Assessment of Water Demand of Cool-season Turfgrass in California Using Cal-SIMETAW

The main purpose of this study was to utilize the daily soil water balance program “California Simulation of Evapotranspiration of Applied Water” or “Cal-SIMTAW” to estimate crop evapotranspiration (ETc) and evapotranspiration of applied water (ETaw) for cool-season turfgrass on a 4 x 4 km grid spacing over California to support calibration of urban per capita water use.

Cal-SIMETAW is a new soil water balance model developed by the California Department of Water Resources and the University of California, Davis to estimate reference evapotranspiration (ETo), crop coefficient (Kc), crop evapotranspiration (ETc), and evapotranspiration of applied water (ETaw) for use in California Water Plan (CWP), which provides a comprehensive report on water supply, demand, and management in California (Orang et al. 2013). ETc is estimated as ETc = ETo x Kc, where Kc is a crop coefficient used to adjust for the difference between ETo and ETc. ETo is an estimate of the evapotranspiration of a virtual vegetated surface with fixed canopy resistance estimated as an inverse function of wind speed. The ETo is approximately equal to the ETc from a 12-centimeter-tall cool-season grass that is not lacking for water. ETaw is the amount of irrigation water needed to match losses from the effective soil root zone due to ETc that are not replaced by precipitation and seepage of groundwater. Cal-SIMETAW was specifically designed to improve the department's estimates of water use and irrigation requirements for agricultural crops and other surfaces for regional water planning. The model requires weather data, soils, crop coefficients, rooting depths, seepage, etc., that influence crop water balance. The model uses the daily climate data, i.e., maximum (Tmax) and minimum temperature (Tmin) and precipitation (Pcp), which were derived from monthly PRISM data (PRISM Group, 2011) and daily US National Climate Data Center climate station data to cover California on a 4 x 4 km grid spacing. The application uses daily weather data to determine ETo, using the Hargreaves-Samani (HS) equation. 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 difference. 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 model uses SSURGO soil characteristic data and crop information with precipitation and ETc data to generate hypothetical water balance irrigation schedules to determine ETaw, which is the amount of applied irrigation water that contributes to crop evapotranspiration or ETc assuming 100% application efficiency. Therefore, ETaw is the amount of diverted water needed to produce a crop or maintain an urban landscape. All of ETaw calculations are done on a daily basis, so the estimation of Er and, hence, ETaw is greatly improved over earlier methods.

In this study, Cal-SIMETAW was utilized to (1) read the daily PRISM climate data to calculate ETo on a 4 x 4 km grid spacing, (2) determine crop coefficient values of cool-season turfgrass, (3) account for factors affecting the Kc values, (4) calculate crop evapotranspiration (ETc), (5) compute a hypothetical irrigation schedule, and (6) estimate the effective precipitation (Er) and ETaw for cool-season turfgrass for each PRISM grid from January 1989 to December 2015. The output data files generated by Cal-SIMETAW consist of climate and calculated ETo, ETc, Er, and ETaw for cool-season turfgrass by latitude and longitude or PRISM grid over the entire state for CY 1989-2015.

Structure of Cal-SIMETAW and Its Database

Cal-SIMETAW was written using Microsoft C# for calculations and Oracle Spatial 11 g for data storage to provide a new tool for obtaining accurate estimates of ETc (crop evapotranspiration), Er (effective precipitation), and ETaw (seasonal ET of applied water) for agricultural crops and other surfaces by PRISM grids and DAU/County (combinations of detailed analysis unit and county) over California. The application uses batch processing to read (1) the daily weather data, (2) the crop coefficient values, (3) growth dates, (4) soil information, (5), crop and irrigation information. Then the program computes daily ETo, Kc (adjusted crop coefficient) factors, ETc, daily soil water balance, effective precipitation (Er), and ETaw for every surface within each PRISM grid for the period of record. The application also estimates soil evaporation using a 2-stage soil evaporation model based on mean ETo and wetting frequency in days. Figure 1 illustrates the structure, database, and lists of input and output data files of the Cal-SIMETAW model.

