Bayesian nitrate source apportionment to individual groundwater wells in the Central Valley by use of elemental and isotopic tracers

American Geophysical Union (AGU) | July 31st, 2016

Groundwater quality is a concern in alluvial aquifers that underlie agricultural areas, such as in the San Joaquin Valley of California. Shallow domestic wells (less tha

Groundwater quality is a concern in alluvial aquifers that underlie agricultural areas, such as in the San Joaquin Valley of California. Shallow domestic wells (less than 150 m deep) in agricultural areas are often contaminated by nitrate. Agricultural and rural nitrate sources include dairy manure, synthetic fertilizers, and septic waste. Knowledge of the relative proportion that each of these sources contributes to nitrate concentration in individual wells can aid future regulatory and land management decisions. We show that nitrogen and oxygen isotopes of nitrate, boron isotopes, and iodine concentrations are a useful, novel combination of groundwater tracers to differentiate between manure, fertilizers, septic waste, and natural sources of nitrate. Furthermore, in this work, we develop a new Bayesian mixing model in which these isotopic and elemental tracers were used to estimate the probability distribution of the fractional contributions of manure, fertilizers, septic waste, and natural sources to the nitrate concentration found in an individual well. The approach was applied to 56 nitrate-impacted private domestic wells located in the San Joaquin Valley. Model analysis found that some domestic wells were clearly dominated by the manure source and suggests evidence for majority contributions from either the septic or fertilizer source for other wells. But, predictions of fractional contributions for septic and fertilizer sources were often of similar magnitude, perhaps because modeled uncertainty about the fraction of each was large. For validation of the Bayesian model, fractional estimates were compared to surrounding land use and estimated source contributions were broadly consistent with nearby land use types.

Biological sensitivities to high-resolution climate change projections in the California current marine ecosystem

Wiley | July 28th, 2022

California Simulation of Evapotranspiration of Applied Water and Agricultural Energy Use in California

Journal of Integrative Agriculture (Elsevier) | August 5th, 2013

The California Simulation of Evapotranspiration of Applied Water (Cal-SIMETAW) model is a new tool developed by the California Department of Water Resources and t

The California Simulation of Evapotranspiration of Applied Water (Cal-SIMETAW) model is a new tool developed by the California Department of Water Resources and the University of California, Davis to perform daily soil water balance and determine crop evapotranspiration (ETc), evapotranspiration of applied water (ETaw), and applied water (AW) for use in California water resources planning. ETaw is a seasonal estimate of the water needed to irrigate a crop assuming 100% irrigation efficiency. The model accounts for soils, crop coefficients, rooting depths, seepage, etc. that influence crop water balance. It provides spatial soil and climate information and it uses historical crop and land-use category information to provide seasonal water balance estimates by combinations of detailed analysis unit and county (DAU/County) over California. The result is a large data base of ETc and ETaw that will be used to update information in the new California Water Plan (CWP). The application uses the daily climate data, i.e., maximum (Tx) and minimum (Tn) temperature and precipitation (Pcp), which were derived from monthly USDA-NRCS PRISM data (PRISM Group 2011) and daily US National Climate Data Center (NCDC) climate station data to cover California on a 4 km×4 km change grid spacing. The application uses daily weather data to determine reference evapotranspiration (ETo), using the Hargreaves-Samani (HS) equation (Hargreaves and Samani 1982, 1985). Because the HS equation is based on temperature only, ETo from the HS equation were compared with CIMIS ETo at the same locations using available CIMIS data to determine correction factors to estimate CIMIS ETo from the HS ETo to account for spatial climate differences. Cal-SIMETAW also employs near real-time reference evapotranspiration (ETo) information from Spatial CIMIS, which is a model that combines weather station data and remote sensing to provide a grid of ETo information. A second database containing the available soil water holding capacity and soil depth information for all of California was also developed from the USDA-NRCS SSURGO database. The Cal-SIMETAW program also has the ability to generate daily weather data from monthly mean values for use in studying climate change scenarios and their possible impacts on water demand in the state. The key objective of this project is to improve the accuracy of water use estimates for the California Water Plan (CWP), which provides a comprehensive report on water supply, demand, and management in California. In this paper, we will discuss the model and how it determines ETaw for use in water resources planning.

