The RefET module calculates hourly or daily reference ET from meteorological data using the approach described in ASCE-NWRI (2005). If needed, the module will estimate solar radiation and dew point temperature, and gap fill meteorological data.
The RefET module requires hourly or daily meteorological data. If the calculated reference ET will be used in the CropET module, care should be taken to ensure this meteorological data is representative of agricultural conditions. Meteorological data can be obtained from :ref:`agricultural weather networks <data-sources-ag-met>`, or :ref:`adjustments <model-description-cropet-aridfctr>` reference ET can be made within the CropET module.
- Date [in YYYY-MM-DD format]
- Tmax = maximum daily air temperature
- Tmin = minimum daily air temperature
- Td = mean daily dew point temperaturea
- ea = actual vapor pressurea
- ux = mean daily wind speed at known heightb
- Rn = calculated net radiation at the crop surfacec
- Pr = daily precipitation (optional)
- Q = specific humidity (optional)
- Sn = daily accumulated snow (optional)
- Sd = snow depth (optional)
a One of these is required. If both Td and ea are not provided, mean monthly dew point depression, K0, must be provided.
b Wind measurement height in meters must be provided in the ini file.
c If Rn is not provided it will be estimated using the approach described in Thornton and Running (1998). The three Thornton and Running coefficients must be provided in the ini file.
- Date [in YYYY-MM-DD HH:MM format]
- Tmean = mean hourly air temperature
- Td = mean hourly dew point temperaturea
- ux = mean hourly wind speed at known heightb
- Rn = calculated net radiation at the crop surfacec
- Pr = hourly precipitation (optional)
- Q = specific humidity (optional)
- Sn = hourly accumulated snow (optional)
- Sd = snow depth (optional)
a One of these is required. If both Td and ea are not provided, mean monthly dew point depression, K0, must be provided.
b Wind measurement height in meters must be provided in the ini file.
c If Rn is not provided it will be estimated using the approach described in Thornton and Running (1998). The three Thornton and Running coefficients must be provided in the ini file.
# HOW IS THE SNOW OR SNOW DEPTH USED?
RefET requires the timeseries weather data to be in delimited columns with header of column names. Column names and units are specified in the ini file. Files are allowed to have header rows, with the number of header rows specified in the ini file. The delimiter is also specified in the INI file.
| Delimiter | Model Notation |
|---|---|
| Comma | , |
| Tab | /t |
- Format: .csv, .txt, .dat
- File Name: (DESCRIBE WILDCARDS)
- Structure:
| Date | Tmax | Tmin | ux | Rn | Tdew |
|---|---|---|---|---|---|
| 2017-10-01 | 9.34 | 3.70 | 3.95 | 120.93 | 3.21 |
| 2017-10-02 | 5.52 | -2.12 | 7.54 | 59.10 | -3.18 |
| ... | ... | ... | ... | ... | ... |
- Units
| Class | Variables | Units | Model Notation |
|---|---|---|---|
| Temperature | Tmax, Tmin, Td |
°C °F °K |
c f k |
| Wind Speed | ux | m s-1 m d-1 mi d-1 |
m/s, mps m/d, m/day miles/d, miles/day, mpd |
| Solar Radiation | Rn | MJ m-2 d-1 W m-2 d-1 cal cm-2 d-1 langley |
mj/m2, mj/m^2, mj/m2/d, mj/m^2/d, mj/m2/day, mj/m^2/day w/m2, w/m^2 cal/cm2', cal/cm2, cal/cm2/d, cal/cm^2/d, cal/cm2/day, cal/cm^2/day langley |
| Precipitation | Pr | in d-1 mm d-1 |
in/d, in/day, inches/d, inches/day mm/d, mm/day |
| Humidity | Q | kg kg-1 | kg/kg |
| Vapor Pressure | ea | kPa | kPa |
| Snow | Sn | in d-1 mm d-1 |
in/d, in/day, inches/d, inches/day mm/d, mm/day |
| Snow Depth | Sg | in mm |
in, inches, in*100 mm |
Mean monthly data are used to calculate a dew point temperature timeseries or gap fill the timeseries data if needed.
