Drought is the most complex and least understood of all natural hazards, affecting more people than any other hazard. Bryant ranked natural hazards on the basis of various criteria, such as severity, duration, spatial extent, loss of life, economic loss, social effect, and long-term impact, and found that drought ranks first among all natural hazards. Drought is a recurring phenomenon that has plagued civilization throughout history. It affects natural habitats, ecosystems, and many economic and social sectors, from the foundation of civilization—agriculture—to transportation, urban water supply, and the modern complex industries. On the basis of the defined drought criteria, the intensity and duration of drought, a number of different indices have been developed to detect, monitor, and evaluate drought, each with its own strengths and weaknesses. Drought indices integrate various hydrological and meteorological parameters such as rainfall, temperature, evapotranspiration, runoff and other water supply indicators into a single number and give a comprehensive picture for decision making.