California Water Plan Update 2023 (Final Version)

California Department of Water Resources (DWR) | April 3rd, 2024

Updated every five years, the Water Plan is the State’s strategic plan for sustainably and equitably managing, developing, and stewarding water resources. Required by W

Updated every five years, the Water Plan is the State’s strategic plan for sustainably and equitably managing, developing, and stewarding water resources. Required by Water Code Section 10005, the plan presents the status and trends of California’s water-dependent natural resources; water supplies; and agricultural, urban, and environmental water demands for a range of plausible future scenarios.

California Water Supply And Demand: Technical Report

Stockholm Environment Institute (SEI) | February 10th, 2011

The California Water Supply and Demand Model (CWSD) examines the ways in which California’s water supply and demand are likely to be affected by climate change; its pur

The California Water Supply and Demand Model (CWSD) examines the ways in which California’s water supply and demand are likely to be affected by climate change; its purpose is to serve as a base for quantifying these impacts in economic terms. California’s water future is modeled under conditions of no adaptation to climate change, and under several projected water use adaptation scenarios taken from the literature; climate change adaptation scenarios include water used for energy, the urban or residential sector, and agriculture. The main CWSD compares key categories of water inputs and outputs on a month-by-month basis to capture seasonality in water availability. A supplementary model allows for the main model’s beginning surface reservoir storage to result from water supply and demand interactions over a stylized previous 100 years. Three areas of water use are both especially critical and vulnerable to climatic change: the energy, agriculture, and urban sectors. In the energy module, water demand is a based on different scenarios of coal, nuclear and renewable power use, conservation technology, state population trends, and projected temperatures. In the agriculture module, crop and animal water use by county is a function of projected summer temperatures by county. In the urban module, residential, industrial/commercial, and public water use are based on projected levels of socio-economic growth.

California Winter Precipitation Change under Global Warming in the Coupled Model Intercomparison Project Phase 5 Ensemble

American Meteorological Society (AMS) | August 23rd, 2013

Projections of possible precipitation change in California under global warming have been subject to considerable uncertainty because California lies between the

Projections of possible precipitation change in California under global warming have been subject to considerable uncertainty because California lies between the region anticipated to undergo increases in precipitation at mid-to-high latitudes and regions of anticipated decrease in the subtropics. Evaluation of the large-scale model experiments for phase 5 of the Coupled Model Intercomparison Project (CMIP5) suggests a greater degree of agreement on the sign of the winter (December–February) precipitation change than in the previous such intercomparison, indicating a greater portion of California falling within the increased precipitation zone. While the resolution of global models should not be relied on for accurate depiction of topographic rainfall distribution within California, the precipitation changes depend substantially on large- scale shifts in the storm tracks arriving at the coast. Significant precipitation increases in the region arriving at the California coast are associated with an eastward extension of the region of strong Pacific jet stream, which appears to be a robust feature of the large-scale simulated changes. This suggests that effects of this jet extension in steering storm tracks toward the California coast constitute an important factor that should be assessed for impacts on incoming storm properties for high-resolution regional model assessments.

California’s Central Valley Groundwater Study: A Powerful New Tool to Assess Water Resources in California’s Central Valley

U.S. Geological Survey (USGS) | June 16th, 2009

Competition for water resources is growing throughout California, particularly in the Central Valley. Since 1980, the Central Valley’s population has nearly

Competition for water resources is growing throughout California, particularly in the Central Valley. Since 1980, the Central Valley’s population has nearly doubled to 3.8 million people. It is expected to increase to 6 million by 2020. Statewide population growth, anticipated reductions in Colorado River water deliveries, drought, and the ecological crisis in the Sacramento–San Joaquin Delta have created an intense demand for water. Tools and information can be used to help manage the Central Valley aquifer system, an important State and national resource. The U.S. Geological Survey (USGS) has released results from a study on the largest water reservoir in the State of California, the Central Valley groundwater system. The findings show continued loss of stored groundwater in the southern part of the valley (see figure below). Since about 1960, groundwater has been depleted by almost 60 million acre-feet, which is, on average, enough to supply every resident of California with water for 8 years. In order to complete the study, the USGS developed an extensive, detailed three-dimensional (3D) computer model of the hydrologic system of the Central Valley (Faunt, 2009). The Central Valley Hydrologic Model (CVHM) simultaneously accounts for changing water supply and demand across the landscape, and simulates surface water and groundwater flow across the entire Central Valley. This new hydrologic modeling tool can be used by water managers to understand how water moves through the aquifer system, predict water-supply scenarios, and address issues related to water competition in California and the Central Valley including: Conjunctive water use (interdependent use of surface water and groundwater); Conservation of agricultural land; Land-use change, including environmental concerns and urbanization, and its effects on water resources; and Effects of climate change.

