by Jay Lund

“The fact that our rivers have been relatively quiet during the last 40 years probably doesn’t mean anything; it’s just a statistical coincidence …. The problem is more psychological. We have become complacent. When we don’t experience a big flood for a while, we tend to forget just how big our floods can be. We have come to think of the federal reservoirs and our levees as protecting us from the effects of big floods, and that isn’t necessarily realistic when we consider our flood history.” John Austin (2015)

The Tulare Lake basin is unusual, even for California.  It has the most human water use of any basin in California, the greatest agricultural water use, the greatest groundwater overdraft, among the least environmental water use, and no outlet to the sea.

Having no outlet to the sea, almost all precipitation and almost water entering the Tulare basin leaves only to the atmosphere by evaporation and evapotranspiration from the landscape and agriculture (some imported water is trans-shipped to Southern California cities).  Today, with the development of extensive agriculture and reservoirs, this water overwhelmingly leaves the basin from evapotranspiration from crops (and the landscape).  Before agriculture, any water not evaporating from the upper watershed tended to pool and evaporate from Tulare Lake and its accompanying wetlands downstream (Figure 2).  This was one of the west’s largest lakes.  With completion of reservoirs on the major rivers by 1961, Tulare Lake disappeared except for partial flooding in 1969, 1983, 1997, and this year.

Tulare Basin Water Uses and Sources

Most parts of California use less water when the state as a whole is experiencing drought.  The Tulare basin’s agriculture, which is 97% of the region’s water use, actually uses substantially more water when the state as a whole is drier (Figure 3).  All of this increased water use comes from additional groundwater pumping (Figure 4). 

Groundwater use increases greatly in drier years, but remains sizable in every year.  Groundwater is the major drought buffer for the region and is the greatest supply in all but the wettest years.  No wonder Tulare Basin has about 2 maf/year of average groundwater overdraft.  This overdraft harms households and communities depending on shallow wells and requires large expenses for well deepening as groundwater levels fall, especially during droughts.

Flooding in Tulare basin this year

2023 is very wet in the Tulare basin. DWR’s runoff forecast for the four largest Tulare basin rivers show more than three hundred percent of average runoff, amounting to about 4 million acre-feet in above-average additional runoff (Table 1).  This runoff has caused local flooding on several rivers, the failure of some local levees, and the accumulation of water restoring, for a time, parts of old Tulare Lake (Moyle 2023).  Because the Tulare basin has no outlet to the sea, high flows can cause flooding on rivers and accumulate at the bottom of the basin to flood the old Tulare Lake bed.

This flooding of the old lakebed has happened only four times since the upstream dams were completed about 60 years ago, implying a recurrence interval of roughly 15 years, or an annual flood probability of about 7%. Local property owners, governments, and water and flood managers should expect to see such flooding once or twice in a career, something that is unusual, but well within the realm of reasonable expectation and preparation.

Land subsidence, from years of groundwater overdraft, have lowered the elevations of many parts of the Tulare basin.  In places, this subsidence could worsen actual and potential flooding beyond what has been prepared for (Henry 2023).

Groundwater Recharge from Floods

This windfall of 4 million acre-feet of additional runoff (perhaps more over the summer) is being eagerly sought for additional groundwater recharge and irrigation water wherever possible in this highly overdrafted basin. Managers of irrigation districts, water infrastructure managers, and farms will be diverting as much water as possible from rivers to groundwater recharge basins and some fields to increase groundwater recharge.  They know this water, while cheap this year, will become quite valuable in coming years with SGMA and drought.

This additional 4 million acre-feet of runoff is about two years of the long-term average groundwater overdraft for the basin, and about 2/3 of the roughly 6 million acre-feet/year of additional pumping that occurs in drought years (e.g., 2014 and 2015) (Lund et al. 2018).  Clearly, flood-MAR (managed aquifer recharge), while helpful, will only fractionally reduce the deep cuts in irrigation water use and irrigated land area needed to end groundwater overdraft (Alam et al. 2020).   Ending groundwater overdraft will require permanent fallowing of about 500,000 to 1 million acres of irrigated land in the basin.

In managing flooding in the old Tulare Lake bed, sometimes lake-bed land owners have built berms to shift flooding to neighbors and then used the flooded area as a reservoir for irrigating unflooded properties (Arax and Wartzman 2005).  While this behavior can be un-neighborly, it will tend to reduce groundwater pumping in the basin for that season.

