But Kathmandu’s 21st century floods differ from what Kirkpatrick and Oldfield described in the 19th century. The situation has changed. Now, it is not just that Valley residents have built where they never used to, on lowlands where floods routinely sweep over. But the environment has also been remade: not just in the floodplains, but the entire landscape, so that the annual floods have grown much worse than before.
Climate change has brought more intense rain. It is part of this new calculus, but only a part. Instead, other widespread changes to the Valley’s environment, especially to the water system, have made floods more frequent and fiercer.
Most important, until a couple decades ago, the Valley’s soil and sand collected much of the year’s monsoon rain soaking it up like a sponge in the summer and releasing it slowly throughout the year. In fact, the ground absorbed and held so much water that the Valley’s bigger rivers did not go dry even during the eight dry months of the year. The soil’s absorbing power slowed flooding during the monsoon’s heavy rains.
“The soil absorbing so much water prevents flooding in the peak season,” water expert Madhukar Upadhya told me. Indeed, historically, the entire water landscape revolved around rainwater’s “gradual absorption and gradual release”.
But, Upadhya adds, regretfully, “We have changed everything very dramatically.”
The biggest change is all the big buildings and concrete that block water flowing into the ground. Instead of soaking into the soil, rainwater now hits the roofs and pavement and shoots directly into low areas, filling river beds to the brim, sometimes within minutes.
“We have sealed all the land. Now water goes straight to the खोला (stream), not to and through the ground.” Upadhya says. “Water ह्वात्तै आउँछ.”
The problem is not just new buildings in the floodplains. All over the Valley, buildings and roads and courtyards and other ‘impervious surfaces’ block the recharging of groundwater. Once a compact city of bricks and mud, wetlands and ponds, Kathmandu and the entire Valley has become a sprawling metropolis of concrete.
Between 1980 and 2010, Kathmandu quadrupled in area, and is still spreading fast. With heavy in-migration, a more mobile population, and bulldozers carving out roads in every direction, Kathmandu is one of the fastest growing cities in one of the world’s fastest urbanising regions.
All this concrete and change has disrupted the Valley’s traditional drainage patterns, blocking absorption and accelerating runoff. “The concrete surfaces and the loss of open spaces and wetlands,” Ajaya Dixit explains, “have taken away buffers and lead to instantaneous surface runoff when high-intensity rains occur.”
Adding to the problem, as Kathmandu grows, is the widespread bulldozing of ढिस्को, the small hillocks of sand that used to dot the Valley’s landscape, especially its northern half.
“We have lost sand hillocks at the foothills around the valley that stored rainwater and released it slowly,” Upadhya pointed out to me.
Owners sell the sand to go into concrete, then sell the flattened land for houses or other construction. They reap double rewards, but the larger ecosystem suffers. The loss of ढिस्को contributed to the big 2018 floods on Bhaktapur’s Hanumante River.
“Before the Hanumante flood lots of hillocks were removed and replaced in the watershed all the way up to Nagarkot,” says Upadhya. The floods caused enormous loss. Because of all these changes, Kathmandu Valley water now flows in new patterns. Altering the Valley’s complicated ecological system has brought unintended consequences.