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’s Next Million Acre-Feet: Saving Water, Energy, and Money

Pacific Institute | September 26th, 2010

A new analysis from the Pacific Institute recommends specific actions that can annually save a million acre-feet of water quickly and at a lower economic and ecological c

A new analysis from the Pacific Institute recommends specific actions that can annually save a million acre-feet of water quickly and at a lower economic and ecological cost than developing new supplies. The assessment notes that new actions are immediately needed to reduce the growing tensions over the state’s water resources and to address California’s persistent water supply challenges. This is a key time for California water: the California Water Bond has been tabled for at least two years and may be scrapped altogether. New reviews from around the state are calling for prompt efforts to use technology, economics, and institutional reform to address the state’s water crisis. All parties seem to agree that the state will need a diverse portfolio of solutions – but it makes the most sense to do the most effective things first. The Pacific Institute’s new report, California’s Next Million Acre-Feet: Saving Water, Energy, and Money, quantifies more than one million acre-feet of water that can be conserved through improved efficiency, with savings coming from the urban and industrial sectors and improvements in agriculture. “There is vast untapped potential to reduce our demand for water without affecting the services and benefits that water provides,” said Heather Cooley, co-director of the Pacific Institute’s Water Program and lead author of the report. “We identified how the next million acre-feet of water can be conserved in California, with approximately 30% of the savings from the urban sector and 70% from the agricultural sector. Both sectors have savings potential far exceeding this amount, and while we could have identified one million acre-feet of water savings annually in either sector alone, we’re showing how all sectors can benefit from these improvements.” In the urban sector, the report identifies water savings from replacing old, inefficient water-using devices with high-efficiency models in our homes and businesses, as well as replacing some lawns with low-water-use plants. In the agricultural sector, best water management practices include weather-based irrigation scheduling, regulated deficit irrigation, and switching from gravity or flood irrigation to sprinkler or drip irrigation systems. The efficiency improvements identified in California’s Next Million Acre-Feet require an upfront investment of less than $1.9 billion, costs that could be borne by a mix of state, federal, and local agencies and individuals – all at a small fraction of the cost of the proposed water bond. The cost of the conserved water is $185 per acre-foot for the agricultural sector and a net savings of $99 per acre-foot for the urban sector, over the lifetime of the efficiency improvement. Conserving water also conserves energy, saves money, and reduces the need for new water and energy projects.

Climate-smart management of soil water storage: statewide analysis of California perennial crops

Environmental Research Letters (IOP) | April 9th, 2019

The FAO-56 dual crop coefficient model was used to simulate site-specific irrigation management to quantify the green water resource (rainfall stored in soil) in five Cal

The FAO-56 dual crop coefficient model was used to simulate site-specific irrigation management to quantify the green water resource (rainfall stored in soil) in five California perennial crops (alfalfa, almonds, grapes, pistachios, and walnuts), considering local soil water holding capacity and climate data from 2003 to 2018. We tested different rooting depths and irrigation management thresholds (allowable depletion) across 1.46 million hectares of cropland to determine how the size of the soil water reservoir affects green water utilization and, consequently, blue water demand (irrigation). The 13-year cumulative green water utilization ranged from 17 to 36 million km3 out of a 57 km3 rainfall input and 162–263 km3cumulative blue water demand. For a deep scenario (2 m rooting; 50% allowable depletion), green water met 12% of cumulative crop water demand. However, green water use was not uniform: 20% of the landscape met over 20% of its annual crop water demand. Deeper rooting or greater allowable depletion reduced blue water demand more than the increase in green water utilization, due to less frequent irrigations, which reduced soil evaporative loss. Compared to a 'business-as-usual' shallow irrigation management scenario (0.5 m rooting; 30% allowable depletion), a moderate scenario (1.0 m rooting; 50% allowable depletion) saved 30 km3 blue water evaporation and increased green water use by 7 km3through 13 years. Such savings would fill California's largest reservoir, Shasta Lake, 6.6 times. This study demonstrates an opportunity for climate-smart management of soil water storage, by delayed spring irrigation, applying deeper irrigations less often, and ending fall irrigation early.

