Monitoring with remote sensing and low-cost sensors: Surface water variability and ecohydrological dynamics of Yuracmayo reservoir

—Lima city in Peru, one of the largest and driest cities in the world, relies heavily on limited water sources, with Yuracmayo reservoir provides 14.6% of drinking water to the city. This study investigates the ecohydrological dynamics and surface water variability from 2017 to 2024, focusing on the contribution of the main river feeding the reservoir. Five low-cost water level sensors have been installed along the river’s course near the reservoir inlet, aiming to provide high-frequency, spatially distributed data on water contributions to the system starting in november 2024. Surface water variability was assessed using remote sensing data from 2017 to 2024, while volume estimations were derived from SWOT satellite imagery available since 2024. A strong correlation (R² = 0.80) between SWOT-derived volumes and reference data confirms the reliability of remote sensing for monitoring water storage dynamics in high Andean systems. Preliminary results indicate significant surface area fluctuations, including a 24% volume reduction during dry years such as 2019 and 2020. Notably, the observed shrinkage of adjacent wetlands (bofedales), critical buffer ecosystems, further exacerbates water scarcity in the system. By integrating remote sensing tools for surface and volume assessment with in-situ monitoring through low-cost sensors, this study presents a cost-effective approach to continuous hydrological observation. Compared to traditional in-situ methods, this hybrid approach offers a cost-effective alternative while ensuring reliable data quality, enhancing the understanding of the ecohydrological dynamics of the Yuracmayo reservoir, which is essential for effective water resource management under changing climate conditions. This approach enhances our ability to monitor and preserve critical ecosystems, such as wetlands, which are relevant in mitigating water shortages. Moreover, it highlights the vulnerability of urban water systems in arid regions, underscoring the need for proactive measures to ensure water security.