- Tmax = mean monthly maximum daily air temperature
- Tmin = mean monthly minimum daily air temperature
- ux = mean monthly wind speed at known height
- K0 = mean monthly dew point depression
- Delimiter:
See Timeseries Data - Delimiter
- Format: .csv, .txt, .dat
- Structure:
| Met Node ID | Met Node Name | Jan | Feb | Mar | Apr | May | Jun | Jul | Aug | Sep | Oct | Nov | Dec |
| BFAM | Blackfeet, MT | 2.6 | 3.0 | 7.3 | 11.6 | 16.8 | 21.5 | 28.3 | 23.5 | 17.9 | 13.6 | 7.3 | 1.7 |
T:sub:`max` example shown. File structure will be the same for Tmin, ux, and K0. Individual files are provided for each variable.
- Units
See Timeseries Data - Units
- Thornton and Running Coefficients * TRb0 * TRb1 * TRb2
Thornton and Running coefficients are used to estimate solar radiation from meteorological data. These coefficients are location-specific and should be calibrated using measured solar radiation data from a representative location. The calibration approach is described in detail :ref:`here <model-calibration-refet-tr>`
- Wind Measurement Height (in meters)
The user must provide daily weather and reference ET data for each ET zone. This includes:
- Date [in YYYY-MM-DD format]
- Tmax = maximum daily air temperature
- Tmin = minimum daily air temperature
- Td = mean daily dew point temperaturea
- ux = mean daily or hourly wind speed at known heightb
- Rn = calculated net radiation at the crop surfacec
- Q = specific humidity (optional)
- Sn = daily accumulated snow (optional)
- Sd = snow depth (optional)
and one of two reference ET values:
- ASCEr - Daily reference ET from Penman–Monteith
- ASCEg - Daily reference ET from Penman–Monteith
- Format: .csv
- Structure:
| Date | TMax | TMin | Precip | Snow | SDep | EstRs | EsWind | EsTDew | ETRef [ASCEr; ASCEg] |
| Units | [C] | [C] | [In] | [In] | [In] | [MJ/m2] | [m/s] | [C] | [mm/day] |
A shapefile containing the locations of each weather station is also required and is used to generate the static input files. The shapefile must contain the following attributes:
- STATION_ID - Weather station ID
- ETZONE_ID - Zone ID. This can include HUC8, HUC10, COUNTRYNAME, OR GRIDMET_ID
- LAT - Weather station latitude
- LON - Weather station longitude
- [optional] ELEV [ELEV_FT; ELEV_M] - Weather station elevation in feet or meters. This field is optional and only required if running the RefET model to estimate reference ET.
- Format: .shp
- Attribute Table Structure:
| STATION_ID | ZONE_ID [HUC8; HUC10; COUNTRYNAME; GRIDMET_ID] | LAT | LON | ELEV [ELEV_FT; ELEV_M] |
The user must provide a study area polygon shapefile with at least one feature. Each feature in the study area shapefile will become a separate ET cell/unit. Currently, only HUC8, HUC10, county, and gridmet cell shapefiles are fully supported by the prep tools.
