GRACE Satellite Observations of Terrestrial Moisture Changes for Drought Characterization in the

Canadian PrairieSitotaw Z. Yirdaw1, Kenneth R. Snelgrove2 and Clement O. Agboma2

J. Hydrology  (2008) 356, 84-92

1University of Manitoba2Memorial University of Newfoundland

Drought Characterization Workshop

Winnipeg, Manitoba

September 26, 2008

Outline

Introduction

Methods

Results and Discussions

Conclusions

Introduction

Objective:

To undertake an investigation of the recent Canadian

Prairie drought by employing Total Water Storage

Anomalies (TWSA) obtained from GRACE remote sensing

satellite mission.GRACE gravity measurements Geopotential

heightMonthly TWSA

Time Series Geopotential heights and TWSA were estimated following Wahr et al. (1998).

From NASA and Center for Space Research (CSR) at the University of Texas.

IntroductionHypothesis:

The gravity measurements obtained from GRACE are

resourceful for the characterization of droughts as evident

in the application for the Canadian Prairie.

Saskatchewan River Basin

The gross drainage area of SRB is 406 000 Km2

Method

�

− = − � ﾶ

+ � �

ﾶ ﾶ

ﾶ

ﾶ ﾶ = ∆

∆+

Atmospherically-based Water Balance

To validate the GRACE-based TWSA

�

∆∆

= − � ﾶ

+ � �

ﾶ ﾶ

ﾶ

ﾶ ﾶ−

�

= = − + ∆∆

�

ﾶ ﾶ

ﾶ

ﾶ ﾶ

is equivalent to GRACE-based TWSA

W (m) is the water content in an atmospheric column is the divergence or net outflow of water vapour across the side of the atmospheric column.

�

�

Result

Terrestrial water storage anomalies in cm of water equivalent thickness

October 2003

November 2003

Result

TWSA derived from GRACE and the atmospheric-based water balance techniques with the corresponding estimated relative uncertainties.

Drought Period

Result

Trends in measured monthly average precipitation and streamflow at the Grand Rapids outlet for the Saskatchewan River Basin

Drought Period

Result

Total Storage Deficit Index (TSDI) : Similar in meaning to the Soil Moisture Deficit Index

(SMDI) developed by Narasimhan and Srinivasan (2005). This index parallels the more popular drought

assessment tool known as the Palmer Drought Severity

Index (PDSI) (Palmer, 1965).

�

= −

−

Total Storage Deficit (TSD)

Where

TSA i,j, is the monthly total storage anomaly.

MTSAj, MaxTSAj, and MinTSAj are respectively, the long-term

mean, maximum and minimum total storage anomaly

i = April 2002 to May 2006 and j= 1-12 months).

Result

�

= − +

Cumulative Total Storage Deficit (TSD) for the Saskatchewan River Basin derived from GRACE-based total water storage.

Drought terminated in the month of May 2004

p and q are duration factors

Result

Total Storage Deficit Index (TSDI)

ﾶ

= − +

Drought terminated in the month of May 2004

Result

Cumulative Total Storage Deficit Index (TSDI) for the SRB

Drought Severity Index

-4 or less Extreme

-3 Severe

-2 Moderate

-1 Mild

A best-fit line with a slope of -3 which is an indication that the last Canadian Prairie drought falls under the ‘‘severe drought’’ classification in accordance with Palmer (1965).

Conclusions

GRACE satellite remote sensing mission has proven

pertinent as an alternate means for studying Prairie

hydrology especially from the perspective of a

scenario of insufficient data on water storage

variations.

Using the TSDI, it was possible to characterize the

2002/2003 Prairie drought episode as “SEVERE DROUGHT” on the basis of Palmer’s drought severity

classification scheme.

This study supports the usefulness of GRACE satellite

remote sensing data as a viable means of estimating

basin total water storage necessary for drought

studies.

References

Ø Narasimhan, R., Srinivasan, R., 2005. Development and evaluation

of Soil Moisture Deficit Index (SMDI) and Evapotranspiration

Deficit Index (ETDI) for agricultural drought monitoring,

Agricultural and Forest Meteorology, 133: 69-88.

Ø Palmer, W.C., 1965. Meteorological drought, Research Paper 45. U.S

Department of Commerce, Weather Bureau, Washington, D.C.

Ø Wahr, J., Molenaar, M., Bryan, F., 1998. Time-variability of the

Earth’s gravity field: Hydrological and oceanic effects and their

possible detection using GRACE, J. Geophys. Res., 103, 30205–

30230.

Ø Yirdaw, S.Z., K.R. Snelgrove, C.O. Agboma (2008) GRACE satellite

observations of terrestrial moisture changes for drought

characterization in the Canadian Prairie, Journal of Hydrology ,

356 (1-2):84-92.