CalSim 3 Results for 2070 Climate Change and Sea Level Projections and Sensitivity Analysis

California Department of Water Resources (DWR) | January 17th, 2024

This Technical Memorandum (TM) summarizes the key findings from a sensitivity analysis performed to analyze operations of the proposed Delta Conveyance Project (DCP) and

This Technical Memorandum (TM) summarizes the key findings from a sensitivity analysis performed to analyze operations of the proposed Delta Conveyance Project (DCP) and potential project water supply benefits under a range of potential scenarios for 2070 conditions. These scenarios consider climate change, sea level rise (SLR), and various water management responses. In addition, this sensitivity analysis also helps to identify whether proposed project operations and potential project impacts detailed in the Final DCP Environmental Impact Report (EIR) would remain similar or differ under a different climate change and SLR scenario under 2070 conditions, a more distant future.

CalSim II Simulation of Historical SWP-CVP Operations Technical Memorandum Report

California Department of Water Resources (DWR) | November 12th, 2003

CalSim is a generalized water resources planning tool developed jointly by the Department of Water Resources (DWR) and the US Bureau of Reclamation Mid-Pacific Region (Re

CalSim is a generalized water resources planning tool developed jointly by the Department of Water Resources (DWR) and the US Bureau of Reclamation Mid-Pacific Region (Reclamation). CalSim II is the application of the CalSim software to model the State Water Project (SWP), the federal Central Valley Project (CVP) and areas tributary to the Sacramento-San Joaquin Delta (Delta). The primary purpose of the CalSim II model is to evaluate the water supply reliability of the CVP and SWP, 1) at current or future levels of development, 2) with and without various assumed future facilities and, 3) with different modes of facilities operations. The purpose of the Historical Operations Study is to evaluate the ability of CalSim-II to represent CVP and SWP operations, in general, and the delivery capability of the projects, in particular, through the monthly simulation of recent historical conditions. The Historical Operations Study is part of a larger CalSim II evaluation process. Other components of the evaluation include a survey of the water community to gather their views and opinions of the model, a model peer review by leading academics and practitioners, and a sensitivity analysis on model inputs. It is hoped that this effort, to assess the quality and limitations of CalSim II, will lead to a wider debate about critical model issues, help direct model development in both the near and long term, and eventually lead to greater public confidence and acceptance of the model.

Carriage Water

California Department of Water Resources (DWR) | September 26th, 2001

Carriage water is defined as marginal export costs, that is, the extra water needed to carry a unit of water across the Delta to the pumping plants while maintaining a co

Carriage water is defined as marginal export costs, that is, the extra water needed to carry a unit of water across the Delta to the pumping plants while maintaining a constant salinity. Or more practically, when the exports are increased by one unit, the Sacramento flow is increased by one unit plus carriage water to maintain a constant Delta salinity. It has been known for several years that the current method of estimating carriage water in DWRSIM, called the Minimum Delta Outflow (MDO) Routine, is not particularly accurate in individual years and a better method needed. The Delta is a complex system and past attempts at developing a useful method for measuring carriage water and ultimately an MDO replacement always had at least one major flaw. An attempt was made to search for carriage water directly in the historical data, that is, to find a period of time when Net Delta Outflow (NDO) is fairly constant, but Sacramento flow and exports are increasing. If carriage water existed, salinity at interior Delta stations should increase. While there are a few times when this seems to be true (e.g. summer 1979 and 1994), the salinity increase could also be explained by antecedent conditions, that is, previous to the period of constant NDO, NDO was much higher, and the salinity increase could be simply due to the Delta gradually reaching new equilibrium. Thus it became apparent that only a model of the Delta could say anything about carriage water.