world is waking up to the news of the horrific scale of the recent flood disaster in the Mahakali basin of Nepal and Uttarakhand in India, several questions are being asked: what kind of climatic events led to this disaster? Could anything have been done to reduce the loss of life and property? What can we learn from this disaster for the future? In this brief note, we address some of these burning questions.
Mahakali flood disaster
The Mahakali river is a transboundary river between Nepal and India with a catchment area of 14,871 km2. It flows for about 223 km in Nepal and around 323.5 km in India to its confluence with the Karnali River in India. The recent rainfall events in the western and far western regions of Nepal and India affected 20 districts in Nepal and several districts in the Indian states of Uttarakhand and Himachal Pradesh. The floods and landslides that ensued have left hundreds of people dead or missing and destroyed property worth millions of dollars. While this is not the first event of this kind (see annexes), it is certainly the most severe in the last 50 years and it happened at the beginning of the monsoon when no one was expecting.
Intense rainfall events
The monsoon rains usually hit Central Nepal around 15 June and Far Western Nepal around 20 June. This year, the monsoon quickly engulfed the region (http://www.imd.gov.in/; Figure 2). The real-time monitoring station in Nepal reported 80.4 mm of rain on 16 June and 221.8 mm on 17 June at Dipayal, which adjoins the Mahakali flood disaster area (http://dhm.gov.np/; Figure 3 and Figure 4). Surrounding areas such as Dadeldhura, Dhangadi, and Birendranagar in the Far Western Development Region of Nepal recorded more than 150 mm of rainfall in 24 hours on 17 June 2013. Continuous rain in the upper catchments caused the water level in the Seti river east of the Mahakali to rise from 6.94 m to 11.56 m and 5.53 m to 12.81 m in the Karnali at Chisapani on 17 June, as measured by Department of Hydrology and Meteorology, Nepal’s real time network. Unfortunately, there are no real time stations installed by the Department on the Mahakali river. One to three day weather forecasts provided by United States National Oceanic and Atmospheric Administration (NOAA) also indicated heavy rainfall on 17 and 18 June on the border of Nepal and India (Figure 5). Cumulative 3 day TRMM rainfall estimates from 16 June to 18 June show heavy rainfall in the flood affected regions of Nepal and India (Figure 6). The discharge in the Mahakali river rose from 139,000 cubic feet per second to 440,716 cubic feet per second on 17 June – well in excess of the flow of 398,000 cubic feet seconds recorded in the 2012 monsoon (http://www.kantipuronline.com/2013/06/18/top-story/massive-floods-in-mahakali-river-6-killed-update/373456/).