The reason the air quality has remained so poor for so long is that there are thousands of fires right across western and central Nepal, as well as parts of Uttarakhand in India. Deficient precipitation in winter and spring, possibly a result of climate change, had turned the forest underbrush dry, making this year’s fire season the worst in living memory.
The fires have been unprecedented in extent and duration. They have added to the already serious pollution from vehicular emission, brick kilns and open garbage burning in Kathmandu Valley. In mid-March there was also a lot of wind-blown sand from the Arabian and Indian deserts.
There have been years like the winter of 2008-2009 when huge fires ravaged the high mountains, blowing plumes of smoke over Kathmandu. But these lasted only a few days and went out after the rains arrived.