Transcript ppt

Ecological Vulnerability to changes in flood
characteristics
Staes Jan & Meire Patrick
Ecosystem management Research Group
University of Antwerp
Follow-up Committee
6 october, 2009
Leuven
Objectives
• Determination of ecological impact of changes in flood
characteristics
• Flooding can have
direct and indirect
impact on many
processes that affect
vegetation
• “Drowning” is the most
direct effect and is
determined by the
flood timing, duration,
depth and frequency
Objectives
• Based on literature and expert judgement, the flood
vulnerability was defined for 68 vegetation types.
• 48 floodtypes were defined as distinct combinations of
flood depth, duration, season and flood frequency.
• The classification of the Biological valuation map (BVM)
was “translated” to the 68 vegetation types
– The first three layers of the BVM were considered
– Often multiple vegetation types apply to a single BVM unit
• Up to 15 potential vegetation types possible
Objectives
• BVM-based Vulnerability maps (48) were derived for
the entire Flemisch Region
– Weighted approach
– Unweighted approach
– Most sensitive
• These maps needed to be combined with model output
– Aggregated impact of the frequency distribution of the
different floodtypes
Objectives
• The modelling failed to provide output on the occurence
of frequent flooding and on aspects of flood duration
and season.
– A traditional modelling that gives maximal water levels,
given a certain return period (5, 10, 25 years).
• This provides no information on how long this “maximal”
water level is maintained.
– Perhaps only for one day => no impact
– Perhaps only in winter => limited impact
• Without information on duration and season, ecological
impact cannot be determined
Objectives
• Why is this so important?
• Let’s look at a flood event between march and june 1989
6/03/1989
6/04/1989
6/05/1989
6/06/1989
6/07/1989
101
91
81
71
Series1
61
Series2
51
Series3
41
Series4
31
21
11
1
• Water levels rise above 1
meter
• Different floodbranches
have a different response to
river hydrology (fast or slow
release, overtopping effect)
• Long duration (+ 14 days)
• March – may is starting of
growing season.
• A flood event in March-May 2001
600
500
Series5
400
Series4
Series3
Series2
300
Series1
Series8
200
Series7
Series6
100
0
6/03/1989
6/04/1989
6/05/1989
6/06/1989
6/07/1989
• Water levels rise above
300 cm ?
• Different response to
river hydrology (fast and
slow release, overtopping
effect)
• Episodes of long
duration + 14 days.
• March – may is starting
of growing season.
Objectives
• The hydrolopgical model was unable to provide pixel
level output on the flood characteristics => no floodtype
frequency maps could be derived
• From the raw data from the modelling of the 37 flood
branches, a statistical distribution of flood duration and
season was derived for the base scenario (1987-2001).
– Spatial allocation of these flood characteristics is not
evident.
– The water level in the flood branches is not equal to the
water level in the floodplain
– For each 10 cm increase in water level, occurrences
were counted for each season and flood duration.
Objectives
• Example
Days
Spring
20
30
40
50
60
70
80
90
100
110
120
130
140
150
160
Summer
50
90
100
110
120
130
Grand Total
1
6
2
1
2
6
1
3
5
4
4
5
4
6
4
7
4
8
4
9
4
10
3
11
2
12
1
13
1
14
1
1
1
1
1
1
1
1
1
1
1
2
1
1
1
1
1
2
1
2
1
1
2
1
1
1
1
1
2
1
1
1
1
1
1
1
1
1
1
1
1
4
3
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
7
1
7
1
1
6
5
5
5
5
5
2
1
Grand Total
49
3
2
1
1
1
2
1
6
4
6
5
7
6
2
2
8
1
1
1
1
3
1
57
Objectives
• Example
Row Labels
Autumn
10
Spring
10
20
30
40
Summer
10
Winter
10
30
40
50
70
Grand Total
1
1
1
2
1
2
1
1
2
1
3 4 5 6 7 8 9
1
1
2 2 2 2 2 2 2
1 1 1 1 1 1 1
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
2
1
2
1
2
1
2
1
2
1
2
1
2
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1 1 1 1 1 1 1 1 1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
5 5 5 5 5 5 5 4 4
3 2 2 2 2 2 2 1 1
4
1
4
1
3
3
3
3
3
3
3
3
3
3
3
3
3
3
3
3
3
3
3
3
3
3
3
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
4
4
1 1 1
1
1 2 2 3 3 3 2 2 2
1 1
8 8 8 7 7 7 7 6 6
1
2
1
2
1
2
1
2
1
2
1
2
1
2
1
2
1
2
1
2
2
2
2
2
2
2
2
2
2
2
2
2
1
1
1
6
6
5
5
5
5
5
4
4
4
4
4
4
4
4
4
4
4
4
4
4
4
4
Objectives
• For each increase of 10 cm water level in the floodbranch, a
contour map of the flooded area is needed.
– A GIS procedure needs to be developped in order to allocate
the statistics of each water level to the different water depths in
the floodplain.
– The different maps then need to be processed into a floodtype
– frequency map.
• This type of information is not only crucial to the determination of
ecological impact, but also for agronomical impact.
– Climate change may shift flood regimes not only in extremity,
but also in terms of duration season ect…
– But the data-processing needs to be automated before wa
analyse the different climate change and mitigation scenario’s
Expected outcome
• Dender is no ideal study area
– The ecological values are mainly determined by other factors
than flooding
– The flooding of the dender valley is rather extreme
• Because the hydrological regime of the dender is extreme
• Because of the embankments there is an overtopping effect, no
gradual flooding exists.