Colorado River Basin August 2022 24-Month Study

U.S. Bureau of Reclamation (USBR) | August 16th, 2022

Cover cropping and no-tillage improve soil health in an arid irrigated cropping system in California’s San Joaquin Valley, USA

Soil and Tillage Research (Elsevier) | January 3rd, 2017

The concept of soil health has attracted considerable attention during the past two decades, but few studies have focused on the effects on soil health of long-term soil

The concept of soil health has attracted considerable attention during the past two decades, but few studies have focused on the effects on soil health of long-term soil management in arid irrigated environments. We investigated the effects of cover cropping and no-till management on soil physical and chemical properties during a 15-year experiment in California’s San Joaquin Valley (SJV) USA. Our objective was to determine if soil health could be improved by these practices in an annual crop rotation. The impact of long-term no-tillage (NT) and cover cropping (CC) practices, alone and in combination, was measured and compared with standard tillage (ST) with and without cover crops (NO) in irrigated row crops after 15 years of management. Soil aggregation, rates of water infiltration, content of carbon, nitrogen, water extractable organic carbon (WEOC) and organic nitrogen (WEON), residue cover, and biological activity were all increased by NT and CC practices relative to STNO. However, effects varied by depth with NT increasing soil bulk density by 12% in the 0–15 cm depth and 10% in the 15–30 cm depth. Higher levels of WEOC were found in the CC surface (0–5 cm) depth in both spring and fall samplings in 2014. Surface layer (0–15 cm) WEON was higher in the CC systems for both samplings. Tillage did not affect WEON in the spring, but WEON was increased in the NT surface soil layer in the fall. Sampling depth, CC, and tillage affected 1-day soil respiration and a soil health index assessment, however the effects were seasonal, with higher levels found in the fall sampling than in the spring. Both respiration and the soil health index were increased by CC with higher levels found in the 0–5 cm depth than in the 5–15 and 15–30 cm depths. Results indicated that adoption of NT and CC in arid, irrigated cropping systems could benefit soil health by improving chemical, physical, and biological indicators of soil functions while maintaining similar crop yields as the ST system.

Drip Irrigation

Scientific American | November 1st, 1977

Some 40 years ago Symcha Blass, an Israeli engineer, observed that a large tree near a leaking faucet exhibited a more vigorous growth than the other trees in the are

Some 40 years ago Symcha Blass, an Israeli engineer, observed that a large tree near a leaking faucet exhibited a more vigorous growth than the other trees in the area, which were not reached by the water from the faucet. Blass knew that conventional methods of irrigation waste much of the water that is applied to the crop, and so the example of the leaking faucet led him to the concept of an irrigation system that would apply water in small amounts. literally drop by drop. Eventually he devised and patented a low-pressure system for delivering small amounts of water to the roots of plants at frequent intervals. The technique, as developed by Blass and subsequently refined by him and various manufacturers, consists in laying a plastic tube of small diameter on the surface of the field alongside the plants and delivering water to the plants slowly but frequently from holes or special emitters located at appropriate points along the tube. The concept, which is now called drip irrigation or trickle irrigation, has gained wide acceptance, proving to be particularly valuable in areas that are arid and have high labor costs. An unforeseen benefit is that the system works well with water that is highly saline, as water in arid regions often is.

Estuary News, August 1996

San Francisco Estuary Partnership (SFEP) | August 15th, 1996

Estuary News, June 1993

San Francisco Estuary Partnership (SFEP) | June 15th, 1993

Estuary News, October 2000

San Francisco Estuary Partnership (SFEP) | October 15th, 2000

Exploring the Potential for Water-Limited Agriculture in the San Joaquin Valley

Public Policy Institute of California (PPIC) | July 21st, 2022

The rollout of California’s Sustainable Groundwater Management Act (SGMA) is altering the state’s agricultural landscape. As groundwater sustainability measures are

The rollout of California’s Sustainable Groundwater Management Act (SGMA) is altering the state’s agricultural landscape. As groundwater sustainability measures are implemented and water scarcity increases, at least half a million acres are projected to come out of irrigated production in the San Joaquin Valley, the state’s agricultural heartland. Rather than widespread land idling—which comes with unintended consequences such as dust, weeds, pests, and soil degradation — a switch from summer irrigated crops to winter crops produced with limited water (including winter cereals and forage crops, among others) might keep some of this land in production. Although water-limited agriculture faces large hurdles, some promising aspects warrant further exploration.