Geoscience Reference
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semiarid regions. In this respect, Africa is one of the 'hot spot' areas. Taylor et al. (
2002
)
stated that the climatic impacts of land-use change in the Sahel region are likely to increase
rapidly in the coming years. So far, the effect of deforestation and reduced vegetation cover
associated with land-use change in Africa has mainly been studied with coarse-grid
(300 km resolution or coarser) global climate models in the form of time slice experiments
and idealized forcing (see, e.g., Feddema et al.
2005
). With these coarse resolution models,
effects on the local and regional climate can usually not be resolved. For this purpose,
RCMs are an adequate tool, such as done by Paeth et al. (
2009
) for West Africa who
conducted long-term transient climate change experiments with the RCM REMO at 50 km
resolution over West Africa where they forced their simulations with increasing green-
house gas concentrations and land-use changes until 2050. Their results indicate that
significant future changes in the near-surface climate may be caused by land-use changes.
A specific form of land use is irrigation, which can considerably affect the regional
climate (Boucher et al.
2004
; Lobell et al.
2009
) and whose feedbacks onto rainfall
(ter Maat et al.
2006
) may become especially important where irrigation coincides with
areas of global hot spots for land surface-atmosphere feedbacks. Koster et al. (
2004
)
identified the Sahel zone as one of the hot spot areas for the feedback of surface soil
wetness to subsequent rainfall. In this semiarid region, irrigation is not a major agricultural
practice, but an increase in dryland agriculture is possible which is sensitive to rainfall
totals. A study of Taylor et al. (
2002
) showed that future likely changes in land cover could
result in a reduction of nearly 10 % in rainfall. Another hot spot of soil moisture-pre-
cipitation coupling is located over India (Koster et al.
2004
). The Indian subcontinent is
one of the most intensely irrigated regions (Fig.
1
a) in the world (Sacks et al.
2009
), and
many studies have shown the role of irrigation in modifying the local climate through
feedback mechanisms (e.g., De Rosnay et al.
2003
; Douglas et al.
2006
,
2009
; Lee et al.
2009
). Effects of irrigation, embedded in South Asian Summer Monsoon (SASM), affect
22 % of world's population and hence play a crucial role in modifying the water resources,
agriculture, economics and human mortality of the region. Therefore, this topic is covered
separately in the following Sect.
2.1
.
2.1 Impact of Irrigation on the South Asian Summer Monsoon (SASM)
As mentioned above, the effects of irrigation on local climate through feedback mecha-
nisms are well known from earlier studies. Saeed et al. (
2011
) found that REMO is able to
reproduce the general characteristics of the SASM; however, over the land areas of north-
west India and Pakistan, a systematic warm temperature bias of more than 5 C can be
noticed (Fig.
2
a, c). The too enhanced simulation of the heat low (Fig.
2
) is a common
systematic error that is present in many regional climate models applied over South Asia
(Lucas-Picher et al.
2011
). For more than a decade, this heat low is used as an important
predictor for SASM rainfall (Singh et al.
1995
). The major part of this heat low region falls
inside the densely irrigated Indus basin (Fig.
1
b), which is the largest contiguous irrigation
network in the world, and its surface water is heavily manipulated by building large dams,
link canals, watercourses, etc., hence resulting in modification of the amount of water in
the soil (Khan et al.
2008
). It is estimated that the Indus River drains only one-eighth of the
*400 km
3
water that annually falls on the basin in the form of rain and snow, with the
remainder used mostly for irrigation and returned to the atmosphere by evapotranspiration
(ET) (Karim and Veizer
2002
).
Saeed et al. (
2009
) applied the regional climate model REMO (Jacob et al.
2007
) over
South Asia at a resolution of degree (*55 km) domain, forced with lateral boundary
