COMMISSIONED REPORT
Commissioned Report No. 054
Trends in soil erosion
(ROAME No. F00AC106)
For further information on this report please contact:
John Gordon
Scottish Natural Heritage
2 Anderson Place
EDINBURGH
EH6 5NP
Telephone: 0131–446 2450
E-mail: [email protected]
This report should be quoted as:
Davidson, D.A. and Grieve, I.C. (2004) Trends in soil erosion.
Scottish Natural Heritage Commissioned Report No. 054 (ROAME No. F00AC106).
This report, or any part of it, should not be reproduced and utilised without the permission of both Scottish
Natural Heritage and Professor Last who retains the intellectual property rights for the data: permission will
not be withheld unreasonably. The views expressed by the authors of this report should not be taken as the
views and policies of Scottish Natural Heritage.
© Scottish Natural Heritage 2004.
COMMISSIONED REPORT
Summary
Trends in soil erosion
Commissioned Report No. 054 (ROAME No. F00AC106)
Contractor: D.A. Davidson and I.C. Grieve, Department of Environmental Science,
University of Stirling.
Background
As part of its environmental audit programme, SNH is investigating changes and trends for natural heritage
reporting and development of indicators. Changes in geomorphological processes are an integral part of
the natural heritage. The aim of this report, part of a series on geomorphological processes, is to document
and analyse trends in soil erosion.
Soil erosion is a natural process involving transport by surface runoff, wind deflation and soil creep. Soil
erosion may be accelerated by human activities, including a range of agricultural and forestry operations
and human trampling. As well as highly visible effects such as rilling and gullying, soil erosion can have
adverse impacts on soil physical and chemical status, organic matter content and biodiversity. Off-site
impacts may include: increased sediment loads in streams, which may bury fish-spawning gravels; increased
nitrate and phosphate loads, leading to eutrophication and depressed dissolved oxygen levels in surface
waters; and sedimentation in reservoirs, reducing their operating life and capacity. Such effects are
generally uncosted but may be significant.
Main findings
1. Although there are a number of well-documented case studies of individual events, any assessment of
trends in soil erosion is seriously hampered by a lack of data at the national scale on the processes,
distribution and rates of soil erosion.
2. In the lowlands, soil erosion by water is most clearly expressed in the formation of gullies which can
vary in depth from c.10cm to >1m. Fields which have been ploughed or are under autumn-sown cereals
are particularly vulnerable to periods of excessive rainfall. Erosion induced by tillage is likely to be of
similar magnitude to water erosion, but there are no Scottish studies on this.
3. Erosion in the uplands is demonstrated by gullying, slope failures and peat hagging. A study of a sample
of grid squares covering 20% of the upland area showed peat erosion in c.6% of the area sampled,
although there were considerable regional variations. Peat erosion has major negative impacts on habitat
and water quality. In detail, it is extremely difficult to establish causal relationships for peat erosion.
For further information on this project contact:
John Gordon, Scottish Natural Heritage, 2 Anderson Place, Edinburgh EH6 5NP.
Tel: 0131– 446 2450
For further information on the SNH Research & Technical Support Programme contact:
The Advisory Services Co-ordination Group, Scottish Natural Heritage, 2 Anderson Place, Edinburgh EH6 5NP.
Tel: 0131–446 2400 or [email protected]
Scottish Natural Heritage Commissioned Report No. 054 ( ROAME No. F00AC106)
Contents
Summar y
1
INTRODUCTION
1
2
SOIL EROSION IN THE LOWLANDS
4
2.1
Erosion rates
4
2.2
Geographical variations
6
2.3
Impacts
6
2.4
Causes
7
2.5
Trends in lowland soil erosion
7
3
4
SOIL EROSION IN THE UPLANDS
8
3.1
Geographical variations
8
3.2
Causes of erosion
9
3.3
Trends in upland soil erosion
9
REFERENCES
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Scottish Natural Heritage Commissioned Report No. 054 ( ROAME No. F00AC106)
1
INTRODUCTION
Environmental audit in Scottish Natural Heritage (SNH) is being developed as a clear and logical process
of assessing status, identifying trends and explaining the main factors influencing change. Natural heritage
trends are therefore being analysed and documented for natural heritage reporting and development of
indicators (Mackey et al., 2001). Changes in geomorphological processes are an integral part of the
natural heritage. This report, part of a series on geomorphological processes, addresses trends in soil
erosion. It provides a review and analysis of the available information and sources used to compile the SNH
Trend Profile for soil erosion.
