In order to promote long-term sustainable water management in northwestern Hungary, decision-makers need to understand the hydrological variability in the region. To better quantify hydrological variability in the region, this study developed rainfall-runoff models of four watersheds in the Little Hungarian Plain. The models were then used to identify variations in runoff characteristics caused by climatic factors or fundamental alterations to the watershed itself through the application of numerical error analysis. By observing the continuous statistical error measurements, changes can be detected in either climatic conditions, watershed characteristics, or may indicate gauging or data collection errors.