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Climate change impacts using multi-model GCM ensemble in a glaciated landscape of Peru

Here we apply WaterWorld 2.88 to examine the impacts of projected climate change in a glaciated landscape near to Huaraz in Peru.  The results do not reflect the consensus view of an area that will dry out as glaciers melt, largely because of projected increases in rainfall for the region alongside the projected warming.  Rainfall projections of general circulation models remain hugely uncertain (see Mulligan et al, 2011).
We must thus avoid over-simplistic projections of the future impacts of climate.  Indeed, more water may be as bad for this steep, poorly vegetated region as less water.  Any change requires adaptation by increasingly complex and sensitive societies and infrastructures - and that has an associated cost.

Hydrological baseline

Baseline water balance for this landscape is highly spatially variable reflecting the dominant influence of rainfall (in the low rainfall areas at high altitude precipitation is falling as snow) and spatial variability in actual evapotranspiration. Fog inputs contribute little in the high mountains but significant volumes in the drier valleys, especially to the west.  Annual snowmelt contributions are high locally to peaks but decline in significance downstream because the s now covered areas are a relatively small fraction of the total landscape and thus snowmelt a small fraction compared with total precipitation inputs.

Impacts of climate change

The following scenario was run:
IPCC Assessment Reportar4
Emissions scenarioA2a
Downscaled byKCL
GCM nameMean of 5 GCMs
Projection year2041-2060

...leading to an increase in rainfall that is particularly pronounced on exposed slopes and in subcatchments draining the Huascaran range. Most areas thus show an increase in water balance even though higher temperatures also lead to higher actual evapotranspiration in all but the highest peaks. The volume of runoff from snowmelt declines throughout the range and its contribution to runoff declines significantly, partly because of increases in rainfall.  Contrary to expectation therefore, runoff thus increases throughout the region and in percentage terms (relative to current runoff) the  change is significant throughout but particularly in the drier west of the area.

Seasonally water balance is similar between the baseline and scenario at the tile scale but with subtle differences in the wet seasons.

The snowpack declines significantly in the wet season as less rainfall falls in the form of snow:
...and as a result the meltwater contribution to runoff declines, especially in the dry season, though this affects the budget little given the extra rainfall.

Spatially, the seasonality in runoff increases in most areas as a result of the changing rainfall distribution affecting seasonality both locally and downstream, but decreases in other smaller areas that are fed by glaciers and snowmelt, though in these areas the effects do not propagate far downstream.

Thus the impacts of climate change in this region are not as you might first expect, largely because a warmer world is projected to be wetter one for this region and for many others.  Rainfall projections of general circulation models remain hugely uncertain (see Mulligan et al, 2011).   We must thus avoid over-simplistic projections of the future impacts of climate.  Indeed, more water may be as bad for this  steep, poorly vegetated region as less water.  Any change requires adaptation by increasingly complex and sensitive societies and infrastructures - and that has an associated cost.