It is natural for soil particles either at the surface or in topsoil to move downslope as a result of surface runoff
or soil creep. Alternatively, soil particles, dominantly fine sands or silts, can be transported by wind action.
A distinction is often made between ‘normal’ and ‘accelerated’ erosion resultant upon land use or
management, but in practice it is extremely difficult to identify the precise impacts of anthropogenic activity.
A soil conservation objective of achieving erosion at rates less than natural rates of soil formation is
commendable, but there are considerable difficulties in estimating the latter. For the UK, soil development
rates in the range of 0.03–0.1mm yr–1 have been proposed, but the effects of cultivation and manuring can
substantially increase this. Thus any overview of trends in soil erosion in Scotland is seriously impaired by
lack of data at the national scale, but furthermore, even if we were fortunate in having many measures of
erosion rates, there would be considerable difficulty in interpreting the significance of the results.
Only one national survey exists which had as its objective the assessment of inherent geomorphological risk
of soil erosion by overland flow (Lilly et al., 2002). The assessment was based on the assumption of no
vegetation present. Overall, 53.4% of Scotland was found to be at moderate risk and a further 32.1% at
high risk. Most mineral soils in Scotland, if not protected by land cover, were assessed to be at moderate
risk, whilst organic soils were at greatest risk (Table 1). These figures need to be treated with caution since
actual erosion risk is substantially less due to the protection afforded by land cover. Figure 1 illustrates soil
erosion risk for Scotland where the map depicts inherent rather than real erosion risk. It intended that the
erosion risk work of Lilly et al. (2002) will be progressed by adding landcover and creating actual erosion
risk maps for Scotland.
Table 1
Propor tion of Scotland in dif ferent erosion susceptibility classes (from Lilly et al.,
2002)
Soil Category
Erosion risk
% of Scotland
Actual area (ha)
Mineral soils
(43.7%)
Low
Moderate
High
8.0
29.6
6.1
618778
2275497
469086
Organic soils
(52.3%)
Low
Moderate
High
2.5
23.8
26.0
193127
1830402
1997975
Bare rock & scree
0.3
23858
Unstable slopes
1.9
147792
Built up area
1.8
142286
Miscellaneous (4.0%)
1
Scottish Natural Heritage Commissioned Report No. 054 ( ROAME No. F00AC106)
Figure 1
Soil Erosion Risk Assessment Map of Scotland (from Lilly et al., 2002).
(Copyright:MLURI/SNH)
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Scottish Natural Heritage Commissioned Report No. 054 ( ROAME No. F00AC106)
Besides the lack of data on the processes, distribution and rates of soil erosion, little is also known about
the consequences of soil erosion. On-site impacts can result in a lowering of crop yield, nutrient status,
organic matter and soil biodiversity; off-site costs can arise from impacts on increased sediment load in
streams, deposition of soil on roads or in ditches following major erosion events, increased nitrate and
phosphate loads in surface waters and accelerated sedimentation in reservoirs. Ecological and landscape
aesthetic impacts in terms of erosion are even more difficult to assess.
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Scottish Natural Heritage Commissioned Report No. 054 ( ROAME No. F00AC106)
2
SOIL EROSION IN THE LOWLANDS
Wind erosion occurs when critical velocities are exceeded and the soil surface is dry, smooth and
unprotected by crop or stubble. Areas under spring-sown crops such as carrots, leeks, calabrese and other
brassicas requiring fine, smooth seedbeds are particularly susceptible. The most obvious expression of soil
erosion by water is the occurrence of gullies which can vary in depth from c. 10cm to well over 1m. Such
gullies can occur in linear patterns due to their origin in tractor wheel tracks, or alternatively they have a
dendritic form reflecting topographic controls. Gullies are not persistent features in fields since farmers usually
infill them in the spring. Difficulties arise over terminology of erosional features, but rills can be defined as
having a depth of incision between 1cm and 10cm. Surface wash is also possible, though this becomes
quickly channelled into rills or gullies. Deposition in the form of individual or coalesced fans occurs at the
base of fields. Substantial subsurface movement of sediment through natural pipes or artificial drains must
occur: for surface water gley soils, Paterson and Mitchell (1977) observed laminated deposits in tile drains.
