Preprints
https://doi.org/10.5194/hess-2021-378
https://doi.org/10.5194/hess-2021-378

  21 Jul 2021

21 Jul 2021

Review status: a revised version of this preprint is currently under review for the journal HESS.

Drastic decline of floodpulse in the Cambodian floodplains (the Mekong River and the Tonle Sap system)

Samuel De Xun Chua1, Xi Xi Lu1, Chantha Oeurng2, Ty Sok2,3, and Carl Grundy-Warr1 Samuel De Xun Chua et al.
  • 1Department of Geography, National University of Singapore, Singapore
  • 2Faculty of Hydrology and Water Resources Engineering, Institute of Technology of Cambodia, Russian Federation Blvd., P.O. BOX 86, Phnom Penh, Cambodia
  • 3Laboratoire Ecologie fonctionnelle et environnement, Université de Toulouse, CNRS, Toulouse INP, Université Toulouse 3 – Paul Sabatier (UT3), Toulouse, France

Abstract. The Cambodian floodplains experience a yearly floodpulse that is essential to sustain fisheries and the agricultural calendar. Sixty years of data from 1960–2019 are used to track the changes to the floodpulse there. We find that minimum water levels in 2010–2019 have increased by up to 1.55 m at Kratie and maximum water levels have decreased by up to 0.79 m at Prek Kdam when compared to 1960–1991 levels, causing a reduction of the annual flood extent. Concurrently, the duration of the flooding season has decreased by about 26 days (Kompong Cham) – 40 days (Chaktomuk), with the season starting later and ending much earlier. Along the Tonle Sap River, the average annual reverse flow from the Mekong to the Tonle Sap Lake has decreased by 56.5 %, from 48.7 km3 in 1962–1972 to 31.7 km3 in 2010–2018. As a result, wet-season water levels at Tonle Sap Lake has dropped by 1.05 m in 2010–2019 since 1996–2009, corresponding to a 20.6 % shrinkage of the Lake area. In addition to known upstream contributors such as hydropower dams, two anthropogenic causes of the drastic alterations to the floodpulse are identified: irrigation and channel incision. We estimate that water withdrawal in the Cambodian floodplains is occurring at a rate of (2.1 ± 0.3) km3/yr and incision-induced water levels reduction is in the order of (0.43–1.02) m. As the floodpulse is essential for the ecological habitats, fisheries and livelihoods of the region, its reduction will pose major implications throughout the basin, from the Tonle Sap system to the Vietnamese Mekong Delta downstream.

Samuel De Xun Chua et al.

Status: final response (author comments only)

Comment types: AC – author | RC – referee | CC – community | EC – editor | CEC – chief editor | : Report abuse
  • RC1: 'Comment on hess-2021-378', Anonymous Referee #1, 16 Aug 2021
    • AC2: 'Reply on RC1', Samuel Chua, 18 Aug 2021
  • RC2: 'Comment on hess-2021-378', Anonymous Referee #2, 16 Aug 2021
    • AC1: 'Reply on RC2', Samuel Chua, 18 Aug 2021

Samuel De Xun Chua et al.

Samuel De Xun Chua et al.

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Short summary
We found that the annual flood at the Cambodian floodplains has been decreasing since 1960. Consequently, the Tonle Sap Lake is experiencing shrinkage. The results are worrying because the local fisheries and planting calendar might be disrupted. Two possible anthropogenic reasons are identified: irrigation and the deepening of the river.