PROPAGATION FROM ATMOSPHERIC TO HYDROLOGICAL DROUGHTS IN BRAZILIAN CATCHMENTS

Código

V-END_II-EBHE0055

Autores

Abderraman Róger Amorim Brandão, André Simões Ballarin, Paulo Tarso Sanches de Oliveira

Tema

13 - Estiagens e Secas;

Resumo

Drought propagation describes how atmospheric water deficits are transferred to hydrological compartments, yet the extent to which droughts reach groundwater remains poorly quantified in tropical catchments. Here, we assessed event-based propagation from precipitation and climatic water balance to streamflow and groundwater across 51 Brazilian catchments linked to 181 unconfined groundwater wells. Drought events were identified separately for precipitation, climatic water balance (P?ET), streamflow and groundwater level using a variable threshold approach based on the 20th percentile of 30-day smoothed daily series. Events were then connected across compartments using a 30-day matching window to estimate propagation fractions and start-to-start lags. Results show that drought propagation to groundwater is selective and delayed. Only 15% of precipitation droughts and 14% of climatic water-balance droughts propagated to groundwater, whereas 37% of streamflow droughts reached groundwater. Propagation lags increased along the hydrological continuum. The transition from precipitation to climatic water balance was rapid, with a median lag of 8 days, whereas transitions to streamflow occurred over intermediate timescales, with median lags of 75 days from P?ET to Q and 109 days from P to Q. Groundwater responses were substantially slower, with median lags of 197 days from P?ET to groundwater, 277 days from streamflow to groundwater and 352 days from precipitation to groundwater. Maximum groundwater lags exceeded 1,000 days. These findings show that groundwater drought is not the automatic final stage of meteorological drought, but a filtered response controlled by storage, recharge timing and subsurface connectivity. This highlights the need for integrated drought monitoring strategies.