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They also show the potential of irrigation for mitigating climate change effects in the
SASM region. The present neglect of irrigation was the main cause of the systematic
REMO model error over the heat low region in NW India and Pakistan that led to a too
enhanced formation (too warm, too deep) of this heat low. The representation of irrigation
has caused the removal of this bias. Similar biases in other RCMs (Lucas-Picher et al.
2011
) suggest that they are also related to the missing irrigation process. Consequently, the
representation of water used for irrigation in climate models is necessary for the realistic
simulation of SASM circulation and associated rainfall. This, together with taking into
account land-use change, has also been emphasized by Gordon et al. (
2005
) for the global
scale.
The impact of resolution on the irrigation effects upon the SASM has not been explicitly
considered up to now. In a recent study of Tuinenburg et al. (
2013
), consistent results to
those presented in Sect.
2.1
were found across an ensemble of three RCMs and one GCM.
Here, the application of irrigation on a large scale led to changes in the large-scale cir-
culation, in which moisture shifted away from the Ganges plain towards the Indus basin
and Pakistan. This has confirmed the results found by Puma and Cook (
2010
) and Asharaf
et al. (
2012
). But generally, a higher resolution leads to an improved simulation of the
SASM. Kumar et al. (
2013
) summarized that most of the GCM studies focusing on the
Indian monsoon region concluded that GCMs have difficulties in simulating the mean
monsoon climate over India. Due to their coarse horizontal resolution, GCMs have limi-
tations in simulating the complex orographic precipitation over India. Also, several RCM
studies have been carried out to simulate the summer monsoon over South Asia, whereat
all have reported an improvement in the simulation of SASM spatial and temporal dis-
tribution compared to coarser global models (Kumar et al.
2013
).
Eighty percentage of Indus basin river flows are attributed to the melt of snow and
glacier. Considering the large impact of irrigation on SASM behaviour, one can assume
that under global warming the changes in the timings of water inflows would shift towards
earlier months, hence causing changes in cropping patterns and subsequently irrigation. As
irrigation is impacting the climate change signal over the SASM, changes in irrigation
patterns over the Indus basin will also affect the SASM circulation and associated rainfall
under climate change. Therefore, not only irrigation itself but also changes in irrigation
patterns need to be regarded for climate change studies over the SASM region.
While irrigation seems to have a positive mitigating impact on the SASM climate, the
picture looks different for areas where the human consumption of water leads to drying and
shrinking of surface waters (Asokan et al.
2010
). Here, the associated decrease in evap-
oration from these surface waters counteracts the direct irrigation effect of increasing
evapotranspiration in irrigated land areas. A very prominent example is the Aral Sea,
which was the fourth largest lake on the globe until 1960, with a surface area of about
68,000 km
2
. But, large irrigation activities in many parts of Middle Asia were mainly
responsible for the catastrophic desiccation of the Aral Sea within the last five decades (see
Breckle and Geldyeva (
2012
) and references therein). How irrigation has affected the
current climate or may affect the future climate under global warming conditions in other
regions is an important subject for future studies. In this respect, a first ESM study was
provided by Guimberteau et al. (
2012
). Irrigation also causes groundwater depletion over
many areas of the globe (D
¨
ll et al.
2012
). How this may affect climate and water resources
is a prospect for future studies as the current knowledge of the impacts of changing
groundwater on climate is limited.
