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 Sustainable Groundwater Legislation and Dairy Business Impact – California Irrigation Institute - 2017

California Irrigation Institute | January 30th, 2017

I have been asked to discuss my thoughts on the effect of SGMA upon the dairy industry. As the General Manager of Stevinson Water District in Merced County, and from a si

I have been asked to discuss my thoughts on the effect of SGMA upon the dairy industry. As the General Manager of Stevinson Water District in Merced County, and from a six-generation California dairy farming family, I have been quite involved in both in dairy farming, the production of milk and the rapidly changing agricultural water business. Most recently, I have been involved in the development of Groundwater Sustainable Agency in the Merced Basin. My comments are based both from my experiences and from information gathered from CDFA agricultural statistics, House of Representative Devin Nunes presentation to his constituencies in September 2016, and from conversations with civil water engineers in the south San Joaquin Valley. -From California Irrigation Institute 2017 Conference: Managing our Water Checkbook: Solutions for a Balanced Bottomline

California Water Plan 2013: Sacramento River Hydrologic Region Report

California Department of Water Resources (DWR) | October 30th, 2014

The Sacramento River Hydrologic Region (see Figure SR-1 includes the entire California drainage area of the Sacramento River (the state’s largest river) and its tributa

The Sacramento River Hydrologic Region (see Figure SR-1 includes the entire California drainage area of the Sacramento River (the state’s largest river) and its tributaries. The region extends from Chipps Island in Solano County north to Goose Lake in Modoc County. It is bounded by the Sierra Nevada on the east, the Coast Ranges on the west, the Cascade and Trinity mountains on the north, and the Sacramento-San Joaquin River Delta (Delta) on the south.  The Sacramento River Basin actually begins in Oregon, north of Goose Lake, a near-sink that intercepts the Pit River drainage at the California-Oregon border. Some key issues for this region are summarized here and discussed further later in this report. Agriculture. Between 2005 and 2010, the region supported about 1.95 million acres of irrigated agriculture on average. Approximately 1.58 million acres is irrigated on the valley floor. The surrounding mountain valleys add about 370,000 irrigated acres to the region’s total — primarily as pasture and alfalfa. The gross value of agricultural production in the Sacramento Valley for 2011 was about $4.1 billion (California Department of Food and Agriculture 2013). Rice and walnuts are the highest grossing crops in the region followed by almonds and tomatoes. The direct, indirect, and induced effects of the agricultural industry to the regional economy are discussed in this report. Groundwater. With a 2005-2010 average annual extraction volume of 2.7 million acre-feet (maf), groundwater pumping in the Sacramento River Hydrologic Region accounts for 17 percent of all the groundwater extraction in California — the third highest among the 10 hydrologic regions in California, behind Tulare Lake Hydrologic Region with 38 percent and San Joaquin River Hydrologic Region with 19 percent of the total. Overall, groundwater contributes to about 31 percent of the total water supply. Most groundwater extraction in the region occurs for agricultural water use (2.4 maf), meeting about one-third of agricultural water demands. Groundwater extraction for urban water use is significantly less (465 thousand acre-feet [taf]), which meets about half of the urban water needs. Groundwater levels for much of the region have declined from 2005 to 2010. Groundwater level declines ranging from 20 to 30 feet are seen in the northwestern portion of the Sacramento Valley Groundwater Basin. Declines ranging from to 10 to 20 feet are seen in the northern, the mid- to south-western, and the southeastern portions of the valley. For the rest of the Sacramento Valley Groundwater Basin and the Redding Area Groundwater Basin, groundwater level declines have ranged from zero to 10 feet. Flood. Exposure to a 500-year flood event in the region threatens approximately one in three residents, almost $65 billion in assets (crops, buildings, and public infrastructure), 1.2 million acres of agricultural land, and over 340 sensitive species. Almost 95 percent of Sutter County residents, more than 55 percent of Yuba County and Yolo County residents, and more than 50 percent of agricultural land region-wide are exposed to the 500-year flood event. Climate Change. Several different climate regions overlie portions of the Sacramento River Hydrologic Region. Air temperature data collected for the past century has been summarized by the Western Regional Climate Center (WRCC) for the different regions which are outlined below. Within the WRCC North Central climate region, mean temperatures have increased by about 0.8 to 1.7 °F (0.4 to 0.9 °C) in the past century, with minimum and maximum temperatures increasing by about 1.2 to 2.1 °F (0.7 to 1.2 °C) and 0.1 to 1.5 °F (0.1 to 0.8 °C), respectively. Within the WRCC North East climate region, mean temperatures have increased by about 0.8 to 2.0 °F (0.5 to 1.1 °C) in the past century, with minimum and maximum temperatures increasing by about 0.9 to 2.2 °F (0.5 to 1.2 °C) and by 0.5 to 2.1 °F (0.3 to 1.2 °C), respectively. Within the WRCC Sierra climate region, mean temperatures have increased by about 0.8 to 2.0 °F (0.5 to 1.1 °C) in the past century, with minimum and maximum temperatures increasing and decreasing by about 1.7 to 2.8 °F (0.9 to 1.5 °C) and by -0.2 to 1.3 °F (-0.1 to 0.7 °C), respectively. Within the WRCC Sacramento-Delta climate region, mean temperatures have increased by about 1.5 to 2.4 °F (0.9 to 1.3 °C) in the past century, with minimum and maximum temperatures increasing by about 2.1 to 3.1 °F (1.2 to 1.7 °C) and by 0.8 to 2.0 °F (0.4 to 1.1 °C), respectively (Western Regional Climate Center 2013). The region also is currently experiencing impacts from climate change through changes in statewide precipitation and surface runoff volumes, which in turn affect availability of local and imported water supplies. During the last century, the average early snowpack in the Sierra Nevada decreased by about 10 percent, which equates to a loss of 1.5 maf of snowpack storage (California Department of Water Resources 2008). Projections and impacts based on modeling of climate change are included in this report.

