Page 265 - Materials Chemistry, Second Edition

10 Life Cycle Impact Assessment 251

• Desertification regulation potential: capacity of dry lands to resist irreversible
degradation on the human time-frame. A multi-indicator system of four
variables, namely climate aridity, soil erosion, aquifer exploitation and fire
risk, determines the desertification ecosystem vulnerability (Núñez et al. 2010)
The land-use impact category is likely the LCA category most affected by
potential problems of double counting. This is because methods for emissions and
methods for land use have been developed under two different, incompatible
approaches. Emission models are bottom-up: the starting point is the elementary
flowin the LCI and the impact model describes stepwise all the mechanisms that
link the cause (the LCI) to the consequence (midpoint or endpoint impact).
Land-use models, in contrast, are top-down. This means that they are based on
empirical observations of the state of the environment, but there is no evidence of
the connection between the consequence and the (supposed) cause. For example,
methods to evaluate biodiversity damage are based on databases of the species
present under different land-use types. The reduction in species richness from e.g. a
forest to an arable intensive agricultural land is driven by many reasons that par-
tially add to each other: cut down of trees and replacement for crops, use of tractor
and other agricultural machinery, emission of pesticides and fertilisers, etc.
However, how and how much each of the reasons above contributes to the actual
biodiversity loss observed in the agricultural land is not known. The development
of mechanistic models such as the ones used to characterise emissions, have the
potential to resolve the issue of double counting. For further details see Chap. 40
and Hauschild and Huijbregts (2015).

10.15 Water Use

10.15.1 Problem

Water is a renewable resource which, thanks to the water cycle, does not disappear.
It is a resource different from any other for two main reasons: (1) it is essential for
human andecosystem life and (2) its functions are directly linked to its geographic
and seasonal availability, since transporting it (and to a lesser extent, storing it) is
often impractical and costly. There is sufficient water on our planet to meet current
3
needs of ecosystems and humans. About 119,000 km are received every year on
land in different forms of precipitation, out of which 62% are sent back directly to
the atmosphere via evaporation and plant transpiration. Out of the 38% remaining,
humans use only about 3%, out of which 2.1% for agriculture, 0.6% for industrial
uses and 0.3% for domestic uses. However, despite these small fractions, there are
still important issues associated with water availability. Many important rivers are
running dry from overuse (including the Colorado, Yellow and Indus), greatly
affecting local aquatic and terrestrial ecosystems. Humans compete for the use of
water in some regions, sometimes leading to the exchange of water rights on the