Integrating satellite observations to enhance reservoir monitoring: a case study facing the emergency shortage of fresh water in Bogotá, Colombia

Colombia, with a water surface of approximately 831,163.7 hectares distributed in swamps, reservoirs, lagoons and marshes, faces significant challenges in monitoring the status of its lentic water bodies. The lack of information places the country in a disadvantageous position for managing its water-related ecosystems. For instance, quantifying water resources and reporting on international initiatives such as SDGs requires implementing robust monitoring systems to track progress on several objectives and indicators (e.g., SDG indicator 6.6.1, "Change in the extent of water-related ecosystems over time"). Moreover, monitoring is crucial for decision-making under extreme hydrometeorological phenomena and climate change.

Bogotá, Colombia’s capital city, is the sixth most populated capital in Latin America, where domestic water demand, flow regulation, and energy generation are supplied by a set of reservoirs located inside and outside the basin where the capital is located. The in-situ monitoring of these bodies of water faces technical, logistical, and economic difficulties, such as high installation costs, low availability of measuring stations, vandalism, and restricted access to data captured by some organizations. These difficulties hinder efficient management and informed decision-making.

Since mid-2024, Bogotá has been experiencing one of its most challenging water shortage emergencies in recent history due to the "El Niño" phenomenon that has brought reservoir levels to critical conditions. This situation has generated the need to explore new sources of hydrological data that complement on-site observations and enable the inclusion of other actors in water management decisions for this region. Satellite data emerges as a viable solution to complement gauge observations. However, consistent assessments of the accuracy of these measurements at the local level are required for this purpose. This study evaluates observations from different types of satellite data to obtain hydrological measurements in high mountain reservoirs and lakes of Bogotá's water supply system. The data assessed includes observations from the Sentinel-3 radar altimeter to get water level data, and amplitude observations from Sentinel-1 to estimate the surface area of the reservoirs.

The evaluation was initially carried out at the Neusa reservoir with daily water level measurements. Data from January 2019 to December 2020 were used for validation. Preliminary results show that Sentinel-3 observations provide water level measurements with good accuracy for the evaluated reservoir, achieving an R2 of 0.99 and RMSE of 0.084 meters (n = 24). Observations were obtained with almost monthly periodicity.

The results provide a first assessment of Sentinel-3's potential for monitoring the reservoirs of the city's water supply system, opening new opportunities for integrating different actors in water monitoring. Future research will focus on using Sentinel-1 to obtain reservoir surface area data and integrate these with level observations to calculate changes in reservoir volume. Finally, the analysis is expected to be expanded to other reservoirs and lakes in Bogotá's water supply system.