Models Supporting Decision-Making and Policy Evaluation - Environmental Modelling: Finding Simplicity in Complexity - page 322

or intervention-assessment processes. The support
provided by the types of process-based spatially explicit
PSS discussed here may include (but is not limited to):

is not a lack of water that limits agricultural productivity
but rather poor management, sharing and reuse of the
water that is available (Cook et al ., 2011), which is in
part because the institutions that manage water oper-
ate in 'silos' with little interinstitutional co-operation
and communication, and lack capacity for effective man-
agement of the resource but also partly because the
water-availability, water-productivity and water-poverty
contexts are poorly understood through lack of data and
tools for assessing the impacts of the suite of available
interventions that might provide solutions. This institu-
tional barrier creates difficulties for implementing both
hard interventions such as soil- and water-management
techniques and soft interventions such as benefit-sharing
mechanisms. Benefit-sharing mechanisms include pay-
ments for ecosystem services schemes that might lead
to better water management in a multiple use context.
There is thus much interest in policy support that can
provide an appropriate baseline for the current status
of water availability and productivity developed and in
less economically developed countries (Mulligan et al .,
2011a). Beyond the baseline there is demand for systems
capable of assessing the potential water and production
impacts of scenarios for climate change (Mulligan et al .,
2011b), specific soil- and water-management interven-
tions or land-use changes and their drivers such as the
development of biofuels.

spatial targeting of suitability for particular land-use or
land-management strategies;

•

analysis of long-term land, water or production sus-
tainability for particular crops or land-management
strategies;

•

analysis of land, water or production sustainability given
impacts of climate change;

•

integrating the impacts of a range of concurrent inter-
ventions and understanding the impacts of runaway
adoption of a particular policy or intervention;

•

choosing between particular interventions such as con-
servation versus land management approaches; and

•

quantifying and negotiating the sharing of common-
pool resources such as water.

•

20.1.3 Whatpolicies?
Globally there is now a clear interest in the need to man-
age better the agriculture-nature mosaics in landscapes
in order to (i) increase food production in line with
population growth and increasing affluence and waste
whilst, (ii) ensuring that sufficient 'wild' nature exists to
provide increasingly urbanized populations with the crit-
ical ecosystem services that regulate climate, water supply
and planetary health. Recent years have seen consider-
able growth in research at the water-energy-environment-
food (WEEF) nexus (Balmford et al ., 2005; Fargione et al .,
2008; Hazell and Wood, 2008; Godfray et al ., 2010) and
there is much interest in scientific policy support for
this from the international development, conservation
and governmental policy communities. This demand is
focused particularly in the areas of water, biofuels and
food, water management for urban supply and hydropowe r
and maintaining ecosystem services .

Water management for urban supply and hydropower
The human population is now more urban than rural,
with population in some continents (North and South
America) > 80% urban and even Africa and Asia are
> 40% urban. Individuals living in these cities are thus

effectively prevented from choosing a subsistence agri-
cultural livelihood, so food and water must be sourced
from outside the cities and supplied by the market. This
situation creates significant demand for careful water
management to supply cities with a stable, clean water
supply and provide the energy required to sustain ever-
bigger and brighter cities. There are now more than 36 000
large dams around the world, capturing water from some
21% of the Earth's land surface (Mulligan et al ., unpub-
lished data), 5 which supply water to irrigation projects,
urban areas and hydropower projects. Each of these dams
is a critical point in the landscape at which water becomes

Water, biofuels and food
The increasing number and affluence of human popula-
tions requires that we grow more food at a time when there
are many other demands on water for hydropower, urban
and industrial use and the maintenance of ecosystems.
Moreover, water supplies are increasingly threatened by
unsustainable use, contamination and climate change.
These threats mean that we will probably need to grow
more food with less available water so that the efficiency
of water use and the equity of water sharing will need to
improve significantly. In much of the developing world it

5 See Mulligan, M. Saenz-Cruz, L., van Soesbergen, A. et al . (2009)
Global dams database and geowiki. Version 1. www.ambiotek
.com/dams (accessed 6 April 2012).