Fig. 1 Flow diagram illustrating the structure, database, and lists of input and output data files of the Cal-SIMETAW model

California Geometry

There are about 26,300 PRISM grids in the Cal-SIMETAW model’s Oracle database to cover California on a 4 x 4 km grid spacing. Cal-SIMETAW provides spatial soil and climate information and it uses crop and irrigation information to compute daily soil water balance. In the Cal-SIMETAW model, soil and climate databases were developed to spatially characterize ETc and ETaw. Using mean soil characteristics and climate and ETo information from the 4 x 4 km grid, Cal-SIMETAW estimates the mean soil characteristics and ETo information by DAU/County (Figure 2).

Fig. 2 Flow diagram illustrating the California geometry of the Cal-SIMETAW model

California Spatial Climate and Soil Data

Daily PRISM Weather Data

Cal-SIMETAW uses the Daily PRISM climate data, (i.e., Tmax and Tmin, and Pcp), which were derived from monthly USDA NRCS PRISM data and daily NCDC climate station climate data to determine ETo on a 4 x 4 km grid spacing over California, using the calibrated H-S equation. Because the H-S equation is based on temperature only, ETo from the H-S equation was compared with CIMIS weather stations distributed across the state. This determined a 4 x 4 km grid of correction factors to convert the H-S ETo to CIMIS ETo to account for spatial climate differences.

SURRGO Soil Data

A database containing the available soil water holding capacity (AWHC) and maximum soil depth (SDx) information for all of California was developed from the USDA NRCS SSURGO database. The database covers all of California on the same 4 x 4 km grid spacing for all locations that are included in the Oracle database, which covers most of California. There are about 26,300 PRISM grids in the model’s database for California (Figure 3).

Fig. 3 Flow diagram illustrating the spatial soil climate data of the Cal-SIMETAW model

Crop and Irrigation Information

The input data include the crop name, begin and end dates, effective rooting depths, allowable depletion, and more. Soil water-holding characteristics, effective rooting depths, and irrigation frequency are used with rainfall and crop evapotranspiration data to calculate a daily water balance and determine effective rainfall and ETaw. This is equal to the seasonal total evapotranspiration (SETc) minus the cumulative seasonal effective seepage contribution (SEspg) minus the cumulative seasonal effective precipitation contribution (SEp) minus the difference in soil water content (ΔWC) from the beginning to the end of the season. The accepted crop coefficients were used to estimate daily crop water use by PRISM grid and DAU/County (Figure 4).

Fig. 4 Flow diagram illustrating the crop and irrigation information requirements for estimating daily soil water balance in the crop root zone

Spatial Weather and Soil Data

Cal-SIMETAW was developed to use the daily weather data from PRISM (PRSIM Group 2011) and soil information from the USDA-NRCS SSURGO database (SSURGO 2011) to determine ETo and perform daily soil water balance to determine ETc and ETaw on a 4 x 4 km grid spacing over California.

Daily PRISM Weather Data

Cal-SIMETAW uses the daily Tmax and Tmin and Pcp, which were derived from monthly USDA NRCS PRISM data and daily NCDC (National Climate Data Center) climate station data to determine ETo on a 4 x 4 km grid spacing, using a calibrated H-S equation. Due to this restricted historical data set we cannot directly compute Penman–Monteith ETo (P-M ETo) as adopted by the Environmental Water Resources Institute - American Society of Civil Engineers. Instead this model uses the calibrated H-S equation for estimating ETo (H-S ETo). ETo from the H-S equation were compared with CIMIS ETo at the same locations using available CIMIS data to determine correction factors to convert H-S ETo to P-M ETo to account for spatial climate differences. To learn more about the ETo correction factors for estimating P-M ETo from the H-S ETo in California, see the documentation on DWR website. Here is the link to see the documentation as a PDF file, http://www.water.ca.gov/landwateruse/models.cfm

Soil Information

Cal-SIMETAW also has a large database of the available soil water holding capacity and soil depth information on a 4 x 4 km grid spacing over California developed using the USDA NRCS SSURGO database.

