Preprints
https://doi.org/10.5194/nhess-2021-65
https://doi.org/10.5194/nhess-2021-65

  12 Mar 2021

12 Mar 2021

Review status: this preprint is currently under review for the journal NHESS.

The Cambodian Mekong floodplain under the future development plans and climate change

Sokchhay Heng1, Alexander Horton2, Panha Hok1, Sarit Chung1, Jorma Koponen3, and Matti Kummu2 Sokchhay Heng et al.
  • 1Faculty of Hydrology and Water Resources Engineering, Institute of Technology of Cambodia, Phnom Penh, Cambodia
  • 2Water and Development Research Group, Aalto University, Espoo, Finland
  • 3EIA Finland Ltd., Espoo, Finland

Abstract. Water infrastructure development is crucial for driving economic growth in the developing countries of the Mekong. Yet it may also alter existing hydrological and flood conditions, with serious implications for water management, agricultural production and ecosystem services, especially in the floodplain regions. Our current understanding of the hydrological and flood pattern changes associated with infrastructural development still contain several knowledge gaps, such as the consideration of overlooked prospective drivers, and the interactions between multiple drivers. This research attempts to conduct a cumulative impact assessment of flood changes in the Cambodian part of the Mekong floodplains. The developmental activity of six central sectors (hydropower, irrigation, navigation, flood protection, agricultural land use and water use) as well as climate change were considered in our modelling analysis. Our results show that the monthly, sub-seasonal, and seasonal hydrological regimes will be subject to substantial alterations under the 2020 planned development scenario, and even larger alterations under the 2040 planned development scenario. The degree of hydrological alteration under the 2040 planned development is somewhat counteracted by the effect of climate change, as well as the removal of mainstream dams in the Lower Mekong Basin and hydropower mitigation investments. The likely impact of decreasing water discharge in the early wet season (up to −34 %) will pose a critical challenge to rice production, whereas the likely increase in water discharge in the mid-dry season (up to +54 %) indicates improved water availability for coping with drought stresses and sustaining environmental flow. At the same time, these changes would have drastic impacts on total flood extent, which is projected to decline up to −18 %, having potentially negative impacts on floodplain productivity whilst at the same time reducing the flood risk to the area. Our findings urge the timely establishment of adaptation and mitigation strategies to manage such future environmental alterations in a sustainable manner.

Sokchhay Heng et al.

Status: open (until 06 May 2021)

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Sokchhay Heng et al.

Sokchhay Heng et al.

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Short summary
We study cumulative impact of future scenarios on floods in the Cambodian Mekong floodplain. The impact of decreasing early wet season flows will pose critical challenges to rice production, whereas the increase in mid-dry season flows indicates improved water availability for coping with drought stresses and sustaining environmental flow. These changes would have drastic impacts on total flood extent, having potentially negative impacts on floodplain productivity whilst reducing the flood risk.
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