Summary report Natural Hazards Risk Analysis Technical Working Group , Cox’s Bazar | Status October 2020

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

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

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

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

1

COMPAS/NASA/UNDP/REACH – landslide inventory (request

form), landslide susceptibility maps, and online dynamic landslide

hazard and exposure model

Nov 2019 All camps In use

2 Landslide definition and classification info sheet & key natural

hazard terminologies info sheet Aug 2019

3 COMPAS/NASA/UNDP – landslide runout impact map (and

buildings exposure map) Nov 2019

Kutupalong-

Balukhali

Expansion

Not used

4 UNHCR/ADPC (V3) – early 2018: slope stability equation Feb.2018 Mega camp Phased out

5 REACH/MapAction/UK Met office – early 2018: landslide

susceptibility Mar 2018 All camps Phased out

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

10 Arup / REACH / IOM – Hydrodynamic flood modelling and

Analysis v1.0 Dec. 2019 Camps 21-27 In use

11 Deltares / WFP/ REACH – Hydrodynamic flood modelling and

Analysis v2.1 Nov 2019

Kutupalong-

Balukhali

Expansion

In use

12 Deltares / WFP – Flood vulnerability Atlas July 2019

Kutupalong-

Balukhali

Expansion

On-going

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

16 UNHCR / ADPC – (V2) Flash flood and riverine flood risk

assessment in Kutupalong May 2018 Mega camp Phased out

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

21 Sander+Partner / UNDP/REACH – Wind assessment and

modelling March. 2020

Kutupalong-

Balukhali

Expansion

In use

22 REACH - Wind Flow Analysis – WindNinja Mar. 2019

Kutupalong-

Balukhali

Expansion

Phased out

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 1: Product inventory

ANNEX 2: Infosheets

Storm Surge Analysis - REACH/IOM/UNHCRCox’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.

• To estimate both 10 & 100 year ARI sea levels, historical sea level 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

• 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

• The aim of this map is to help planners and decision makers to iden-tify priority areas for interventions at camp level. It is primarily de-signed as a macro- level site planning tool.

• The product can be used to quickly identify areas which may be at higher risk. All insights gained from the product must be investigated in the field.

• The scenarios mapped by the NatHaz TF (link) are based on, a.) a combined 10 year cyclonic storm surge & rainfall event and, b.) a combined 100 year cyclonic storm surge & 10 year rain event. How-ever, additional data for both 10 & 100 yearr cyclonic storm surge event combined with 1,2 , and 5 year rain events are available upon request.

• Map results need to be ground verified and decisions combined with specific on-site evaluation and appropriate technical expertise. They are not ground proofed and are inherently limited by the quality of the input data and/or model assumptions. The flood zones do not necessarily imply exposure and similarly, the areas outside the flood zones are not necessarily free from any danger.

• Although the two maps represent the combined effects of both a 10 & 100 year ARI storm surge events with 10 year rain events, the probability of two such events occurring simultaneously is not 1 in 10 years or 1 in 100 years. Joint probability modeling was beyond the scope of this assessment. Nonetheless, it is likely that a cyclonic storm surge event would be accompanied by heavy precipitation. Therefore, the combined effects provide useful insights into areas susceptible to high flood depths.

• Planning decisions should incorporate supplemental analyses in ad-dition to ground validation.

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)

What is it meant for?

Methodology in short

Main input data

Limitations

Extent

Wind Asssessment - UNDP & REACHCox’s Bazar | May 2020

Product descriptionThe 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.

• The assessment was designed to investigate the following three hazardous wind regimes known to occur in the region which could harm living conditions in the camps, a.) Cyclone (Cat 1), b.) Mon-soon winds, and c.) pre-monsoon winds. The historical events which have been simulated can be seen in the table below.

• First historical weather records were obtained for time periods rep-resented in the table below. Historical weather conditions were then reproduced using the WRF model which is run at multiple nested 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.

• The aim of this map is to help planners and decision makers to iden-tify priority areas for interventions at camp level. It is primarily de-signed as a macro- level site planning tool.

• The product can be used to quickly identify areas which may be at higher risk. All insights gained from the product must be investigated in the field.

• It is NOT designed as a stand-alone tool for detailed site planning decisions.

• Map results need to be ground verified and decisions combined with specific on-site evaluation and appropriate technical expertise. The results are not ground proofed and inherently limited by the quality of the input data and/or model assumptions.

• The modeling did not account for turbulent effects which can cause local gusts, heavily meandering wind features and wind wakes. Ad-ditionally rapid changes in wind velocities were shown to occur in the camps. This can result in strong wind shear which has high potential for damage to both infrastructure and individuals.

• The effects of wind shear are not adequately displayed on this map. Therefore, these mapped results are not suitable for the delineation of safezones.

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)

What is it meant for?

Methodology in short

Main input data

Limitations

Extent

Scenario Time PeriodCyclone (Cat 1) 25 November 1994 (0300-2400 hrs)Monsoon 16-19 June 2011Pre-Monsoon 03-08 March 1995

Factsheet – Pluvial Flooding Model – ARUP with IOM & REACH Cox’s Bazar | February 2020

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.

