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A Three-Tier System for Forecasting Precipitation and River Discharge in the Monsoon Regions:

A Three-Tier System for Forecasting Precipitation and River Discharge in the Monsoon Regions: Potential Application to the Mekong River System Tom Hopson CFAB: CU/GT/ADPC. To date, forecasting of river discharge and regional precipitation

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A Three-Tier System for Forecasting Precipitation and River Discharge in the Monsoon Regions:

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  1. A Three-Tier System for Forecasting Precipitation and River Discharge in the Monsoon Regions: Potential Application to the Mekong River System Tom Hopson CFAB: CU/GT/ADPC

  2. To date, forecasting of river discharge and regional precipitation has been confined to Bangladesh and India under the auspices of the Climate Forecast Applications in Bangladesh (CFAB) Project funded by USAID and NSF.

  3. Currently regional precipitation and river discharge (Brahmaputra and Ganges) forecasts are made on three time scales: ==> 1-10 days ==> 15-30 days ==> 1-6 months These forecasts are issued routinely by CFAB on an experimental basis and used by the Bangladesh Meteorological Department and the Flood Forecasting and Warning group.

  4. The question is whether the system can be applied to the Mekong • River system. • Most certainly the 1-6 month and the 1-10 day forecasts are directly • applicable. Preliminary analysis indicates that the system used for • the 15-30 day forecasts may also be applicable. • To this end, we propose to develop a three-tier system for the lower, • middle and upper Mekong for both precipitation and river discharge.

  5. Overview The Climate Forecast Applications in Bangladesh (CFAB) project 2. The three-tier forecast system for precipitation and river discharge Potential application to the Mekong System Ways forward

  6. The Climate Forecast Applications Project CFAB Bangladesh lies at the confluence of three major rivers, the Meghna, Brahmaputra and Ganges. No stream flow data is available in Bangladesh beyond its borders. Furthermore, the catchment areas of the latter two rivers are very large.

  7. CFAB’s problem was how to produce flood forecasts for Bangladesh without detailed upstream data for mega-flood years like 1998 (a) or regular flooding during the wet season (b). (a) September 1998 (b) August 2002 floods

  8. The only data available were the long records of river discharge of the two major rivers as they entered Bangladesh Brahmaputra and Ganges Discharge into Bangladesh Brahmaputra Ganges A further problem was how would the forecasts be disseminated to the user communities once they were produced?

  9. Experimental Operational Forecasts in Bangladesh • Prior to 2000, Bangladesh had no numerical meteorology/hydrological capability • 10 Different agencies each operating independently (GoB, NGOs ….) • Primary Job: Create cooperative infrastructure • Utilized Asian Center for Disaster Prevention (ADPC) for in-country connections • Formed steering committee in 2000 which meets every month

  10. Infrastructure Development …… • Steering group acts as interface between US scientists, GoB technical and administration and the user community • Forecasts are now prepared and disseminated to the GoB network of agricultural extension, flood units, disaster relief and etc. • Much work still to be done in capacity building and utilization of forecasts at base user level • Current work in developing a user metric system for interpretation of forecasts in probabilistic and meaningful context.

  11. Three-Tier Overlapping Forecast SystemDeveloped for Bangladesh SEASONAL OUTLOOK: “Broad brush” probabilistic forecast of rainfall and river discharge. Updated each month. Reliable for 3 months especially early in season. 20-25 DAY FORECAST: Forecast of average 5-day rainfall and river discharge 3-4 weeks in advance. Updated every 5 days. 1-10 DAY FORECAST: Forecast of rainfall and precipitation in probabilistic form updated every day. Considerable skill out to 5-days. Moderate skill 5-10 days.

  12. Utility of a Three-Tier Forecast System SEASONAL OUTLOOK: Long term planning of agriculture, water resource management & disaster mitigation especially if high probability of anomalous season (e.g., flood/drought) 20-25 DAY FORECAST: Broad-scale planning schedules for planting, harvesting, pesticide & fertilizer application and water resource management (e.g., irrigation/hydro-power determination). Major disaster mitigation resource allocation. 1-10 DAY FORECAST: Detailed agriculture, water resource and disaster planning. E.g., fine tuning of reservoir level, planting and harvesting.

  13. What if rainfall forecasts had been available for the Ganges Valley during the summer of 2002 The summer of 2002 was a major drought year in India. The total summer rainfall in the Ganges Valley was 15% below average and in other regions far worse. Over India, total rainfall was -19%. The extended late-June to mid-July drought was crippling. -15% -20% -60%

  14. Availability of skillful seasonal (1-6 month) forecasts • In general, seasonal forecasts, even if skillful are of limited • utility as they are generally made for a large area. They also • do not give spatial or temporal variability of rainfall and omit • important details such as active and break periods of the monsoon. • However, if the forecast is for an extreme season then they • are of use because most areas are of similar sign in their • anomaly. • For example, a forecast of the 1998 flood year or the 2002 • drought year would have been most useful for long term, • planning

  15. Availability of skillful 15-30 day forecasts • Arguably, the time scale of a forecast on which water • resource management and agriculture can benefit is on the • multi-week time scale. • However, these forecasts have been difficult to produce with • skill or accuracy. However, under the auspices of CFAB, we have • started to produce multi-week forecasts of the average 5-day • rainfall and river discharge. • The utility of a 20-25 day forecast can be seen from the • following example

