# Two Decades of Groundwater Variability in Peru Using Satellite Gravimetry Data
## 5 Conclusions  
This study offers the first comprehensive assessment of GWS variability in Peru from 2003 to 2023 using satellite gravimetry data (GRACE and GRACE-FO). The findings reveal a significant decline in GWS--ranging from 30% to 40%--in coastal and Andean regions (e.g., Piura, Lambayeque, Lima, Ica, Arequipa, Mougugua, Tacna), corroborated by in situ well data. In contrast, the Amazon region remained relatively stable, likely due to high recharge rates, although deforestation observed during the study period poses a risk to this stability. Climatic variability, primarily driven by El Nino and La Nina events, accounted for up to 70% of water storage fluctuations in the Amazon region. In contrast, aquifer depletion in coastal and agricultural zones was predominantly attributed to anthropogenic overextraction (60-80%). This study not only provides critical insights for Peru but also serves as a model for other regions with diverse hydrogeological settings facing similar groundwater depletion challenges. The socioeconomic consequences of groundwater depletion are severe: rising costs for urban water supply (notably in Lima), stress on export-oriented agriculture, and threats to the water security of rural populations. To confront this crisis, we recommend the following:  
1. Launching pilot projects for artificial aquifer recharge in high-risk areas. 2. Enforcing strict groundwater extraction regulations, paired with efficient irrigation technologies. Developing a national monitoring and early warning system based on GRACE data and an expanded network of observation wells. Given GRACE's coarse spatial resolution (~300 km), results should be further refined using high-resolution hydrological models such as MODFLOW (~1 km). Additionally, we recommend establishing at least 50 new monitoring wells strategically distributed across critical aquifers. Groundwater management should be informed by natural recharge rates rather than reactive extraction thresholds, ensuring long-term sustainability and system resilience. Implementing the recommended measures requires strategic capital investment. Based on international benchmarks, launching pilot artificial recharge projects in critical aquifers (e.g., Ica, Tacna, Lima) would require approximately USD 3-9 million. Transitioning to efficient irrigation technologies across 10,000 priority hectares may demand an additional USD 12-20 million. Establishing a national monitoring and early warning system, including 50 new wells and a digital platform integrating GRACE and hydrological models, would cost around USD 1.75-3 million. Thus, a targeted initial investment of USD 17-32 million could enable sustainable groundwater management in Peru's most vulnerable regions, with high socioeconomic and environmental returns. Conceptualization: E.G., methodology: E.G. and V.A., software: V.A., validation: E.G. and K.G., formal analysis: all authors, investigation: E.G., V.A. and K.G., resources: E.G. and K.G., data curation, E.G., writing--original draft preparation: all authors, writing--review and editing: all authors, supervision: E.G. All authors have read and agreed to the published version of the manuscript. This research received no external funding. Not applicable. The data presented in this study are available in [GRACE Tellus] at [[https://hydrol.gesdisc.eosdis.nasa.gov/data/GRACEDA/GRACEDADM_CLSM025](https://hydrol.gesdisc.eosdis.nasa.gov/data/GRACEDA/GRACEDADM_CLSM025) GL_7D.3.0/]([https://hydrol.gesdisc.eosdis.nasa.gov/data/GRACEDA/GRACEDADM_CLSM025](https://hydrol.gesdisc.eosdis.nasa.gov/data/GRACEDA/GRACEDADM_CLSM025) GL_7D.3.0/) (accessed on 15 November 2023). Special thanks to [PERSON] for his technical review. The authors declare no conflicts of interest. The funders had no involvement in the study design; data collection, analysis, or interpretation; manuscript preparation; or the decision to publish the results.