1. Shraddhanand Shukla Andrew W. Wood
Drought Monitoring with Hydrologic Models an alternative to standard indices?
Shraddhanand Shukla
Andrew W. Wood

2. Drought: The Creeping Disaster
Drought in the United-States result in an estimated avg annual damage of $6-8 billion

3. Monitoring Drought Severity Lack of Precipitation Antecedent Moisture
Averaged over different periods
Hydrologic Condition
Socio-economic Status
Precipitation
Temperature
Snowpack
Streamflow
Reservoir
Lack of observed data
Weighting scheme
Palmer Drought Indices (PDI)
Precipitation
Temperature
Available Water Holding Capacity
Simplified Water Balance model
Precipitation
Temperature
Cold season process
Complex water and
energy balance scheme
No info of socio-economic
conditions
Intensity
Duration
Standardized Precipitation Index (SPI)
Surface Water Supply Index (SWSI)
Hydrologic Model-Based Indices
Severity

4. U.S. Drought Monitor

5. Short-Term Drought Indicator blend

6. Long-Term Drought Indicator Blend

7. CPC Soil Moisture Model (Huang et al. 1996)
Where:
W(t) = the soil Moisture at any time t
P(t) = the mean areal precip over any
area A
E(t) = the mean areal evap over any
R(t) = the net streamflow divergence
from area A
G(t) = the net groundwater loss from area A

8. Objectives
To analyze historical drought events in Washington state using model derived Soil moisture and runoff
To compare model-based indices with other independent drought indicators
To reconstruct the historical drought events at monthly time-scale and evaluate the model performance in monitoring drought

9. Characteristics of a Drought Index
Adaptable to the appropriate time scale
Quantitative measure of the large spatial and temporal scale drought conditions
Applicable to different types of drought
Can be used for the retrospective analysis

10. Hydrologic Model-Based Indices
Soil moisture and runoff percentiles
(Scheffield 2004, 2007; Andreadis 2005, 2006)
Beta Distribution
Empirical Distribution (Weibull Plotting Position)
(84 years of data)
Standardized Runoff Index
(Wood and Shukla, 2007)
Fitted Distribution (ln2,3; gamma, GEV)
Transformation of Cum. Prob. to a Standard Normal Deviate

11. Soil Moisture Percentile (Justin 2004)

12. Severity-Area-Duration Curve (Andreadis, 2005)

13. Standardized Runoff Index (Wood and Shukla, 2007)

14. Standardized Runoff Index (Wood and Shukla, 2007)

15. Historical Droughts in WA State
Meteorological Drought:
1934,1941,1945,1952,
1973,1976, 1996,2001,
2005
Model based indices can
identify all the historical
drought events

16. Drought
Wet winter of and relatively abundant precipitation through the spring and summer of 1976.
Drought began in Sep Persisted through the February 1977.
Precipitation less than 75 nearly everywhere and for some areas even less than that.
Slight relief to the western Washington in March 1977 but things remained ugly in the Eastern Washington state.
Series of storms brought rainfall well above normal in the month
of September and October 1977

17. 1976-77 Drought : Simulated Water Balance

18. 1976-77 Drought : SWE and SM Percentiles

19. 1976-77 Drought: SM, SRI, SSI Onset of agricultural
and hydrological drought around September 1976
Recovered by October 1977

20. Drought : SM, SRI, SSI

21. 2001 Drought: November and December 2000 were unusually dry
Abnormally dry weather in winter.
By mid-March all most every corner of the state was in water scarcity.
Statewide drought was declared on March 14, 2001
In effect till Dec, 2001.
(Source:

22. 2001 Drought: Simulated Water Balance plots

23. 2001 Drought SWE and SM Percentiles

24. Drought 2001: SM,SRI,SSI Onset of drought in winter 2001
Recovered by the end of the year

25. Drought 2001: SM,SRI,SSI

26. Summary
The VIC model simulated soil moisture and runoff based indices identify the major historical drought events
The model is reasonably accurate in monitoring drought onset, duration and spatial extent
It is implemented at 1/8-1/16th deg and daily time step thus suitable for the real-time drought monitoring and prediction
Hydrologic models should be used as one of the decision tools for monitoring drought and given more weight in the Drought Monitor

27. Expected Soil Moisture Deficit Recover Period
Future Work
Expected Soil Moisture Deficit Recover Period
Soil Moisture Deficit
Normal Soil Moisture
Current Soil Moisture
Ensembles of Expected
Recovery Period

28. Questions