ateam - Potsdam Institute for Climate Impact Research
ateam - Potsdam Institute for Climate Impact Research
ateam - Potsdam Institute for Climate Impact Research
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ATEAM final report Section 5 and 6 (2001-2004) 52<br />
has a far lower biodiversity (1477 vascular plant species (van der Meijden et al. 1996)), but a very high<br />
grain yield (8.1 t ha -1 <strong>for</strong> 1998-2000 average (Ekboir 2002)). While providing useful in<strong>for</strong>mation about<br />
the stock of resources at a European scale, absolute differences in species numbers or yield levels are<br />
not good measures <strong>for</strong> comparing regional impacts between these countries. Expressing a relative<br />
change would overcome this problem (e.g. -40% grain yield in Spain versus + 8% in The Netherlands),<br />
but also has a serious limitation: the same relative change can occur in very different situations. Table<br />
14 illustrates how a relative change of –20 % can represent very different impacts, both between and<br />
within environments. There<strong>for</strong>e comparisons of relative changes in single grid cells must be interpreted<br />
with great care and cannot easily be compared.<br />
We used the recently developed Environmental Classification of Europe (see next section) to put the<br />
results into their environmental context. The highest ecosystem service supply achieved within an<br />
Environmental Zone is used as a reference value (ESref, Table 14) to stratify potential impacts.<br />
Stratified potential impacts are calculated as the fraction of modelled ecosystem service value relative to<br />
the highest achieved ecosystem service value in that environmental zone, giving a value with a 0-1<br />
range. Because the environmental context is altered by global change, consistent environmental strata<br />
are determined <strong>for</strong> each time slice, so that the ecosystem service reference value (ESref) changes over<br />
time. As shown in Figure 39, the stratified potential impact map shows more regional detail than the<br />
original potential impact map. This is the regional detail required to compare potential impacts across<br />
regions.<br />
In addition to comparing regions, the change of stratified sensitivity potential impact over time can be<br />
seen by looking at three time slices through the 21 st century, 2020, 2050 and 2080 relative to the 1990<br />
baseline (Figure 39, third row of maps). The change in stratified potential impact compared to baseline<br />
conditions shows how changes in ecosystem services affect a given location. Regions where ecosystem<br />
service supply relative to the environment increases have a positive change in potential impact and vice<br />
versa. This change in potential impact is used to estimate vulnerability (see below).<br />
Our method to express changes in potential impacts leads to a small risk of ‘false’ zero or positive<br />
change. If relative to the previous time slice the reference value decreases more than the modelled<br />
ecosystem service supply value <strong>for</strong> a grid cell, the stratified potential impact may stay the same or even<br />
increase. This is the case when the potential of an environmental zone to provide an ecosystem service<br />
decreases as a whole, but in a specific grid cell the modelled supply does not change very much so that<br />
it remains high or unchanged relative to the reference. This is what happens in grid cell B of<br />
environment 1 in Table 14. The environmental potential (indicated by the reference value ESref)<br />
decreases by 0.3, but the modelled value in the grid cell decreases only by 0.2, resulting in a change in<br />
potential impact of zero. This means at t and t+1 the same fraction of the reference value is supplied by<br />
the grid cell, even though the absolute supply of ecosystem service goes down. When interpreting maps<br />
of changing potential impacts or vulnerability, one needs to keep this rare case in mind. This is one of<br />
several reasons (discussed later) to look also at the constituting indictors separately when interpreting<br />
vulnerability of a region.