The Cambodian Mekong floodplain under future development plans and climate change

In: Natural hazards and earth system sciences: NHESS, Band 22, Heft 3, S. 967-983

Abstract

Abstract. Water infrastructure development is considered necessary to drive economic
growth in the Mekong region of mainland Southeast Asia. Yet the current
understanding of hydrological and flood pattern changes associated with
infrastructural development still contains several knowledge gaps, such as
the interactions between multiple drivers, which may have serious
implications for water management, agricultural production, and ecosystem
services. This research attempts to conduct a cumulative assessment
of basin-wide hydropower dam construction and irrigation expansion, as well
as climate change, implications on discharge, and flood changes in the
Cambodian Mekong floodplain. These floodplains offer important
livelihoods for a considerable part of the 6.4 million people living on
them, as they are among the most productive ecosystems in the world –
driven by the annual flood pulse. To assess the potential future impacts, we
used an innovative combination of three models: Mekong basin-wide
distributed hydrological model IWRM-VMod, with the Mekong delta 1D flood
propagation model MIKE-11 and 2D flood duration and extent model IWRM-Sub
enabling detail floodplain modelling. We then ran scenarios to approximate
possible conditions expected by around 2050. Our results show that the
monthly and seasonal hydrological regimes (discharges, water levels, and
flood dynamics) will be subject to substantial alterations under future
development scenarios. Projected climate change impacts are expected to
decrease dry season flows and increase wet season flows, which is in
opposition to the expected alterations under development scenarios that
consider both hydropower and irrigation. The likely impact of decreasing
water discharge in the early wet season (up to −30 %) will pose a
critical challenge to rice production, whereas the likely increase in water
discharge in the mid-dry season (up to +140 %) indicates improved water
availability for coping with drought stresses and sustaining environmental
flows. At the same time, these changes would have drastic impacts on total
flood extent, which is projected to decline by around 20 %, having
potentially negative impacts on floodplain productivity and aquaculture,
whilst reducing the flood risk to more densely populated areas. Our findings
demonstrate the substantial changes that planned infrastructural development
will have on the area, potentially impacting important ecosystems and
people's livelihoods, calling for actions to mitigate these changes as well
as planning potential adaptation strategies.