It is increasingly being realised that rates of downslope soil movement as induced by ploughing can be as
great as, or indeed greater than, surface erosion by fluvial processes (eg Govers et al., 1994). The previous
view was that tillage would result in a soil surface more susceptible to erosion, but the direct effect of one
ploughing event on downslope movement has been estimated from one experiment at 10 t ha-1. Thus
Govers et al. (1994) argue that tillage should be considered as a soil degradation process per se. No
research has been done on tillage erosion in Scotland.
There has been no systematic monitoring of soil erosion by wind in Scotland. The consequences of wind
erosion are very evident in particular years and localities, expressed in fine sand and silt banked up like
snow against field boundaries and even as drifts across roads. Data on water erosion have been derived
from a variety of sources including field survey of features following erosion events, sedimentation rates in
reservoirs, analysis of aerial photographs, suspended and bedload measures from rivers, and Cs137
determinations. Palaeoenvironmental investigations based on pollen and sediment cores have also
demonstrated that phases of accelerated soil erosion have occurred throughout much of the Holocene as
demonstrated, for example, by Mercer and Tipping (1994) for the Bowmont valley in south east Scotland.
2.1
Erosion rates
Soil erosion is extremely variable in space and time, posing major difficulties to field survey and rate
determination. Several studies report erosional damage following specific rainfall events. Kirkbride and
Reeves (1993) describe the results of a survey in 1992 following over 50mm of rainfall in a 24hr period.
For the study area near Forfar, 30% of fields suffered from rill erosion, especially on bare soil ploughed in
a downslope direction. Similarly, Davidson and Harrison (1995) found 76 out of a total of 206 fields
exhibited erosional features following exceptional rainfall and snowmelt during the first 2 weeks of January
1993; erosion was limited to fields which had been ploughed or were under autumn-sown cereals. But not
every major rainstorm event necessarily results in substantial erosion as demonstrated by Frost and Speirs
(1996) who found little evidence for erosion on arable land in East Lothian caused by 80mm of rainfall
during a 20hr period on 6 October 1990.
Results from measuring sediment yield from specific erosion events are given in Table 2.
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Scottish Natural Heritage Commissioned Report No. 054 ( ROAME No. F00AC106)
Table 2
Sediment yield from specific erosion events (modified from Kirkbride & Reeves,
1993)
Location
Sediment
yield
(t ha–1)
Rainfall
amount
(mm)
Duration
(hr)
Date
Source
Kelso
80
28.1
24
28/12/82
Frost & Speirs, 1984
Kelso
48
12.7
n.d.
27/05/83
Frost & Speirs, 1984
Town Yetholm
75
110
72
30/03/92 to 1/04/92
Davidson & Harrison, 1995
Lambielethan
69
78.1
57
21 to 23/09/85
Duck & McManus, 1988
14.7
n.d.
31
20 to 23/09/85
Duck & McManus, 1987
Douglastown
1.7
55
24-27
31/03/92
Kirkbride & Reeves, 1993
Kincaldrum
1.2
55
24-27
31/03/92
Kirkbride & Reeves, 1993
Hatton
2.2
55
24-27
31/03/92
Kirkbride & Reeves, 1993
Barry
Long-term mean erosion rates have been estimated from reservoir sedimentation (Duck and McManus,
1990). Some results are: 31.3 t km–2 yr–1 for Glenfarg, an arable catchment, and 9.0 t km–2 yr–1 for
Glenquey, a catchment under rough grazing and forestry. Overall rates estimated by this approach are likely
to underestimate erosion, given that not all sediment will be trapped by reservoirs and, furthermore, eroded
soils from fields may not necessarily be delivered to stream channels in the short to medium term. There is
much current interest in the use of the Cs137 technique for estimating soil erosion, the advantage being that
the results reflect erosional and tillage effects over the last c. 40 years. Figure 2 is a map of soil erosion
rates determined by this technique for a field on fluvioglacial sands and gravels near Blairgowrie. As can
be seen, the upper slope convexity is subject to an annual erosion rate of 2.0mm yr–1, corresponding to
c. 30 t ha–1 yr–1. Interestingly, this erosion rate could be achieved by the occurrence of only a few of the
types of event listed in Table 2.
