Tulare Lake

Urban and Agricultural Water Use in California, 1960–2015

Pacific Institute | June 22nd, 2020

Water is the lifeblood of California. It provides for the household needs of 40 million people. It generates electricity and cools power plants. It supports one of the mo

Water is the lifeblood of California. It provides for the household needs of 40 million people. It generates electricity and cools power plants. It supports one of the most productive agricultural regions in the world and various commercial and industrial activities, ultimately fueling the fifth largest economy in the world. Water is also critical to the health and viability of the state’s diverse aquatic and terrestrial ecosystems. This paper examines statewide urban and agricultural water-use trends from 1960 to 2015 using data from the California Department of Water Resources (DWR). We find that California has experienced a dramatic decoupling between water use and growth. Since 1967, California’s population has doubled, and its economic output has increased by a factor of five. Yet statewide water use increased by only 20 percent over this period due to improvements in urban and agricultural efficiency, as well as a shift to higher-value crops and less water-intensive commercial and industrial activities.  Despite positive signs, water use in California remains high. Across the state, rivers and streams are under stress from overuse, and groundwater is over-tapped. Climate change and continued growth are increasing pressure on the state’s water resources, including on water supply, demand, and quality. To address these challenges, we must continue and even expand efforts to improve the water-use efficiency of our homes, businesses, industries, and farms. Moreover, we urge the state to improve data collection and online systems to make data more easily, quickly, and readily available.

Urban Water Management Plan Guidebook

California Department of Water Resources (DWR) | January 30th, 2026

In 1983, the State of California Legislature (Legislature) enacted the Urban Water Management Planning Act (UWMP Act). The UWMP Act requires an urban water supplier (Supp

In 1983, the State of California Legislature (Legislature) enacted the Urban Water Management Planning Act (UWMP Act). The UWMP Act requires an urban water supplier (Supplier) providing water for municipal purposes to more than 3,000 customers or serving more than 3,000 acre-feet annually to adopt an Urban Water Management Plan (UWMP) every five years, demonstrating water supply reliability in normal, single dry, and multiple dry water years. The UWMP Act also requires the California Department of Water Resources (DWR) to report to the Legislature on the status of UWMPs. Appendix A contains copies of the UWMP Act and other sections of the California Water Code relevant to UWMPs. Appendix B shows revisions to the UWMP Act and to Water Code. There have been no requirement changes since 2020; only definitions have been added or updated. 

User Manual for the California Central Valley Groundwater-Surface Water Simulation Model

California Department of Water Resources (DWR) | June 13th, 2013

This report describes the input and output files for the California Central Valley Groundwater-Surface Water Simulation Model (C2VSim). C2VSim is an integrated numeri

This report describes the input and output files for the California Central Valley Groundwater-Surface Water Simulation Model (C2VSim). C2VSim is an integrated numerical model simulating land surface processes and groundwater and surface water flows in the main alluvial aquifer system of California’s Central Valley (figure 1). C2VSim was developed using the Integrated Water Flow Model (IWFM) application, which couples a three-dimensional finite element groundwater simulation process with one-dimensional land surface, stream flow, lake, unsaturated zone and smallstream watershed simulation processes. The C2VSim version described in this report runs under IWFM version 3.02 and utilizes a coarse grid, and is thus referred to as version 3.02-CG. In addition, the input files for the C2VSim model are regularly updated to correct errors, incorporate improved input data or extend the simulation time period. These updates are referred to as revisions; this report describes the data in revision R374, released in June 2013. The C2VSim model inputs include monthly historical precipitation, stream inflows, surface water diversions, land use and crop acreages for the simulation period, October 1921 through September 2009. C2VSim dynamically calculates crop water demands, allocates contributions from precipitation, soil moisture and surface water diversions, and calculates the groundwater pumpage required to meet the remaining demand. The coarse grid version of the C2VSim model incorporates a finite element grid with 1392 elements, grouped into 21 water budget subregions (figure 1), which are further grouped by drainage basin into five hydrologic regions. The model subregions are based on Depletion Study Areas (DSAs), originally created by the DWR Division of Planning for estimating regional water supplies and demands. Hydrologic parameters (including hydraulic conductivities, storage parameters and recession coefficients) were calibrated to match observed values including groundwater heads, groundwater head differences between well pairs, surface water flows, and stream-groundwater flows for the period between September 1975 and October 2003. The model simulates the historical response of the Central Valley’s groundwater flow system to historical stresses, and can also be used to simulate the response to projected future stresses. Agricultural groundwater pumping is not monitored in the Central Valley, and the C2VSim model provides pumpage estimates that are considered robust because they are constrained spatially and temporally by the estimated demand and surface water supplies. The calibrated model is also being used as the basis for the groundwater flow component of CalSim 3, a water resources planning model for simulating operation of the California State Water Project (SWP) and Federal Central Valley Project (CVP).

