Climate Change Impacts on Groundwater: More Than Just Drought

We all know that a lack of precipitation (AKA drought) impacts groundwater recharge. But few know the proportionality between changes of precipitation and recharge. For example, does 10% less precipitation cause 10% less recharge? To illustrate this distinction, precipitation examples are shown which produce the same amount of annual precipitation, but when applied to hydrology models they yield quite different reductions of recharge.

Statistically significant trends in precipitation timing patterns have been calculated from the decades of daily climate observations from many weather stations. Applying these timing trends to local basin hydrology models without any change in total precipitation, produces substantial changes in recharge.

Change of temperature alone might cause impacts on groundwater recharge. The ET fraction of total precipitation can be quite high at 50%–70%. Therefore even a moderate increase in such ET could represent a considerable water loss. This is demonstrated by applying the predicted 7°F temperature increase to basins and showing the impacts on groundwater recharge.

Predictions of West Coast sea level rise are as much as 4½ feet. Coastal basins can only be protected from the additional seawater intrusion induced by this sea level rise through a corresponding rise of inland water levels. It is shown how such a protective action can be translated into a virtual loss of recharge. In other words, some recharge has no value for gaining supplemental supply, but instead just worthwhile for offsetting sea level rise impacts.

Note that I did present a similar talk at the NGWA conference last month in New Mexico. Dr. John Hawley, another presenter, said I need to be a keynote speaker in as many water meetings as possible. With such encouragement I am trying to see if you have an interest in this talk too.