The severe floods this year

Floods in Bangladesh are not new and people are used to the natural monsoon floods. What is unexpected is the high of the flood peak which is getting higher and higher

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, Ichamati, Gur, Little Jamuna, Tangoan, Korotoa, Ghagot and in their tributaries in the north central of Bangladesh. Sever floods are also observing in Asham in India which is the upstream of the Brahmaputra river. Last week we also observed floods that major rivers of the Meghna basins such as Surma, Kushiyara, Jadukatha, Bhugai, Kangsha, Someswwati, Sari gowain, Manu. The north, north-central and north east districts of Bangaldesh are currently suffering from major floods.

Floods in Bangladesh are not new and people are used to the natural monsoon floods. However, what is unexpected is the high of the flood peak which is getting higher and higher in recent times. When water level crossed a certain level know as Danger Level (DL), it is considered as floods. Water level above danger level often causes damage to property, infrastructures, crops, livestock and some cases causes human fatalities. This year we have already observed floods in these two basins and now we are passing through the second wave of the monsoon foods which normally occurs between June and September. The past sever floods occurred in 1988 (which has return periods on 100 years in the Brahmaputra rivers), 1998 (prolonged floods of having duration more than two months in some places), 2004 (severely affected Meghna river basin having a return period of 100-years in some stations), 2007(also affected Dhaka city) and in 2016 (affected more than 25 districts of Bangladesh). However, this year flood water 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. During this week, it will cross the RHWL at Bahdurabad in Jamuna river and then Sirajganj in Jamuna river. It may touch the RHWL of the Kusiyara at Sheola in this week. Table 1 presents a list of stations where peak of the 2017 floods will cross the RHWL and the expected date of crossing. Last year at Baghdadabad in Jamuna river, peak flood also crossed the pervious RHWL and it was above 11 cm above the previous RHWL in 1988 (20.6m). This is alarming that RHWL will be crossed in many stations of this Brahmaputra-Jamuna river again during this monsoon season. This indicates the extremity of the floods has been increased in recent decades in our major rivers of Bangladesh.

It was not completely unexpected that the severity of the floods in the major rivers of South Asia will be increased due to climate change. In many study, it was shown that floods in the Ganges, Brahmaputra and Meghna basins will be more intense and sever.  Due to the global warming, the global mean temperature has already increased about 1 degree centigrade from the pre-industrial periods. It has predicted by IPCC that global warming will be continuing and earth will be much warming at the end of the century due to the anthropogenic green-house gas emissions. Global warming will alter the hydrological cycles and floods will be more severe in south Asian regions. Results from a recent collaborative study of BUET under a collaborative research project entitled ‘High End Climate Impact and Extremes (HELIX)’ funded by the European Union under the Seventh Framework Programme FP7/2007-2013 has also confirmed this. This study was carry out for assessing impact of the extreme climate change in Bangladesh and its impact of the river discharge. It has been found that the floods in the Brahmaputra river basin of having 100 year return periods will carry more than 10%, 17% and 24% more discharge during the 2020s (2011-2040), 2050s (2041-2070) and 2080s (2071-2100) than the pre-industrial periods (1851-1880) ) .These predictions are based on the high Greenhouse gases emission pathways which is known as Representation Concentration Pathways, RCP 8.5 – a scenario where the amount of Greenhouse gases concentration in the future projected if we follow the present path of emission without any mitigation. Although Paris Agreement in 2015 brings hope that global emission will be reduced to such a level that global mean temperature rise will not be above 2-degree centigrade from the pre-industrial periods, UNFCC countries that signed the agreement must implement this agreement. Otherwise, the most climate vulnerable countries like Bangladesh will suffer the most from extreme climate events like floods!

The rise of sea level due to climate change will put additional threats to the flooding of our country as it will have backwater effect on floods. Such back water effect will have prolonged the duration of the floods and also increase the flood height of the peak floods. Perhaps this floods in 2017 will not be prolonged as 1998 floods as the water level in the Ganges river is well below the danger level and there is not much chance of synchronizing of three peaks of the three major rivers: Ganges, Brahmapura and Meghna. Moreover, the spring tide will be occurred in coastal rivers after the new moon on 21st August. This will provide enough time for the flood water in the Jamuna and Meghan river systems to recede in many places. However, there is no doubt that extreme events like severe floods becomes more frequent and more intense than before. Bangladesh will be more and more vulnerable in the coming days due to global warming and consequent climate change.