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Scottish Natural Heritage Commissioned Report No. 054 ( ROAME No. F00AC106)
Figure 2
Erosion and deposition rates (mm yr –1 ) as estimated from Cs 137 determinations in
a field with Neolithic post holes (from Davidson et al., 1998). (Reprinted from
Journal of Archaeological Science 25, 1998 © 2003, with permission from
Elsevier)
2.2
Geographical variations
Soils subject to wind erosion are widely distributed throughout the Moray coast region, Strathmore, more
locally in the Howe of Fife, East Lothian and the lower Tweed valley and along most of the raised beaches
of the east coast. Wind erosion can be substantial on machair land in the Western Isles and Northern Isles;
when the protective vegetation cover is cultivated, this can help to sustain the machair ecosystem which to
a certain extent relies upon soil erosion. Soils susceptible to erosion by water are mainly in central and
eastern parts of Scotland, especially where the soils are derived from Old Red Sandstone drifts. In particular
winters or springs, features such as rills, deepened tractor wheel tracks, gullies, surface wash and alluvial
spreads can be seen on arable land in Perthshire, Angus, Fife, the Lothians and the Tweed basin.
2.3
Impacts
There are virtually no studies in Scotland to determine either on-site or off-site impacts of erosion. Though
damage to fields as expressed as gullies, rills or alluvial spreads can appear quite striking following
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Scottish Natural Heritage Commissioned Report No. 054 ( ROAME No. F00AC106)
erosional events, the extent of such damage in individual fields is often very limited, for example less than
5%. Furthermore, many farmers just view such incidents as a nuisance and damage can be quickly rectified
by infill of gullies and spring ploughing. Frost and Speirs (1984) investigated the impacts of erosion on a
farm near Kelso in 1982; they worked out a cost to the farmer at the time of £26.50 ha–1 which they
considered to be economically minor. Furthermore, on the basis of available soil depth, they estimated that
the rate of soil loss could be maintained for at least 400 years on this particular farm. However, such a
finding was from one farm and extrapolation on a wider basis could be very misleading. Following the
precautionary principle, land management measures should be taken in those areas susceptible to erosion
on arable land. The maintenance of some plant cover over the winter months and the avoidance of
cultivation along maximum slope directions are needed in areas susceptible to erosion. Another important
reason for minimising reduction in soil depth is to protect archaeological features. Extensive crop marks are
evident on aerial photographs from lighter textured soils in central and eastern Scotland, the very areas
susceptible to erosion on arable land. A reduction in soil depth by erosion means that plough damage
extends to greater depth resulting in the loss of critical archaeological evidence.
2.4
Causes
Field surveys have demonstrated that erosional features such as gullies, rills, surface wash and alluvial
spreads dominantly occur in fields with bare or almost bare surfaces during the winter and spring (Davidson
and Harrison, 1995). Despite substantial roughness, gullies can also form in fields which have been
ploughed and left unplanted in the autumn. Soils planted in autumn-sown cereals are particularly vulnerable
given the smooth nature of the seedbeds and the low interception value of germinated seedlings. In the
1970s and 1980s, there was a trend of increasing acreages of land under autumn cereals, leading to
greater erosion risk. This has coincided with a pattern of increasing rainfall, especially in central and western
regions of Scotland. Furthermore, this increase in rainfall has been mainly during the winter months, the very
time when soils under autumn cereals are at their most vulnerable. The effects of the Common Agricultural
Policy, for example through the set-aside scheme, have been to limit continued expansion of autumn-sown
cereals, though industrial crops such as oil seed rape and linseed have expanded. Models for predicting
soil erosion, in addition to land cover characteristics, place much importance on rainfall erosivity. The few
studies on soil erosion in Scotland downplay the significance of rainfall intensity, but instead emphasise the
importance of antecedent soil moisture conditions, especially if rapid snow melt is involved (Kirkbride and
Reeves, 1993; Davidson and Harrison, 1995).
2.5
Trends in lowland soil erosion
Given that there is no systematic monitoring of soil erosion on arable land, it is difficult to identify distinct
trends. Speirs and Frost (1985) described the increasing incidence of soil erosion in eastern Scotland
between 1969 and 1985, although the incidence then appeared to decline. In the 1990s, erosional
damage to fields occurred occasionally, roughly every 3 years and only in particular localities. Erosion was
particularly evident in 1992 and 1993. Any policy change leading to an increase in autumn-sown crops,
when combined with potential rainfall increases, would lead to an enhanced risk of soil erosion.