The model output provides information about expected

flooded area, water depth and speed of water flow for

the various scenarios. It is primarily designed as a macro-

level site planning tool. The product can be used to

quickly identify areas which may be at higher risk. All

insights gained from the product must be investigated in

the field.

The scenario mapped by the NatHaz TF (link) is based on

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).

The model is based on assumptions that need to be

verified with on the ground data collection (i.e. water

level in rivers).

The results of the model are not interpreted and entails

a degree of uncertainties and artefacts.

Site planning decisions should not solely rely on the

results, but need a sound on-site evaluation.

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.

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)

What is it meant for?

Product description

Limitations

Extent Methodology in short

Main input data

.

Main input data

Main input data

https://www.humanitarianresponse.info/en/operations/bangladesh/emergency-preparedness-and-response-taskforce

mailto:npmbangladesh@iom.int

AUTOMATED RAIN-WATER GAUGES IN COX’S BAZAR

JULY 2018

RAIN-WATER GAUGES INSTALLED BY UNDP AND THE GEOLOGICAL SURVEY OF BANGLADESH IN THE ROHINGYA CAMPS RECORD RAINFALL IN REAL-TIME AND SEND LANDSLIDE RISK ALERTS ___________________________________________________

The United Nations Development Programme (UNDP) in partnership with UNHCR, the UN refugee agency, the Geological Survey of Bangladesh (GSB) and the Norwegian Geotechnical Institute (NGI) have installed state of the art rain gauges in three landslide-prone areas around the Rohingya refugee sites in Cox’s Bazar, Bangladesh. The rain gauges will enable decision-makers to monitor the weather situation in the areas around the camps, and send alerts when high-intensity rainfall is significantly increasing the risk of landslides.

While the whole of Bangladesh is highly prone to floods, Cox’s Bazar district and the Chittagong Hill Tracts are also particularly vulnerable to flash floods and landslides. In the past, GSB and NGI installed four automated rain gauges in Chittagong, Cox’s Bazar town and Teknaf town. Equipped with solar panels and a SIM card, the rain gauges were programmed to register and upload rainfall values to the web every 15 minutes, as well as send alert SMSes to relevant government agencies when rainfall levels were intense enough to increase the general risk of rainfall significantly. Alerts from the gauges in enabled the district authorities to warn people living close to steep slopes in Cox’s Bazar town before a landslide occurred during heavy rains on 11th 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, deforestation and digging – within the camps, the actual risk thresholds are most likely lower. The rain gauges alerts will not be able to predict every landslide or soil erosion event, but will give notice to central stakeholders that the general landslide risk level has increased. This information can be used by the government and UN stakeholders to take early action for warning, response preparedness and operational adjustments. Protocols for action following receipt of the SMS/text messages alert are under discussion as of July 2018.

The SMS alert messages follow the below format: “Rainfall 3hr Alert (300) at UN_Kuturc_1279”

The central information in the alert is the threshold value reached – in the example above, 75 mm in 3 hours or less – and the ID and location of the rain gauge – in this case gauge 1279 at the Kutupalong RC. The number given in parenthesis – “(300)” – is a number related to the functionality of the gauge and is not a record or predictor of rainfall.

Alert messages are sent to the following bodies:

1. The Office of the Deputy Commissioner’s, Cox’s Bazar

2. The Office of the Refugee Relief and Repatriation Commissioner, Cox’s Bazar

3. The offices of the Upazila Nirbahi Officers, Ukhia and Teknaf

4. The Geological Survey of Bangladesh, the Bangladesh Meteorological Department, the Department of Disaster Management, the Fire Service and Civil Defence, Dhaka

5. The ISCG Emergency Coordination Cell

6. The DRR Technical Advisory Unit, UNDP Cox’s Bazar

7. UNDSS and security focal officers of UNHCR and IOM, Cox’s Bazar

8. Norwegian Geotechnical Institute (NGI), Oslo

The recipient list is maintained by UNDP and GSB and updated quarterly or upon request from any of the institutions on the list.

Together with the landslide and flash flooding incident reports being compiled by the ISCG Site Management sector, the rainfall gauge data from the 2018 monsoon season will enable the GSB, UNDP and humanitarian actors to gain a better understanding of how vulnerable the camp and settlement areas are to rainfall-triggered landslide. UNDP will work together with GSB, NGI and the Intersectoral Coordination Group (ISCG) secretariat to analyse the data and improve risk analysis for the camps. Access to the online record is available to other stakeholders upon request.

The ability of the rain gauges to automatically upload data and send alert messages is dependant on cell phone network coverage. At present, lack of coverage prevents the installation of rain gauges in the western camps in Ukhia. Lag time for the online record has been known to occur when the network coverage is interrupted or overloaded.

For more information, please contact: Cathrine Haarsaker, Project Manager DRR UNDP Cox’s Bazar +8801722121412 Cathrine.haarsaker@undp.org