Distributed Hydrology Soil Vegetation Model (DHSVM) was successfully applied in Mākaha watershed to investigate the hydrologic impact of groundwater pumping on the streamflow. DHSVM was calibrated (1971-1980) and validated (1981-1990) against observed streamflow during pre-development conditions. Monthly observed and simulated streamflows after the development (after 1990) were compared to quantify the decline in streamflow. Simulation results indicate that declines in streamflow could be attributed to: (i) an increase in the fraction of gross rainfall converted into evapotranspiration (ET); and (ii) groundwater pumping. Groundwater pumping from additional groundwater development in the form of new pumping wells starting in 1991 has significantly reduced the streamflow, especially during the summer. The fraction of gross rainfall converted into ET has significantly increased by 7% during 1991-2009 compared to the pre-development period. Based on the model results, in the absence of the groundwater development in the upper part of Mākaha watershed, the observed cumulative streamflow could have been 11% higher than its current level. On an annual basis, total additional groundwater pumping accounts for 26% of the recharge with a significant seasonal variability (12% in wet and 180% in dry season). Relative to recharge, higher groundwater pumping during the dry season could have been the reason behind the significant streamflow decline during the summer. This study clearly emphasizes the importance of temporal patterns in groundwater withdrawal which are often ignored while determining safe yield. © 2012 Elsevier B.V.