Crop and Irrigation Information

To utilize Cal-SIMETAW to perform daily soil water balance in the crop root zone to determine ETc and ETaw for cool-season turfgrass on each PRISM grid, the application also requires the crop and irrigation information. The input data include as following:

  • Crop name.
  • Beginning and ending dates.
  • Irrigation frequency is the number of days between irrigation events during the initial growth period (30 days is the default value). If a value more frequent than 30 days is input, the input irrigation frequency will be used.
  • Crop coefficients (Kc).
  • Percentage of season.
  • Maximum effective rooting depth during growing season.
  • Allowable depletion (percent).

ETo Estimates Using the PRISM Temperature Data

Since only temperature data were available prior to 2004, it was decided to use daily maximum and minimum air temperature and the Hargreaves and Samani (1982; 1985) equation to calculate reference evapotranspiration (HS) as an approximation for ETo. Using recent climate data from CIMIS, comparisons were made between HS ETo and CIMIS ETo and discrepancies were noted depending on regional climate differences. In general, HS ETo was lower than CIMIS ETo under windy conditions and it was higher than CIMIS ETo under calm conditions. Using CIMIS weather stations distributed across the State, a 4 x 4 km grid of correction factors for the HS ETo equation was developed. There are many daily temperature and precipitation weather stations in California, but the PRISM data set, which was developed by Oregon State University (PRISM Group, 2011) provided a long-term GIS data base of historical daily maximum and minimum temperature and precipitation on the same 4 x 4 km grid as the correction factor GIS map. Thus, using the PRISM historical temperature data to compute HS ETo and the calibration factors, Cal-SIMETAW is able to produce CIMIS ETo estimates on a 4 x 4 km grid over the State from October 1921 to December 2015. The HS equation requires only the latitude of the site of interest and the minimum and maximum daily air temperatures. The HS equation for ETo is:

ETo = 0.0023 (Tc + 17.8) Ra (Tr 0.5)

Where Tc is the monthly mean temperature at the site, Ra is the extraterrestrial solar radiation (MJ m-2 d-1), and Tr is the difference between the maximum and minimum temperatures for the month. A calibrated HS equation was used in this study to provide ETo.

Verification of Cal-SIMETAW Predictions of ETo

CIMIS network station measurements are among the most reliable direct datasets of daily weather variables including solar radiation (Rs), maximum air temperature (Tmax), minimum air temperature (Tmin), wind speed (U2), dew point temperature (Td), and etc. Reference evapotranspiration (ETo), computed by the daily (24-hour) Penman-Monteith equation, has been recommended by both America Society of Civil Engineers (ASCE) and United Nation FAO. The daily ETo values estimated by Cal-SIMETAW, using daily PRISM and Spatial CIMIS weather data were validated against CIMIS ETo estimates from October 2004 to September 2010 at Davis, Gerber, Durham, and Nicolaus in the Sacramento Valley. The CIMIS weather stations at these sites were chosen because; 1) they have high quality weather data; 2) they contain longer weather records; 3) they are distributed almost evenly across the entire Sacramento Valley. The results in appendix A show reasonably good agreement among CIMIS-based estimates of ETo and those calculated from the calibrated HS equation using daily PRISM weather data and daily Penman-Montieth equation using Spatial CIMIS weather data. Please see Appendix A.

Crop Coefficients (Kc)

Crop evapotranspiration is estimated as the product of reference evapotranspiration (ETo) and a crop coefficient (Kc) value. Crop coefficients are commonly developed by measuring ETc, calculating ETo, and determining the ratio Kc = ETc / ETo. While crop coefficients are continuously developed and evaluated, Cal-SIMETAW was designed for easy updates of both Kc and crop growth information. The Kc values and corresponding growth dates are included by crop in the model. These dates and Kc values are used to estimate daily Kc values during a season.