The writer is a Professor of the Institute of Water and Flood Management (IWFM) at the Bangladesh University of Engineering and Technology (BUET), Bangladesh. Email: [email protected]; [email protected]

The severe floods this year

Floods in Bangladesh are not new and people are used to the natural monsoon floods. What is unexpected is the high of the flood peak which is getting higher and higher

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, Ichamati, Gur, Little Jamuna, Tangoan, Korotoa, Ghagot and in their tributaries in the north central of Bangladesh. Sever floods are also observing in Asham in India which is the upstream of the Brahmaputra river. Last week we also observed floods that major rivers of the Meghna basins such as Surma, Kushiyara, Jadukatha, Bhugai, Kangsha, Someswwati, Sari gowain, Manu. The north, north-central and north east districts of Bangaldesh are currently suffering from major floods. Floods in Bangladesh are not new and people are used to the natural monsoon floods. However, what is unexpected is the high of the flood peak which is getting higher and higher in recent times. When water level crossed a certain level know as Danger Level (DL), it is considered as floods. Water level above danger level often causes damage to property, infrastructures, crops, livestock and some cases causes human fatalities. This year we have already observed floods in these two basins and now we are passing through the second wave of the monsoon foods which normally occurs between June and September. The past sever floods occurred in 1988 (which has return periods on 100 years in the Brahmaputra rivers), 1998 (prolonged floods of having duration more than two months in some places), 2004 (severely affected Meghna river basin having a return period of 100-years in some stations), 2007(also affected Dhaka city) and in 2016 (affected more than 25 districts of Bangladesh). However, this year flood water 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. During this week, it will cross the RHWL at Bahdurabad in Jamuna river and then Sirajganj in Jamuna river. It may touch the RHWL of the Kusiyara at Sheola in this week. Table 1 presents a list of stations where peak of the 2017 floods will cross the RHWL and the expected date of crossing. Last year at Baghdadabad in Jamuna river, peak flood also crossed the pervious RHWL and it was above 11 cm above the previous RHWL in 1988 (20.6m). This is alarming that RHWL will be crossed in many stations of this Brahmaputra-Jamuna river again during this monsoon season. This indicates the extremity of the floods has been increased in recent decades in our major rivers of Bangladesh. It was not completely unexpected that the severity of the floods in the major rivers of South Asia will be increased due to climate change. In many study, it was shown that floods in the Ganges, Brahmaputra and Meghna basins will be more intense and sever. Due to the global warming, the global mean temperature has already increased about 1 degree centigrade from the pre-industrial periods. It has predicted by IPCC that global warming will be continuing and earth will be much warming at the end of the century due to the anthropogenic green-house gas emissions. Global warming will alter the hydrological cycles and floods will be more severe in south Asian regions. Results from a recent collaborative study of BUET under a collaborative research project entitled High End Climate Impact and Extremes (HELIX) funded by the European Union under the Seventh Framework Programme FP7/2007-2013 has also confirmed this. This study was carry out for assessing impact of the extreme climate change in Bangladesh and its impact of the river discharge. It has been found that the floods in the Brahmaputra river basin of having 100 year return periods will carry more than 10%, 17% and 24% more discharge during the 2020s (2011-2040), 2050s (2041-2070) and 2080s (2071-2100) than the pre-industrial periods (1851-1880) ) .These predictions are based on the high Greenhouse gases emission pathways which is known as Representation Concentration Pathways, RCP 8.5 a scenario where the amount of Greenhouse gases concentration in the future projected if we follow the present path of emission without any mitigation. Although Paris Agreement in 2015 brings hope that global emission will be reduced to such a level that global mean temperature rise will not be above 2-degree centigrade from the pre-industrial periods, UNFCC countries that signed the agreement must implement this agreement. Otherwise, the most climate vulnerable countries like Bangladesh will suffer the most from extreme climate events like floods! The rise of sea level due to climate change will put additional threats to the flooding of our country as it will have backwater effect on floods. Such back water effect will have prolonged the duration of the floods and also increase the flood height of the peak floods. Perhaps this floods in 2017 will not be prolonged as 1998 floods as the water level in the Ganges river is well below the danger level and there is not much chance of synchronizing of three peaks of the three major rivers: Ganges, Brahmapura and Meghna. Moreover, the spring tide will be occurred in coastal rivers after the new moon on 21st August. This will provide enough time for the flood water in the Jamuna and Meghan river systems to recede in many places. However, there is no doubt that extreme events like severe floods becomes more frequent and more intense than before. Bangladesh will be more and more vulnerable in the coming days due to global warming and consequent climate change. The writer is a Professor of the Institute of Water and Flood Management (IWFM) at the Bangladesh University of Engineering and Technology (BUET), Bangladesh. Email: [email protected]; [email protected]