– A high fragmentation of natural vegetation, permanent
grasslands and agriculture
• Dessication during summer is probably more determining.
– Adverse effects... Lower areas have a higher impact from
flooding, but are less vulnerable to dessication during summer.
Expected outcome
• Dender is no ideal study area
Although the
valley is nature
area according
to spatial
destination
plans…
Expected outcome
1. There is a high fragmentation of natural vegetation,
permanent grasslands and agriculture
To what extent is
drainage,
agricultural
management and
fertiliser
application
determining for the
ecological values?
Dessication during summer is probably more determining
Expected outcome
2. A low differentiation of flooding regimes?
Depth/frequency
natural flooding, shallow at R 25
Embankment, Shallow at R 10, no flooding at R5-25
natural flooding, shallow at R 10-25
Embankment, deep at R 25, Shallow at R 10, no flooding at R5
Embankment, deep at R 10, no flooding at R5-25
natural flooding, shallow at R 5
Anomaly, shallow at R 5-25, no flood at R10
natural flooding, shallow at R 5-10-25
natural flooding, shallow at R 5 -10, deep at R25
Anomaly, shallow at R 5-25, deep at R10
natural flooding, shallow at R 5, deep at R 10-25
Anomaly, deep at R 5, shallow at R 10 - 25
Anomaly, deep at R 5-25, shallow at R10
embankment effect, deep flooding (R-5-10-25)
R5
0
0
0
0
0
< 50
< 50
< 50
< 50
< 50
< 50
> 50
> 50
> 50
R10
0
< 50
< 50
< 50
> 50
0
0
< 50
< 50
> 50
> 50
< 50
< 50
> 50
R25
< 50
0
< 50
> 50
0
0
< 50
< 50
> 50
< 50
> 50
< 50
> 50
> 50
Biodiversity
Acreage
low medium
26%
9%
72%
1%
18%
11%
19%
15%
48%
5%
75%
0%
63%
11%
23%
11%
10%
9%
11%
10%
8%
9%
22%
1%
16%
7%
9%
9%
High
65%
27%
71%
66%
47%
25%
27%
66%
80%
78%
83%
77%
77%
82%
Area
3,8
0,3
2,8
2,1
2,4
0,3
0,3
7,3
6,2
0,9
9,6
0,4
0,4
74,1
13%
78%
111
9%
% area
3,4%
0,3%
2,6%
1,9%
2,2%
0,3%
0,3%
6,6%
5,5%
0,8%
8,6%
0,3%
0,3%
66,8%
For the flood return maps it appears that 67 % of the valley is
flooded above 50 cm each 5 years
(and there are indications of long flood duration)
Expected outcome
2. A low differentiation of flooding regimes?
A large proportion
of the valley is
severely impacted
by current flooding
regimes
OR
Winter
+ 50 cm
+ 14 days
every 5 years
Current ecological
values are most of
the time in
“recovery mode”
Because the hydrological regime of the dender is extreme
Because of the embankments there is an overtopping effect,
no gradual flooding exists and flood water remains behind
Expected outcome
3. The ecological values are not well distributed within the
modelled area
•5 % alluvial forest
•2,5 % leaf forest
•5,5 % wetland vegetation
•4,5 % open water
•53 % grassland
•13,5 % poplar plantations
•12 % impacted (urban, recreation, infrastructure)
Plans for the next three months
OPTIONS (not feasible to do them all !)
• Further elaborate the translation of the model output to spatial explicit
maps
– For the base scenario only, manually
– Analyse if patterns of current ecological values can be accredited
to spatial patterns of flood characteristics.
• Automate the procedure to extract the flood type maps
• Analyse the model results for the climate change and flood mitigation
scenario’s?
– Detailed analysis of changes in flood characteristics (duration,
season, frequency).
– If model data is available?
• Make an assessment of the nature development plans for the Dender
Valley (together with ANB?)
– A more clear description of the achievable vegetation types, given
current flooding regimes.
Recommendations
•
Model output was several times postponed and finally there was no output
that was usable for ecological impact assessment
•
Clear communication on model limitations and the achievability of output
results.
– Modelling of frequent flooding
– Modelling of low flow an drought impacts
Automated output on flood frequency, duration and season for a series of
water levels.
– Was expected as model output but appeared to be not straightforward
– This kind of information is not only valuable for ecological assessment,
but also crucial for impact on agriculture.
•
Recommendations
• No catchment approach to mitigate climate change impacts
• More efforts should be put on the development of integrated
models
– to provide more integrative and conceptual assessment of
mitigation and adaptation measures against climate change
impacts.
– Many non-technical measures cannot be assessed with the
current models.
– Therefore a cost-benefit analysis is biased towards technical
solutions.
• How to push this forward is a major question!
– Writing another integrated water management handbook will
not do the trick…quantification methods are needed!!!
– Need for spatial explicit process-based models that include
manipulation of hydrology and land-use interactions.
Recommendations
• The study area was not really ideal for ecological impact
determination
• The current floodings are perhaps already so extreme
that changes due to climate change can be expected of
marginal influence (to be concluded…)
• For ecological impact assesment, vegetation mapping
will be neccesary.
– The BVM does not make enough distinction between
vegetation types.