The research presented here attempts to bridge science and policy through the quantification of climate change impacts and the analysis of a science-fed participatory process to face a sustainability challenge in the San Pedro Basin (Arizona). Paper 1 presents an assessment of a collaborative development process of a decision support system model between academia and a multi-stakeholder consortium created to solve water sustainability problems in a local watershed. This study analyzes how science-fed multi-stakeholder participatory processes lead to sustainability learning promoting resilience and adaptation. Paper 2 presents an approach to link an ensemble of global climate model outputs with a hydrological model to quantify climate change impacts in the hydrology of a basin, providing a range of uncertainty in the results. Precipitation projections for the current century from different climate models and IPCC scenarios are used to obtain recharge estimates as inputs to a groundwater model. Quantifying changes in the basin's water budget due to changes in recharge, evapotranspiration (ET) rates are assumed to depend only on groundwater levels. Picking on such assumption, Paper 3 explores the effects of a changing climate on ET. Using experimental eddy covariance data from three riparian sites, it analyzes seasonal controls on ET. An approach to quantify evapotranspiration rates and growing season length under warmer climates is proposed. Results indicate that although atmospheric demand will be greater, increasing pan and reference crop evaporation, ET rates at the studied field sites will remain unchanged due to stomatal regulation. However, the length of the growing season will increase, mainly with an earlier leaf-out and at a lesser level by a delayed growing season end. These findings - implying decreased aquifer recharge, increased riparian water use and a lesser water balance - are very relevant for water management in semi-arid regions. Paper 4, in which I am second author, explores the theory relating changes in area-average and pan evaporation. Using the same experimental data as Paper 3, it corroborates a previous theoretical relationship and discusses the validity of Bouchet's hypothesis.