Upstream Satellite-derived Flow Signals for River Discharge Prediction

Tom Hopson1

F. A. Hirpa2; T. De Groeve3; G. R. Brakenridge4;M. Gebremichael2; P. J. Restrepo5

1

2Uconn; 3Joint Res Counc; 4U. of CO; 5Office Hydro Devel

OutlineI. Monitoring river flows using Satellite-based

Passive-Microwave data II. Case study: Bangladesh’s vulnerability to

floodinga) Estimating flood wave celerityb) River discharge estimation “nowcasting”c) Discharge forecasting

III. Future Work

-- Advanced Microwave Scanning Radiometer - Earth Observing System (AMSR-E) & NASA TRMM(Future: Global Precipitation Measurement System) -- Utilizing 36-37Ghz (unaffected by cloud)-- pixel size ~20km-- ~2day complete global coverage (night-time brightness temperatures)-- data range: 1997 to present

Objective Monitoring of River Stage and Flow:Satellite-based Passive Microwave Radiometer

Other Approaches: satellite altimeter-derived water level (and discharge derived through rating curve):e.g. Birkett, 1998; Alsdorf et al. 2000; Jung et al. 2010, Papa et al. 2010, Alsdorf et al. 2011, Biancamaria et al. 2011

One day of data collection(high latitudes revisited most frequently)

=> On average, global coverage 1-2 days

Example: Wabash River, Indiana, USA

Black square shows measurement pixel. White square is calibration pixel.

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Brakenridge, et al, 1998, 2005, 2007

GDACS, JRC Gridded Approach

De Groeve, et al, 2009, 2010

=> Use “M/C” ratio

s =MC

=Tb,measurement

Tb,calibration

(World Food Program)

Damaging Floods:large peak or extended durationAffect agriculture: early floods in May, late floods in September

Recent severe flooding: 1974, 1987, 1988, 1997, 1998, 2000, 2004, and 20071998: 60% of country inundated for 3 months, 1000 killed, 40 million homeless, 10-20% total food production2004: Brahmaputra floods killed 500 people, displaced 30 million, 40% of capitol city Dhaka under water2007: Brahmaputra floods displaced over 20 million

Case Study: Bangladesh River Flooding

Hardinge Bridge gauge(Ganges)

Gauging data reference: Hopson 2005; Hopson and Webster 2010

Bahadurabad gauge(Brahmaputra)

Ganges

Brahmaputra

Correlation vs. lag time and distance between Gage Q & satellite signals

Ganges Brahmaputra

Estimating the kinematic wave celerity

Assumptions (large): hydraulic parameters homogenous; rainfall predominantly upper-catchment; wave speed variation with depth lower-order; dynamic wave effects lower-order (confirmed through rating curve analysis – not shown), etc.

Independent analysis: Kleitz-Seddon Law for kinematic wave celerity c: W channel top-width, Q discharge, y the river stage.Brahmaputra at Bahadurabad: 4m/s < c < 8m/s; Ganges at Hardinge Bridge: 2m/s < c < 6m/s.

c =1W

dQdy

Generation of Nowcasts and Forecasts

Regressor and model selection procedure:

i) Correlate all variables with gauged observations

ii) Sort in decreasing level

iii) Select using step-wise forward-selection using K-fold cross-validation and RMSE cost function

iv) Repeat ii) – iii) for all lead-times

Discharge estimation “Nowcasting”

Ganges 2003 Brahmaputra 2007

1-, 5-, 15-day Forecasts

Skill Scores

Nash-Sutcliffe efficiency(fraction of variance explained):

-- 80% (1-day) to 55% (15-day) explained

Now, generate a forecast including “persistence”:

-- satellite information improves forecasts by 10-20% at all lead-times

SS =Aforc −Aref

Aperf −Aref

Future WorkBlend with ECMWF-derived forecasts

(Hopson and Webster 2010; Operational in 2003)

2007 Brahmaputra Ensemble Forecasts and Danger Level Probabilities

7-10 day Ensemble Forecasts 7-10 day Danger Levels

7 day 8 day

9 day 10 day

7 day 8 day

9 day 10 day

Summary

Satellite-based passive microwave imagery useful tool for monitoring river conditions for limited-gauged basins

Useful for estimating:-- flood wave celerity-- discharge estimates (nowcasts) including filling in missing data

Combined with other methodologies, a potentially useful tool for flood forecasting of large river basins

Further questions: hopson@ucar.edu

MODIS sequence of 2006 Winter Flooding

2/24/2006 C/M: 1.004 3/15/2006 C/M: 1.029 3/22/2006 C/M: 1.095

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Site 98, Wabash River at New Harmony, Indiana, USA