Geoscience Reference
In-Depth Information
be difficult to distinguish among different change drivers (e.g., agriculture, forest, irriga-
tion developments, various land-cover changes and/or land productivity changes) and from
the impacts of global, natural and anthropogenic climate change. Nevertheless, among
different regional land-water use changes, irrigation in particular has been found to greatly
enhance evapotranspiration (ET) (Gordon et al.
2005
; Shibuo et al.
2007
; Asokan et al.
2010
), and thereby affect regional climate (Boucher et al.
2004
; Kueppers et al.
2007
;
Bonfils and Lobell
2007
; Lobell et al.
2009
; Destouni et al.
2010
; Lee et al.
2011
), as well
as future hydrological responses to forthcoming climate change (Jarsj ¨ et al.
2012
).
With regard to regional irrigation effects on hydro-climatic change, Destouni et al.
(
2010
) developed a hydrological approach to estimating irrigation-driven changes in ET,
latent heat flux (F) and surface temperature (T) and distinguishing these change contri-
butions from the regional effects of global climate change. The approach is data-driven and
relatively simple, utilizing seasonal differences in actually observed historic T changes
within a hydrological drainage basin, along with fundamental water balance constraints
that corresponding, historic water flux observations imply for the basin. Destouni et al.
(
2010
) specially developed and applied this basin-wise data-driven approach to the Central
Asian system of the Aral Sea and its drainage basin.
Irrigation effects on ET and other hydrological changes, however, can differ greatly
among hydrological basins in different world regions with different hydro-climatic con-
ditions (Destouni et al.
2013
). As noted by Destouni et al. (
2010
), irrigation effects may
also differ between hydrological basins of different types (V
¨
r
¨
smarty et al.
2000
), such as
an endorheic
1
basin, draining into terminal surface waters like the Aral Sea, which depends
greatly on that specific regional runoff, and an exorheic
2
type of basin, draining into the
ocean, which does not depend so much on the runoff from just one specific basin.
In view of such cross-regional differences, the present paper aims at comparatively testing
the applicability of the basin-wise data-driven approach proposed by Destouni et al. (
2010
) and
comparing its hydro-climatic change results across two different world regions: the Aral
region in Central Asia that includes the terminal Aral Sea and the endorheic Aral Sea drainage
basin draining into it, which has already been studied using this approach, and the Mahanadi
River Basin (MRB) in India, which is a novel application of the approach. The MRB is an
exorheic basin, draining into the Bay of Bengal, with monsoon-driven hydro-climatic con-
ditions and seasonality (Asokan et al.
2010
) that differ greatly from those in the Aral Sea region
(Shibuo et al.
2007
; Destouni et al.
2010
). In addition to extending and testing the applicability
of the approach across different world regions, another main aim of this comparative study is to
investigate and identify which regional conditions may lead to large and important hydro-
climatic changes and impacts driven by irrigation. In the following sections, we first provide a
literature review (Sect.
2
), followed by a description of sites and methodology in Sect.
3
, cross-
regional results and their comparison in Sect.
4
and main conclusions in Sect.
5
.
2 Literature Review
In general, vegetation interacts with climate to regulate the partitioning of precipitation
(P) into ET and runoff (R) at the land surface (Gordon et al.
2005
; Douglas et al.
2006
;
1
An endorheic basin is a closed drainage basin that retains water and allows no outflow to other external
bodies of water such as oceans, but converges instead into lakes. Here the water loss is through evaporation,
evapotranspiration and seepage.
2
An exorheic basin is a drainage basin that discharges into ocean.
