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2. Changnon, S.A. and Huff, F.A. 1971. Evaluation of Potential Benefits of Weather Modification on Agriculture 77Champaign: Illinois State Water Survey.
3. Changnon, S.A., Achtemeier, G., Hilberg, S., Knapp, V., Olsen, R., Roberts, W.J. and Vinzani, P. 1987. Detecting Drought Conditions in Illinois. Circular 36Champaign: Illinois State Water Survey.
4. On the definition of droughts
5. Huff, F.A. and Changnon, S.A. 1963. Drought Climatology of Illinois. Bulletin 108champaign: Illinois State Water Survey.