSD incident database allowing incidents to be directly linked
1 Hydrodynamic flood modeling for southern camps is new since previous update 2 COMPAS/NASA/UNDP landslide models have been finalized since previous update 3 New since previous update 4 New since previous update to field-measured weather data. This database also serves to document available field instrumentation over time. More details on field instrumentation is available below. The database is available upon request 2020 Hydrometeorological - SMSD Incident Database: based partner feedback, the 2019 database and an updated database was created for 2020. The database is available here. Landslide inventory recording previous landslide events. It is based on field investigation and aerial imagery analysis (satellite and drone) inside and outside the camp area. Technical note on landslide classification. It has been specifically adapted to the context of the camps, based on field observations and analysis Info sheet about key terminologies and definitions related to natural hazards and risk
What is on-going?
New models since previous update: A new storm surge model has been developed for the coastal camps (Shamlapur and Teknaf/Leda camps). Two scenarios were mapped and are available with the links that follow. Scenario a: combined 10-year coastal storm surge and 10-year precipitation event., scenario b: combined 100-year storm surge and 10-year precipitation event. An improved flood map version 2.1 has been released for pluvial flooding covering the Kutupalong Balukhali Expansion site (KTP BE). The map can be found here. New hydrodynamic flood modeling covering camps 21-27. The resulting map can be found here and is referred to as version 1.0 since it is the first hydrodynamic flood modeling covering this region. A new wind assessment commissioned by UNDP for KTP BE. Three scenarios are investigated: landfall of cat. 1 cyclone near Cox’s Bazar, strong monsoon storm and pre-monsoon thunderstorm (Kalbaisakhi). The resulting map can be found here.
Field Instrumentation New field instruments have been installed in the camps between June and September 2019 to get baseline information about river-level changes, wind, rain, temperature and other weather-related data. The information has been retrieved and consolidated into the 2020 Hydrometeorological – SMSD Incident Database. All data limitations and instrumentation updates available can be found in the database.
Joint capacity sharing initiative UNDP, in coordination with NatHaz TWG, developed a two days training and field exercise module about natural hazards to support the site management Joint Capacity Sharing Initiative. Three two day trainings and field exercises for CiCs were conducted in December 2019 and January 2020.
Some Additional Collaborations Environment & Energy Technical Working Group: collaboration to help plan 2020 slope stabilization planting. Emergency Response Preparedness Working Group (EPRWG): Collaboration to help refine numbers for damage estimates in camp context based on a variety of scenarios and TWG hazard products (analysis currently under review). Contact
All inquiries to be submitted to ISCG Information Management Unit; data requests using the request form
ANNEX 1: Product inventory
The table below shows the main natural hazard products investigated and endorsed by the NatHaz TWG. Greyed out items are either not being use or have been phased out by improved products. Minor version iterations which have been phased out are not included.
Landslide Last release Extent Status COMPAS/NASA/UNDP/REACH – landslide inventory (request 1 form), landslide susceptibility maps, and online dynamic landslide Nov 2019 All camps In use hazard and exposure model Landslide definition and classification info sheet & key natural 2 Aug 2019 hazard terminologies info sheet Kutupalong- COMPAS/NASA/UNDP – landslide runout impact map (and 3 Nov 2019 Balukhali Not used buildings exposure map) Expansion 4 UNHCR/ADPC (V3) – early 2018: slope stability equation Feb.2018 Mega camp Phased out REACH/MapAction/UK Met office – early 2018: landslide 5 Mar 2018 All camps Phased out susceptibility 6 IOM/UNHCR - slope and slope impact analysis - Jan.2018 Mega camp Phased out 7 REACH – slope analysis Aug. 2018 All camps Phased out 8 UNHCR/ADPC (V1) – early 2018: slope analysis Jan.2018 Mega camp Phased out 9 UNHCR/ADPC (V2) – early 2018: combination of factor maps Feb.2018 Mega camp Phased out Flood Arup / REACH / IOM – Hydrodynamic flood modelling and 10 Dec. 2019 Camps 21-27 In use Analysis v1.0 Kutupalong- Deltares / WFP/ REACH – Hydrodynamic flood modelling and 11 Nov 2019 Balukhali In use Analysis v2.1 Expansion Kutupalong- 12 Deltares / WFP – Flood vulnerability Atlas July 2019 Balukhali On-going Expansion 13 REACH - Standing water extend All camps Mar. 2019 All camps Phased out 14 UNOSAT - Standing water extend 2018/19? All camps Not used 15 UNHCR / ADPC – (V1) Flood Risk Assessment in Kutupalong Jan.2018 All camps Phased out UNHCR / ADPC – (V2) Flash flood and riverine flood risk 16 May 2018 Mega camp Phased out assessment in Kutupalong 17 COMPAS/NASA - Regional dynamic flood warning model n/a All camps Not used Storm surge 18 Arup / REACH / IOM / UNHCR – Storm surge modelling May 2020 Coastal camps In use 19 REACH – Storm surge analysis Mar. 2019 Coastal camps Phased out 20 UNIDSR/CIMNE – Global model of storm surge hazard Jan 2015 All camps Not used Wind Kutupalong- Sander+Partner / UNDP/REACH – Wind assessment and 21 March. 2020 Balukhali In use modelling Expansion Kutupalong- 22 REACH - Wind Flow Analysis – WindNinja Mar. 2019 Balukhali Phased out Expansion 21 REACH – Wind hazard susceptibility Mid 2018 All camps Phased out 22 UNIDSR/CIMNE – Global model of cyclone wind Jan 2015 All camps Not used