The season is separated into initial (date A-B), rapid (date B-C), midseason (date C-D), and late season (date D-E) growth periods. Kc values are denoted KcA, KcB, KcC, KcD and KcE at the ends of the A, B, C, D, and E growth dates, respectively. The Kc values for cool-season turfgrass are typically a constant value during the year, so KcA=KcB=KcC=KcD=KcE=0.8. Cool-season turfgrass is a field crop with a fixed crop coefficient all year (January 1 - December 31). Table 1 describes the crop and irrigation information of cool-season turfgrass stored in the model’s database.

Table 1: An example of 16 columns of crop and irrigation information of cool-season turfgrass.

Table 1.png

Estimates of ETc for Cool-season Turfgrass

In this study, reference evapotranspiration was calculated from daily PRISM weather data and daily crop evapotranspiration is calculated as the product ETc = ETo x Kc on each day. A sample plot of daily calculated ETo and ETc for cool-season turfgrass using one year of daily weather data from PRISM is shown in Figure 2.

Daily crop evapotranspiration (ETc) and reference evapotranspiration (ETo) using one year of PRISM weather data to calculate ETo.

Daily Soil Water Balance Calculations

Soil water-holding characteristics, effective rooting depths, and irrigation frequency are used with precipitation and ETc data to calculate a daily water balance and determine effective precipitation and ETaw, which is the seasonal total ETc, minus the change in stored soil water during the season and minus any in-season effective rainfall. Irrigations are timed so that the estimated soil water depletion (SWD) does not exceed the manageable allowable depletion (MAD), which is calculated as the product of the allowable depletion and the plant available water content within the crop rooting depth. The MAD is used to make a crop and soil specific irrigation schedule. The plant available water content is computed as the product of the soil available water-holding capacity and the effective rooting depth. The allowable depletion is a crop and soil specific factor that defines the fraction (or percentage) of the available water content within a rooting zone that can be depleted between irrigation events. For many crop and soil combinations, an allowable depletion of 50% is adequate. During the growing season, the SWD is updated by adding the ETc on the current day to the SWD on the previous day (Fig. 6). If rainfall occurs, SWD is reduced by an amount equal to the rainfall. However, the SWD is not allowed to fall to less than zero. This procedure automatically determines the effective rainfall as equal to the recorded rainfall if the amount is less than the SWD. If the recorded rainfall is more than the SWD, then the effective rainfall equals the SWD. The method ignores runoff and water running onto the field, but this is a minor problem in most irrigated fields in California. Irrigation events occur on dates when the SWD would exceed the MAD. It is assumed that the SWD returns to zero on each irrigation date.

By definition, ETaw is the amount of applied irrigation water that contributes to ETc; therefore, ETaw is the sum of the net irrigation applications during a cropping season. The ETaw for n irrigation events is therefore calculated as: ETaw = NA1 + NA2 + - - - + NAn. The ETaw can be computed from the net applications after the last NA is applied. This is the method used to determine the ETaw in Cal-SIMETAW. An example of a daily soil water balance data file format for the PRISM grid within PCWA-Roseville is shown below in Table 2. The first row contains a brief description of the water balance output data for cool-season turfgrass, including the PRISM grid ID number. The second row shows the variables and the third row has the units. The water balance data files contain daily values of ETo, Kc, ETc, Pcp, Er, ETaw, SWD, field capacity (FC), soil water content (SWC), manageable allowable depletion (MAD), and net application (NA) for cool-season turfgrass of a PRISM grid during 1995. The table is wrapped to fit on the page.

Table 2: A sample of daily soil water balance output data file of a PRISM grid (38.765_-121.267) during 1995.

Table 2.png
Table 2.2.png

Figures 6 through 8 show daily water balance in the crop root zone for cool-season turfgrass during the 1995 and 1997 growing seasons for three PRISM grids within PCWA-Roseville, City of Fresno, and Arroyo Grande illustrating the estimation of ETaw.