  16. Discussing optimal forecasting times and the 2002 drought over central India, A. R. Subbiah (ADPC) noted: “The minimum length of time of a forecast that will allow a farming community to respond and take meaningful remedial actions … about 10 days although 3 weeks would be optimal… Assuming (such) were available by the third week of June 2002… farmers could have been motivated to postpone agricultural operations saving investments worth billions of dollars… water resource managers could have introduced water budgeting measures…”

  17. Availability of skillful 1-10 day forecasts • Accurate short- term forecasts of 1-10 days allow for • modification of longer term plans and the opportunity for • detailed plans water resource management and agricultural • practices. • These forecasts are the most accurate and are updated daily. • Considerable skill and utilization has been demonstrated in • CFAB for both the Ganges and Brahmaputra.

  18. Three concurrent overlapping precipitation and river discharge forecasts are produced continually throughout the spring and early summer for Bangladesh (and Indian rainfall districts) SEASONAL OUTLOOK 1-6 month forecasts in probabilistic mode issued each month Current Experimental Forecasts Scheme:A Three-Tier System

  19. Seasonal: May plus 6 months

  20. Seasonal: June plus 6 months

  21. Seasonal: July plus 6 months

  22. Seasonal: August plus 6 months

  23. Seasonal Outlook Forecasts • Based on ECMWF coupled model output plus statistical hydrological modelling • Forecast of least confidence: provides excellent 3 month forecasts spring ==> summer but loses predictability late in season. • Provides important “broad-brush” outlook potentially allowing long-term planning • Scheme in which we expect greatest improvement

  24. Three concurrent overlapping precipitation and river discharge forecasts are produced continually throughout the spring and early summer for Bangladesh (and Indian rainfall districts) 15-30 DAY FORECASTS 15-30 day forecasts of pentad rainfall issued every five days Current Experimental Forecasts Scheme:A Three-Tier System

  25. 20-day forecasts for Ganges Plain

  26. 20-day forecasts for Orissa

  27. 20-day forecasts for Rajasthan

  28. Brahmaputra and Ganges Discharge into Bangladesh

  29. H&W(2003)

  30. Intermediate Forecasts • Arguably the most important time scale forecasts for agricultural and water resources planning and disaster mitigation • Provides good skill • Need to learn how to implement • Forecasts based on wide range of data • Will couple with ECMWF output next year (model based empirical forecasts) • Provides ideas for numerical modeling

  31. Three concurrent overlapping precipitation and river discharge forecasts are produced continually throughout the spring and early summer for Bangladesh (and Indian rainfall districts) 1-10 DAY FORECASTS Forecasts of precipitation and river discharge issued every day in probabilistic mode Current Experimental Forecasts Scheme:A Three-Tier System

  32. Brahmaputra Discharge Ganges Discharge 1 day 2 day 2 day 1 day 3 day 4 day 3 day 4 day Observed Q 51 ensemble 5 day 5 day Members in color Black dash

  33. Brahmaputra Discharge Ganges Discharge 7 day 6 day 6 day 7 day 9 day 8 day 8 day 9 day 10 day 10 day

  34. Brahmaputra Flood Probability Ganges Flood Probability 1 day 1 day 2 day 2 day 3 day 4 day 3 day 4 day 5 day 95% 5 day 95% 50% 50%

  35. Short-term Forecasts • Based on ECMWF 51-member forecasts. • Shows excellent skill out to 5-7 days. • Extends Bangladeshi forecasts to 7-9 days • Incorporated into Bangladesh flood warning program • Added value if used in conjunction with the intermediate (15-30 days) forecasting system

  36. The Mekong River system Define three zones for the Mekong: A: Upper B: Middle C: Lower These definitions are initially arbitrary. Final choice would be made on the basis of common meteorology and hydrology A B C

  37. Can the CFAB schemes be adapted for use in the Mekong River system? • Short-term (1-10 days) and seasonal forecast schemes can be adapted immediately. • Intermediate forecasts (15-30 days) depend on the “form” of the weather disturbances that exist in a region. There is a need for intraseasonal variability to be a major component of the climate. Most likely, 15-30 day forecasts will be possible but some basic work is required. mid-Mekong rainfall climatology Middle Mekong precipitation rate for year 1999. Note variability on 15-30 day time scales

  38. Plan of Action • Determine the meteorological and hydrological homogeneity of the three regions: make adjustments of areas as necessary. Requires analysis of precipitation (in situ and satellite) and stream flow data. • Design a three-tiered forecast system (as per the CFAB bangladesh system) for the three regions of the Mekong. • Produce a time table of work from design to operational implementation including training, technology transfer and etc. • Prepare a detailed proposal to the MRC if invited. Proposal and MOU would be between MRC, Georgia Institute of Technology and the Asian Disaster Preparedness Center (ADPC)

  39. Note on the Forecast Modules • The three forecast modules are relatively simple and can • be adapted for workstation or laptop. • The major problem is the transmission of considerable • amounts of data upon which the modules depend. The • Problem is simply one of band width • To use the modules, interpret the results and modify the • modules for other uses or extensions requires some basic • training.

  40. Thank you

  41. Thank you

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