We are currently observing severe floods in the Brahmaputra-Jamuna and Meghna rivers and their tributaries for the second time in this year.
The previous floods occurred in these two river basins during the middle of July. Water levels currently crossed the Danger Levels (DLs) in the Jamuna, Teesta, Dharala, Atrai, Jamunaswary, Ichhamati, Gur, Little Jamuna, Tangoan, Korotoa, Ghagot, and in their tributaries in the north central of Bangladesh.
Similar floods have also been observed in Assam in India, which is the upstream of the Brahmaputra River
Last week, we also observed floods in the major rivers of the Meghna basins such as Surma, Kushiyara, Jadukatha, Bhugai, Kangsha, Someswwati, Sari Gowain, and Manu.
The north, north-central, and northeast districts of Bangladesh are currently suffering from major floods.
Floods in Bangladesh are nothing new, and people are used to natural monsoon floods. However, what is unexpected is the frequency and intensity of flood in recent times.
When water levels cross a certain level known as Danger Level (DL), it is considered a flood.
Water levels above the danger level often cause damage to property, infrastructure, crops, livestock, and, in some cases, even causes human fatalities.
Alarming patterns and statistics
This year we have already observed floods in the two basins, and now we are passing through the second wave of the monsoon floods which normally occur between June and September. Severe floods occurred in 1988 (a return period of one in 100 years in the Brahmaputra river), 1998 (prolonged floods lasting more than two months in some places), 2004 (a return period of one in 100 years in some stations), 2007 (also affected Dhaka city) and in 2016 (affecting more than 25 districts of Bangladesh).
However, this year, the rise of floodwater will be unprecedented in our recent history, considering the height of the peak flood. It has already crossed the Record High Water Level (RHWL) in various stations of many tributaries of the Brahmaputra-Jamuna river systems such as Mohadevepur in Atrai, Badarganj in Jamuneswari, Kurigram in Dharala, and Dalia in the Teesta.
This week, it will cross the RHWL at Bahadurabad in Jamuna river and then Sirajganj in Jamuna river. It may touch the RHWL of the Kusiyara at Sheola in this week. Last year, at Baghdadabad in Jamuna river, peak flood also crossed the previous RHWL, and it was above 11cm above the previous RHWL in 1988 (20.6m).
Such a backwater effect will prolong the duration of the floods and also increase the water level of the peak floods
It is alarming that RHWL will be crossed in many stations of this Brahmaputra-Jamuna river again during this monsoon season. This indicates that the severity of the floods have been increased in recent decades in our major rivers of Bangladesh.
Blame climate change
It was not completely unexpected that the severity of the floods in the major rivers of South Asia would increase due to climate change.
In many studies, it was shown that floods in the Ganges, Brahmaputra, and Meghna basins would be more intense.
Due to global warming, mean global temperatures have already increased by about 1 degree centigrade from the pre-industrial period. It has been predicted by IPCC that Earth will be much warmer at the end of the century due to the anthropogenic green-house gas emissions.
Global warming will alter the hydrological cycles, and floods will become more severe in South Asian regions. Results from a recent collaborative study by BUET under a collaborative research project titled “High End Climate Impact and Extremes (HELIX)” funded by the EU under the Seventh Framework Program FP7/2007-2013 also confirmed so. This study was carried out to assess the impacts of the extreme climate change in Bangladesh and its impact of the river discharge.
Although the Paris Agreement in 2015 brought hope that global emissions will be reduced to such a level that global temperature rise will not be above 2C from the pre-industrial period, UNFCC countries which signed the agreement must make good on it.
Otherwise, the most climate vulnerable countries like Bangladesh will suffer the most from extreme climate events like floods.
The rise of the sea level due to climate change will put additional threats to the flooding of our country, as it will have a “backwater effect” on floods. Such a backwater effect will prolong the duration of the floods and also increase the water level of the peak floods. Perhaps the floods in 2017 will not be as prolonged as the 1998 floods, as the waters in the Ganges river is well below the danger level, and there is not much chance of synchronised three flood peaks of the three major rivers: Ganges, Brahmapura, and Meghna.
Moreover, the spring tide will occur in coastal rivers after the new moon on August 21. This will provide enough time for the floodwater in the Jamuna and Meghan river systems to recede in many places. However, there is no doubt that extreme events like severe floodings have become more frequent, and more intense than before. Bangladesh, concerningly, will become more and more vulnerable in the coming days.
AKM Saiful Islam is a Professor of the Institute of Water and Flood Management (IWFM) at the Bangladesh University of Engineering and Technology (BUET), Bangladesh.