Depletion of water resources, triggered by population growth, climate change, and pollution, remains a serious threat to human well-being and ecosystems. Rainwater harvesting (RWH), known for its feasibility and sustainable environmental benefits, has emerged as a solution to this problem.

Standard traditional approaches to identify suitable RWH sites often rely on GIS-based Multi-Criteria Decision Analysis (MCDA) techniques, using proxy indicators such as slope, land use, drainage density, and runoff characteristics. While these approaches provide valuable pixel-based specific insights, they typically overlook the temporal variability of rainfall, which is a factor that plays a key role in determining the actual availability and reliability of the potentiality of harvesting water.

This study addresses this gap by focusing the importance of rainfall variability in assessing RWH potential. By integrating long-term inter-annual spatial variability in temporal rainfall patterns into the evaluation framework, the method captures fluctuations in rainfall that affect both the quantity and time of water availability. The strategy is applied to the Upper Tiber River basin in central Italy, showing that addressing rainfall variability leads to more realistic and dynamic assessments of RWH potential.

Therefore, this study depicts how addressing year-to-year changes in rainfall significantly influences the performance and resilience of rainwater harvesting systems. This highlights the need for informed planning in water resource management, reinforcing the importance of adaptive and data-driven strategies.