ANNEX 2: Infosheets
Storm Surge Analysis - REACH/IOM/UNHCR Cox’s Bazar | May 2020
Product description This product consists of a map and dataset of storm surge analysis performed by Arup (2019). The area of coverage is limited to the Rohingya Ref- ugee camps at potential risk to storm surge. The purpose of this analysis is to gain an understanding of the potential effect of a range of storm surge scenarios throughout the region, in preparation for cyclone seasons (March-May and September-December). This map & accompanying simplified GIS files display predicted inundation depths (m) derived from the simulation of a combined 10-year average recurrence interval (ARI) rain event and both 10 & 100-year ARI cyclonic storm surge events. Data inputs to this model include the 0.5 m UAV orthographic DEM (NPM, 2018/2019), his- torical sea level records (University of Hawaii), and 3 & 24 hr maximum precipitation values for a 1, 2, 5, and 10-year ARI rain events (Deltares, 2019).
Download GIS files on request; summary map (May 2020) found at this link.
What is it meant for? Limitations • The aim of this map is to help planners and decision makers to iden- • Map results need to be ground verified and decisions combined with tify priority areas for interventions at camp level. It is primarily de- specific on-site evaluation and appropriate technical expertise. They signed as a macro- level site planning tool. are not ground proofed and are inherently limited by the quality of • The product can be used to quickly identify areas which may be at the input data and/or model assumptions. The flood zones do not higher risk. All insights gained from the product must be investigated necessarily imply exposure and similarly, the areas outside the flood in the field. zones are not necessarily free from any danger. • The scenarios mapped by the NatHaz TF (link) are based on, a.) a • Although the two maps represent the combined effects of both a combined 10 year cyclonic storm surge & rainfall event and, b.) a 10 & 100 year ARI storm surge events with 10 year rain events, the combined 100 year cyclonic storm surge & 10 year rain event. How- probability of two such events occurring simultaneously is not 1 in ever, additional data for both 10 & 100 yearr cyclonic storm surge 10 years or 1 in 100 years. Joint probability modeling was beyond event combined with 1,2 , and 5 year rain events are available upon the scope of this assessment. Nonetheless, it is likely that a cyclonic request. storm surge event would be accompanied by heavy precipitation. Therefore, the combined effects provide useful insights into areas Methodology in short susceptible to high flood depths. • Planning decisions should incorporate supplemental analyses in ad- • To estimate both 10 & 100 year ARI sea levels, historical sea level dition to ground validation. data were obtained from offshore tide gauges. The Annual Maxima method was applied to the historical records to estimate ARI sea levels, as a combination of high tide plus storm surge Extent • For Camp 23, wave setup and wave run-up calculations were also performed using the estimated sea level rise. For Camps 24-27, the calculated sea level was input into a TUFLOW hydrodynamic model which was used to simulate flooding up the Naf River to Camps 24-27 Main input data Mapped Data • Water innundation depth (Arup, 2019) • Structure Footprint (UNOSAT-REACH, 2019) • Roads (©OpenStreetMap Contributors)
Main Analysis Inputs • Sea level records (University of Hawaii, Joint Archive for Sea Level Holdings) • Digital Elevation Model (NPM Jan 2019/Oct 2018) • 3 & 24 hr max precipiation 10 year ARI precipitation (Deltares, 2019) Wind Asssessment - UNDP & REACH Cox’s Bazar | May 2020
Product description The product is the result of a wind assessment for disaster risk management completed by Sanders and Partners comissioned by UNDP. Wind velocities magnitude and direction were simulated for three historical wind events meant to represent three hazardous wind regimes known to occur in the region: a.) Categery 1, Saffir-Sampson Scale, cyclone (1994), b.) monsoon wind conditions (2011), and c.) pre-mon- soon wind conditions, also known as the Kalbaishakhi - Nor’Western (1995). Historical meteorological records were used to determine re- gional wind speeds and directions and input into the model. The study area considered is the region where in which the current Kutupalong- Balukhali Expansion site is located. For pre-monsoon and monsoon scenarios