- Hydrology Drought: Processes and estimation. Edited by: Lena M. tallaksen, and Heney A. J. Netherlands. 2004. P8.
- Lowy. William P. Weather and life. Academic Press. New York. 1967.
- Nagarajan. R Dtought assessment. Netherlands. 2009.
- -www. National Drought Mitigation Center. Understanding and Defining Drought df. Mht.