Quantitative sustainability of water resources requires that annual water withdrawals do not exceed renewable water resources. Therefore, accurate estimation of renewable water is essential for sustainable water resources planning and management. This study estimated renewable water resources of the Kashkan sub-basin, Lorestan Province, Iran, for three-time scales: a long-term period (27 years), a short-term period (10 years), and the 2023-2024 water year. Monthly mean precipitation and temperature data from meteorological stations within the sub-basin were used for the 1997-1998 to 2023-2024 water years. Spatial precipitation and temperature maps were generated using Kriging interpolation in a GIS environment. Mean precipitation and temperature values were extracted, and renewable water was estimated using the modified Thornthwaite method. Renewable water resources were estimated at 2,227.72, 2,458.88, and 1,618.26 million cubic meters (MCM) for the long-term period, the short-term period, and the 2023–2024 water year, respectively. Renewable water increased by 10.38% during the short-term period compared with the long-term period but decreased by 34.19% and 27.36% in the 2023-2024 water year relative to the short-term and long-term periods, respectively. The results indicate that renewable water variability was governed by the combined effects of precipitation and temperature. Increased precipitation during the short-term period largely offset the impact of rising temperature, whereas reduced precipitation combined with higher temperatures during the 2023-2024 water year caused a substantial decline in renewable water resources. These findings emphasize the importance of continuous climate monitoring for sustainable water resources management.