How can we support the development of robust groundwater sustainability plans?

California Agriculture (UCANR) | March 13th, 2018

Three years after California passed the Sustainable Groundwater Management Act (SMGA), groundwater sustainability agencies (GSAs) are now preparing to develop their groun

Three years after California passed the Sustainable Groundwater Management Act (SMGA), groundwater sustainability agencies (GSAs) are now preparing to develop their groundwater sustainability plans (GSPs), the blueprints that will outline each basin’s road to sustainability. Successful GSPs will require an effective participatory decision-making process. We tested a participatory process with the Yolo County Flood Control and Water Conservation District, a water-limited irrigation district in the Central Valley. First, we worked with district stakeholders to outline the parts of the plan and set measureable objectives for sustainability. The district defined seven management strategies, which the research team evaluated against climate, land use and regulatory uncertainties using a water resources model. Together, we explored model results using customized interactive graphics. We found that the business-as-usual strategy was the most unlikely to meet sustainability objectives; and that a conjunctive use strategy, with winter groundwater recharge and periphery ponds storage, achieved acceptable measures of sustainability under multiple uncertainties, including a hypothetical pumping curtailment. The process developed a shared understanding of the vulnerabilities of the local groundwater situation and proved valuable in evaluating strategies to overcome them.

How freeing rivers can help California ease flood risks and revive ecosystems

Los Angeles Times | February 20th, 2024

Natural floodplains — the lush green lands along rivers that historically flooded, retained water, and nourished life in the heart of the valley — were mostly drained

Natural floodplains — the lush green lands along rivers that historically flooded, retained water, and nourished life in the heart of the valley — were mostly drained and converted to farmland generations ago as the state’s waters were dammed and diverted. Today, an effort to bring back some of those floodplains is flourishing at the 2,100-acre Dos Rios Ranch Preserve near Modesto, where workers years ago planted native trees on retired farm fields and removed berms to create space for water to spread out again.

How much potable water is saved by wastewater recycling? Quasi-experimental evidence from California

Resources, Conservation & Recycling (Elsevier) | October 6th, 2021

Recently, California has made large investments in wastewater recycling to replace applications that use potable water. It may be expected that the use of recycled water

Recently, California has made large investments in wastewater recycling to replace applications that use potable water. It may be expected that the use of recycled water reduces potable water use, but such an equivalency is not assured. The addition of recycled water infrastructure in a large Californian water district creates a natural experiment where this work tests how recycled water usage affects primary potable water. This is done using econometric methods for causal inference in an observational setting that mirror a randomized control trial (RCT). From 2001 to 2014, a number of public parks were given recycled water infrastructure, while others in those regions remained exclusively on potable supply. A two-way fixed effects regression is used to produce a difference-in-differences estimate of the average treatment effect of recycled water on total and potable water usage. The results indicate that potable water usage is reduced significantly when a park is connected to the recycled water supply. The estimated rate of displacement in the study period is 81.7%, meaning each unit of recycled water use avoided 0.817 units of potable water usage, which implies the connection of parks to recycled water supply increases total water use. The analysis provides, to the best of our knowledge, the first empirical estimate of the water savings claimed by urban water recycling programs, and the first empirical estimate of displacement using quasi-experimental methods. The methodology can be utilized to evaluate the effectiveness of recycling programs around the world.

How Much Snow?

Scientific American | March 1st, 1939

Last winter, at 682 different locations in the Rockies and high Sierras, more than 30,000 exact measurements of snow depth and water content were taken, in order to e

Last winter, at 682 different locations in the Rockies and high Sierras, more than 30,000 exact measurements of snow depth and water content were taken, in order to estimate how much water the mountain snowfields would supply in the run-off during summer months. To make this survey cost more than $100,000. On it was predicated the expenditure, and saving, of millions. While the science of surveying snow is still in its infancy, its extent and importance are increasing rapidly. Ridiculed at first, in the last few years it has taken on world-wide aspects. To grasp its significance in our western states, picture a series of snow-covered mountain ranges that by their streams make life possible in dry intervening valleys. Abundant snow means abundant water. Abundant water means power, and cheap electricity. More important still, it means abundant crops. Dearth of snowfall in the mountains means dry river beds in August, machinery standing idle, thirsty cattle, and dying plants.

