In agricultural regions where there is insufficient rainwater for cultivation, understanding the dynamics of surface water and groundwater is critical to assess the impact of increased well pumping on the water balance. The western region of the state of Bahia-Brazil, the largest area of agribusiness in the state, has experienced progressive occupation since the 1980s, resulting in pressure on water resources - mainly after the introduction of irrigation - and conflicts among water users. This study analyzed the effects of groundwater extraction by wells in a portion of the Urucuia Aquifer System. The methodology used was the simulation of groundwater flow in steady-state for three scenarios: i) without withdrawal of water by pumping wells; (ii) with current withdrawal rates; and (iii) with 60% additional extraction. After defining well production rates from field surveys (4.6 m3 s-1) and modeling of the aquifer base geometry (maximum thickness of 535 m), the steady-state models with and without pumping show that, in the long term, groundwater storage decreases by 2 km3 (0.8 m on average in the aquifer) without interference in the regional flow direction. The mass balance shows that the base flow of the main rivers is reduced by approximately 6% after current groundwater extraction and an additional 2.5% after additional extraction. The results point to a greater impact on surface water caused by a reduction in groundwater storage and related river base flow. This indicates the importance of maintaining and expanding the groundwater-level monitoring network. ; In agricultural regions where there is insufficient rainwater for cultivation, understanding the dynamics of surface water and groundwater is critical to assess the impact of increased well pumping on the water balance. The western region of the state of Bahia-Brazil, the largest area of agribusiness in the state, has experienced progressive occupation since the 1980s, resulting in pressure on water resources - mainly after the introduction of irrigation - and conflicts among water users. This study analyzed the effects of groundwater extraction by wells in a portion of the Urucuia Aquifer System. The methodology used was the simulation of groundwater flow in steady-state for three scenarios: i) without withdrawal of water by pumping wells; (ii) with current withdrawal rates; and (iii) with 60% additional extraction. After defining well production rates from field surveys (4.6 m3 s-1) and modeling of the aquifer base geometry (maximum thickness of 535 m), the steady-state models with and without pumping show that, in the long term, groundwater storage decreases by 2 km3 (0.8 m on average in the aquifer) without interference in the regional flow direction. The mass balance shows that the base flow of the main rivers is reduced by approximately 6% after current groundwater extraction and an additional 2.5% after additional extraction. The results point to a greater impact on surface water caused by a reduction in groundwater storage and related river base flow. This indicates the importance of maintaining and expanding the groundwater-level monitoring network. ; Em regies agrcolas onde h insuficincia de chuva para o cultivo, entender a dinmica das guas, superficiais e subterrneas, fundamental para avaliar o impacto do crescente bombeio de poos sobre o balano hdrico. O Oeste do estado da Bahia-Brasil, maior rea de agronegcio do estado, experimenta uma progressiva ocupao a partir da dcada de 80, ocasionando presso sobre os recursos hdricos, principalmente aps a introduo da irrigao, e j apresentando conflitos entre usurios das guas. Objetivou-se neste trabalho, analisar os efeitos da extrao de guas subterrneas por poos em uma poro do Sistema aqufero Urucuia. A metodologia utilizada foi a simulao de fluxo hdrico subterrneo em regime estacionrio para trs cenrios: i) sem bombeio; ii) com bombeio atual e; iii) com 60% a mais de extrao por poos. Aps definio das vazes de produo dos poos atuais (4,6 m3 s-1) e da modelagem da geometria da base do aqufero (espessura mxima de 535 m), os modelos estacionrios sem bombeio e com bombeio mostram que, a longo prazo, o armazenamento de gua subterrnea diminui em 2 km3 (rebaixamento mdio no aqufero de 0.8 m) sem interferncias na direo de fluxo regional. O balano de massa mostra que o fluxo de base dos rios principais reduzido em aproximadamente 6% aps a extrao de gua subterrnea atual e mais 2,5% aps acrscimo de extrao. Resultados apontam para um impacto maior sobre rios, causado por uma reduo no armazenamento e fluxo de base. Os estudos indicam a importncia de manter e expandir a rede de monitoramento dos nveis dgua.