A document by Fabian Quichimbo. Click on the document to view its contents.

Climate change, inter-annual precipitation variability, recurrent droughts, and flash flooding, coupled with increasing water needs, are shaping the co-evolution of socioeconomic and cultural assemblages, water laws and regulations, and equitable drinking water access and allocation worldwide. Recognizing the need for mitigation strategies for drinking water availability in urban areas, the Isotope Hydrology Section of the International Atomic Energy Agency (IAEA) coordinated a state-of-the-art global assessment to evaluate water sources and distribution of drinking water supply in urban centers, an initiative entitled “Use of Isotope Techniques for the Evaluation of Water Sources for Domestic Supply in Urban Areas (2018-2023)”. Here, we report on a) current research trends for studying urban drinking water systems during the last two decades and b) the development, testing, and integration of new methodologies, aiming for a better assessment, mapping, and management of water resources used for drinking water supply in urban settings. Selected examples of water isotope applications (Canada, USA, Costa Rica, Ecuador, Morocco, Botswana, Romania, Slovenia, India, and Nepal) provide context to the insights and recommendations reported and highlight the versatility of water isotopes to underpin seasonal and temporal variations across various environmental and climate scenarios. The study revealed that urban areas depend on a large spectrum of water recharge across mountain ranges, extensive local groundwater extraction, and water transfer from nearby or distant river basins. The latter is reflected in the spatial isotope snapshot variability. High-resolution monitoring (hourly and sub-hourly) isotope sampling revealed large diurnal variations in the wet tropics (Costa Rica) (up to 1.5‰ in δ 18O) and more uniform diurnal variations in urban centers fed by groundwater sources (0.08 ‰ in δ 18O) ([Ljubljana](https://www.google.com/search?client=firefox-b-1-d&sca_esv=f5a20a2e9138d638&sca_upv=1&sxsrf=ADLYWIKR6-DvBtjaWqFYRhn6VgnegOa8kg:1717189104058&q=Ljubljana&stick=H4sIAAAAAAAAAONgVuLQz9U3SMrNNXnEaMwt8PLHPWEprUlrTl5jVOHiCs7IL3fNK8ksqRQS42KDsnikuLjgmngWsXL6ZJUm5WQl5iUCAAFa64FOAAAA&sa=X&ved=2ahUKEwjMrrz047iGAxWyG9AFHSVwCBgQzIcDKAB6BAgTEAE), Slovenia). Similarly, while d-excess was fairly close to the global mean value (+10 ‰) across all urban centers (10-15‰), reservoir-based drinking water systems show significantly lower values (up to ~ -20 ‰) (Arlington, TX, USA and Gaborone, Botswana), as a result of strong evapoconcentration processes. δ 18O time series and depth-integrated sampling highlighted the influence of the catchment damping ratio in the ultimate intake water composition. By introducing new, traceable spatial and temporal tools that span from the water source to the end-user and are linked to the engineered and socio-economic structure of the water distribution system, governmental, regional, or community-based water operators and practitioners could enhance drinking water treatment strategies (including more accurate surface water blending estimations) and improve urban water management and conservation plans in the light of global warming.

To support the hydrological assessment of Alpine ecosystems, we studied the suitability of the SWAT model to simulate neotropical alpine grasslands or so-called Andean Paramo. Given the paucity of observational data in paramo catchments, data-driven models are usually underutilized, and their outcomes are arguable. However, our research examined if SWAT can reasonably represent the hydrological response of grassland-dominated paramo catchments under data-abundance conditions. Therefore, we set up a soil-based SWAT model that emphasized the role of the soil in the hydrological response and the dominance of saturation excess surface runoff over infiltration excess. Specifically, we incorporated detailed characteristics of Andean soils by horizons, parameterized SWAT to replicate high infiltration rates and high lateral flow in the hillslopes, and restricted groundwater interactions to replicate local streamflow responses. Our soil-based modeling approach reasonably reproduced daily discharge during dry and wet periods throughout the year and the cumulative occurrence of high and low flows. The ratio of precipitation and simulated runoff and the partitioning of the total runoff into the lateral flow and surface runoff were physically meaningful. More significantly, SWAT was able to simulate saturation excess overland flow, which is dominant compared to infiltration excess, and it is a distinctive characteristic of paramo catchments. Based on the overall model performance, we conclude that SWAT can reasonably simulate the hydrological response of Andean paramo catchments, and therefore, its application can extend to similar tropical alpine catchments. Nevertheless, the model showed limitations for simulating low flows.