Real time 2D urban flood forecasting: a case study

Real time 2D urban flood forecasting:
a case study
July 2014
In recent years 2D flood models have been applied routinely in the UK, but
not for real time forecasting, where fast and robust models are essential.
Meanwhile several groups have developed 2D models designed to achieve
shorter run times.
One strategy is to deploy fast Graphics
Processing Units (GPUs) as parallel co-processors
to speed up the model code.
4: Wingrove
Avenue
This case study tested a GPU-based 2D model,
JFlow+, in a real-time forecasting context for a
flood event that happened on 28 June 2012, in
Newcastle-upon-Tyne, North East England.
After this event, Newcastle University gathered
photographic evidence about the depth of flood
water. We looked at data from four city centre
locations
1: Civic
Centre
F
3: The
Gate
Observation 2:
Lovers Lane
Depth estimated at van
bumper approx 0.5m
Forecast and actual rainfall data
2: Lovers
Lane
Four rainfall forecasts (produced at different
lead times, see below) were tested, along with
estimates of the actual rainfall from weather
radar and from rain gauges.
Photo credit
Interpretation
Lead time (hours ahead of forecast outputs)
6
2
Numerical Weather Prediction
(NWP) forecasts for 36 hours into
future, made every six hours
16:30
1
0.5
Short Term Ensemble Prediction
System (STEPS) forecasts for six
hours ahead, made every 30 minutes
Radar
15:00
15:00
STEPS, 2-hours
ahead forecasts
Time of forecast flood event
Radar, real time
0
Radar and rain
gauge estimates
in real time
Radar
16:30
The research described here is based on a study completed by Marion Duprez as part of her MEng in Civil Engineering at Newcastle
University. Marion’s work was supported by her supervisor Dr Vedrana Kutija and I-Hsien Porter of JBA Consulting’s Newcastle office.
We are grateful to the Met Office, CEH and Environment Agency for access to data. JBA Trust project W13-5610
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Real time 2D urban flood forecasting:
a case study
July 2014
Results are shown for each rainfall input and for two spatial model resolutions,
2m and 4m. Buildings were included in the DTM, and the rain gauge inputs were
adjusted to represent drainage systems, both using the methods applied for the
Environment Agency’s national flood maps for surface water.
The radar data and forecast products did not include a drainage adjustment.
Observations are shown as fuzzy data in view of uncertainties in photo interpretation.
Model results at the observation points
1: Civic Centre
3: The Gate
2.0
Observation approx
0.2m at 17:00
Time (hh:mm)
2: Lovers Lane
18:45
16:45
14:45
22:45
2D model (13km 2)
20:45
18:45
16:45
14:45
10:45
12:45
22:45
22:45
22:45
20:45
20:45
18:45
12:45
22:45
16:45
10:45
18:45
22:45
Rain gauges 2m
Rain gauges 4m
Radar 2m
STEPS 2m (1hr)
Time (hh:mm)
Radar 4m
STEPS 2m (2hr)
NWP 2m
STEPS 4m (30 min)
STEPS 4m (1hr)
NWP 4m
STEPS 4m (2hr)
STEPS 2m (30 min)
STEPS 2m (1hr)
STEPS 2m (2hr)
STEPS
4m (30
min)
Run times: Newcastle
city
centre
STEPS 4m (1hr)
STEPS 4m (2hr)
Rain gauges 2m
Rain gauges 4m
Radar 2m
Radar 4m
NWP 2m
NWP 4m
STEPS 2m (30 min)
STEPS 2m (1hr)
STEPS 2m (2hr)
STEPS 4m (30 min)
STEPS 4m (1hr)
STEPS 4m (2hr)
22:45
16:45
18:45
16:45
14:45
Depth (m)
14:45
12:45
12:45
10:45
16:45
20:45
10:45
14:45
18:45
12:45
20:45
Depth (m)
Rain gauges 2m
Rain gauges 4m
Radar 2m
Observation approx
Radar 4m
0.2m at 17:00
0.5
1.5TimeRain
(hh:mm)
gauges 2m NWP 2m
prox
Rain gauges 4m NWP 4m
STEPS 2m (30 min)
Rain gauges 2m 1.0
Radar 2m
0.0
STEPS 2m (1hr)
Rain gauges 4m
Radar 4m
STEPS 2m (2hr)
Radar 2m
NWP 2m
0.5 Time (hh:mm)
STEPS 4m (30 min)
Radar 4m
NWP 4m
NWP 2m
STEPS 2m (30 min)STEPS 4m (1hr)
NWP 4m forecasts
STEPS 2m
(1hr) STEPS 4m (2hr)
0.0
The STEPS rainfall
were
slightly
Time
(hh:mm)
STEPS
2m (30 min)
STEPS 2m (2hr)
inaccurate spatially,
leading to
generally
STEPS 2m (1hr)
STEPS 4m (30 min)
Time (hh:mm)
STEPS
2m
(2hr)
shallower and later flooding predictions.
STEPS 4m (1hr)
STEPS 4m (30 min)
STEPS 4m (2hr)
STEPS 4m
(1hr)
Predictions
based
on
NWP and radar were
Time
(hh:mm)
STEPS 4m (2hr)
2.0
20:45
Observation approx
0.2m at 17:00
22:45
Depth (m)
Depth (m)
1.0
2.0
20:45
20:45
4: Wingrove Avenue
1.0
Rain
gauges 2m
Observation approx
Rain gauges 4m
0.8
0.2m at 18:00
Radar 2m
Radar 4m
0.6
NWP 2m Rain gauges 2m
NWP 4m Rain gauges 4m
0.4
STEPS 2mRadar
(30 min)
2m
STEPS
2mRadar
(1hr) 4m
0.2
STEPS 2mNWP
(2hr)2m
STEPS
(30 min)
0.0 4mNWP
4m
STEPS 4m (1hr)
STEPS 4mSTEPS
(2hr) 2m (30 min)
Observation approx
0.5m at 16:24
Observation approx
0.2m at 17:00 1.0
0.0
Rain gauges 2m
Rain gauges 4m
Radar 2m
Radar 4m
NWP 2m
NWP 4m
STEPS 2m (30 min)
STEPS 2m (1hr)
STEPS 2m (2hr)
STEPS 4m (30 min)
STEPS 4m (1hr)
STEPS 4m (2hr)
Time (hh:mm)
1.5
0.5
1.5
18:45
10:45
22:45
20:45
18:45
16:45
14:45
10:45
12:45
0.0
16:45
0.5
14:45
1.0
12:45
Depth (m)
1.5
Depth (m)
1.5
Rain
gauges 2m
Observation approx
Rain gauges 4m
0.6m at 17:15
Radar 2m
1.0 4m
Radar
NWP 2m
NWP 4m
STEPS
0.5 2m (30 min)
STEPS 2m (1hr)
STEPS 2m (2hr)
STEPS
0.0 4m (30 min)
STEPS 4m (1hr)
STEPS 4m (2hr)
deeper than those based on rain gauge data,
but this difference would be reduced if the
rainfall forecasts were also adjusted to account
for drainage.
At six hours ahead the NWP-based forecast
could potentially indicate likely areas and
approximate timing of flooding, although local
terrain and drainage systems mean the
modelled flood depths should not be treated as
precise predictions.
2D model run times are becoming comparable to
operational requirements for early warnings as
technology advances.
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