A. R. Nejadmohammad Namaghi - Hasheminejad High Education Center, Khorasan Razavi, Mashhad, Iran
J Farzadmehr - Assistant Professor at Birjand University

Drought is one of unsensible natural disaster due to rainfall deficiency relatively long-term periods usually a season or longer. This deficiency is due to want of water for some activity in ecosystem. Drought must be considered relatively with some average condition of long term balance of between precipitation and evapotranspiration and transpiration. Usually in every area there is a particular status as a normal condition defined.