California's Central Valley Groundwater Wells Run Dry During Recent Drought

American Geophysical Union (AGU) | February 27th, 2020

Declining water tables are causing wells to run dry in California, but the prevalence and spatial distribution of wells that have run dry are not known beyond anecdotal a

Declining water tables are causing wells to run dry in California, but the prevalence and spatial distribution of wells that have run dry are not known beyond anecdotal and voluntary reports. Here, we apply a new, simple, and measurement‐driven method to calculate a localized water table; we show, for the first time using observations, that up to one‐in‐five wells now runs dry in California's Central Valley. The spatial distribution of wells identified as having dried up replicates hot spots of wells identified as having run dry in a voluntary reporting system, while also capturing impacts on groundwater wells that have not reportedly run dry. We assess the rates of drilling throughout the Central Valley and find, surprisingly, that domestic wells are being drilled deeper at a rate that exceeds agricultural wells across much of the central Central Valley. Because new groundwater wells are costly (i.e., $10,000 to $100,000), we suggest explicitly considering dry wells in groundwater sustainability planning to protect homes and farms from the loss of access to reliable water supplies in the future.

California’s First Farmer-Led Groundwater Market

Nature Conservancy | July 12th, 2018

Ventura County, located in California’s south coast, is one of United States’ most productive agricultural counties (ranked 10th in California and 11th in th

Ventura County, located in California’s south coast, is one of United States’ most productive agricultural counties (ranked 10th in California and 11th in the US)1, with agricultural production valued at $2.1B in 2016.2 California’s landmark groundwater law, the Sustainable Groundwater Management Act (SGMA), requires that 127 groundwater basins, including those in Ventura County, develop Groundwater Sustainability Plans that ensure pumping within sustainable limits. In western Ventura County, where over 70 percent of groundwater use is agricultural, the California Department of Water Resources has designated two groundwater basins as being in critical overdraft under SGMA. The local management agency may have to reduce groundwater use in these basins by as much as 40 percent to achieve a sustainable yield. While these reductions are critical to achieving long-term sustainability of water use, which includes nature’s needs, they also pose significant challenges to wisely managing reduced water allocations to keep irrigated agricultural land in production. The Nature Conservancy (TNC) has a vested interest in preserving farming in the county because it buffers important river and wetland habitat from nearby urban lands. Growers in the region quickly identified water markets as an important tool for managing limited groundwater resources.