What would it take to restore Tulare Lake?

Tulare Lake was historically enormous and the centerpiece of a wondrous native ecosystem in the Tulare basin (Moyle 2023; Figure 2).  Using some very rough calculations, what might be the water and land use impacts of restoring part of Tulare Lake?

The historical extent of Tulare Lake was about 650 square miles (416,000 acres) and would have evaporated about 2.5 million acre-feet of water at 6 ft of evaporation per year.  This is somewhat less than the average runoff from the basin’s major rivers.  Most cropland in the Tulare basin loses about 4 ft of water to evapotranspiration annually, so the reduced natural lake evaporation would support about 600,000 acres of cropland.  Adjacent wetlands would have evaporated additional water, and currently supports additional cropland.

The Tulare basin already experiences sizable water scarcity and groundwater overdraft of about 2 million acre-feet per year.  Eliminating this overdraft will require fallowing more than 500,000 acres of farmland.

So the effects of restoring a sizable portion of Tulare Lake permanently would be comparable or larger to the reductions in irrigated agriculture needed to end groundwater overdraft.  The combined effects of ending irrigation for both ending overdraft and restoring some of Tulare Lake would be increasing agricultural and employment losses, since greater fallowing affects more productive and profitable lands, with some compensation from the recreational benefits of partial lake restoration.  There would be many challenges and costs to restore Tulare Lake, but also some important benefits.

Conclusions

The Tulare basin and Tulare Lake have been neglected in recent decades by state, federal, and academic studies relative to the region’s statewide importance in water use, agriculture, groundwater storage and overdraft, ecosystems, and rural poverty.  The Sustainable Groundwater Management Act (SGMA) and climate change are bringing the Tulare basin’s regional and statewide importance to the fore and are helping to motivate more systematic and integrated discussions and work on this unusual and unusually important region.

California’s wet and dry climate extremes are being amplified by climate change.  This will make the management of floods, droughts, and groundwater in the Tulare basin still more important.  Eliminating these floods and droughts was never possible and will not be possible in the future.  Tulare Lake will likely re-form more frequently in the wettest years, perhaps as part of more planned overall basin management.  Preparing for such flooding events and sustaining groundwater availability for droughts will be essential for maintaining the region’s economic productivity and hopefully improving its environment.

Jay Lund is Vice-Director of the Center for Watershed Sciences and a Professor of Civil and Environmental Engineering at the University of California – Davis.  This blog is a sequel to Peter Moyle’s visionary blog post on April 16.

Further reading

Alam, S., et al. (2020), “Can Managed Aquifer Recharge Mitigate the Groundwater Overdraft in California’s Central Valley?” Water Resources Research 56, no. 8 (2020): e2020WR027244.

Arax, M. and R. Wartzman, 2005. The King of California: J. G. Boswell and the making of a secret American empire. Perseus Books. 

Austin, J.T. (2015), Floods and Droughts in the Tulare Lake Basin, 2^nd Edition, Sequoia Natural History Association, Three Rivers, CA, 500 pp.

Henry, L. (2023), “Raising a levee on sinking ground”, SJVwater.org, May 4, 2023. 

Henry, L. (2023), “Kern River water heads north through flood channel but won’t hit Tulare Lake – yet,” SJVwater.org, April 27, 2023

Lund, J.R., J. Medellin-Azuara, J. Durand, and K. Stone, “Lessons from California’s 2012-2016 Drought,” J. of Water Resources Planning and Management, Vol 144, No. 10, October 2018

Moyle, P. (2023) Lake Tulare (and its fishes) shall rise again, CaliforniaWaterBlog.com, April 16, 2023

NASA, Tulare Lake satellite images: https://earthobservatory.nasa.gov/images/151284/tulare-lake-grows

Vad, J. (2023), “Allensworth residents no longer under evacuation order but are still struggling with White River flood water, other issues,” SJVwater.org, March 30, 2023

Vad, J. (2023), “Kaweah River water managers prepare for more high water as the valley heats up,” SJVwater.org, April 27, 2023

Wikipedia, Tulare Lake, https://en.wikipedia.org/wiki/Tulare_Lake