Figure 6 Figure 7 Figure 8
Fig 6.png Fig 7.png Fig 8.png

Fig. 6 An annual water balance for cool-season turfgrass for a PRISM grid within PCWA-Roseville showing fluctuations in soil water content between field capacity (FC) and management allowable depletion (MAD) for cool-season turfgrass during 1995.
Fig. 7 Daily fluctuations in soil water content between field capacity and management allowable depletion for cool-season turfgrass for a PRISM grid within City of Fresno, 1990.
Fig. 8 Daily fluctuations in soil water content between field capacity and management allowable depletion for cool-season turfgrass for a PRISM grid within Arroyo Grande, 1997.

Alternatively, we can calculate ETaw as the seasonal total crop evapotranspiration (CETc) minus the cumulative effective precipitation contribution (CEr) minus the difference in soil water content (ΔSWC) from the beginning to the end of the season (Figures 9 through 11).

Therefore, the ETaw can also be expressed as

ETaw = CETc – CEr – ΔSWC

The ΔSWC is unknown until the end of the season, however, so it cannot be computed until the end of a cropping season using this method. The ETaw can be computed from the net applications after the last NA is applied. Figures 9 through 11 illustrate how one can determine ETaw from CETc, CEr, and ΔSWC.

Figure 9 Figure 10 Figure 11
Fig 9.png Fig 10.png Fig 11.png

Fig. 9 Plot of CETc, CEr, and CDsw for cool-season turfgrass for PCWA-Roseville using the 1995 daily water balance data.
Fig. 10 Plot of CETc, CEr, and CDsw for cool-season turfgrass for City of Fresno using the 1990 daily water balance data.
Fig. 11 Plot of CETc, CEr, and CDsw for cool-season turfgrass for Arroyo Grande using the 1997 daily water balance data.

The results from this study are output to tables consisting of

  • Daily ETo, Kc, ETc, water balance, and ETaw for cool-season turfgrass on each PRISM grid over the entire state for the period of 1989 to 2015.
  • Monthly total of ETc , Er, and ETaw on a 4 x 4 km grid spacing over the same time period.
  • Seasonal and annual total of ETc, Er, and ETaw for each PRISM grid over California.

After the daily water balance calculations are completed, the output data files created by Cal-SIMETAW are stored in a specified folder using the file name “Gnn.nnn_-nnn.nnnMPRISMET.csv”. The Gnn.nnn_-nnn.nnn identifies the PRISM grid by latitude and longitude. The character M identifies that output data files are monthly. The character PRISM indicates that the input ETo data is calculated using daily weather data from PRISM. Table 3 shows an example of a monthly soil water balance data file format for cool-season turfgrass within a PRISM grid from Cal-SIMETAW. The first row contains a brief description of the water balance data output, including the PRISM grid number. The second row shows the variables and the third row has the units. Each file contains daily mean maximum and minimum air temperature, reference evapotranspiration (ETo), total precipitation, total ETc, total Er, and total ETaw by month from January 1989 to December 2015.

Table 3 Monthly output data file for cool-season turfgrass within a PRISM grid.

Table 3.png

For more information and publication on the Cal-SIMETAW model, Please visit the DWR web site at http://www.water.ca.gov/landwateruse/models.cfm

Appendix A. Verification of Cal-SIMETAW Predictions of ETo

CIMIS network station measurements are among the most reliable direct datasets of daily weather variables including solar radiation (Rs), maximum air temperature (Tmax), minimum air temperature (Tmin), wind speed (U2), dew point temperature (Td), and etc. Reference evapotranspiration (ETo), computed by the daily (24-hour) Penman-Monteith equation, has been recommended by both America Society of Civil Engineers (ASCE) and United Nation FAO.

