Flash Flood Flash Flood Forecasting and Early Warning System (FFEWS)

Transcription

1 Stakeholder Workshop of Haor Area Livelihoods Improvement Project (HALIP) 15 January 2016, Sunamganj, Bangladesh Flash Flood Flash Flood Forecasting and Early Warning System (FFEWS)

2 BUET Study Team Prof AKM Saiful Islam, Principal Investigator Prof G.M. Tarekul Islam, Co-Investigator Prof Mashfiqus Salehin, Co-Investigator Prof Sujit Kumar Bala, Co-Investigator Prof M. Shahjahan Mondal, Co-Investigator Shammi Haque, Co-Investigator Binata Roy, Co-Investigator Partha Das, Co-Investigator Mohan Kumar Das, Research Associate Md. Samiun Basir, Research Assistant Diponkar Saha, Research Assistant Md. Jamal Uddin Khan, Research Assistant

3 Outline Introduction and objectives of FFEWS Project Flash Flood Modeling Improving rainfall forecasting using high resolution weather modeling. Developing hydrological modeling for basin flow forecasting Improving hydrodynamic forecasting of the major rivers Developing early warning dissemination systems Capacity building of the Flash Flood Forecasting of the Haor Regions of Bangladesh through action research and training.

4 Phenomenon of floods Convective Cloud Heavy Excessive Rainfall Sudden Runoff Excessive Runoff- Floods

5 Flash Flood A flash flood is characterized by flood occurred from heavy or excessive rainfall in a short period of time over a relatively small area. In flash flood, water level rises and falls quite rapidly with little or no advance weather forecast or warning. Typically, flash flood occurs in areas where the upstream basin topography is relatively steep and the concentration time of the basin is relatively short. In Bangladesh, flash floods generally occur in the north-east (Known as Haor areas) during pre-monsoon season (March-May).

6 How Flash Flood occur

7 Flash Flood Forecasting Flash floods represent forecast and detection challenges because they are not always caused simply by meteorological phenomena. Flash floods result when specific meteorological and hydrological conditions exist together. Although heavy rainfall is usually a factor, a given amount and duration of rainfall may or may not result in a flash flood, depending on the hydrologic characteristics of the watershed where the rain is occurring.

8 Necessity of Flash Flood Forecasting

9 Flash Flood Forecasting Project Forecasting flash flood and proper dissemination of information are challenging tasks considering the complex topography, observed data availability, computation resources availability, lead time requirements and institutional ability to disseminate information. In this context, Institute of Water and Flood Management (IWFM) of Bangladesh University and Engineering and Technology (BUET) has proposed this research study for comprehensive modeling and community based forecasting system, which will be delivered to the Flood Forecasting and Warning Center (FFWC) of Bangladesh Water Development Board (BWDB).

10 FFEWAS The proposed research study has been funded by the Climate Adaptation and Livelihood Improvement Project (CALIP) of the International Fund for Agricultural Development (IFAD) and Government of Bangladesh. This fund will be used in assisting national organizations (e.g. FFWC of BWDB, IWM and BMD for their capacity building through providing professional trainings and knowledge products. This study will carry out a research to develop a feasible, open source supported modeling tools to forecast flash flood in the Haor region of Bangladesh and assisting national organizations (e.g. FFWC of BWDB, IWM and BMD) for their capacity building through providing professional trainings and knowledge products.

11 Objectives 1. To analyze the hydro-meteorological data under seasonal climate variability of the Haor regions of Bangladesh. 2. To examine the relationship between seasonal climate fluctuations and flash floods in the Haor regions of Bangladesh. 3. To set-up of Weather Research Forecasting (WRF) model in order to generate rainfall forecasts over the study area. 4. To determine appropriate Data Assimilation techniques for improving rainfall forecasts. 5. To calibrate and validate the WRF model using the available observed, radar and any other satellite based rainfall data.

12 Objectives 6. To development of Rainfall-Runoff model for the basins hydraulically connected to the Haor regions of Bangladesh. 7. To develop 1D-Hydrodynamic model for the river systems of the Haor regions of Bangladesh. 8. To predict flash floods using hydrological and hydrodynamic modeling for the Haor regions of Bangladesh. 9. To assist national organizations (e.g. FFWC of BWDB, IWM and BMD) for their capacity building through providing professional trainings and knowledge products. 10. To develop climate smart community based disseminating system for flash flood forecasting and warning in the study area.

13 Rainfall-Runoff modeling

14 Flow Chart of Methodology WRF Data Assimilation WRF Rainfall forecasting Rainfall Runoff modeling Hydraulic Modeling Flood Inundation Modeling Flood information at the Gauge stations and flood maps

15 Weather modeling

16 Weather modeling using WRF The WRF model has been used for simulation of the MCSs associated with squalls in this study. The WRF model is a new generation mesocale NWP system designed to serve both operational forecasting and atmospheric research needs (NCAR 2009). It features multiple dynamical cores, a 3DVAR data assimilation system, and a software architecture allowing for computational parallelism and system extensibility. WRF is suitable for a broad spectrum of applications across scales ranging from meters to thousands of kilometers. Applications of WRF include research and operational NWP, data assimilation and parameterized physics research, downscaling climate simulations, driving air quality models, atmosphere-ocean coupling, and idealized simulations (i.e., boundary layer eddies, convection, baroclinic waves).

