Floodwaters from Noru ravage houses and properties in Ubon Ratchathani province. Credit: ONWR

Noru leaves huge flood impacts behind as it dissipates

Authorities are now rushing to discharge floodwaters flowing into major reservoirs countrywide to ensure safety for communities downstream while the world’s meteorological organisation, WMO, has remarked that climate change is expected to lead to an increase in the proportion of major tropical cyclones and in heavy rainfall associated with these events

The National Water Command Center supervising water crisis management has examined impacts caused by Super Typhoon Noru and learned that up to 11,500 million cubic metres (m3) of water would be flowing into 35 major reservoirs countrywide as assessed until October 10, according to Dr. Surasee Kittimonton, Secretary-General of the Office of National Water Resources (ONWR), the NWA’s secretary. The storm has so far affected 32 provinces, mostly in the North, the Northeast, and the Central Plains.

Following his inspection on the flooding in the Northeast today, especially in Ubon Ratchathani province, which was first hit by the storm here on Wednesday evening (September 28), Dr. Surasee said Deputy PM Gen Prawit Wongsuwan was concerned about the impacts caused by Noru as it has left vast areas along the Mun and Chi Rivers extensively flooded. In some parts, such as near the main bridge in the province’s downtown, the water level was raised nearly three meters and is expected to reach its peak on October 6 before returning to a normal level near the end of the month, or around October 28.

Dr. Surasee said Noru alone has brought more rainwater than that brought together by the tropical storms, Podul and Kajiki, which hit the region in 2019. While the impacts from the storm are considered to be less when compared with the two previous storms, partly due to a more proactive response, concerns are growing over excess water that is flowing into the major reservoirs where the storm has passed, mainly in the North and the Northeast.

Dr. Surasee said altogether, up to 11,500 million m3 of water would be flowing into these reservoirs, gradually filling them up despite the fact that the storm has dissipated. At least 14 of them have already been filled up, according to ONWR. This includes the 960-million-m3 Pasak Jolasid in the Central Plains, and two out of three largest dams in the Northeast; 2,431-million-m3 Ubonratana and 1,966-million-m3 Sirindhorn. The two largest dams in the North, 13,462-million-m3 Bhumibol and 9,510-million-m3 Sirikit have stored around 72% and 65% of their maximum storage capacity already, or 9,678 and 6,193 million m3, respectively, according to the Hydro-Informatics Institute.

This has prompted concerned officials to seriously discuss how best to discharge the excess water so that it would not flood communities downstream.

According to ONWR, the run-off river Chao Praya dam on the Chao Praya River in Chainat province, which principally regulates water flows for the Central Plains, will discharge water around 2,600-2,700 m3 per second over the next week. This is only slightly below its maximum capacity of around 2,850 m3/s, or it would overflow the river banks, otherwise. The excess amount of water will be diverted to vast rice fields in the East and the West “as much as possible”, according to ONWR’s latest announcement today. Altogether, 10 vast rice fields of the Central Plains could help retain around 1,300 million m3 of water.

ONWR said the excess water from Pask Cholsid, another key water regulation in the Central Plains, would be around 800 million m3, and the authorities concerned will try to discharge it in step so that it would not add to the Chao Praya River and flood the residents.

Still, the new water regulation over the next week could prompt the water levels in the Pasak and Chao Praya Rivers to rise between 0.25-1.5 metres. Residents living by the rivers are warned to prepare themselves for the flood impacts.

Bangkok Metropolitan Administration, meanwhile, has also issued a warning to Bangkok residents to prepare themselves for possible overflows and flash floods over the next week.

Typhoon Noru as of Wednesday morning. Credit: Gistda/ JMA

Noru’s anatomy

Noru weakened to a tropical depression on Wednesday evening (September 28) as it entered Thailand’s Ubon Ratchathani provinces, according to the Meteorological Department. It is reported to have dissipated yesterday. (Read: Thailand braces for first direct storm Noru

According to the Japan Meteorological Agency, the storm was observed as forming in the Philippine Sea last Wednesday (September 21) as a disturbance before being recorded as a tropical depression and locally named as Karding the next day by the Philippine Atmospheric, Geophysical, and Astronomical Services Administration or PAGASA.

It was then further monitored before developing into a tropical storm and then a Typhoon two days later. But within one day, on September 25, the typhoon was reinforced with the so-called “explosive intensification” due to a favourable environment for rapid intensification over the sea. Its wind speed was recorded at 90 km/h. Noru then developed further into a Super Typhoon as classified by PAGASA before hitting Quizon of the Phillippines with the wind speed measured at 185 km/h in the evening. 

The storm had weakened as it traversed through the country before entering the South China Sea. There, it regained its strength and re-intensified into a typhoon of Category 4 again before hitting Vietnam’s North in the early morning of Wednesday. It then traversed inland through Lao PDR as a tropical storm and Thailand as a tropical depression before dissipating eventually.

Hurricane Ian is tracked south of Florida on Sep 26 by the National Oceanic and Atmospheric Administration. Credit: UN News/ NOAA

Hurricane Ian

Almost at the same time, in the opposite part of the world, the Atlantic, Hurricane Ian had been developing before wreaking havoc in Cuba and Florida with the classification of Category 4.

The behaviours and frequencies of these tropical cyclones now are puzzling climate scientists. WMO said in the space of two weeks, the world has witnessed successive powerful tropical cyclones with devastating winds, extreme rainfall, and flooding in densely populated parts of the world. 

These new tropical cyclones follow closely on the heels of Hurricane Fiona, which caused deadly flooding in the Caribbean and was the strongest hurricane on record to hit Canada, and Typhoon Nanmadol which prompted the evacuation of nine million people in Japan, the organisation said.

The organisation remarked that climate change is expected to lead to an increase in the proportion of major tropical cyclones and in the heavy rainfall associated with these events, while sea level rise and coastal development are worsening the impact of coastal flooding.

“Climate science is increasingly able to show that many of the extreme weather events that we are experiencing have become more likely and more intense due to human-induced climate change. We have seen this repeatedly this year, with tragic effect. 

“It is more important than ever that we scale up action on early warning systems to build resilience to current and future climate risks in vulnerable communities,” said WMO Secretary-General Prof. Petteri Taalas.

Hurricane Ian during Sep 25-29, 2022. Credit: NASA Earth Observatory