Abstract
Abstract. The Mekong River Basin is a key regional resource in Southeast Asia for sectors that include agriculture, fisheries and electricity production. Here we explore the potential impacts of climate change on freshwater resources within the river basin. We quantify uncertainty in these projections associated with GCM structure and climate sensitivity, as well as from hydrological model parameter specification. This is achieved by running pattern-scaled GCM scenarios through a semi-distributed hydrological model (SLURP) of the basin. Pattern-scaling allows investigation of specific thresholds of global climate change including the postulated 2 °C threshold of "dangerous" climate change. Impacts of a 2 °C rise in global mean temperature are investigated using seven different GCMs, providing an implicit analysis of uncertainty associated with GCM structure. Analysis of progressive changes in global mean temperature from 0.5 to 6 °C above the 1961–1990 baseline (using the HadCM3 GCM) reveals a relatively small but non-linear response of annual river discharge to increasing global mean temperature, ranging from a 5.4 % decrease to 4.5 % increase. Changes in mean monthly river discharge are greater (from −16 % to +55 %, with greatest decreases in July and August, greatest increases in May and June) and result from complex and contrasting intra-basin changes in precipitation, evaporation and snow storage/melt. Whilst overall results are highly GCM dependent (in both direction and magnitude), this uncertainty is primarily driven by differences in GCM projections of future precipitation. In contrast, there is strong consistency between GCMs in terms of both increased potential evapotranspiration and a shift to an earlier and less substantial snowmelt season. Indeed, in the upper Mekong (Lancang sub-basin), the temperature-related signal in discharge is strong enough to overwhelm the precipitation-related uncertainty in the direction of change in discharge, with scenarios from all GCMs leading to increased river flow from April–June and decreased flow from July–August.
Highlights
Changing availability of freshwater resources is likely to be one of the most important consequences of projected 21st century climate change, critically affecting the potential for sustainable development of life and livelihoods (Bates et al, 2008; Todd et al, 2011)
As part of the wider Quantifying and Understanding the Earth System (QUEST)-GSI project (Todd et al, 2011; http://www. met.reading.ac.uk/research/quest-gsi/, accessed April 2011), this study addresses the important issue of GCM uncertainty by driving a hydrological model of the Mekong River Basin with outputs from seven different CMIP-3 GCMs (CCCMA CGCM31, CSIRO Mk30, IPSL CM4, MPI ECHAM5, NCAR CCSM30, UKMO HadCM3, UKMO HadGEM1)
The overwhelming dependence on the GCM used for projections of future availability of freshwater resources has been demonstrated, which indicates that single-GCM or ensemble mean evaluations of climate change impacts are unlikely to provide a representative depiction of possible future changes in river flow
Summary
Changing availability of freshwater resources is likely to be one of the most important consequences of projected 21st century climate change, critically affecting the potential for sustainable development of life and livelihoods (Bates et al, 2008; Todd et al, 2011). The need for climate change adaptation strategies is prescient for the Mekong given the reliance on the river for agriculture and fish, the vulnerability of the low-lying delta region including large flood-prone areas, and the relative absence of river management infrastructure This situation is likely to be exacerbated by the projected substantial increases in population, in particular in the lower Mekong Basin (from 55 to 90 million by 2025, MRC 2003). Met.reading.ac.uk/research/quest-gsi/, accessed April 2011), this study addresses the important issue of GCM uncertainty by driving a hydrological model of the Mekong River Basin with outputs from seven different CMIP-3 GCMs (CCCMA CGCM31, CSIRO Mk30, IPSL CM4, MPI ECHAM5, NCAR CCSM30, UKMO HadCM3, UKMO HadGEM1) These GCMs are driven by the policy relevant scenario of a 2 ◦C rise in global mean temperature, a presumed threshold of “dangerous” climate change (Todd et al, 2011). The hydrological impacts of a progressive change in global mean temperature (from 0.5 to 6 ◦C) using one GCM, UKMO HadCM3, are investigated
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