Transcript Slide 1

H53C-0644
THE POTENTIAL FOR MEDIUM-RANGE GLOBAL FLOOD PREDICTION
Nathalie Voisin1, Andrew W. Wood1, Dennis P. Lettenmaier1, and Eric F. Wood2
1Department
2Department
of Civil and Environmental Engineering
University of Washington, Seattle, WA
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Introduction
While weather and climate forecast methods have advanced greatly over the last
two decades, this capability has yet to be evidenced in mitigation of water-related
natural hazards (primarily floods and droughts), especially in the developing world
(Lettenmaier et al, 2006). For instance, Mozambique experienced major droughts in
2005 and 2002 which resulted in widespread food shortages and major floods in 2000
and 2001 which affected large parts of the country. In Southeast Asia, early monsoon
rains that began in July 2000 resulted in flooding of the Mekong River and its
tributaries in Cambodia, Vietnam, Laos and Thailand. It was the worst flooding in
several decades and affected more than 4.5 million people and killed several
hundreds. Mitigation of these events through advance warning was at best modest;
despite the above noted improvement in weather and climate forecasts, there is at
present no system for forecasting of floods and droughts globally, notwithstanding
that the potential clearly exists. We describe development of a methodology that is
eventually intended to generate global flood and drought predictions routinely. It
draws heavily from the experimental North American Land Data Assimilation System
(NLDAS) and the companion Global Land Data Assimilation System (GLDAS) for
development of nowcasts, and the University of Washington Experimental Hydrologic
Prediction System to produce ensemble hydrologic forecasts based on the NCEP
Global Forecast System for lead times from seven days to six months using the
University of Washington/Princeton University Variable Infiltration Capacity (VIC)
macroscale hydrology model. In the prototype (tested using retrospective data), VIC
is driven globally up to the time of forecast with daily ERA40 precipitation (rescaled on
a monthly basis to a station-based global climatology), ERA40 wind, and ERA40
average surface air temperature (with temperature ranges adjusted to a station-based
climatology). In the retrospective forecasting mode, VIC is driven by global NCEP
ensemble 15-day reforecasts provided by Tom Hamill (NOAA/ERL), bias corrected
with respect to the adjusted ERA40 data and further downscaled spatially using
higher spatial resolution Global Precipitation Climatology Project (GPCP) 1dd daily
precipitation. Downward solar and longwave radiation, surface relative humidity, and
other model forcings are derived from relationships with the daily temperature range
during both the retrospective (spinup) and forecast period. The initial system is
implemented globally at one-half degree spatial resolution. We evaluate model
performance retrospectively for predictions of major floods for the Rhine and Meuse
in 1995.
2
of Civil and Environmental Engineering
Princeton University, Princeton, NJ
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Step 1: GFS Reforecasts Bias Correction
Step 2: Downscaling from 2.5 to 0.5 degree
Precipitation is downscaled using the Schaake Shuffle (Clark et al. 2004)
with the satellite product 1997-2005 GPCP1dd (Huffman et al. 2001) used
as observations. GFS reforecast precipitation is scaled using the ratio
of GPCP1dd values at 0.5 degree over the value at 2.5 degree:
The similar quantile-quantile method as
used in (Wood et al. (2005) is applied
directly to the GFS reforecast values. This
step ensures that the forecasts are
consistent ( signal characteristics) with the
dataset used during the spinup period.
Pr ecipGFS ,0.5 
Pr ecipGPCP1dd ,0.5
Pr ecipGPCP1dd , 2.5
The daily temperature average is downscaled via an inverse
square distance interpolation. The daily temperature range is
assigned using a Schaake Shuffle type of selection using
Adam et al. (2006) global temperature dataset:
T max0.5  Tavgint erpolated
. Pr ecipGFS , 2.5
T min0.5  Tavgint erpolated 
ERA40 cumulative distribution function (CDF)
15 ensembles Jan 20th, 1995 GFS
reforecasts at cell (50oN,2.5oW) – observed
precipitation events sorting as part of the
Schaake Shuffle
GFS reforecast CDF
GFS control run ( deterministic forecast)
bias corrected GFS reforecast value
GFS reforecast value

