This study aimed to assess the health of the Kalaji watershed based on relative and absolute approaches and highlight their differences. First, the status of sub-watersheds was evaluated regarding geomorphological, hydrological, water quality, and landscape criteria using five indicators, including specific erosion, specific flood, landslide density, specific sediment, and the percentage of natural land uses. The overall health index was calculated by combining the weights (by AHP) and values of the indicators. The findings indicate a significant difference in the results of the two approaches. The minimum, maximum, and average values of the health index of sub-watersheds are 0.302, 0.758, and 0.601, respectively, in the relative approach, while they are equal to 0.194, 0.753, and 0.308, respectively, in the absolute approach. The results also showed that the relative approach has a higher health index and a more healthy class than the absolute approach. The findings emphasize that the appropriate approach should be chosen according to the desired goals before assessing the watershed's health. Overall, this study provides a better understanding of the two approaches to watershed health assessment, especially the absolute ones.
