In the hydrological system, each component is interconnected, the vadose zone water, groundwater and river runoff respond to each other, and the hydrological cycle is in a state of dynamic balance.
As an input to the hydrological system, precipitation has an important impact on the hydrological cycle. Precipitation shortage leads to drought in different components of the hydrological system (vadose zone, groundwater and surface water) through the hydrological cycle. Insufficient precipitation leads to a reduction in soil moisture content, making it difficult for soil moisture to sustain plant growth and resulting in agricultural drought. The depletion of soil moisture content leads to Groundwater recharge decreases, groundwater levels decline, underground runoff decreases, and hydrological drought eventually occurs.
The process from meteorological drought to agricultural drought and then to hydrological drought is called " drought propagation".
Domestic and foreign scholars' research on drought evolution mainly focuses on two aspects: drought lag time and drought characteristics (drought duration, drought loss amount/intensity) response.
The drought evolution process has four characteristics:
(1) Pooling: meteorological drought is combined with a long-lasting hydrological drought;
(2) Attenuation: from meteorological drought to agricultural drought and hydrological drought, the degree of drought is weakened ;
(3) Lag: The starting time of agricultural drought and hydrological drought will lag behind meteorological drought; (4
) Lengthening: From meteorological drought to agricultural drought and hydrological drought, the duration of drought becomes longer.