Heavy rainfall to persist as major rivers expected to rise across Nepal

Nepal is set to receive widespread rainfall over the next several days as a deep depression over the Bay of Bengal moves inland across eastern India, raising the risk of floods, landslides, inundation and debris flows in several parts of the country.

The Department of Hydrology and Meteorology (DHM) said the system had crossed the northern Andhra Pradesh and southern Odisha coast near the Visakhapatnam–Gopalpur area after developing into a deep depression over the Bay of Bengal. The system is expected to move northwestward initially before turning north-northwest and gradually weakening over the next 24 hours.

Although the weather system is not expected to enter Nepal directly, its circulation is already influencing weather conditions across the country. The DHM has warned of heavy to very heavy rainfall in several provinces and urged residents and relevant agencies to remain alert.

According to the department's latest three-day forecast, heavy to very heavy rainfall is possible in parts of Koshi, Madhesh, Bagmati, Gandaki and Lumbini provinces on Thursday, with thunderstorms and strong winds also possible in parts of the Tarai.

The rainfall is expected to continue on Friday, when heavy to very heavy rain is forecast in parts of Koshi, Madhesh, Bagmati, Gandaki, Lumbini and Karnali. The DHM has also warned that isolated locations in Gandaki and Lumbini could receive extremely heavy rainfall.

On Saturday, the focus of the heavier rainfall is expected to shift westward, with heavy to very heavy rain possible in parts of Gandaki, Lumbini, Karnali and Sudurpaschim. Rain and thunderstorms are expected across much of the country.

The weather system has already produced significant rainfall in parts of Nepal. Heavy to very heavy rainfall has been recorded particularly around Lumbini, while heavy rainfall has also occurred in parts of Koshi and Gandaki.

DHM rainfall records cited in the report show 123 mm of rain at Bhagwanpur in Kapilvastu, 117.8 mm at Mainar, 91.4 mm at Simalpani in Arghakhanchi and 131 mm at Baldyanggadhi in Palpa over the preceding 12 hours. Heavy rainfall has also been reported in Tanahun, Kaski, Sindhupalchok, Khotang and Sankhuwasabha.

The system is not expected to strengthen further after entering India and is likely to gradually weaken from a deep depression into a depression. However, rainfall in Nepal could remain significant today and Friday.

Some weather models had indicated the possibility of exceptionally heavy rainfall, but the current situation did not point to such an extreme scenario. At the same time, meteorologists caution that the threat should not be taken lightly because the ground is already saturated following earlier monsoon rainfall.

The combination of saturated soil and additional rainfall could increase the risk of landslides, floods and debris flows, particularly in vulnerable areas. Urban and Tarai areas could also face waterlogging and inundation.

Major rivers expected to rise

The Flood Forecasting Division under the Center of Hydrology and Water Resources Research has separately forecast a significant rise in water levels in major rivers and their tributaries over the next five days. 

The forecast covers major river systems including the Koshi, Narayani, Karnali, Mahakali, Kankai, Kamala, Bagmati, East Rapti, West Rapti and Babai.

Within the Koshi basin, water levels are expected to rise in rivers including the Saptakoshi, Tamor, Arun, Dudhkoshi, Tamakoshi and Sunkoshi. In the Narayani basin, the Narayani, Trishuli, Budhigandaki, Marsyangdi, Seti and Kaligandaki are also expected to see rising flows.

Similarly, increased water levels are forecast in the Karnali, Bheri, Tila, West Seti and Mahakali, as well as in the Kankai, Kamala, Bagmati, East Rapti, Tinau, Banganga, West Rapti and Babai rivers.

The flood forecasting authorities have warned that some rivers and watersheds could experience flash floods. Smaller rivers and streams from Taplejung to Kanchanpur are also expected to see significantly increased flows, with the possibility of sudden flooding in some locations. 

Authorities have therefore urged people living along riverbanks and in other flood- and landslide-prone areas to remain alert and closely monitor updated warnings.

The DHM continues to update its forecasts and warning information regularly. Its current website also provides real-time rainfall and hydrological monitoring, and lists 1155 as the toll-free number for extreme weather and flood early-warning information. 

With rainfall expected to remain active through the weekend and river levels forecast to rise, authorities are advising the public to exercise caution around rivers, streams, steep slopes and areas vulnerable to inundation, while travellers should remain alert to possible disruption to roads and air services.