Data on surface water bodies like rivers, dams, reservoirs, and related  flow characteristics, along with assessments for water risks, stress, and flood risk. 

freshwater

Freshwater

Data related to water scarcity, water quality, flood risk, and water stress.

water-risks

Water Risks

### Overview  
  
Groundwater table decline measures the average decline of the groundwater table as the average change for the period of study (1990-2014). The result is expressed in centimeters per year (cm/yr). Higher values indicate higher levels of unsustainable groundwater withdrawals. These values were then converted into risk scores based on the thresholds defined in the methodology. These risk scores range from low risk of decline (<0 cm/yr) to extremely high risk of decline (>8cm/yr). Values are available per aquifer as defined by the [World-wide Hydrogeological Mapping and Assessment Programme (WHYMAP)](https://www.whymap.org/whymap/EN/Home/whymap_node.html).  
  
### Methodology  
  
Aqueduct used the global hydrological model, PCRaster Global Water Balance (PCR-GLOBWB
2), to calculate five indicators. Groundwater table decline is one of those indicators and was calculated by coupling PCR-GLOBWB 2 with MODFLOW to account for lateral groundwater flow processes. This indicator used gridded 14 years of monthly groundwater heads between January 1990 and December 2014.

  
  
In mountainous areas, very deep groundwater influences the averages in mountainous cells and is not representative. These cells were therefore discarded from the calculations following the method in [de Graaf et al. (2015)](https://doi.org/10.5194/hess-19-823-2015). 

  
  
After masking the mountainous areas, the results were aggregated to groundwater aquifers derived from the [WHYMAP data set (BGR and UNESCO 2018)](https://www.whymap.org/whymap/EN/Home/whymap_node.html). 

  
  
Next, the monthly results were fit with first-order regression. The slope of this regression line (cm/yr) indicates the existence of a downward (or upward) trend. The trend was assessed using the coefficient of determination (R-squared) and the p value. If R-squared was greater than or equal to 0.9 and the p value was less than or equal to 0.05, the trend was accepted. 

  
  
Finally, raw groundwater table decline values were converted to risk scores between 0 and 5, based on quantiles. These scores were placed into categories indicating how high the risk for this indicator is. The thresholds for raw groundwater table decline values and the corresponding risk scores that were used in each category are defined below as Risk Category (Risk Scores): Raw Value Thresholds.

- Low (0-1): < 0 cm/yr
- Low to medium (1-2): 0 - 2 cm/y
- Medium to high (2-3): 2 - 8 cm/yr
- High (3-4): 4 - 8cm/yr
- Extremely high (4-5): > 8 cm/yr

  
  
For the full documentation, please see the source [methodology](https://www.wri.org/publication/aqueduct-30).  
  
### Additional Information  
  
Resource Watch shows only a subset of the dataset. For access to the full dataset and additional information, click on the “Learn more” button.  
  
### Disclaimer  
  
Excerpts of this description page were taken from the source metadata.

Aqueduct

Aqueduct Groundwater Table Decline

1990 to 2014 Groundwater Table Decline