Using Landsat and MODIS satellite collections to examine extent, timing, and potential impacts of surface water inundation in California croplands

Remote Sensing Applications: Society and Environment (RSASE) | October 1st, 2022

The state of California, United States of America produces many crop products that are both utilized domestically and exported throughout the world. With nearly 39,000 km

The state of California, United States of America produces many crop products that are both utilized domestically and exported throughout the world. With nearly 39,000 km2 of croplands, monitoring unintentional and intentional surface water inundation is important for water resource management and flood hazard readiness. We examine inundation dynamics in California croplands from 2003 to 2020 by intersecting monthly surface water maps (n = 216 months) derived using two satellite remote sensing platforms (Landsat and Moderate Resolution Imaging Spectroradiometer [MODIS]) with a high-quality cropland map generated by the California Department of Water Resources. Surface water maps were produced using the Dynamic Surface Water Extent model, in which satellite image pixels are classified into different levels of detection confidence. Our analysis focused on calculating monthly and annual occurrence of “high confidence” water for each satellite collection across eight cropland types and 58 counties. Results indicate that 49.9% (MODIS) to 56.4% (Landsat) of croplands were inundated at least once during the 18-year timespan. Rice crops, due to their unique need of consistent surface water and dominance as a crop type in CA, had the highest proportion of and mean annual inundation area, while citrus crops had the lowest. Mean monthly inundation patterns in most croplands followed California's precipitation patterns with high inundation during the winter and spring rainy season. At the county level, croplands in the southern Central Valley typically had high occurrences of inundation in conjunction with large crop areas. Exposure and sensitivity of inundation for three crop types (citrus, deciduous, and vineyards) that are typically less associated with intentional inundation were geographically variable, but overall were generally highest in counties in the southern Central Valley, California's primary agricultural region. Flood and precipitation related crop insurance claims indicated that rice had the highest mean indemnity payout for any month with damages typically occurring in March and April. Insurance claims were also high in deciduous fruit and nut crops, which had peak damages in February. A comparison between inundation results and insurance claims suggests that the inundation mapped by our process coincides with claim activity. These data elucidate water inundation patterns across the state that can serve to inform farmers, insurers, decision makers, resource managers, and flood mitigation professionals.

Using machine learning to predict 1,2,3-trichloropropane contamination from legacy non-point source pollution of groundwater in California's Central Valley

Elsevier | May 6th, 2023

1,2,3-tricholoropropane (TCP) is an impurity common in nematicides applied to agricultural soils from the 1940s to the 1980s. Evidence from animal studies indicates t

1,2,3-tricholoropropane (TCP) is an impurity common in nematicides applied to agricultural soils from the 1940s to the 1980s. Evidence from animal studies indicates that TCP is a probable human carcinogen. TCP leaches through the soil into groundwater where it persists and contaminates thousands of wells in Asia, Europe, and North America. In California, TCP contaminates drinking water wells, with the highest levels of TCP beneath agricultural land used to grow grapevines. This study performs a mass balance and evaluates the ability of three types of tree-based machine learning models to predict TCP concentration in California's Central Valley aquifer system: classification and regression trees (CART), Random Forest (RF), and Boosted Regression Trees (BRT). To construct the models, multiple spatial explanatory variables were used, including historical agricultural land use data, irrigation levels, precipitation, soil type, groundwater age, redox state, and the presence of the co-contaminant nitrate. To estimate the amount of TCP applied to farmland in California, state historical pesticide and land use documents were used in the mass balance. Between 110,000 and 4,300,000 kg of TCP are estimated to have accumulated in the subsurface. Machine learning models indicate that the most important explanatory variables to predict TCP contamination of groundwater are precipitation, redox state, and the presence of the co-contaminant nitrate. Additionally, a 1000-m buffer area offers a slightly higher predictive performance as compared to 500-m and 1500-m buffers. Furthermore, the RF model outperforms CART and BRT for predictive performance. Finally, modeling using decision trees can predict TCP contamination levels in areas where monitoring is lacking, help target future TCP monitoring efforts, and aid in identifying areas to avoid when drilling new drinking water wells.