results were obtained on a daily basis for the duration of event, while for the cyclone scenario results were obtained on an hourly basis. The maximum windspeed resulting for the entire duration of each scenario was extracted and mapped by the Natural Hazard Task Force. The resulting map can be found at the following link and underlying data and GIS files can be requested from the ISCG. What is it meant for? Limitations • The aim of this map is to help planners and decision makers to iden- • It is NOT designed as a stand-alone tool for detailed site planning tify priority areas for interventions at camp level. It is primarily de- decisions. signed as a macro- level site planning tool. • Map results need to be ground verified and decisions combined with • The product can be used to quickly identify areas which may be at specific on-site evaluation and appropriate technical expertise. The higher risk. All insights gained from the product must be investigated results are not ground proofed and inherently limited by the quality in the field. of the input data and/or model assumptions. • The modeling did not account for turbulent effects which can cause Methodology in short local gusts, heavily meandering wind features and wind wakes. Ad- • The assessment was designed to investigate the following three ditionally rapid changes in wind velocities were shown to occur in the hazardous wind regimes known to occur in the region which could camps. This can result in strong wind shear which has high potential harm living conditions in the camps, a.) Cyclone (Cat 1), b.) Mon- for damage to both infrastructure and individuals. soon winds, and c.) pre-monsoon winds. The historical events which • The effects of wind shear are not adequately displayed on this map. have been simulated can be seen in the table below. Therefore, these mapped results are not suitable for the delineation • First historical weather records were obtained for time periods rep- of safezones. resented in the table below. Historical weather conditions were then reproduced using the WRF model which is run at multiple nested Extent resolutions down to 1 km. The WRF results are then fed into the CALMET boundary layer model to downscale results to 10 m reso- lution over the area of interest. • Wind speed and direction results were obtained at hourly intervals for the cyclone conditions and daily time intervals for the pre-mon- soon and monsoon • The Natural Hazard Task Force mappeed the highest wind speed obtained for each scenario through the duration of the event.
Scenario Time Period Cyclone (Cat 1) 25 November 1994 (0300-2400 hrs) Monsoon 16-19 June 2011 Pre-Monsoon 03-08 March 1995
Main input data Mapped data • Max wind velocity magnitude (Sanders & Partners, 2019) • Structure Footprint (UNOSAT-REACH, 2019) • Roads (©OpenStreetMap Contributors) • Hillshade (derived from UAV Orthographic DEM, NPM, January 2019) Main Model Inputs • Meteorological data (ERA-Interim6) • topographical data (1 m from NPM & 30 m open source) • Soil surface characteristics • Vegetation/NDVI Maps (FAO) Factsheet – Pluvial Flooding Model – ARUP with IOM & REACH Cox’s Bazar | February 2020
Product description
This product is the result of flood modelling carried out for the camps located in Teknaf Upazila. The model generated simulates three different probability defined rainfall events: 1, 5, and 10-year Average Reoccurrence Interval (ARI) storms. The maximum of two different rainfall duration/intensity scenarios for each storm (3 & 24 hr max precipitation) is modelled. These scenarios were chosen to ensure comparability with the flood modelling work performed earlier by Deltares/WFP in the Kutupalong Megacamp area (see previous infosheet). Product released February 2020. Shapefiles available through the request form.
What is it meant for? Limitations
The model output provides information about expected The model is based on assumptions that need to be flooded area, water depth and speed of water flow for verified with on the ground data collection (i.e. water the various scenarios. It is primarily designed as a macro- level in rivers). level site planning tool. The product can be used to quickly identify areas which may be at higher risk. All The results of the model are not interpreted and entails insights gained from the product must be investigated in a degree of uncertainties and artefacts. the field. Site planning decisions should not solely rely on the The scenario mapped by the NatHaz TF (link) is based on results, but need a sound on-site evaluation. a 10 year ARI rainfall event. However, the modelled depth and velocity data is available for 1, 5, and 10 year ARI events (detailed data available upon request).
Methodology in short Extent
The model simulates three different storm events based on probability (1, 5, and 10-year average reoccurrence interval) based on the maximum of two different rainfall duration/intensity scenarios for each storm (3 & 24 hr max precipitation).
After hydrologic correction of input terrain data a direct rainfall (TUFLOW) model applied to extract all major/minor flow paths and simulate pluvial flooding.