7
Scottish Natural Heritage Commissioned Report No. 054 ( ROAME No. F00AC106)
3
SOIL EROSION IN THE UPLANDS
Soil erosion rates in upland areas are often high, related to steep slopes and greater extremes of climate.
Processes include gullying of both peat and mineral soils, wider scale removal of peat and erosion of vehicle
tracks and footpaths. Soil erosion has both on- and off-site implications, including loss of soil productivity
and carbon storage, loss of landscape quality, deposition of sediments and increased transfer of nutrients to
fresh waters.
Reports commonly describe and explain specific erosion events. One recent national survey documented the
spatial extent of erosion in the uplands of Scotland (Grieve et al., 1995), but there is no regular monitoring
from which trends might be assessed. Trends must therefore be assessed from the factors which are known
to control erosion occurrence and rates.
3.1
Geographical variations
Grieve et al. (1995) quantified the spatial extent of soil erosion in the uplands by analysis of aerial
photographs from a sample of 20% of the upland area. A total of 12% of the area was affected by soil
erosion. Peat erosion was the most extensive type (6% of the area), but gullies on steeply sloping mineral
soils were also extensive (Table 3, Figure 3).
Table 3
Spatial extent of different types of erosion in upland Scotland (as % of area sampled)
Erosion type
Scotland
Monadliath
E Grampians
Cairngorms
Peat erosion (% of area sampled)
6.02
20.43
7.99
1.54
Gullies (% of area sampled)
4.69
3.59
0.71
0.91
Debris flows & landslides (% of area sampled)
0.69
0.09
0.00
6.80
5
0
22
72
40
44
183
34
Footpaths (m km–1)
Vehicle tracks (m km–1)
Regional variations in the severity of peat erosion
th
er
So
n
Up
ut
he
la
nd
rn
s
Up
(E
la
)
nd
s
(W
Lo
)
Ce
c
nt
ha
ra
be
lH
r
ig
hl
an
M
ds
on
ad
lia
Ca
th
Ea
i
r
st
ng
er
or
n
m
Gr
s
am
pi
Ea
an
st
s
er
Ro
ss
100%
90%
80%
70%
60%
50%
40%
30%
20%
10%
0%
So
u
Figure 3
8
Severe
Gullies
Minor
Scottish Natural Heritage Commissioned Report No. 054 ( ROAME No. F00AC106)
The greatest areas of severe peat erosion were found in eastern Scotland, such as the eastern Grampians
and eastern Southern Uplands (Figure 3), areas with the greatest extent of upland management such as
burning (32 and 35% respectively) or vehicle tracks (Table 3). Nationally the extent of eroded footpaths was
small (5m km–1), but almost entirely found in popular mountain areas such as the Cairngorms (72m km–1).
3.2
Causes of erosion
Most instances of severe erosion in the uplands can be linked to human activities. Bayfield (1985) has
documented substantial increases in footpath widths in the Cairngorms and Wester Ross since the 1960’s
due largely to increases in visitor numbers (Lance et al., 1991). There is clear evidence that forest planting
and harvesting has increased erosion rates in the past (Battarbee et al., 1985; Ferguson and Stott, 1987;
Carling et al., 1993). Sensitive harvesting can substantially reduce losses (Ferguson et al., 1991). Moorland
burning also results in a temporary increase in erosion rates until vegetation recovers (Kinako and
Gimingham, 1980) and drainage also increases erosion (Stewart and Lance, 1983).
3.3
Trends in upland soil erosion
Likely trends in soil erosion can be predicted from trends in the factors which control erosion rates (Table 4).
Land management pressures have been increasing in recent decades with, for example, 9.4 million sheep
in Scotland in 1999 compared to 7.6 million in the 1930s (SEPA, 2000). Grieve et al. (1995) reported a
60% increase in sheep numbers between 1977 and 1992 in Grampian Region and a 250% increase in
deer numbers in the East Grampian census area between 1968 and 1986. Total deer numbers in Scotland
are now 710,000 (DETR, 1998). The continuing increase in visitor numbers to upland areas (Lance et al.,
1991) may further increase footpath erosion despite repair programmes. Predicted increases in rainfall
particularly in autumn and winter (Kerr et al., 1999) may exacerbate these trends. However, the Forests and
Water Guidelines (Forestry Commission, 2000) should reduce the impacts of forestry on soil erosion rates
in the future (Carling et al., 2001).
