In the context of a changing climate and increasing environmental pressures, the demand for data to understand the mechanisms of change and their interactions with the hydrological cycle has grown significantly. Further, a gap in data availability remains between the Global North and the Global South. This thesis contributes to the research into the capabilities of citizen science as a recent approach to data collection in water resources. Data obtained via citizen contributions, mainly through social media mining, has been shown to achieve accuracy comparable to authoritative sources and provide valuable inputs for hydrodynamic modelling. Nonetheless, aligning the spatial and temporal resolution of citizen-generated data with modelling requirements remains a challenge.....

Climate change poses prodigious challenges to water resource management. In addressing these challenges, traditional grey measures lack adaptability and long-term sustainability. In contrast, Nature Based Solutions (NBSs) offer flexible, sustainable and eco-friendly alternatives. The design and effectiveness of NBS-based adaptation strategies could be potentially assessed through integrated hydrological models, which simulate both surface and subsurface complex hydrological processes. However, the accuracy of models to efficiently simulate the hydrological processes significantly depends on the quality and availability of input data. Earth Observation (EO) datasets offer a wide range of hydrological data with comprehensive spatial and temporal coverage, yet their quality remains uncertain and requires evaluation across different scales and regions.....