Streamflow prediction for flood warning and satellite-based inundation mapping for the HKH region

02 Aug 2020

Heavy monsoon rain has caused widespread flooding and inundation in Bangladesh. (Photo: Shakil Ahmed)

The monsoon floods in the Hindu Kush Himalayan (HKH) region are worsening the humanitarian crises caused by the COVID-19 pandemic and the recent Cyclone Amphan in Bangladesh and India. Millions of people have been affected in Nepal, India (Bihar and Assam), and Bangladesh. The crisis is far from over, with more monsoon rain forecast in the coming days and weeks.

In this context, timely information on current and upcoming floods can help government and humanitarian agencies manage disaster response and relief activities better. Here at ICIMOD, we have been working with national agencies in the region to provide support for streamflow prediction and satellite-based inundation mapping.

Streamflow prediction for flood warning

With technical assistance from NASA and Brigham Young University, our SERVIR-HKH Initiative has developed a streamflow prediction system to support flood early warning. The regional streamflow prediction system, which is based on the European Center for Medium Range Weather Forecasting (ECMWF), can be accessed at http://tethys.icimod.org/apps/streamflowhkh/. The system predicts streamflow in a river for 10 days.

Figure 1

Figure 1: ECMWF-based regional streamflow prediction system. The picture shows prediction for 28 July 2020. The colour code shows the probability of streamflow that would match or exceed the flow volume for different return periods during the next 10 days (red: 20 years; orange: 10 years; yellow: 2 years; blue: normal drainage). A return period, also known as a recurrence interval, is an average time or estimated average time between events.

Additionally, a streamflow prediction system for Nepal has also been developed on the basis of an ensemble weather forecast to provide 48-hour flow predictions based on local rainfall to support flash flood warning. We have been jointly validating the system with the Department of Hydrology and Meteorology, Government of Nepal. The system can be accessed at http://tethys.icimod.org/apps/hiwatnepal/.

Figure 2: HIWAT-based streamflow prediction for Nepal showing prediction for 29 July 2020.

Flood inundation mapping

We have worked on using synthetic-aperture radar satellite remote sensing to provide near real-time inundation maps for supporting flood response, such as during the 2019 Bangladesh floods. Flood inundation maps for the region are prepared with latest available satellite imagery and an application has been developed to visualize the inundation (Figure 1). The application can be accessed at http://geoapps.icimod.org/Flood2020/. Currently, we are developing an automated flood inundation mapping system in collaboration with NASA and University of Alaska Fairbanks under a NASA Applied Science Project.

Figure 3: Map showing flood-inundated areas in the HKH region using Sentinel-1 imagery from 1 July to 25 July. The light-blue sections indicate flood-inundated areas and deep blue indicates perennial water bodies. (Source: Google Earth Engine).

Inundation situation

Based on the maximum inundation in July, the total inundated area in different parts of the region is shown in Figure 4. The details of the inundated areas are presented in Table 1

Figure 4: Inundated areas in different regions: a. Nepal Terai; b. Bangladesh; c. Assam, India; d. Bihar, India.

Source: Estimated by ICIMOD from Sentinel-1 imagery

This piece was first published on the ICIMOD website on 2 August 2020.

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