How Native Americans will Shape the Future of Water in the West

New Yorker | January 27th, 2023

As a child, Stephen Lewis heard stories about a river that, for the most part, no longer flowed. “How I grew up was that it was a theft, that it was stolen from us,”

As a child, Stephen Lewis heard stories about a river that, for the most part, no longer flowed. “How I grew up was that it was a theft, that it was stolen from us,” he told me late last year. “There was what we used to call the Mighty Gila River, and now it was just pretty much dry. There was no water.” Lewis is the governor of the Gila River Indian Community (gric), a group that has occupied land south of Phoenix for centuries. When I met him, in the dining room of the Whirlwind Golf Club, which the tribe owns, Lewis had recently returned from Santa Fe. There, he’d attended a celebration marking the centennial of the Colorado River Compact, an agreement that continues to shape water politics in the Southwest. In Santa Fe, Lewis took note of a black-and-white photograph of the compact’s signers—white men in dark jackets, gathered around a wooden desk.

How to address agriculture’s water woes

Nature Portfolio (Springer Nature) | June 19th, 2024

How unusual is the 2012–2014 California drought?

American Geophysical Union (AGU) | December 30th, 2014

For the past three years (2012–2014), California has experienced the most severe drought conditions in its last century. But how unusual is this event? Here we use two

For the past three years (2012–2014), California has experienced the most severe drought conditions in its last century. But how unusual is this event? Here we use two paleoclimate reconstructions of drought and precipitation for Central and Southern California to place this current event in the context of the last millennium. We demonstrate that while 3 year periods of persistent below-average soil moisture are not uncommon, the current event is the most severe drought in the last 1200 years, with single year (2014) and accumulated moisture deficits worse than any previous continuous span of dry years. Tree ring chronologies extended through the 2014 growing season reveal that precipitation during the drought has been anomalously low but not outside the range of natural variability. The current California drought is exceptionally severe in the context of at least the last millennium and is driven by reduced though not unprecedented precipitation and record high temperatures.

Hudson v. Dailey

Supreme Court of California | December 1st, 1909

Human alteration of global surface water storage variability

Nature Portfolio (Springer Nature) | March 3rd, 2021

Knowing the extent of human influence on the global hydrological cycle is essential for the sustainability of freshwater resources on Earth. However, a lack of water leve

Knowing the extent of human influence on the global hydrological cycle is essential for the sustainability of freshwater resources on Earth. However, a lack of water level observations for the world’s ponds, lakes and reservoirs has limited the quantification of human-managed (reservoir) changes in surface water storage compared to its natural variability. The global storage variability in surface water bodies and the extent to which it is altered by humans therefore remain unknown. Here we show that 57 per cent of the Earth’s seasonal surface water storage variability occurs in human-managed reservoirs. Using measurements from NASA’s ICESat-2 satellite laser altimeter, which was launched in late 2018, we assemble an extensive global water level dataset that quantifies water level variability for 227,386 water bodies from October 2018 to July 2020. We find that seasonal variability in human-managed reservoirs averages 0.86 metres, whereas natural water bodies vary by only 0.22 metres. Natural variability in surface water storage is greatest in tropical basins, whereas human-managed variability is greatest in the Middle East, southern Africa and the western USA. Strong regional patterns are also found, with human influence driving 67 per cent of surface water storage variability south of 45 degrees north and nearly 100 per cent in certain arid and semi-arid regions. As economic development, population growth and climate change continue to pressure global water resources, our approach provides a useful baseline from which ICESat-2 and future satellite missions will be able to track human modifications to the global hydrologic cycle.

Human contributions to evapotranspiration mitigate swings in dry-to-wet year transitions

Nature Portfolio (Springer Nature) | January 9th, 2026

California’s food and economic security depends on water availability, particularly under increasingly extreme climate scenarios. A key component of the water balance i

California’s food and economic security depends on water availability, particularly under increasingly extreme climate scenarios. A key component of the water balance is evapotranspiration, the combination of soil and surface evaporation and plant transpiration. Evapotranspiration is influenced by natural drivers (e.g., climate, vegetation cover) and human intervention (e.g., irrigation, land management). Here, we analyze the transition between one of California’s driest years (2022) to an exceptionally wet year (2023) to assess evapotranspiration responses to climate extremes. Despite increased precipitation, total statewide evapotranspiration changed less than 10%. In 2022, human contributions accounted for 30% of statewide evapotranspiration and 80% in managed lands. In 2023, natural evapotranspiration increased, and human contributions fell by 30%, yet still comprised nearly 50% of evapotranspiration in managed areas. Our findings underscore the enduring role of human activity on California’s hydrology, even during wet years, and demonstrate a framework to separate natural and anthropogenic controls on evapotranspiration.