The uncertainty in the prediction of flash floods in the Northern Mediterranean environment; single...
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The uncertainty in the prediction of flash floods in the Northern Mediterranean environment; single site
approach and multi-catchment system approach
CIMA - Centro di Ricerca Interuniversitario in Monitoraggio Ambientale, Università di Genova, Università della Basilicata
R. Rudari
Thanks to: L. Ferraris, F. Siccardi, G. Boni, F. Giannoni
Civil Protection Authorities have to take decisions based on probability
assessment of the possible land effects
Scenarios and Civil Protection plans
Warnings: from 24 to 12 hours before the possible events
Scales of the basins of interest
La Barbera, P.; Lanza, L. G. 2001 On the cumulative area distribution of natural drainage basins along a coastal boundaryWater Resour. Res. Vol. 37 , No. 5 , p. 1503
Land effects
22/09/1992 - 10.45 22/09/1992 - 15.30
22/09/1992 - 15.40 22/09/1992 - 15.45
DETERMINISTIC Single Site
0
500
1000
1500
2000
2500
3000
1-ot
t-96
3-ot
t-96
5-ot
t-96
7-ot
t-96
9-ot
t-96
11-o
tt-96
13-o
tt-96
15-o
tt-96
17-o
tt-96
19-o
tt-96
21-o
tt-96
23-o
tt-96
25-o
tt-96
27-o
tt-96
29-o
tt-96
31-o
tt-96
2-no
v-96
Q (m
^3/s)
Forecast Hydrograph
Cumulative Distribution Function of peaks discharge in Tanaro at Belbo for 5 LAM-TEPS
0 100 200 300 400 500 600 700 800 900 1000
Discharge [m3s-1]
Observed from rainguages
Estimated from the LAM-TEPS 1
P[Q
>q* ]
.5
.2
.1
.05
.01
.005
.3
.4
PROBABILISTIC
Downscaling
CDF of peak discharges
GCM LAMEPS LEPS
DHM
Cumulative Distribution Function of peaks discharge in Tanaro at Montecastello for 5 LAM-TEPS
2000 3000 4000 5000 6000 7000 8000 9000 10000 11000 12000
Discharge [m3s-1]
Hydrometric hydrographEstimated from the
CTRL=RM1
P[Q
>q
* ]
.5
.2
.1
.05
.01
.005
.3
.4
.8
Example of single site
PLAM-TEPS1= 0.51 PLAM-TEPS2= 0.17PLAM-TEPS3= 0.12PLAM-TEPS4= 0.12PLAM-TEPS5= 0.08
PLAM-TEPS1= 0.51 PLAM-TEPS2= 0.17PLAM-TEPS3= 0.12PLAM-TEPS4= 0.12PLAM-TEPS5= 0.08
Conditioned CDFConditioned CDF
CDFCDF
1994 Piemonte flood1994 Piemonte flood
Ferraris, L., Rudari, R. and F. Siccardi, 2002 The uncertainty in the prediction of flash floods in the northern Mediterranean environment Journal of Hydrometeorology (AMS) in press.
Admission of ignorance
• Aggregate the rainfall volume to the scale where we have a reliable evaluation of its probability of occurrence on that area through the use of EPS.
• We downscale from the aggregate scale down to the scale of interest with a purely stochastic model
Single site & multi-catchment approach• The limit among single site and multi-catchment system approaches
is in the scale at which EPS can give a reliable estimation of the probability of the rainfall volume: The bigger the aggregation area, the smaller the stochastic ensemble, the bigger the catchment where I can apply the single site warning
n=1…N
Area Dimension Stochastic ensemble size Drainage Area Distribution
Different approach – multi-catchment distributed warning
Class A (< 10 km2)Class B (10 < Area < 150 km2)Class C (> 150 km2)
PROBABILISTIC Multi-catchment approach
Downscaling
EPS LEPS
DHM
Exceeding probability
curves
STATISTICALLY HOMOGENEOUS REGION Peak discharge values of the Liguria regionbelong to the same statistical distribution
Within a regional procedure it is possible to make dimensionless all the simulated discharge peak values (TCEV)
Bisagno at la Presa - 97 km2
-2
-1
0
1
2
3
4
5
6
7
0 100 200 300 400 500 600Discharge[m3s-1]
u [
-]
T=2.9
T=10
T=50
T=100
T=200
T=500
T=5
T=30
Local probability curve obtained by the expected
time series value
DRiFt Model
Historical data
Local probability obtained by the index discharge value (DRiFt T=2.9)
Through the Qindex is possible to specify the growth curve in each site of the region
Regional framework
0
0.2
0.4
0.6
0.8
1
0 10 20 30 40 50 60 70 80 90 100
Exc
eed
ence
Pro
bab
ilit
y
Q QQQQQQQQQ
Single site
Exceeding probability of a given discharge quantile in one catchment chosen randomly inside the multi-basin system
F1 F1
0
0.2
0.4
0.6
0.8
1
0 10 20 30 40 50 60 70 80 90 100
Ex
ce
ed
en
ce
Pro
ba
bili
ty
Q QQQQQQQQQ
Single site
Regional (indepedent
basins)
If catchments and simulations were independent it would be possible to compute exceedence probability of a given quantile
in at least one site of the multi-basin system directly from probability theory
NF1NF1
0
0.2
0.4
0.6
0.8
1
0 10 20 30 40 50 60 70 80 90 100
Exc
eed
ence
Pro
bab
ilit
y
Q QQQQQQQQQ
Single site
Regional
Regional (indepedent
basins)
Discharge realizations are not independent. Each disaggregation history is considered separately
Questions to be answered by:The EPS community:
• What is the scale where I have a reliable estimation of rainfall volumes with their probability?• How does it change when a different target region is concerned?• How does it change when a different synoptic condition is concerned?• What do I gain from LAMs?• What do I loose by clustering?• What are we calling probability?
The Downscaling community:• What is the best downscaling model (stochastic, physical, mixed approach)?• Is it possible to exploit better the Meteorological model info at different scales (Data fusion)?
The Hydrologic community:• How do I improve the I. C. of the hydrological models (remote measures, data assimilation)?
All the communities:• How do the uncertainty propagates through the chain?• How do we convey the Probabilistic Information?
Hydrologic scale inconsistency
0
700
20/06/96 18.00 21/06/96 6.00 21/06/96 18.00 22/06/96 6.00
Time
Dis
ch
arg
e [
m3 s-1
]
Recorded
5 MIN
15 MIN
60 MIN
180 MIN
Pebble creek June 20 1996
0
700
20/06/96 18.00 21/06/96 6.00 21/06/96 18.00 22/06/96 6.00
Time
Dis
ch
arg
e [
m3 s-1
]
Recorded
1 X 1 km
2 X 2 km
4 X 4 km
8 X 8 km
16 X 16 km
Pebble creek June 20 1996
Pebble creek
Space Time
Giannoni, 2001