The daily ETo values estimated by Cal-SIMETAW, using daily PRISM and Spatial CIMIS weather data were validated against CIMIS ETo estimates from October 2004 to September 2010 at Davis, Gerber, Durham, and Nicolaus in the Sacramento Valley. The CIMIS weather stations at these sites were chosen because; 1) they have high quality weather data; 2) they contain longer weather records; 3) they are distributed almost evenly across the entire Sacramento Valley. The results show reasonably good agreement among CIMIS-based estimates of ETo and those calculated from the calibrated HS equation using daily PRISM weather data and daily Penman-Montieth equation using Spatial CIMIS weather data. The list of the four stations and their latitude and longitude information and PRISM grid numbers are shown in Table A1.

Table A1. List of four CIMIS weather stations used for evaluating the ETo values estimated with Cal-SIMETAW based on the calibrated Hargreaves-Samani equation.

Table A1.JPG

Cal-SIMETAW PRISM ETo vs. CIMIS ETo

To determine the influence of limited weather data of PRISM for estimating ETo, using a calibrated Hargreaves-Samani equation for California, a comparison of the calibrated HS ETo from Cal-SIMETAW and CIMIS-based estimates of ETo with data from Davis, Gerber, Durham, and Nicolaus in the Sacramento Valley are shown in Figures 5-8. The results show that estimates of ETo for WY 2005-2010 closely approximate ETo values from CIMIS; for example, the mean ETo estimates from Davis for the period of 2004-2010 were 3.69 mm and 3.88 mm with standard deviations of 2.16 mm and 2.43 mm for the calibrated Hargreaves-Samani model and CIMIS, respectively. The difference between the two approaches was small. However, the ETo would have been overestimated by the HS equation at this site due to clouds and/or underestimated when they were influenced by a windy, arid environment. The results indicate that calibration of this equation was necessary in some microclimates. The calibrated form of the equation will compensate for the important climatic factors affecting ETo. As seen in the table 2 and figures 4-7, a close agreement exists between CIMIS-based estimates of ETo and those of the Cal-SIMETAW model (HS ETo) in all cases. Figures A5-A8 compare daily ETo estimates of the two different methods at four different sites within the Sacramento Valley from October 2004 to September 2010 and show close agreement between CIMIS-based estimates of ETo and those of the Cal-SIMETAW model using the historical PRISM temperature data.

Table A2. Evaluation of Cal-SIMETAW model predictions of ETo at eight different CIMIS stations for WY 2005-2010.

Table A2.JPG


Fig. A5 Cal-SIMETAW PRISM ETo vs. CIMIS ETo at Davis California (PRISM grid 99_62). Fig A5.png Fig A5.2.png
Fig. A6 Cal-SIMETAW PRISM ETo vs. CIMIS ETo at Gerber, California (PRISM grid 57_54). Fig A6.png Fig A6.2.png
Fig. A7 Cal-SIMETAW PRISM ETo vs. CIMIS ETo at Durham, California (PRISM grid 69_61). Fig A7.png Fig A7.2.png
Fig. A8 Cal-SIMETAW PRISM ETo vs. CIMIS ETo at Nicolaus, California (PRISM grid 90_67). Fig A8.png Fig A8.2.png


Cal-SIMETAW Spatial CIMIS ETo vs CIMIS ETo

Cal-SIMETAW Spatial CIMIS ETo was also validated against CIMIS ETo estimates at the CIMIS stations within the Sacramento Valley from October 2004 to September 2010 (Figures 9-12).

Fig. A9 Cal-SIMETAW Spatial CIMIS ETo vs. CIMIS ETo at Davis California (PRISM grid 99_62). Fig A9.png Fig A9.2.png
Fig. A10 Cal-SIMETAW Spatial CIMIS ETo vs. CIMIS ETo at Gerber, California (PRISM grid 57_54). Fig A10.png Fig A10.2.png
Fig. A11 Cal-SIMETAW Spatial CIMIS ETo vs. CIMIS ETo at Durham, California (PRISM grid 69_61) Fig A11.png Fig A11.2.png
Fig. A12 Cal-SIMETAW Spatial CIMIS ETo vs. CIMIS ETo at Nicolaus, California (PRISM grid 90_67). Fig A12.png Fig A12.2.png


Cal-SIMETAW PRISM ETo vs. Spatial CIMIS ETo

Cal-SIMETAW ETo estimates based on the calibrated HS equation were also compared with Spatial CIMIS ETo estimates at the same CIMIS sites within the Sacramento Valley from October 2004 to September 2010 (Figures 13A-16A).

