UC Santa Cruz

ABSTRACT

Climate change projections are for higher temperatures and extreme droughts by the end of the 21st century. This will alter the natural recharge of groundwater, including decreased inflow from runoff, increased evaporative losses, and warmer and shorter winter seasons, impacts that are likely to exacerbate already existing groundwater overdraft in many basins. Additionally, the imported surface water that can be delivered from the Central Valley Project (CVP) and State Water Project (SWP) to areas reliant on this water for groundwater recharge and consumptive use is projected to be less reliable and more expensive. Yet groundwater is a critical water supply source during drought when it compensates for reduced surface water supplies. The need for proactive adaptation strategies to address the extreme droughts projected under climate change are frequently discussed, yet there are limited examples of such groundwater management strategies. This paper therefore explores:

1) How groundwater management agencies are planning for drought

2) What new approaches are currently being used that show promise for addressing the more extreme droughts projected under climate change?

First, the paper provides a review of the research on drought and groundwater management including strategies currently used to address drought. Second, case studies illustrate newer and varied approaches being used to reduce drought impacts. Highlighted are the different approaches used by groundwater managers to both increase storage and develop drought reserves. These strategies can help to reduce vulnerability to the extreme droughts projected under climate change. Two additional case studies discuss the limits of a drought reserve strategy and indicate that more is needed under climate change to address the range of basin conditions and the varied needs of communities reliant on groundwater.

Several overall groundwater management trends are noted:

A shift from voluntary to mandatory requirements for the sustainable management of groundwater after the 2014 passage of SGMA; An increase in the use of recycled water from 190,000 AF in 1976 to 714,000 AF in 2016 that can be used for groundwater recharge to enhance storage; An increase in the development of groundwater drought reserves;

Suggested future research projects include:

Benefits and challenges of long-term strategies to manage groundwater under climate change and extreme droughts; Practices implemented during past droughts that were effective in reducing drought vulnerability in subsequent droughts

The different approaches presented in this paper to increase groundwater storage specifically for use during drought are important first steps to proactively manage groundwater to adapt to the higher temperatures and future extreme droughts projected under climate change.

Keywords: drought, climate change, groundwater management strategies, drought reserves