17 Nested Domains of weather modeling GFS boundary data of 50km resolution is simulated using WRF modeling downscaled up-to 6km

18 WRF Model Configurations

19 3-hourly accumulated rainfall forecasting using WRF (5-day lead)

20

21 Hydrological and Hydrodynamic modeling Hydrologic modelling system is essential to simulate precipitation-runoff process in a watershed system. The entire procedure requires pre-processing of necessary data to develop basin hydrology. Considering all the aspects, the objectives of this study have been set as follows: To delineate the watershed and stream network of Upper Meghna Basin by using Arc Hydro tools and HEC-GeoHMS. To setup a distributed hydrologic model of Upper Meghna basin in HEC-HMS. To calibrate and validate the model using flow data at Bhairab Bazar station as well as other flash flood occurring points. To find out flows at 25 flash flood warning points which will use as boundary conditions for HEC RAS model development.

22 Ganges Brahmaputra Meghna Delta

23 Meghna basin

24 Meghna Basins in the Haor Regions

25 North East Bangladesh

26 Eastern Hilly rivers Lukha river Kongsho river Surma river

27 Basin modeling using HEC-HMS HEC-HMS omits any detailed accounting of movement of water within the soil. It includes models of infiltration from the land surface. But it does not model storage and movement of water vertically within the soil layer. It implicitly combines the near surface flow and overland flow and models this as direct runoff. It does not include a detailed model of interflow or flow in the groundwater aquifer, instead representing only the combined outflow as base flow.

28 HMS Hydrological Modeling of the basin

29 Stream Networks of the basin

30 Zoomed view of river network

31 Basin Model 22 sub basins 11 gauge stations Bhairab bazar

32 Curve Number Grid Land use and soil data are used to generate Curve number grid for each subbasin CN (Curve Number) value ranges from 71 to 100

33 Necessary Data and Sources of the Study Data Source Resolution/Period DEM HydroSHEDS (source: 30s Stream HydroSHEDS 30s Network Land use map GlobCover (source: 1:5,000,000 Soil data map FAO (source: 1000 m /en/) Precipitation BWDB & NASA 2005, 2006 Discharge BWDB 2005, 2006 Future Precipitation RCP 8.5 scenario ( Model name: CCSM4; Lead Research Center: National Center for Atmospheric Research) 2030, 2050, 2080

34 Model Calibration & Validation Elements Parameters Final Lag time, tp (hr) For all Sub basins For all Reaches Peaking coefficient, Cp Initial Discharge (m 3 /sec) 100 Recession constant Initial Abstraction, Ia to Muskingum K (hr) Muskingum X Performing Sensitivity Analysis we have made a ranking of parameters for Optimization. 1. Peaking Co-efficient,, Cp 2. Muskingum K 3. Recession Constant 4. Muskingum X 5. Lag time, tp (hr) 6. Initial Abstraction,, Ia 7. Initial Discharge (m 3 /sec)

35 Flow ( cumec) Simulated Flow ( cumec) Model Calibration Calibration Observed Flow Simulated Flow R² = Time Period (Year 2005) Observed Flow (cumec) NSE RSR PBIAS

36 One dimensional river flow modeling

37 Hydrodynamic modeling of NE Regions using HEC-RAS 1D-2D model

38 Hydrodynamic modeling using Open Source HEC-RAS Model The open source software HEC-RAS will be applied for assessing flow of the North East region of Bangladesh. HEC-RAS, which is dependent on finite difference solutions of the Saint-Venant equations- (1) (2) Here A = cross-sectional area normal to the flow; Q =discharge; g = acceleration due to gravity; H = elevation of the water surface above a specified datum, also called stage; So = bed slope; Sf = energy slope; t = temporal coordinate and x = longitudinal coordinate. Equations (1) and (2) are solved using the well known fourpoint implicit box finite difference scheme.

39 Steady Flow Simulation

40 Steady Flow Simulation

41 Unsteady Boundary data (Using Rating Curve) SW53_Q SW53_Q May Oct Feb Jul Nov Apr Aug-13

42 Existing Forecasting Stations of FFWC

43 Existing and proposed flash flood forecasting stations of BWDB

44 Capacity building and knowledge sharing and dissemination Two short courses will be held during the project period on- Weather modeling Hydrological and Hydrodynamic modeling A number of national seminars and workshops (like this workshop) will be held like this workshop to gather feedbacks from the participants. Research reports will be published and will be presented in the disseminating workshop.

45 Thank you Questions?