Thailand’s changing climate patterns has led to instability and challenges to the people and the nation’s economy. Groundwater is an increasingly important resource to human populations in Thailand as it has been served as the secondary source of drinking and agricultural water in drought-hit provinces in the majority of Chao Phraya river basin. The massive usage of groundwater is the major cause of the declining of the shallow groundwater elevation worldwide, especially in Sukhothai province of Thailand where local farmers usually have their rice farming at least 3 times a year. Drought caused by irregular rainfall has become a significant issue in Thailand in the most recent years. Long periods of droughts are impacting rice and other cash crops production. Water scarcity is a global threat that is estimated to hit Thailand hard and the country is in need to develop a long-term plan to deal with these challenges. Effective water management needs to be practiced and conjunctive use of surface water and groundwater is being implemented. This thesis therefore aims to comprehensively understand movement and distribution processes within the hydrological systems for a sustainable resource development without adverse effects on the environment, and isotope techniques are effective tools for fulfilling critical hydrogeological information needs. Forty five water samples from the study area were collected and further analyzed in the laboratory using isotope mass spectrometer. The results indicated that the origin of the groundwater in Sukhothai was composed of 69.33% rainfall and 30.67% of Yom river water. Additionally, SWAT model was employed for spatio-temporal surface water simulation and the estimation of groundwater recharge rates. Sensitivity analysis, calibration, validation, and uncertainty analysis were performed by SWAT-CUP software. Due to the semi-distributed features of SWAT and the difficulty of calculating groundwater distributed parameters, recharge values estimated by SWAT were used in a MODFLOW model for groundwater simulation at steady and unsteady states. Surface water and groundwater potentials in Sukhothai province of Thailand were estimated based on aquifer hydrodynamic coefficients from calibrated and validated modeling results. SWAT and MODFLOW models were successfully tested and the results of the combination of the two models were found acceptable. SWAT simulation results revealed the annual average groundwater recharge rate of 882 MCM per year or accounted for 11.06% of the total rainfall in the study area. The data from rainfall-runoff model were utilized as input data for groundwater flow model (i.e., MODFLOW) for the study the flow characteristics and assess the groundwater potential from natural recharging process into the shallow aquifer. The results indicated that the groundwater yield of 287 MCM per year is available in the study area.