Online Drought Indicators and Indices

Soil Moisture Deficit Index (SMDI)


Index name: Soil Moisture Deficit Index (SMDI).

Ease of use: Red.

Origins: Developed from research at the Texas Agricultural Experiment Station, United States by Narasimhan and Srinivasan in 2004.

Characteristics: A weekly soil moisture product calculated at four different soil depths, including the total soil column, at 0.61, 1.23 and 1.83 m, and can be used as in indicator of short-term drought, especially using the results from the 0.61m layer.

Input parameters: Modelled data from a hydrologic model with the SWAT model are used initially to compute soil water in the root zone on a weekly basis.

Applications: Useful for identifying and monitoring drought affecting agriculture.

Strengths: Takes into account the full profile as well as different depths, which makes it adaptable to different crop types.  

Weaknesses: The information needed to calculate SMDI is based upon output from the SWAT model. There are auto-correlation concerns when all the depths are being used.

Resources: The calculations are provided and explained thoroughly in the reference below. Information on the SWAT model can be found at

References: Narasimhan, B. and R. Srinivasan, 2005: Development and evaluation of Soil Moisture Deficit Index (SMDI) and Evapotranspiration Deficit Index (ETDI) for agricultural drought monitoring. Agricultural and Forest Meteorology, 133(1): 69–88.

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