What is a Drought?
A period when precipitation falls significantly below recorded normal levels, resulting in a serious disturbance of the hydrological balance. Drought is a relative term; therefore, arguments based on lack of rainfall should not be based on the rainfall-related activities being studied at the time. For example, in general, lack of rainfall affects crop production and ecosystem activities during the growing season (soil moisture deficit, also known as agricultural drought), while during runoff and percolation it mainly affects water resources (hydrological drought). Changes in soil moisture and groundwater are influenced by observed reductions in rainfall as well as increases in actual evaporation and transpiration. A period characterized by an abnormal lack of rainfall is defined as a meteorological drought. A mega drought is a drought that lasts much longer and over a much larger area than normal, usually a decade or more.