On 31 July this newspaper carried a report titled ‘Kathmandu’s Flash Floods Are 4 Decades in the Making’. The analysis by Tom Robertson stated that there was nothing ‘sudden’ about floods in Kathmandu Valley, and they would get much worse.
We derive no satisfaction in saying, ‘we told you so.’ On the night of 5 September the capital received over 100mm of rain in just 3 hours early on Monday morning. The rain was heaviest recorded in the Valley for decades.
Monsoon modelling by the South Asia Climate Outlook Forum had predicted 20% higher than normal rainfall in most of Nepal this year, but the total precipitation has been even heavier than that in many places causing death and destruction. The rains have been sustained and relentless, and we saw nearly as much rain as Kathmandu gets in the whole of September falling on just Sunday and Monday.
Scientists are much more categorical than they have ever been in drawing a correlation between such extreme weather events and the climate crisis. A warming atmosphere means more water vapour in the air, which translates into more than normal rain.
This year saw record-breaking downpours in the Ahr Valley of Germany, floods in China’s Henan province in July killed 300 people, and remnants of Hurricane Ida dumped 80mm of rain in just one hour on New York, leaving 50 people dead across northeastern US, including three Nepalis.
Meanwhile, Siberia, the Canadian Arctic and California baked in unprecedented heat waves and droughts, with wildfires sweeping across them for a second northern summer in a row. Nepal itself had a five month drought last winter which sparked historic forest fires that engulfed the whole country in smoke.
Nearly 80% of Kathmandu’s annual rain falls in just four months: June-September. People in Nepal and the Indo-Gangetic plains have learnt to live with the annual floods, and need them to replenish their farms with nutrients valuable for next year’s crops.
Kathmandu has seen cloudbursts before. The destructive floods of 1981 dumped 170mm of rain in 24 hours on Godavari, unleashing floods on the Bagmati’s tributaries. Makwanpur saw an unimaginable 540mm of rain in 24 hours, and the resulting debris flows filled up the Kulekhani reservoir and wiped out half its life-span.
Such extreme events will be more intense and frequent as the atmosphere warms up. That is a given. But instead of preparing for them, we are making them even more disastrous by impounding water with new housing, perimeter walls, or garbage blocking drains.
Blaming just the climate for this week’s inundation of Kathmandu is a copout. Though heavy, the Valley’s natural drainage system of the Bagmati and Bishnumati would have been able to absorb the excess water by letting it spill over what used to be wide floodplains.
As Robertson notes, those areas are now built over, natural drainage has been blocked and impermeable concrete and asphalt prevent water from seeping into the ground. In the past 40 years, Kathmandu’s population grew four times. More houses were built, and as land got scarce they encroached into the flood plains. The rivers have been constricted into narrow channels.
Bulldozers are clawing at the Valley rim, removing the slopes that used to store rainwater like gigantic sponges, and let it out slowly. Now, with the buffers gone, even moderate intensity rainfall leads to direct runoff and flooding.
The problem is the same in the Tarai. Sand mining and logging of the Chure has increased flash floods downstream, sedimentation raises river beds, and new highways and embankments in Nepal and across the border in India act as dams, inundating towns and farms.
The problem is slightly different in the mountains. Haphazard road construction has increased landslide danger, but as we are seeing with Melamchi this year, there is rain where snow used to fall on loose glacial deposits and this is washing them down in deadly debris flows.
Glaciologist Rijan Bhakta Kayastha in a recent Nepali Times op-ed made a case for more weather stations in the high mountain catchment areas to measure the intensity of rainfall in real time, communicate the data to the National Disaster Risk Reduction and Management Authority so settlements downstream can get early warning.
All that is well and good, but as long as we continue to block the natural drainage of rivers, floods will get worse. And there is no point blaming climate change for that.