Fig. A13 Cal-SIMETAW PRISM ETo vs. Cal-SIMETAW Spatial CIMIS ETo at Davis California (PRISM grid 99_62). Fig A13.png Fig A13.2.png
Fig. A14 Cal-SIMETAW PRISM ETo vs. Cal-SIMETAW Spatial CIMIS ETo at Gerber, California (PRISM grid 57_54). Fig A14.png Fig A14.2.png
Fig. A15 Cal-SIMETAW PRISM ETo vs. Cal-SIMETAW Spatial CIMIS ETo at Durham, California (PRISM grid 69_61). Fig A15.png Fig A15.2.png
Fig. A16 Cal-SIMETAW PRISM ETo vs. Cal-SIMETAW Spatial CIMIS ETo at Nicolaus, California (PRISM grid 90_67). Fig A16.png Fig A16.2.png


List of Acronyms and Abbreviations, Their Common Units and Definitions

  • AD: allowable depletion
  • area: acres for a crop category within a DAU/County
  • AWHC: available soil water holding capacity
  • BD: begin date
  • CCKc: cover crop coefficient contribution for tree and vine crops
  • CEr: mm - seasonal effective precipitation
  • CETaw: mm - cumulative ET of applied water
  • CETc: mm - seasonal cumulative crop evapotranspiration
  • CF: seasonal consumed fraction
  • CNA: mm - cumulative net application
  • DAU: data analysis unit
  • DAU/County: detailed analysis unit and county combination unit
  • DOY: day of the year
  • ED: end date
  • Er: effective precipitation
  • Espg: mm - effective seepage
  • ETaw: monthly total values of ET of applied water in mm averaged over the period of the data set
  • ETc: mm - crop evapotranspiration
  • ETo: mm - reference evapotranspiration
  • FAO : Food and Agriculture Organization of the United Nations
  • FC: field capacity
  • H-S equation: Hargreaves-Samani equation
  • IKc: in-season Kc factor
  • Kc: adjusted crop coefficient
  • MAD: mm – manageable allowable depletion
  • NA: net application
  • NCDC: U.S. National Climate Data Center
  • NRD: number of rainy days per month
  • OKc: off-season Kc factor
  • Pcp: mm - precipitation
  • P-M equation: Penman-Monteith equation
  • PWP: mm - permanent wilting point
  • RDx : maximum root depth
  • Rs: solar radiation
  • Sdx: maximum soil depth
  • Spg: mm - seepage
  • SWC: mm - soil water content = FC-SWD
  • SWD: mm - soil water depletion below field capacity
  • SWDx: maximum soil water depletion for scheduling
  • Tdew: dew point temperature
  • Tmax: maximum air temperature
  • Tmin: minimum air temperature
  • U2: wind speed
  • USDA NRCS: U.S. Department of Agriculture Natural Resources Conservation Service
  • YT: mm - yield threshold
Has end use subjectPlants +
Has end user subjectLandscape professionals +, Resource conservation professionals + and Water or energy utility managers +
Has general subjectLandscape +
Has introductionThe main purpose of this study was to util
The main purpose of this study was to utilize the daily soil water balance program “California Simulation of Evapotranspiration of Applied Water” or “Cal-SIMTAW” to estimate crop evapotranspiration (ETc) and evapotranspiration of applied water (ETaw) for cool-season turfgrass on a 4 x 4 km grid spacing over California to support calibration of urban per capita water use.
calibration of urban per capita water use. +
Has primary imageFig 5.png +
Has source fileWater Demand of Cool-season Turfgrass.pdf +
Is publication typeReports and studies +