Modelling future climate - Climate Change: A Very Short Introduction - page 62

provide a better understanding of the potential impacts of climate change (see Figure 16 ) .
This is called down-scaling and is a huge problem recognized in the modelling commu-
nity, because precipitation is spatially and temporally highly variable but essential to mod-
el if human impacts are to be understood. Ultimately the cascade of uncertainty leads to a
huge range of potential futures at a regional level that are in some cases contradictory. For
example, detailed hydrological modelling of the Mekong River Basin using climate model
input from just a single GCM by the UK Met Office (HadCM3) lead to projected future
changes in annual river discharge ranging from a decrease of 5.4 per cent to an increase of
4.5 per cent. Changes in predicted monthly discharge are even more dramatic ranging
from ‒16 per cent to +55 per cent. Advising policy makers becomes extremely hard when
the uncertainties do not even allow one to tell if the river catchment system in the future
will have more or less water.