Floodplain loss: Basins of Irrawaddy, Tapi, Indus, Cauvery rivers flowing through India altered most due to human activities

The July deluge in Delhi along the Yamuna stretch highlighted the critical role of floodplains, not just in the capital city but across all river basins in India. It demonstrated how human activities can impact the natural flow of a river.

In that context, a group of researchers, for the first time, has “developed the first publicly available global dataset that quantifies human alterations in 15 million square kilometres of floodplains along 520 major river basins during the recent 27 years (1992-2019)”.

A floodplain, according to the Federal Emergency Management Agency, is “any land area susceptible to being inundated by floodwaters from any source”.

According to the report titled Human alterations of the global floodplains 1992–2019, over 460,000 square kilometers of floodplain area was lost to agriculture, while another 140,000 square kilometers was redeveloped to new areas over the existing floodplain during the study period. 

Continent-wise, Asia lost the biggest area of floodplains — a little over 200,000 square kilometers — among all the continents. It was followed by South America (92,000 square kilometres) and Africa (73,000 square kilometres).

Further, the study highlighted specific floodplain alterations like the one they identified in the Amazon and Yangtze river basins, which translates to proportional increase in agricultural extent and subsequent decrease in forest area. 

Down To Earth accessed the dataset to identify which river basins in the Indian subcontinent had the highest floodplain loss due to human activities.

River basins often share drainage areas with neighbouring countries. The Indus, for instance, flows from India and into Pakistan and the Brahmaputra flows across three countries. So, it was not possible to independently calculate the actual floodplain loss in India. 

But river basin-wise, Irrawaddy witnessed the highest alteration (4.6 per cent loss), according to the data. While Irrawaddy majorly flows across Myanmar the river-basin extends to some parts in Northeast India (seen in the map). 

In the rest of India, and as seen in the map, Tapi river basin recorded the highest alteration with over 3 per cent of the floodplain area lost due to human activities, followed by Indus (3.2 per cent) and Cauvery (2.7 per cent).

The study further explained how it quantified human alteration by taking stock of three geospatial datasets for the said time period (1992-2019). First, they identified the global extent of floodplain, from which they identified how land use change has unfolded of the corresponding time period and finally, they used river basin boundaries to quantify the process for the rivers assed in the study.

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