Kathmandu became the most polluted city in the world for a few days in January and February 2021.
The long-term seasonal forecast does not show promising signs as below normal precipitation has been forecast until May, which indicates the drought will be extreme and winter crop production will be badly affected. Overall, the impact of this dry spell and severe drought will be seen in the country's economy, and the farmers will be hard hit
Generally, air pollution level in Kathmandu is 7 times higher than the standards set by the World Health Organisation.
Long dry spells in the post-monsoon and winter months may raise air pollution to a higher level.
There are different sources of pollution, and Kathmandu has been suffering from high air pollution in recent decades.
However, the dry condition over a long period was the main reason for the highest pollution level because there has not been rain after the summer monsoon. The post-monsoon and winter season (October-February) of 2020/2021 became the driest season that elevated the air pollution in Kathmandu to its worst level.
Nepal receives most of the precipitation (more than 70%) from June to September that is called the summer monsoon season.
Summer monsoon precipitation is important not only for agriculture but also for water resources in Nepal. Monsoon precipitation also creates extreme weather events of floods and landslides that are common natural disasters during the monsoon.
During the last monsoon season (2020), landslides and floods took 155 lives, 38 are still missing, and around 6,000 families were affected. The remaining seasons (eight months) only produce 30 per cent of the annual precipitation.
However, the importance of that precipitation is no less than the monsoon rain.
The southwesterly and southeasterly winds bring moisture from the Indian Ocean during the summer monsoon, while winter precipitation is associated with the westerly wind that not only plays an important role for the winter crops and to maintain the Himalayan snow and glaciers, but also helps to reduce the air pollution.
The winter precipitation usually occurs in the form of snow over the higher terrain and in the form of rain in the valleys and Tarai regions.
Winter precipitation has considerable spatial and temporal variability, with maximum rainfall over the western hills, with decreasing influence eastwards.
Although dry season precipitation (October-February) is only about 10 per cent of the annual precipitation, it is important for winter crops while maintaining the glaciers in the northern high Himalaya, which is the primary source of drinking water and irrigation of the country.
Post-monsoon and winter precipitation also helps to minimise the pollution level across the country.
Therefore, dry season precipitation holds great importance for Nepal.
According to ERA (European satellite product) data set, in October 2020-February 2021, the country received anomalously low rainfall. Rainfall across Nepal in October, November, December, January and February was recorded as 28 mm, 22 mm, 17 mm, and 25 mm and 35 mm, respectively, which is significantly less than the average precipitation from 1950 to 2021.
Moreover, the Tarai and hilly areas of the Western region received 60-80 per cent less than the normal rainfall during the post-monsoon and winter seasons. Overall, the country witnessed a 60 per cent deficit in rainfall, and the dry season was one of the driest between 1950 and 2021. The higher precipitation in the monsoon season helped to maintain average annual precipitation over the country; however, a long dry spell during the post-monsoon and winter season created a water stress in most parts of the country, which is reeling under severe drought, impacting winter crops and raising the pollution level.
Nepal has a history of drought and long dry spells in the past. The last five months of the post-monsoon and winter season suffered from 60 per cent rainfall deficit across the country compared to the rainfall data over the last 72 years.
According to the World Meteorological Organisation's El Niño-La Niña Update, during October-November 2020, La Nina peaked with moderate strength and may remain until April 2021. These might be the reason for the long dry spells over Nepal during October 2020-February 2021.
The occurrence of consecutive years of drought in different regions of Nepal is a great threat to the farmers in cultivating field crops.
According to a report published on August 23, 2016, low winter precipitation in 2015/2016 reduced winter crop yield, affecting 87 per cent of the population across Western Nepal.
The recent scientific study on drought impacts on agriculture reveals that the frequency of droughts has increased during the winter wheat cropping season.
It is also noted that winter crops need high rainfall during the growing period (December-February) for high crop yield, particularly for wheat, as it supplements the crops with moisture and maintains low temperature due to the sweeps of cold and dry air, which is essential for the development of the crops.
The continuous dry months of post-monsoon and winter may result in a severe drop in winter crop production and may lead to food insecurity in Nepal.
Most areas of the country have received less than average rainfall during the last five months, which may create the same situation as the 2008/2009 and 2015/2016 winter drought on crop production and food insecurity.
The long-term seasonal forecast does not show promising signs as below normal precipitation has been forecast until May, which means the drought will be extreme and winter crop production will be badly affected.
Overall, the impact of this dry spell and severe drought will be seen in the country's economy, and the farmers will be hard hit.
Early prediction of droughts would help the farmers and water managers.
More scientific research is needed in this area for early preparation to deal with the drought.
Sharma is Research Associate and Pokharel is Associate Professor at the Central Department of Hydrology and Meteorology, TU
A version of this article appears in the print on March 30, 2021, of The Himalayan Times.