The water content of the rivers is formed by atmospheric precipitation and underground waters. Influence of underground waters on water content of the rivers cannot be measured. It is shown that the volume of underground water exchange is underestimated and can be commensurable with a volume of atmospheric precipitation. Change of level of underground waters is defined by changes of volume of the geological environment during geodeformations. It is offered to consider geodeformations as one of the reasons of floods and droughts. Studied the changes the gravitational field and geodeformations during droughts and floods in the Amazon in 2005-2006. Studied the hydrological regime of the River Nile. Shows the influence of geodeformation on the level of Danube and Dniester. Proposed detailed study the causes of floods in Europe in 2002. Influence of the Earth’s surface deformation on floods and droughts is very important and requires special detailed study. Changes in volume of rocks during Earth’s surface deformation are accompanied by dilatancy which influence on the amount of drought and flooding has turned out to be significant. Study of the processes considered in the thesis gives grounds to expect that floods and droughts associated with deformations of the geological environment will be successfully predicted.