California’s San Joaquin Valley: A Region in Transition

Congressional Research Service (CRS) | December 12th, 2005

CRS was requested to undertake a study of the San Joaquin Valley (SJV) and a comparison with another U.S. region. The eight-county San Joaquin Valley, part of California�

CRS was requested to undertake a study of the San Joaquin Valley (SJV) and a comparison with another U.S. region. The eight-county San Joaquin Valley, part of California’s Central Valley, is home to 5 of the 10 most agriculturally productive counties in the United States. By a wide range of indicators, the SJV is also one of the most economically depressed regions of the United States. This report analyzes the SJV’s counties and statistically documents the basis of current socioeconomic conditions. The report further explores the extent to which the SJV shares similarities with and differs from the Appalachian Regional Commission (ARC) area and a 68-county Central Appalachian subregion which contains some of the most economically distressed counties in Appalachia. The report also examines the role of federal expenditures in the cities and counties of the SJV. During the past twenty-five years, population growth rates in the SJV were significantly higher than for California or the United States and their projected growth rates over the next 20 years are also significantly higher. In 2000, the SJV also had substantially higher rates of poverty than California or the United States. Poverty rates were also significantly higher in the SJV than in the ARC region, although the rate is somewhat lower than that of the Central Appalachian subregion. Unemployment rates in the SJV were higher than in California or the United States and the ARC area. Per capita income and average family income were higher in the SJV than in Central Appalachia, but per capita income in the SJV was lower than in the ARC region as a whole. SJV households also had higher rates of public assistance income than did Central Appalachian households. Madera County ranked among the 10 lowest per capita income Metropolitan Statistical Areas (MSAs) in the United States in 2003, and the other 5 MSAs in the San Joaquin were all in the bottom 20% of all U.S. MSAs. Other indicators of social well-being discussed in the report showed that the SJV is a region of significant economic distress.

California’s Severe Drought Has Only Marginal Impacts on Food Prices

University of California Giannini Foundation of Agricultural Economics | May 14th, 2015

The extreme drought that has gripped California over the past several years is causing onerous adjustments in the natural and human environments. Agriculture, which uses

The extreme drought that has gripped California over the past several years is causing onerous adjustments in the natural and human environments. Agriculture, which uses much of the state’s water, is at the center of many of these arduous responses. The 2015 impacts of the continuing drought are still underway, but in this special Agriculture and Resource Economics Update issue, we project responses and consequences within agriculture and more broadly. In this issue, Hanak and Mount put this drought in the context of California’s history and put agriculture in the context of water institutions, management, and distribution throughout the state. Next, Medellin-Azuara and co-authors develop detailed, and albeit preliminary, assessments of 2015 irrigation water distribution. They estimate a cut to agriculture of about 8.8 million acre-feet, or about 30% of what might be available in a normal year. (This number may be an underestimate given recent events.) During droughts, farms increase groundwater pumping. The authors estimate that farmers and ranchers will replace about 6.2 million acre-feet of lost surface water deliveries with costly increases in groundwater pumping, where possible in 2015. Another painful response to drought is to leave land idle. The authors estimate about 564,000 more acres, mostly field crop land in the Central Valley (including irrigated pastures), will be idled in 2015. This too may be an underestimate. USDA reported on June 30, that 2015 California acreage of “principal crops,” (defined as field crops such as hay, grains, oilseeds, cotton and potatoes) is about 900,000 acres below the 2013 total of about four million acres. Over this period, tree nut and tomato acreage increased by about 180,000 acres. So, even accounting for the steady shift to tree nuts and some other higher revenue per acre (and per acre-foot) crops, there is a strong indication of severely accelerated reductions in field crop acreage in California. The economic toll of the drought is fewer jobs and smaller value of output and economic contribution that would have otherwise occurred. Based on 564,000 idled acres, Howitt et al. estimates farm revenue losses of $1.8 billion, economy-wide revenue losses of $2.7 billion, and 18,600 fewer jobs due to the agricultural drought. That these economic impacts are not even larger is a testament to the extraordinary efforts and innovations by farmers, and others in California agriculture. Idling land, shifting water across crops, and using each acre-foot more economically all have led to smaller losses of revenue and jobs, and only very small price increases for consumers.

