Transcript Слайд 1 - Hydrograph Model

Estimation of hydrological response of small
Mediterranean watershed to fire by data analysis
and modelling approach
Lebedeva L.1,3, Semenova O.2,4, Folton N.5
1Nansen Environmental and Remote Sensing Centre, St. Petersburg, Russia
2Gidrotehproekt Ltd, St. Petersburg, Russia
3State Hydrological Institute, St. Petersburg, Russia
4St. Petersburg State University, St. Petersburg, Russia
5National Research Institute of Science and Technology for Environment and Agriculture, Aixen-Provence, France
Motivation and goal
Forest fires are reported to have crucial effect
on runoff formation
Non-stationarity is still not accounted for in
most hydrological models
The goals of the research:
- to quantify the hydrological response of the
small Mediterranean watershed to wild fire on
daily and hourly timescales
- to investigate an ability of the process-based
hydrological model to cope with non-stationary
post-fire conditions
Methodology
Detection of fire-induced
landscape changes based on
literature review
Detection of fire impact on
hydrological regime by data analysis
Runoff formation process-based
modelling with fixed parameters
Assessment of the hydrological change by
model detection method
Simulation of the post-fire runoff, taking into account
the changes in vegetation and soil properties
• simulated hydrographs and variable states for pre- and post-fire periods
• detection of changes in hydrological regime after the fire
• modelling approach applicable in non-stationary conditions
Study area: the Ruisseau du Rimbaud at Collobrieres,
France
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Area 1.46 km2; elevation 470 - 620 m; daily and hourly data available for 1968-2004
Mediterranean climate with intense autumn rains and summer drought
Precipitation - 1200 mm/year, flow - 700 mm/year, PE - 900 mm
Shrubby maquis and a degraded forest of cork oak, chestnut and maritime pines
Thin, sandy soils of the ranker type
August 1990 fire destroyed 85 % of the watershed
Fourcade B. , Coudrain-ribstein A. , Martin C. 2002 What can be deduced from chemical measurement in an
open-field raingauge? An example in the Maures Massif, southeastern France. Hydrological Sciences
Journal Vol. 47, Iss. 3
Vine P., Puech C., Clement B., Bouguerzaz F.
1996. Remote sensing and vegetation recovery
mapping after a forest fire. EARSel Advances in
remote sensing. Vol.4, No 4 - XI
Peak flood discharge vs rainfall on daily time step
There is no changes of the peak floods on daily time step after the fire
Peak flood discharge vs rainfall on hourly time step
Increase of hourly peak discharges can be detected during
three years after the fire (1990–1992)
Instantaneous peak flood discharge vs rainfall
Relationship between instantaneous peak flood discharge and
precipitation within 24 hours throughout the autumn-winter period
(September, October, November and December) . Period after the fire:
September 1990 - November 1994 (Cosandey et al. 2005)
Cosandey C, Andréassian V, Martin C, Didon-Lescot JF, Lavabre J, Folton N, Mathys N, Richard D. 2004. The hydrological impact of the
Mediterranean forest: A review of French research. Journal of Hydrology 301:1–15
Hourly discharge, m3/s
0
15
100
P = 53 mm
10
P = 40 mm
P = 45 mm
200
Qpeak = 0.65 m3/s
Qpeak = 0.71
m3/s
Qpeak = 0.59 m3/s
5
300
0
400
1968
1972
1976
1980
1984
1988
1992
1996
2000
2004
Years
hourly discharge
rainfall in 24 hours before the event
Median peak floods increased in three post-fire years and
decreased after opposite to rainfall changes
Rainfall in 24 hours before the event, mm
Median peak floods before and after the fire
Process-based hydrological modelling
 Employs dynamic set of
parameters which can change
with time
 Minimum calibration
(parameters
can be obtained apriori)
 Basic input data, daily or
hourly resolution (air humidity
and temperature, precip)
 Free of scale problem (from
soil column to large basin)
initially developed by Prof. Yury Vinogradov
www.hydrograph-model.ru
Detection of hydrological change by modelling
Hourly data
Daily data
Modelling results do not detect any significant changes after the fire on
a regular basis
NSE
1968-2004
NSE
1990-1992
0.52
0.76
0.45
0.76
Results of the Hydrograph model application to Rimbaud
watershed, daily time step
2
1.5
1.5
1
1
0.5
NS 0.5
Bias
0
0
-0.5
1968
1972
1976
1980
Precipitation, mm
-1
1984
1988
Nash
1992
1996
2000
2004 -0.5
-1
Bias
2000
1500
1000
500
1968
1972
1976
1980
1984
1988
1992
1996
2000
2004
Precipitation
The NS and bias show strong positive correlation with annual rainfall and are
not to be considered as adequate model evaluation criteria
Hourly observed vs simulated peak floods
Slight underestimation of hourly high flood peaks greater than
2 m3/s and overestimation of floods lower than 2 m3/s
Detection of separate floods influenced by fire
Hourly observed vs simulated peak floods
Peak flood discharge vs rainfall
Four flood events in post-fire period have shown a 25–50% increase in
peak discharge compared to the events caused by the same rainfall in
the reference period.
The Hydrograph model was applied with new landscape parameters
Development of post-fire model parameters for 1990-1992
1) Bare soil increased up to 90 % immediately after the fire (Vine et al.
1996). Related vegetation parameters were modified:
before fire
after fire
shadow fraction by vegetation, %
30
0
interception storage capacity, mm
2
0
landscape albedo, %
20
10
coefficient of evaporation, 10-8hPa s
0.3
0.17
2) Water-repellent, or hydrophobic soil layer formation (DeBano (2000)
was reflected by the following soil parameters:
coefficient of infiltration, mm min-1 :
before fire
after fire
upper soil layer
3.75
1.5
middle and lower layers
1.5
0.75
variation coefficient of infiltration
0
0.7
Observed and simulated with pre- and post-fire
parameters hydrographs of selected peak floods
A newly developed set of model parameters improved the
efficiency to a certain extent.
Conclusions
No significant changes in hydrological regime of the Rimbaud
watershed after the fire in 1990 are detected on daily scale
Fire impact is localized on increase of hourly peak discharges
during three years after the fire (1990–1992) in wet season
The Hydrograph model continuous simulations at hourly and
daily time steps satisfactorily fit the whole period 1967-2004
Post-fire model parameters reflecting changing environment
result in slightly improved efficiency of simulations of selected
outstanding flood peaks
Discernible fire impact is localized on separate floods events
only and has nonlinear character
Changing in time observable model parameters are
prospective for simulations in non-stationary conditions
Thank you for your attention!
Analysis of peak floods and rainfall data
The response to heavy rain is particularly violent after the fire
(Lavabre and Martin, 1997).
134 daily and 190 hourly flood events were investigated:
- precedent rainfall higher than 20 mm
- wet season from September to December only
- 1967–1989 and 1993–2006 – the reference periods
1990–1992 – the post-fire period