T min

Obs , 0.5
 T maxObs ,0.5 ) 
2
T minObs ,0.5  T maxObs ,0.5 )
2
Jan 20th, 1995 GFS reforecast of one ensemble, at one 2.5 degree cell
(50oN,2.5oW)
Precipitation downscaling
Temperature downscaling
Bias correction applied to cell (50oN,2.5oW) for the GFS reforecast of Jan 20th, 1995
Precipitation
Daily Average Temperature
Original GPCP 1dd precipitation value
PrecipGPCP1dd ,2.5  used for downscaling the
corresponding bias corrected 2.5 degree
GFS reforecast PrecipGFS ,2.5 
Approach
This schematic is similar experimental procedure as used by Wood and Lettenmaier
(2006) West-wide seasonal hydrologic forecast system. Hydrologic simulations are
performed using the Variable Infiltration Capacity model developed at the University
of Washington and Princeton University.
15 (ensembles) 2.5 degree GPCP1dd
precipitation events PrecipGPCP1dd ,2.5 
assigned to the 15 ensemble GFS
reforecast value PrecipGFS ,2.5 
25 GPCP 1dd values PrecipGPCP1dd ,0.5  used
for downscaling the corresponding bias
corrected 0.5 degree GFS reforecast
Precip
GFS , 0.5

Daily average 2.5 degree bias corrected GFS
reforecast temperature TavgGFS , 2.5 
25 daily temperature averages ( at 0.5 degree)
obtained by interpolation TavgGFS ,int erpolated,0.5


25 values ( at 0.5 degree) of Tmin as a function
of Tmax T max0.5 and T min0.5 
In this poster
Daily ECMWF
ERA40
Adjusted daily
ECMWF ERA40
Weather
input into
the
hydrologic
model
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Hydrologic Simulations , January 1995 Rhine and Meuse Floods ( GFS reforecast as of Jan 20th, 1995 )
5-day accumulation Precipitation
GFS ens. Avg
GFS det. Fcst
ERA40
5-day accumulation Runoff
GFS ens. Avg
GFS det. Fcst
ERA40
5-day change in soil moisture
GFS ens. Avg
GFS det. Fcst
Daily streamflow forecasts
ERA40
Fcst of Jan 20th,
1995
Section 3
Daily ERA40 downscaled
to 0.5 degree using linear
inverse square distance
interpolation.
Monthly ECMWF ERA40
has been rescaled to
match observations based
Adam et al. (2006)
precipitation and
maximum and minimum
temperatures.
NCEP Reforecasts (Hamill 2006)
15 ensemble members – 15 day forecast
– 2.5 degree
(fixed GFS version of 1998)
Bias correction with respect to
adjusted ERA40
(Ensures consistency between spinup
and the reforecasts)
Fcst of Jan 22th,
1995
Later on:
Update of
initial
conditions
Section 4
Downscaling from 2.5 to 0.5 degree
using higher spatial resolution satellite
(GPCP1dd, Huffman et al. 2001)
precipitation and the Schaake Shuffle (
Clark et al. 2004)
GFS ens. Avg : average of the 15 GFS reforecast ensembles
GFS det. Fcst : GFS reforecast control run – GFS deterministic forecast
ERA40 : ECMWF 40 year reanalysis, surrogate for observations
Section 5
Hydrologic model
spin up
(0.5 degree global
simulation)
Several years back
INITIAL
STATE
Nowcasts
Climatology monthly flow
Hydrologic forecast simulation
Climatology daily flow
References
(0.5 degree global simulation: stream flow,
soil moisture, SWE, runoff )
Adam, J.C., E.A. Clark, D.P. Lettenmaier, and E.F. Wood, 2006: Correction of
Global Precipitation Products for Orographic Effects .J. Climate,19 (1), 1538.
Clark, M.P., S. Gangopadhyay, L.E. Hay, B. Rajagopalan, and R.L. Wilby
(2004): The Schaake Shuffle: A method to reconstruct the space-time
variability of forecasted precipitation and temperature fields. Journal of
Hydrometeorology, 5, 243-262.
Huffman, G.J., R.F. Adler, M. Morrissey, D.T. Bolvin, S. Curtis, R. Joyce, B
McGavock, J. Susskind, 2001: Global Precipitation at One-Degree Daily
Resolution from Multi-Satellite Observations. J. Hydrometeor., 2, 36-50.
Lettenmaier, D.P., A. de Roo, and R. Lawford, 2006. Towards a capability for
global flood forecasting, WMO Bulletin 55, 185-190.
Wood, A.W. and D.P. Lettenmaier, 2006, A testbed for new seasonal hydrologic
forecasting approaches in the western U.S., Bulletin of the American
Meteorological Society (in press).
Medium range forecasts
( up to 2 weeks)
The hydrologic model is essentially uncalibrated, see ongoing
improvement section.
CONTACT:
[email protected]
[email protected]
6 Ongoing Improvements
- Improve VIC calibration (presently
essentially uncalibrated)
- Apply to more events: Mozambique floods
2000 and 2001, Danube floods 2000, 2002
and 2006, Mississippi floods 1993, Mekong
floods 2000, Yangtze floods 1998, Oder floods
1997,etc.