California’s Water: Water for Farms

Public Policy Institute of California (PPIC) | October 1st, 2016

California is the nation’s largest farm state and a global market leader. Farms have steadily improved productivity per unit of water used, but the latest drought h

California is the nation’s largest farm state and a global market leader. Farms have steadily improved productivity per unit of water used, but the latest drought has exposed agriculture’s growing vulnerability to water shortages. This brief describes a number of opportunities to strengthen agricultural water management for the long term. This publication is part of a briefing kit that summarizes a dozen of the state’s most pressing water management issues.

Central Coast Groundwater: Seawater Intrusion and Other Issues

California Water Foundation | August 4th, 2014

The Central Coast area relies on groundwater for more than 80 percent of its water supplies, a greater percentage than any other region in the state. Over 40 percent of t

The Central Coast area relies on groundwater for more than 80 percent of its water supplies, a greater percentage than any other region in the state. Over 40 percent of the groundwater basins in the Central Coast region were ranked as either “high” or “medium” priority as part of the California Statewide Groundwater Elevation Monitoring (CASGEM) prioritization released in June 2014, indicating that they are among the most threated by present or future increases in groundwater demand. Central Coast groundwater supplies are seriously threatened by over-pumping that causes seawater intrusion, a challenge unique to coastal communities. Seawater intrusion results in saline groundwater that is unsuitable for irrigation or domestic use, directly threatening the Central Coast’s economy, where many high-value, salt-sensitive crops, such as strawberries, are grown. Groundwater basins in the Monterey and Salinas Valley area are in a state of long-term overdraft, resulting in falling groundwater levels, regional seawater intrusion, and reduced groundwater storage. Seawater intrusion reaches more than five miles inland in the Salinas Valley and three miles inland in the Pajaro Valley. In addition to salinity issues, several groundwater contaminants are present in these aquifers, including elevated levels of total dissolved solids, iron, manganese, nitrates, and other trace elements. The Paso Robles groundwater subbasin supplies water for 29 percent of the population and an estimated 40 percent of the agricultural production of San Luis Obispo County. Groundwater levels in the basin have been dropping rapidly in recent years, with many areas experiencing groundwater level declines of more than 70 feet. As a result, many wells have gone dry and groundwater users have been forced to deepen their wells or drill new wells. In July 2013, over 100 rural property owners complained to the San Luis Obispo County Board of Supervisors that their wells were running dry and in August 2013 the Board adopted the “Paso Robles Groundwater Basin Urgency Ordinance” as a temporary action to prevent new pumping from worsening overdraft conditions. Additionally, land surface subsidence has been noted in the Paso Robles area, and the recent rapid groundwater level declines may have triggered additional subsidence in this area. Although groundwater levels in the Oxnard Plain area have been relatively stable or have shown an increasing trend, in the coastal regions this stability is largely due to seawater intrusion and results in water of unusable quality replacing high quality groundwater. Rising groundwater levels in the Las Posas Valley are a result of active management to increase groundwater recharge beneath the Arroyo Las Posas. Seawater intrusion began in the Oxnard Plain area by 1930s and was widespread as early as the 1940s. Changes in groundwater management, including pumping reductions, shifting of pumping locations, construction of the Freeman Diversion, and the operation of the Pumping Trough and Pleasant Valley pipeline systems have significantly reduced seawater intrusion, but seawater intrusion conditions persist. Other contaminants present in the region include nitrates, iron, manganese and sulfate. In addition to causing seawater intrusion, over-pumping also caused irreversible land subsidence ranging from 2 .5 to 5 feet in several areas of the basin. The Central Coast is critically dependent upon groundwater, but this resource is under serious threat in a number of basins. In light of the limitations of existing state policies, the following measures would improve the effectiveness of groundwater planning and support sustainable management of California’s Central Coast’s groundwater resources . Establish a statewide policy to manage groundwater sustainably. Organize and empower local groundwater agencies to manage groundwater subbasins. Require the development and implementation of groundwater sustainability plans by local groundwater agencies. Provide local agencies with technical guidance and financial support from the state. Empower the State to oversee and ensure the implementation of groundwater sustainability plans.

Central Kings Groundwater Sustainability Agency Groundwater Sustainability Plan

Central Kings Groundwater Sustainability Agency (CKGSA) | December 11th, 2019