Ali Shafqat Akanda, Antarpreet Jutla & Shafiqul Islam

Overview Motivation and goals of study Geography and Hydrology Existing forecasting practices Seasonal streamflow forecasts Seasonal Cholera forecasts Downscaling / Interpretation

Motivation Bangladesh is a land of natural calamities Costly droughts and floods each year Droughts and floods followed by cholera Exiting flood forecasting system has a lead-time of only 2-6 days and no cholera forecasts. A monthly-to-seasonal forecasts could provide planning, preparation and preemption time.

Satellite Image of eastern South Asia showing the topography of the region and the Ganges (dark blue) and Brahmaputra (light blue) basin rivers (Courtesy: ESRI) The Eastern Himalayas

Five countries India Nepal Bhutan Bangladesh China Three mighty rivers Ganges Brahmaputra (Tsangpo in China) Meghna The Ganges-Brahmaputra-Meghna Basin Region Key facts about the river basins: 1)92% of the basin areas lie outside Bangladesh (thus no infrastructural solutions). 2)G-B-M average annual precipitation are 1500, 2500, and 4000 mm, respectively.

Spring Onslaught of Drought

Lowest flow of the season in Feb and March Only half a day of rainfall in winter on average Salt water intrusion in Ganges estuary region Severe water shortage in Sundarbans mangrove Spring cholera outbreak in coastal districts

Then comes the Floods …

Intense monsoon rainfall in 4 months (JJAS) Peak Floods usually in August and September Entire country is the floodplain! Loss of lives, crops and infrastructure Massive outbreak of diarrheal diseases More cholera outbreaks in Autumn (OND)

Existing Forecasting System Flood Forecasting and Warning Centre Bangladesh Water Development Board Issues 24 and 48 hour river stage forecasts and countrywide flood inundation maps Using experimental 2-6 days forecasts by CFAB group in Georgia Tech, USA. No cholera forecasts. Little coordination between Health and Water Departments.

Existing Forecasting System

Research Questions What are the key processes? Are Ganges, Meghna, Brahmaputra governed by same moisture sources? What are the significant predictors? How can the probabilistic forecasts be used with existing ones? How do these river basins affect cholera outbreak patterns in spring and autumn, separate/together? How can the forecasts be salient? Which information would be most useful to the local and real users?

Research Questions What are the key processes? Are Ganges, Meghna, Brahmaputra governed by same moisture sources? What are the significant predictors? How can the probabilistic forecasts be used with existing ones? How do these river basins affect cholera outbreak patterns in spring and autumn, separate/together? How can the forecasts be salient? Which information would be most useful to the local and real users?

What forecasts do we need? Droughts Expected time and amount of rainfall Local water table fluctuations If drought year, for how long will it be? Extent of salinity intrusion in South Floods Arrival and intensity of monsoon rainfall Crop impacts (most important variable!) Extent of Inundation area and duration Flood displacement and rehabilitation. Cholera Timing of spring & autumn peaks. Expected Intensity of each peak Which areas are most vulnerable? Social, economic, and health impacts.

The Hydrology of G-B-M

The Hydrology of Cholera First outbreaks in Spring (March – May) during low water availability More outbreaks in Autumn about 2 months after floods (October – December) Significant inter-annual & intra-annual variability Role of Hydrology?

Role of Hydrology in Cholera

Two separate hydro-climatological processes may explain the two cholera peaks separately Water scarcity causes cholera in Spring, while Water abundance causes cholera in Autumn A stronger drought year shows more cholera, and A higher flood year also shows more cholera

Conclusion Seasonal flow and cholera forecasts are vital Emphasis needed on interpreting forecasts Relate to local variables: water availability, drought duration, salinity intrusion areas, inundation scenarios, agricultural options, areas more vulnerable to cholera Presentation of scientific information Socio-economic-health impacts

Future Work Obtain Complementary Evidence: Detailed salinity intrusion analysis Remote Sensing for flood inundation Examine seasonal phytoplankton patterns Employ Forecasting Model Choice of predictor variables Integrate Biology-Hydrology-Remote Sensing Assessment of Socio-economic-health impacts Cholera burden/vulnerability analysis

Acknowledgements Tufts School of Engineering, Boston, MA Water: Systems, Science, and Society Program at Tufts University, Boston, MA Bangladesh University of Engineering and Technology, Dhaka, Bangladesh International Centre for Diarrhoeal Disease & Research, Dhaka, Bangladesh