Space Technology Inputs to Operationalise Flood Early Warning System (FLEWS) in Assam
North Eastern-Space Applications Centre (NE-SAC), located at Shillong, is a joint initiative of DOS and North Eastern Council (NEC) to provide developmental support to the North Eastern Region (NER) using space science and technology. The Indian sub-continent is one of the most affected due to chronic flood events mostly induced by periodic monsoon rainfall. In India, the north eastern state of Assam has a complex fluvial systems of rivers, mainly, with two inter-connected river valleys namely Brahmaputra and Barak which together enter the bay of Bengal. Due to enormous sediment transport from the upper catchment areas and subsequent lack of carrying capacity of the channels in these two river valleys, flooding is a periodic phenomenon every year during the peak monsoon months of June, July, August and September causing extensive damage to life and property.
There has been little improvement in the flood mitigation scenario due to the conventional early warning systems (based on gauge to gauge correlation). However, still due to limitations like inadequate lead time, lack of ability to predict spatial spread of flooding against a particular warning, etc., administrative machinery often expresses the opinion that this conventional flood alerts are not actionable decision support for planning effective flood mitigation measures. After a devastating flood event in Lakhimpur district of upper Assam in June 2008, at the request of the Government of Assam, NE-SAC took the responsibility of piloting an exercise with application of space based numerical rainfall prediction and a physics based distributed hydrological model in GIS platform.
This particular service of flood early warning has been carried out with inputs from meteorology, hydrology and Remote Sensing and GIS in watershed scale. Prime services under this activity are: early warning of flood in magnitude (severity), location (revenue circle/ group or cluster of villages) and probable time, High rainfall warning with location and time, post monsoon status of embankments in various flood causing rivers, etc.
The technical component of this exercise comprises of two sub components namely the numerical rainfall prediction model called the Weather Research Forecast (WRF) supported by a qualitative synoptic weather monitoring exercise and a GIS based distributed hydrological model known as the Hydrologic Engineering Centre - Hydrologic Modeling System (HEC-HMS). The first sub component, predicts the rainfall values in different grid resolutions such as 27 km, 9 km, 5 km and 3 km at three hourly intervals for coming 24-hour period. The second sub-component intake the predicted rainfall values into a spatially distributed mesh of inter-connected hierarchy of watershed run-off models giving predicted values of peak discharge as well as hydro-graphs which in turn is compared with established flooding threshold discharge values of the river or tributaries concerned in order to generate the flood alerts and disseminated accordingly to the Revenue circles and district concerned in terms of simple flood advisories with satellite images pertaining to the concerned Revenue circle and district lying in the flood plain under the said flood alert.
With one pilot district having four tributaries of river Brahmaputra in 2009, with periodic requests from the Government of Assam for the inclusion of additional districts in annual phases, by the year of 2016, all existing 27 districts and 7 newly created districts of Assam have been taken up by NESAC, taking the total number of major watersheds to 43 covering both Brahmaputra and Barak valley. After the initial pilot phase from 2009 to 2011, the Government of Assam expressed its willingness to fund and operationalise this activity for the first phase from 2012 to 2014 and again the second phase from 2015 to 2017.
An average year-to-year alert success score of 75% and an average alert-to-alert lead time of 24 to 36 hours have been maintained during these years. FLEWS was declared as a Professional Best Practice by the Department of Administrative reforms under Union ministry of Public Grievances and Pensions in the year 2012. The same year FLEWS was also short-listed as a finalist for Prime Minister’s award for innovations in Public Administration. FLEWS was also honoured as the Winner of e-North East award for e-Governance and citizen services delivery by the North East development foundation, New Delhi in the year 2013. With the success of FLEWS, a full fledged node for risk reduction of other relevant disasters (Landslides, Forest fire, Cyclone, Thunderstorm, epidemics, etc.) in NE region of India in the name of NER-DRR has also been set up at NESAC. Presently, alerts issued under FLEWS are uploaded in the user website (www.asdma.gov.in).
The soundness of an effective flood early warning system under FLEWS has collectively played a major role in effective management of flood disaster while incorporating and improving many factors. During the course of the project, more robust flood hydrological modeling tools are getting tested for implementation into the FLEWS operational block. Accuracy of weather prediction is planned to be scaled to finer grids and domains using multiple system resources. A web-enabled decision support system with dynamic update interface is planned to provide support to the user community.
With the inspiration gathered from its success in Assam, preparations are on to expand its ambit to the other remaining states of NER. The present focus is on extension of FLEWS to other flood prone areas of North Eastern states and presently the NESAC Team is working on building the model for Meghalaya and Nagaland.
WRF Rainfall Prediction HEC-HMS Hydro Modelling Predicted Run-off Values
Seasonal Success Score of Last Four Flood Seasons