The variation in land use/land cover (LULC) and climate have a direct impact on the accuracy of any hydrological prediction. However, quantification of the effect of these two factors in an ungauged catchment setting is less discussed. Soil and Water Assessment Tool (SWAT) in combination with two regionalization techniques, i.e., Inverse Distance Weighted and Kriging were applied on 32 catchments in India where each catchment was considered as ungauged at least once. The combined and isolated impacts of LULC change (LULCC) and climate variability on streamflow for the period of 1990–2011 were quantified at an annual scale through four different cases. Satisfactory results were obtained from SWAT for the analysis of both the gauged and ungauged set-up. The overall outcomes suggest that, due to the influence of the combined effects of LULCC and climate variability, there was a decrease in the annual streamflow volume by more than 21% from the first period (1990–2000) to the second period (2001–2011) in the selected catchment treated as ungauged. The variable climate factor overshadowed the effect of LULCC. The result may be correlated with the increase in temperature and the decrease in rainfall volume, which is distinctive in a monsoon-dominated country like India.