Assemblage of satellite information to produce insights into ground-water storage in Colombia’s five major basins

Measuring the existing amount of groundwater in a specific region is no easy task. It is well known that this resource is one of the hardest to acquire and at the same time it is close to one third of existing freshwater on the earth. Satellite data stands as a convenient source of information in developing countries where groundwater levels monitoring remains scarce, but groundwater pressure keeps rising because of the increase of population and global climatic changes.

In this work, satellite data from the World GRACE Land Water Equivalent and GLDAS Terrestrial Water Storage measurement programs were downloaded and processed using the programming language Python. By applying a simple hydrological balance and masking the worldwide downloaded information to Colombia’s extent, groundwater anomalies were estimated.

 Different representations were used in order to comprehend groundwater anomalies data under its possible scopes: geographic, temporal, and extreme value analysis were made for the Colombian region and its five major basins, finding useful information about each region like average, minimum, and maximum values; time-related behavior was observed in early and late times from measurement timestamps; extreme value heat maps allowed us to identify historical geographic outlier regions; a mean value heat map was generated for the full time span of measurement as a reference value for each region; finally, a combined scope helped us identify extreme events geographically and temporally.

As a result, among the observations studied since the first GRACE mission in 2002, until the last downloaded information in February 2023, the Pacific basin showed the least fluctuations in groundwater storage anomalies. This behavior can be attributed to the high precipitation rates in this region and likely the soil's saturation state. Meanwhile, in the Caribbean region, the fluctuations were significant, with a strong tendency toward groundwater depletion. This unique behavior may be linked to the region's geographic exposure to climatic phenomena like El Niño/La Niña.

Lastly, leveraging diverse perspectives on groundwater, we conducted focused seasonal analyses to comprehend its behavior under El Niño and La Niña conditions. We also performed a brief comparison to assess the resemblance between precipitation patterns and groundwater estimations. Considering the Oceanic Niño Index (ONI) for the 2009-2012 La Niña period, groundwater anomalies were generally positive across all studied basins. Conversely, during the 2014-2017 El Niño period, anomalies were predominantly negative, particularly in the Caribbean and Magdalena Cauca basins, highlighting their vulnerability to these climatic phenomena.