What is AgriMet?
AgriMet, a conjunction of the words
"agricultural" and "meteorology", is a satellite-based network of
automated agricultural weather stations operated and maintained by the U.S. Bureau of
Reclamation. The stations are located in irrigated agricultural areas throughout the
Pacific Northwest and are dedicated to regional crop water use modeling, agricultural
research, frost monitoring, and integrated pest and fertility management
What do AgriMet Weather Stations
do?
Following is a representative list of the type of data
gathered by an AgriMet station:
Air
Temperature (degrees F)
Rainfall, Cumulative
(inches of water)
Solar Radiation, Cumulative (Langleys)
Diffuse Solar Radiation, Cumulative (Langleys)
Dew Point (degrees F)
Relative Humidity (%)
Wind Travel, Cumulative
(miles)
Wind Direction (degrees)
Peak Wind Gust in last 15 minutes (miles per hour)
Average Wind Speed in last hour (miles per hour)
Soil Temperature at 2 inches depth (degrees F)
Soil Temperature at 4 inches depth (degrees F)
Soil Temperature at 8 inches depth (degrees F)
Soil Temperature at 20 inches depth (degrees F)
Soil Temperature at 40 inches depth (degrees F)
How many AgriMet weather station
are there in the Northwest?
As of 1999, there are 54 weather stations within the
AgriMet net work.
How do I get
AgriMet information ?
There are two ways to obtain Agrimet
information:
1. Click here to select the AgriMet region and then the
station closest to you.
2. Go to the AgriMet web site and select the county you are
interested in.
What is CIMIS ?
CIMIS stands for California Irrigation
Management Information System. It is a network of standardized
weather stations scattered throughout California which report weather data on an hourly
basis. More importantly, the weather stations use this data to calculate ETo, which is a reference point for evaporative demand for that
micro-region.
How do I get
CIMIS information ?
There are two ways to obtain CIMIS
information:
1. Click here to select the region in California and then
the station closest to you.
2. Go to the CIMIS web site and register with their system.
What is ET ?
ET is the abbreviated acronym for evapotranspiration,
which is the combination of soil evaporation and plant transpiration. These
two processes represent the water loss from the plant-soil system due to evaporative
demand of the atmosphere.
What is ETo, versus ETp,
versus ETpan?
ETo is simply a reference number which represents an
estimate of evapotranspiration (ET) from an extended surface of 3 to 6 inch (8 - 15 cm)
tall green grass cover of uniform height, actively growing, completely shading the ground,
and not short on water. All of the CIMIS weather stations
throughout the state are situated within a small grass field which is optimally irrigated.
Thus, instruments attached to the weather station datalogger measure weather parameters
that would directly affect ETo estimates such as solar radiation, air temperature,
humidity, wind and rain. This data is incorporated within the weather station's database
and calculates a reference evapotranspiration (ETo) number every hour.
ETp is another type of reference ET, but is the ET from a full-growth field of
alfalfa. It was one of the earliest references used for irrigation scheduling and is
still used in many systems.
ETpan is another type of reference, probably the most widely used in the world.
It is the evaporation from a U.S. Weather Bureau Class A evaporation pan. This pan,
like sites used for gathering data needed to compute ETo and ETp, has standards for size,
color, installation, water depth, screening for birds, etc. etc.
What is a Crop Coefficient ?
A crop coefficient (normally identified as Kc) is merely a
numerical factor that relates the ET of the individual crop (ETc) to the reference
ET.
ETc = Kc * reference ET
Note that there are several types of reference ET.
The ETo reported by the CIMIS weather station network is just one type. Make sure
that the Kc that you are using has been developed for the reference ET that you are
using. That is, do not use a Kc developed for use with ETp if your reference ET is
ETo.
How many CIMIS weather
station are there in California?
As of early 1998, there are 95 weather stations within the
CIMIS net work.
Where is the closest CIMIS
station to me ?
Refer to the state and
district maps to find your local CIMIS station.
What is irrigation scheduling
and why is it important ?
Irrigation scheduling is a generic term for a number of
techniques that aide the irrigator in determining when and how much to irrigate.
When to irrigate is usually an agronomic question. That is, do you want to irrigate
to avoid stress or, as is the common situation with a crop like wine grapes, irrigate to
induce a certain amount of stress. How much to irrigate generally depends on the
type of irrigation system. If it is a low-frequency flood-type system, furrows or
border checks, "how much" to irrigate is generally the soil moisture deficit in
the root zone plus any leaching fractions needed to maintain a salt balance. With
high-frequency, micro-irrigation systems the "how much" is a calculation of
required hours of operation based on the estimated crop water use.
What is irrigation efficiency
?
Irrigation efficiency (IE) is a measure of how much applied
water is used beneficially. A general equation for irrigation efficiency would be:
IE = Beneficial Use of Applied
Water / Total Applied Water
The two main beneficial uses are crop water use
(evapotranspiration, ETc) and leaching to maintain a salt balance. The problem
in determining an exact number for IE is that IE involves both a question of physical
boundaries and time. That is, is IE determined for the individual irrigation on a
field, for an entire season on the field, for the farm, for the irrigation district,
etc.? It is not generally possible to achieve 100% IE due to immediate evaporation
losses during an irrigation. An exception might be a sub-surface drip system that
was managed to under-water the crop.
What is distribution
uniformity?
Distribution uniformity (DU) is a measure of how evenly
water is applied across a field. If 4 inches of water infiltrates in one part of a
field during an irrigation and 2 inches infiltrates in another, that is poor
uniformity. There are many ways to calculate DU. One of the most common is
termed the "low 1/4 DU".
DUlow 1/4 = average depth of
infiltration in the 25% of the field receiving the least applied water
average depth of infiltration in the entire field
You might also see a DU determined using the average depth
in the least-watered 1/8 of the field, or even using the lowest measured infiltration.
What is emission uniformity?
Emission Uniformity or EU is a term strictly applied to
microirrigation systems. Emission Uniformity is a more complicated equation than
distribution uniformity and involves measured emitter flows, the number of emitters per
plant, and the coefficient of manufacturing variation. Like DU, EU can be calculated
using different basis, the lowest 25% of measured emitter flows, lowest 1/8 of emitter
flows, absolute lowest flow, etc. The equation is:
EU(%) = 100 * (1.0 - 1.27 / n½ * Cv) * Qn / Qa
where:
EU(%) = Emission Uniformity as a percent
n = number of emitters per plant
Cv = coefficient of manufacturing variability
Qn = the average (or absolute minimum) flow of the basis (i.e. if the basis was low
1/4, then this would be the average of the lowest 25% emitters measured)
Qa = average emitter flow
Looking at the equation one can see as Cv is higher, then
the EU is lower. That is, as the variability of the manufacturing process increases,
the expected uniformity in the field decreases. Conversely, as the number of
emitters per plant increases, then the EU will increase. This is because it is
expected that the effects of Cv (variability in the manufacturing process) will be random,
thus some emitters will flow lower than design, some higher. The more emitters per
plant, the more this variability will be "evened out".