Main input data
0.5 m resolution Digital Elevation Model (DEM) from UAV drone survey (IOM-NPM; January 2019) Building footprint (REACH-UNOSAT, Jan 2019) Precipitation data (BMD/Deltares)
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Main input data
Main input data
AUTOMATED RAIN-WATER GAUGES IN COX’S BAZAR
JULY 2018
RAIN-WATER GAUGES INSTALLED BY UNDP AND THE While the whole of Bangladesh is highly prone to floods, Cox’s GEOLOGICAL SURVEY OF BANGLADESH IN THE ROHINGYA Bazar district and the Chittagong Hill Tracts are also particularly CAMPS RECORD RAINFALL IN REAL-TIME AND SEND vulnerable to flash floods and landslides. In the past, GSB and LANDSLIDE RISK ALERTS NGI installed four automated rain gauges in Chittagong, Cox’s ______The United Nations Development Programme (UNDP) in partnership Bazar town and Teknaf town. Equipped with solar panels and a with UNHCR, the UN refugee agency, the Geological Survey of SIM card, the rain gauges were programmed to register and Bangladesh (GSB) and the Norwegian Geotechnical Institute (NGI) upload rainfall values to the web every 15 minutes, as well as send have installed state of the art rain gauges in three landslide-prone alert SMSes to relevant government agencies when rainfall levels areas around the Rohingya refugee sites in Cox’s Bazar, Bangladesh. were intense enough to increase the general risk of rainfall The rain gauges will enable decision-makers to monitor the weather significantly. Alerts from the gauges in enabled the district situation in the areas around the camps, and send alerts when high- authorities to warn people living close to steep slopes in Cox’s th intensity rainfall is significantly increasing the risk of landslides. Bazar town before a landslide occurred during heavy rains on 11 July 2015.
Recognising the high risk of landslide and erosion in the Rohingya camps and settlements, UNDP with the support of UNHCR has worked with GSB, technical experts from NGI, and a Early Warning specialist deployed by RedR Australia to install three further rain gauges in June 2018. When the recorded rainfall values exceed a pre-determined risk threshold, the rain gauge alert system sends SMS/text messages to 20 designated Government of Bangladesh and UN agencies located in Cox’s Bazar and Dhaka. The threshold values for the Rohingya camp areas are:
3 hours: 75 mm 24 hours: 200 mm 72 hours: 350 mm
Based on analysis of soil and past landslides in the district, GSB and NGI consider that general landslide risk is significant when these thresholds are reached within the given time period. Due to the extent of human interference with the slopes – cutting, 5. The ISCG Emergency Coordination Cell deforestation and digging – within the camps, the actual risk 6. The DRR Technical Advisory Unit, UNDP Cox’s Bazar thresholds are most likely lower. The rain gauges alerts will not be able to predict every landslide or soil erosion event, but will give 7. UNDSS and security focal officers of UNHCR and IOM, notice to central stakeholders that the general landslide risk level has Cox’s Bazar increased. This information can be used by the government and UN 8. Norwegian Geotechnical Institute (NGI), Oslo stakeholders to take early action for warning, response preparedness and operational adjustments. Protocols for action following receipt of The recipient list is maintained by UNDP and GSB and updated the SMS/text messages alert are under discussion as of July 2018. quarterly or upon request from any of the institutions on the list. Together with the landslide and flash flooding incident reports The SMS alert messages follow the below format: being compiled by the ISCG Site Management sector, the rainfall “Rainfall 3hr Alert (300) at UN_Kuturc_1279” gauge data from the 2018 monsoon season will enable the GSB, UNDP and humanitarian actors to gain a better understanding of The central information in the alert is the threshold value reached – in how vulnerable the camp and settlement areas are to rainfall- the example above, 75 mm in 3 hours or less – and the ID and location triggered landslide. UNDP will work together with GSB, NGI and of the rain gauge – in this case gauge 1279 at the Kutupalong RC. the Intersectoral Coordination Group (ISCG) secretariat to The number given in parenthesis – “(300)” – is a number related to analyse the data and improve risk analysis for the camps. the functionality of the gauge and is not a record or predictor of Access to the online record is available to other stakeholders rainfall. upon request.
Alert messages are sent to the following bodies: The ability of the rain gauges to automatically upload data and send alert messages is dependant on cell phone network 1. The Office of the Deputy Commissioner’s, Cox’s Bazar coverage. At present, lack of coverage prevents the installation of rain gauges in the western camps in Ukhia. Lag time for the 2. The Office of the Refugee Relief and Repatriation online record has been known to occur when the network Commissioner, Cox’s Bazar coverage is interrupted or overloaded. 3. The offices of the Upazila Nirbahi Officers, Ukhia and Teknaf For more information, please contact: 4. The Geological Survey of Bangladesh, the Bangladesh Cathrine Haarsaker, Project Manager DRR Meteorological Department, the Department of Disaster UNDP Cox’s Bazar Management, the Fire Service and Civil Defence, Dhaka +8801722121412 [email protected]