Impact of the Uncertainty of Future Climates on Discharge in the Nam Ou River Basin, Lao PDR

Abstract

Climate change is likely to increase the global mean temperature in future decades, increasing evapotranspiration and affecting precipitation and discharge. However, there is always uncertainty in future climate projection which might be due to the use of different general circulation models (GCMs), greenhouse gas emission scenarios, downscaling techniques, or other factors. This uncertainty in future climates may affect quantification of discharge. This chapter aims to describe the impact of climate change and uncertainty on future climate projection, specifically on discharge in the Nam Ou River Basin, Lao PDR. The Long Ashton Research Station Weather Generator (LARS-WG) was used to downscale daily precipitation, and maximum and minimum temperatures using 8 GCMs for future periods 2011–2030, 2046–2065, and 2080–2099 under scenarios A1B and A2, respectively. Probability density functions (PDFs) were constructed to estimate the uncertainty of future climates. The maximum and minimum temperatures are expected to increase and change for precipitation in future and are observed to be multidirectional. The temperature and precipitation projection due to the GCMs varied by a higher range under both scenarios for the 2090s compared to the 2020s and 2055s. The inter-model variability and variance of the future projections increased in the latter part of the century compared to the early and mid-centuries. In order to assess the impact of these uncertainties in future climates, the soil and water assessment tool (SWAT) model was used. An increase in annual discharge of 5.7 % is observed during the 2055s and 3.13 % during the 2090s under A1B scenario and of 9.23 % during the 2090s under A2 scenario. At the same time, the discharge is estimated to decrease by 0.33 % during the 2020s under A1B and by 1.15 % during the 2055s under A2 scenario. Thus, an increase and decrease in discharge is expected for future periods when all GCMs are considered under A1B and A2 scenarios.