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.

Human Costs of Nitrate-contaminated Drinking Water in the San Joaquin Valley

Pacific Institute | March 1st, 2011

While most Californians take for granted that safe water is readily available at the turn of a tap, a growing number of communities, primarily in the San Joaquin Valley a

While most Californians take for granted that safe water is readily available at the turn of a tap, a growing number of communities, primarily in the San Joaquin Valley and other agricultural areas of the state, face very real impacts from nitrate contamination of the drinking water sources serving their homes and schools. New research led by the Pacific Institute, The Human Costs of Nitrate-Contaminated Drinking Water in the San Joaquin Valley, finds that nitrate contamination of groundwater has wide-reaching effects on California’s health, economic vitality, and environmental well being, disproportionately affecting low-income households and Spanish-speaking residents. The analysis brings a stark reality check to the fore as the Central Valley Water Board considers a new regulatory program for irrigated lands, the primary source of nitrate contamination in the San Joaquin Valley. There have never been any regulatory requirements on irrigated agriculture to protect groundwater from fertilizers, which are the primary source of nitrate in the valley. Nitrate levels have increased dramatically in drinking water supplies over the last few decades. The new study, The Human Costs of Nitrate-Contaminated Drinking Water in the San Joaquin Valley, a collaboration of the Pacific Institute, Community Water Center, Clean Water Fund, and California Rural Legal Assistance Foundation, focuses on the household costs of avoiding nitrate-contaminated drinking water connected to community water systems and the costs to these systems of removing or avoiding nitrates, and it points to key policies and further research needed to better understand and resolve this entrenched challenge. The eight-county San Joaquin Valley has some of the most contaminated aquifers in the nation: 92 drinking water systems in the San Joaquin Valley had a well with nitrate levels above the legal limit from 2005-2008, potentially affecting the water quality of approximately 1.3 million residents. In addition to public water systems, the State Water Board sampled 181 domestic wells in Tulare County in 2006 and found that 40% of those tested had nitrate levels above the legal limit.

Human emissions drive recent trends in North Pacific climate variations

Nature Portfolio (Springer Nature) | August 14th, 2025

Click here for a plain language discussion of the article by co-authors Pedro N. DiNezio and Timothy M. Shanahan

Click here for a plain language discussion of the article by co-authors Pedro N. DiNezio and Timothy M. Shanahan

Human Impacts Dominate Global Loss of Lake Ecosystem Resilience

American Geophysical Union (AGU) | June 5th, 2024

Human influence on joint changes in temperature, rainfall and continental aridity

Nature Portfolio (Springer Nature) | July 6th, 2020

Despite the pervasive impact of drought on human and natural systems, the large-scale mechanisms conducive to regional drying remain poorly understood. Here we us

Despite the pervasive impact of drought on human and natural systems, the large-scale mechanisms conducive to regional drying remain poorly understood. Here we use a multivariate approach to identify two distinct externally forced fingerprints from multiple ensembles of Earth system model simulations. The leading fingerprint, FM1(x), is characterized by global warming, intensified wet–dry patterns and progressive large-scale continental aridification, largely driven by multidecadal increases in greenhouse gas (GHG) emissions. The second fingerprint, FM2(x), captures a pronounced interhemispheric temperature contrast, associated meridional shifts in the intertropical convergence zone and correlated anomalies in precipitation and aridity over California, the Sahel and India. FM2(x) exhibits nonlinear temporal behaviour: the intertropical convergence zone moves southwards before 1975 in response to increases in hemispherically asymmetric sulfate aerosol emissions, and it shifts northwards after 1975 due to reduced sulfur dioxide emissions and the GHG-induced warming of Northern Hemisphere landmasses. Both fingerprints are statistically identifiable in observations of joint changes in temperature, rainfall and aridity during 1950–2014. We show that the reliable simulation of these changes requires combined forcing by GHGs, direct and indirect effects of aerosols, and large volcanic eruptions. Our results suggest that GHG-induced aridification may be modulated regionally by future reductions in sulfate aerosol emissions.

Human Use of Restored and Naturalized Delta Landscapes

University of California, Davis (UC Davis) | October 31st, 2016

Current legislation and state plans for the California Delta call for large-scale restoration of aquatic and terrestrial habitats, which will require significant changes

Current legislation and state plans for the California Delta call for large-scale restoration of aquatic and terrestrial habitats, which will require significant changes in land uses and cultural patterns to achieve. Yet landscapes that are restored for habitat for other-than human species will remain subject to human uses. This report looks at how human presence can and will continue after restoration, and considers how these uses can be best reconciled with cultural, ecological and adaptive management goals. Our one year study builds off other research projects that have explored the California Delta from an integrative human-environment perspective. It uses a landscape planning approach that attempts to push beyond single sectoral methods, seeking a holistic integration of multiple goals and land use agendas spanning across ecological, social, economic and political domains. This report’s findings are based on surveys, interviews, review of existing Delta planning literature, field work and specific landscape case studies. In general, our research supports the advancement of a reconciliation approach, which seeks synergies between ecosystem needs and the desires of those who live, work and play in the Delta, both now and in the future.