# Two Decades of Groundwater Variability in Peru Using Satellite Gravimetry Data
## 3 Results
### GWS Trend in Peru (2003-2023)
#### 3.1.1 Regional GWS Variability  
From 2003 to 2023, GWS in Peru showed a consistently declining trend across the Northern, Central, and Southern climatic zones, with 95% confidence intervals (\(\pm\)5% uncertainty). Figure 4 shows a sustained decline in GWS across Peru's three regions, with  
Figure 3: **(a)** Spatial distribution of groundwater storage percentiles in Peru (2003–2014), indicating conditions from extreme drought (percentile 0–10, red color) to extreme storage (percentile 90–100, blue color). **(b)** Spatial distribution of groundwater storage percentiles in Peru (2003–2014), indicating conditions from extreme drought (percentile 0–10, red color) to extreme storage (percentile 90–100, blue color).  
proportional decreases ranging from 30% to 40%. Although the curves appear nearly parallel--suggesting a possible climatic control--precipitation remained stable, ruling it out as the main cause. Instead, intensive overextraction is identified as the primary common driver of depletion. A temporary increase in 2017 coincides with the Coastal El Nino event, which triggered short-term aquifer recharge; however, the downward trend resumed immediately afterward, indicating that anthropogenic pressures far outweigh the effects of episodic climatic inputs. -  
The **Southern Zone** experienced the steepest and most sustained depletion, dropping from ~70% in 2003 to a critical low of 32% by 2023, reflecting the relative level of groundwater storage with respect to its estimated historical capacity. The decline observed in the Southern Zone is not attributed to reduced precipitation--which remained virtually stable--but rather to intensive overextraction and limited natural recharge typical of this arid region. This interpretation is supported by satellite data and recorded extraction rates. -  
The **Central Zone** declined from ~75% to 44%, with notable drops during 2007-2010 and 2015-2023, despite a brief recovery to ~70% around 2014. -  
The **Northern Zone** started at ~80%, declined to ~65% by 2010, partially recovered (~75%) around 2011-2014, but ultimately fell to 45% by 2023.  
These trends reflect the combined impact of extreme climatic events (e.g., El Nino and La Nina) and anthropogenic pressures, with the Southern Zone being the most critically affected, underscoring the urgent need for integrated groundwater management.  
Table 2 summarizes the most critical periods of GWS decline across Peru's three main regions--North, Central, and South--between 2003 and 2023. The table highlights the years  
Figure 4: Annual GWS variability in Peru (2003–2023) across Northern, Central, and Southern climatic zones. The curves reveal a general downward trend in GWS, with the Southern zone exhibiting the most severe depletion. Values are expressed as percentages relative to the historical maximum observed during the 2003–2023 period. Shaded areas represent the 95% confidence intervals (\(\pm\)5% uncertainty). These results reflect the influence of both extreme climatic events (e.g., El Nino, La Nina) and anthropogenic extraction, with the Southern region experiencing the highest stress on groundwater reserves.  
with the most severe depletion, the regions most affected, and the overall trend in GWS reduction by percentage. This comparative overview allows for a quick identification of the areas under greatest hydrological stress, which is essential for targeted water management interventions. Appendix A (Table A7) presents a detailed overview of GWS variability by zone from 2003 to 2023.  
Figure 5 illustrates visible trends. The Chillon-Rimac (located in the Lima metropolitan area) aquifer exhibits the highest extraction rates, primarily driven by Lima's high demand, which proportionally contributes to groundwater decline. Aquifers such as Caplina and Lurin demonstrate high deficits relative to recharge, suggesting increased vulnerability, while Tumbes exhibits a more balanced behavior, probably due to monsoon recharge.