Using Sentinel‐1 and GRACE satellite data to monitor the hydrological variations within the Tulare Basin, California

Nature Portfolio (Springer Nature) | March 9th, 2022

Subsidence induced by groundwater depletion is a grave problem in many regions around the world, leading to a permanent loss of groundwater storage within an aquifer and

Subsidence induced by groundwater depletion is a grave problem in many regions around the world, leading to a permanent loss of groundwater storage within an aquifer and even producing structural damage at the Earth’s surface. California’s Tulare Basin is no exception, experiencing about a meter of subsidence between 2015 and 2020. However, understanding the relationship between changes in groundwater volumes and ground deformation has proven difficult. We employ surface displacement measurements from Interferometric Synthetic Aperture Radar (InSAR) and gravimetric estimates of terrestrial water storage from the Gravity Recovery and Climate Experiment (GRACE) satellite pair to characterize the hydrological dynamics within the Tulare basin. The removal of the long-term aquifer compaction from the InSAR time series reveals coherent short-term variations that correlate with hydrological features. For example, in the winter of 2018–2019 uplift is observed at the confluence of several rivers and streams that drain into the southeastern edge of the basin. These observations, combined with estimates of mass changes obtained from the orbiting GRACE satellites, form the basis for imaging the monthly spatial variations in water volumes. This approach facilitates the quick and effective synthesis of InSAR and gravimetric datasets and will aid efforts to improve our understanding and management of groundwater resources around the world.

Water Accounting in Western US, Australia, and Spain: Comparative Analysis

American Society of Civil Engineers (ASCE) | January 10th, 2020

Water Allocation in California - Legal Rights and Reform Needs

Golden Gate University (GSU) | March 31st, 1982

FOREWARD: Water supply, allocation, use and conservation are constantly debated in California, often appearing as highly charged political issues in candidates' races and

FOREWARD: Water supply, allocation, use and conservation are constantly debated in California, often appearing as highly charged political issues in candidates' races and on election ballots. This year is no exception, with major ballot propositions already scheduled for the June primary election and being circulated to qualify for the November general election. Accordingly this Research Paper on legal aspects of water allocation is being published for the valuable background it affords readers wishing to learn more about the subject. The author draws on his legal expertise, as well as his experience as Staff Director of the Governor's Commission to Review California Water Rights Law. The paper emphasizes the crucial role of water rights in California water management, and it points to the need for and present lack of a political consensus on water law reform. The author concludes by suggesting forces that could bring about interest-group realignments and other developments favorable to achieving the needed consensus on water law and management reform that so far has eluded Californians. Stanley Scott Assistant Director Institute of Governmental Studies March 1982

Water and Energy in California

Public Policy Institute of California (PPIC) | December 6th, 2022

Water and the Future of the San Joaquin Valley

Public Policy Institute of California (PPIC) | February 14th, 2019

The San Joaquin Valley—California’s largest agricultural region and an important contributor to the nation’s food supply—is in a time of great change. The valle

The San Joaquin Valley—California’s largest agricultural region and an important contributor to the nation’s food supply—is in a time of great change. The valley is ground zero for many of California’s most difficult water management problems—including groundwater overdraft, drinking water contamination, and declines in habitat and native species. Local water supplies are limited, particularly in the southern half of the region. To irrigate their crops, many farmers use water imported from the Sacramento–San Joaquin Delta. But in many places farmers have also relied on groundwater overdraft—pumping groundwater in excess of the rate at which it is replenished. Worsening droughts, increasing regulations to protect endangered native fishes, and growing demand by Southern California for Delta imports have compounded surface water scarcity. The state’s Sustainable Groundwater Management Act (SGMA) requires local water users to bring groundwater use to sustainable levels by the early 2040s. This will have a broad impact on valley agriculture and the regional economy in coming years—likely including some permanent idling of farmland. This report explores three key challenges facing the San Joaquin Valley and reviews the most promising approaches to address them:  Balancing water supplies and demands. To close the groundwater deficit, groundwater sustainability agencies in the valley’s overdrafted basins will have to augment supplies, reduce demands, or use some combination of these two approaches. A range of options are under consideration but they are not equally effective or practical.  Addressing groundwater quality challenges. Poor groundwater quality impairs drinking water supplies in disadvantaged rural communities, reduces long-term agricultural prosperity, and degrades ecosystems. Providing safe drinking water is an urgent priority. Over the longer term, parties will also need to manage water quantity and quality together, to take advantage of synergies and avoid unintended consequences. The necessary coordination will be challenging because the various programs addressing valley water quality issues are carried out by numerous local and regional entities, whose lines of responsibility and geographic boundaries do not neatly align.  Fostering beneficial water and land use transitions. Effectively addressing water scarcity and the resulting land use changes in the San Joaquin Valley offers opportunities to put lands coming out of production to good use—and gain “more pop per drop” from limited water resources. Multiple-benefit approaches to water and land management can enhance groundwater recharge and improve air and water quality. They can also promote healthier soils, new recreational opportunities, additional flood protection, improved habitat, and new revenue streams for private landowners engaging in conservation-oriented management. Addressing these complex and intertwined issues requires significant changes in water and land management and a major ramp-up in cooperation and coordination among a wide circle of stakeholders. Pursuing solutions that deliver multiple benefits will boost the chances of success overall. The entire region—and California as a whole—will benefit if solutions to these challenges are cost-effective and support the valley’s economy while improving public health and the natural environment.