Shapefiles containing features (polygons) attributed with AWC and hydrologic soils group information are required for running zonal statistics on the soil properties for each of the ETZones in the cell shapefile. The following attributes are required/used in the examples:
Available Water Capacity Shapefile (AWC_WTA_0to152cm_statsgo.shp is the example)
- AWC = available water capacity (in/in)
Percent Clay Shapefile (Clay_WTA_0to152cm_statsgo.shp is the example)
- Clay = percent clay (decimal)
Percent Sand Shapefile (Sand_WTA_0to152cm_statsgo.shp is the example)
- Sand = percent sand (decimal)
File Formats
Format: .shp
Attribute Table Structure (examples’ file structures shown):
AREA SYMBOL, SPATIALVER, MUSYM, MUKEY, MUKEY_1, AWC (or Clay or Sand depending on which shapefile)
Shapefiles containing features (polygons) attributed with a CDL code are required for ETDemands. The features should only include agricultural areas within the ETZones; the example CDL shapefile has removed all non-agricultural areas within the respective ETZones. The shapefile should have the following field:
- CDL (Int)
File Formats
- Format: .shp
- Attribute Table Structure:
CDL
These files will be generated automatically by the CropETPrep module
Crop coefficient curves for each crop. Generally, these values should not be modified. The crop coefficients are used in ETDemands to reflect changes of vegetation phenology of a particular crop or vegetation type over the growing season. The crop coefficient curves (60 count) represent changes in vegetation phenology, which can vary from year to year depending on the start, duration, and termination of the growing season, all of which are dependent on air temperature conditions during spring, summer, and fall. Three methods were used to define the shape and duration of the crop coefficient curves to allow curves to be scaled differently each year according to weather conditions based on relative time scales or thermal units. These methods are:
- Normalized cumulative growing degree-days from planting to effective full cover, with this ratio extended until termination (1=NCGDD)
- Percent time from planting to effective full cover, with this ratio extended until termination (4=%PL-Term)
- Percent time from planting to effective full cover and then number of days after full cover to termination (3=%PL-EC+daysafter)
File Format:
- Format: .txt
- Structure:
Curve no.: 1-60 Curve type: ‘1=NCGDD: 2=%PL-EC: 3=%PL-EC+daysafter: 4=%PL-Term Percent PL-EC or PL-TM (type 1-2-4) and/or Percent PL-EC+ days after (type 3)
GDD Base C GDD Type CGDD Planting to FC CGDD Planting to Terminate CGDD Planting to Terminate-alt Comment: Comment 2:
Crop parameters that can/should be modified during calibration.
- Format: .txt
- Structure:
Crop number and flag for crop type: negative is annual; positive in perennial Irrigation flag: 1-yes, 2-reg., 3-required Days after planting/green up for earliest irrigation: days Fw: assume sprinkler Winter surface cover class: 1-bare, 2-mulch, 3-sod Kc max: max of value or Kcb+0.05 MAD during initial and development stage: percent MAD during midseason and lateseason: percent Initial rooting depth, m: On alfalfa, 2nd cycle, start at max Maximum rooting depth, m: mrd End of root growth, as a fraction of time from pl to EFC (or term if type 4) Starting crop height, m: sch Maximum crop height, m: mch Crop curve number: ccn Crop curve name: ccn Crop curve type: 1=NCGDD, 2=%PL-EC, 3=%PL-EC,daysafter, 4=%PL-Term Flag for means to estimate pl or gu: 1=CGDD, 2=T30, 3=date, 4 is on all the time T30 for pl or gu or CGDD for pl or gu Date of pl or gu (can be blank): A negative value is an offset to the prior row, pos is months (fraction) For nCGDD based curves: Tbase: Temp Min. C (neg. For spec.)
CGDD for EFC: cgdd efc CGDD for termination: cgdd term
- For time based curves:
- Time for EFC: days after pl or gu Time for harvest (neg to extend until frost): Use as max length for CGDD crops
Killing frost temperature: C Invoke Stress: 1-yes, 0-no, 2-yes and will wake up after severe stress (Ks<0.05) Curve number:
Coarse soil Medium soil Fine soil
Flags controlling which crops to simulate. If using the prep workflow, the flags will initially be set based on the CDL acreage.
- Format: .txt
- Structure:
Number of Crops: XX, Crop Number (CDL): XX... ET Cell ID/ET Index, ET Cell Name, Ref ET ID/Met Node Id, ET Cell Irrigation (0 is off; 1 is on)
Reference ET scale factors by month for each ET cell. This file could be used to account for a seasonal bias in the input weather data. This file is optional.
- Format: .txt
- Structure:
Met Node ID, Met Node, Month….
Soil properties and weather station data for each ET cell. This file links the stations and the ET cells.
- Format: .txt
- Structure:
Sets the assumed number of alfalfa cuttings. This is important since the CropET module will use different crop coefficient curves for the first and last cutting.
- Format: .txt
- Structure:
ET Cell ID, ET Cell Name, Lat (DD), Number Dairy, Number Beef