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Karstic water systems are usually characterized by high heterogeneity and lack boreholes and points of observation. Thus, a study of the karstic water system using lumped parameters may help distinguish the degree of the flow structure, the influence of any wide conduits, the controlling effect of stored reserves, and other hydrologic factors. A modified Darcian model derived from Criss and Winston (Geophys Res Lett 30 (6): [1314][1315][1316][1317] 2003) was developed in this study and used to model spring discharges in a highly karstified water system in Houzhai, Guizhou Province, China. The modified model successfully reproduced the discharge responses of the Houzhai karstic water system by using two lumped parameters. After analyzing 28 storm events, the authors obtained the parameter values which reflect the lag time to the rainfall input signal and verified the parameter values by spectral analysis results. The sensitivity analysis of the two lumped parameters indicated that the immediate rainfall event is the dominating factor influencing the discharge response.