Over the longer term, for debris flows, Ballantyne (2002) showed that flow events have occurred over most
of the last 7000 years, although the frequency and extent appear to have increased in the last few centuries.
9
Scottish Natural Heritage Commissioned Report No. 054 ( ROAME No. F00AC106)
Table 4
Trends in soil erosion in the uplands
Cause
Trend
Forest ploughing
Sediment losses of 7 to 30kg m–1 length of plough furrow, but usually diminish at
canopy closure (Carling et al., 1993).
Recent afforestation
Sediment deposition from undisturbed catchments = 0.1cm yr–1, increased to > 2cm
y-1 during planting. Recovery to pre-disturbance levels with canopy closure after c. 10
years (Battarbee et al., 1985).
Forest clear-felling
Increased sediment concentrations in runoff following felling are mainly from erosion of
timber loading areas and roads; locally up to 50g l–1 from such areas (Ferguson &
Stott, 1987).
Forest clear-felling
No significant increase in sediment loss from a Trossachs catchment when timber
extraction carried out by a cable crane system (Ferguson et al., 1991).
Moor draining and burning Sediment yield from drained and burned peat catchment = 2.26m3 y–1; from drained
catchment = 0.46m3 y–1, but negligible yield from control catchment (Stewart &
Lance, 1983).
Erosion losses of 1.27 to 3.85 Mg ha–1 following heather burning, mainly within the
first 8 months. Recovery by 15 to 20 months (Kinako & Gimingham, 1980).
Grazing pressure
Change in sheep numbers,
Grampian Region
Change in deer numbers,
East Grampian census area.
900000
30000
800000
25000
20000
700000
Red Deer
Sheep
Heather burning
600000
15000
10000
500000
400000
1975
5000
1980
1985
1990
1995
0
1965 1970 1975 1980 1985 1990
(from Grieve et al., 1995 © 2003 John Wiley & Sons Ltd. Reproduced with
permission.)
Human trampling
Increase in bare soil width on paths on Stac Pollaidh from 0.6 to 3.1m between
1968 and 1983 and in Cairngorms from 2.1 to 7.3m (Bayfield, 1985). Further
increases of 0.8 and 0.5m for two paths on Cairngorm between 1986 and 1990
(Lance et al., 1991).
Human trampling
Reduction of median total organic matter in Cairngorm plateau soils with vegetation
disturbance from 9.5 to 4.6kg m–2 (Grieve, 2000).
Skiing
Disturbed land had more surface grit, more plant damage, more rills and less soil
organic matter (Watson, 1985).
Visitor numbers
Mean number of visitors on Cairngorm plateau increased from 0.5 per day in 19431959 to 64.8 per day in 1980–1988 (Watson, 1991).
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4
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Bayfield, N.G. (1985). Effects of extended use on footpaths in mountain areas of Britain. In: Bayfield, N.G.
and Barrow, G.C. (eds), The Ecological Impacts of Outdoor Recreation on Mountain Areas in Europe and
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103, 44-46.
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Balquhidder catchments, central Scotland. Transactions of the Royal Society of Edinburgh, 78, 379-384.
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Forestry Commission (2000). Forests and Water Guidelines. Forestry Commission, Wetherby.
Frost, C.A. and Speirs, R.B. (1984). Water erosion of soils in south-east Scotland – a case study. Research
and Development in Agriculture, 1, 145-152.
Frost, C.A. and Speirs, R.B. (1996). Soil erosion from a single rainstorm over an area in East Lothian,
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Govers, G., Vandaele, K., Desmet, P., Poesen, J. and Bunte, K. (1994). The role of tillage in soil
redistribution on hillslopes. European Journal of Soil Science, 45, 469-478.
Grieve, I.C. (2000). Effects of human disturbance and cryoturbation on soil iron and organic matter
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Grieve, I.C., Davidson, D.A. and Gordon, J.E. (1995). Nature, extent and severity of soil erosion in
upland Scotland. Land Degradation and Rehabilitation, 6, 41-55.
Kerr, A., Shackley, S., Milne, R. and Allen, S. (1999). Climate Change: Scottish Implications Scoping
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