Crop Library

This screen is used in conjunction with the MABIA Method for catchment hydrology and crop water requirements.  For the Plant Growth Method, see Plant Growth Model Method, Crop Library

WEAP comes with a built-in library of crop data for over 100 crops and land use types, some with multiple entries for different climates or regions of the world.  (Many of these data and the descriptions of them come from FAO Irrigation and Drainage Paper No. 56.  This document is an excellent resource for computing crop water requirements.  Full text is available online at (PDF) and (HTML).)  These data are used to estimate evapotranspiration, irrigation requirements, and yields.  You can edit this library or add to it.  Buttons on the toolbar at the top allow you to add, delete or rename crops.  The Copy button will create a new crop as a copy of the highlighted crop.  You can export one or more crops to a comma separated value (CSV) file, which can be edited in Excel or a text editor.  All the crops currently shown on screen will be exported.  You can import crops from a CSV file--new crops can be added in this way, or data for existing crops can be updated.  When reading in from the file, WEAP will match both the crop name and typical planting month.  This is because there can be multiple entries for the same crop, but with different planting dates.  The format for the CSV file to import must be the same format as is created when exporting--the same columns of data in the same order.  Each WEAP area (dataset) has its own copy of the Crop Library.  Therefore, changes made to the library in one area will not affect the library of another area.  You can use import and export to move values from one area's library to another.

By default, the Crop Library screen will at first show you only the crops that are currently in use in your area (those that have been assigned to catchment branches in the Data View, under Land Use).  To see all crops in the library, change the selection in the upper left from "Show Only Crops in Use" to "Show Entire Crop Library."  You can also search for a crop by entering all or part of its name or the name of its category, in the search box on the upper right of the toolbar.  For example, type Fruit into the search box.  You can view multiple crops at once (List View) or one at a time (Single View).

The following columns of information exist for each crop:

Crop or Land Use

The name of the crop or land use, including a specific climate or region to which the data are relevant.  Note that you can use the MABIA Method to model both agricultural crops as wells as non-agricultural land classes, such as forests and grasslands.  The first "crop" in the list is a special one named "Fallow," which will automatically be used to model the days before and after other crops are active.  For example, if spinach was planted April 15 - July 23, "Fallow" would be used from January 1 - April 14, and July 24 - December 31.  If you would prefer to differentiate the fallow period after different crops, e.g., the period after a spinach crop vs. after a wheat crop, you could create other "Fallow" crops, such as "Fallow after spinach" and "Fallow after wheat", assign the appropriate characteristics to these after-harvest states, and then choose those fallow "crops" after the main crops in the Crop Scheduling Wizard.


The crops are grouped into categories, such as Small Vegetables, Legumes, and Oil Crops.  You can change the category of a crop using the selection box in the grid.  You can also edit the list of categories--click the "Category" button on the toolbar at the top.

Typical Planting Month

This text field is for information only.  You will need to specify the planting day and month for any crops you use in your analysis.  Note that in some cases there are multiple entries for the same crop (e.g., Lettuce (Mediterranean)) with different typical planting months.  For example, look at Lettuce (Mediterranean), whose entries for April and Nov/Jan have different stage lengths (the Winter crop has a longer season).

Stage Length

Stage length provides general lengths for the four distinct growth stages for various types of climates and locations: Initial period (planting or green ground cover), Crop Development period (from 10% ground cover until about 70% ground cover and higher), Mid-season period (from 70% ground cover to the beginning of the late season period and the onset of senescence), and Late Season period (beginning of senescence or mid grain or frost-kill, or full senescence).  Perennial crops should have a total growing period of 365 days.

The lengths of the initial and development periods may be relatively short for deciduous trees and shrubs that can develop new leaves in the spring at relatively fast rates.  The rate at which vegetation cover develops and the time at which it attains effective full cover are affected by weather conditions in general and by mean daily air temperature in particular. Therefore, the length of time between planting and effective full cover will vary with climate, latitude, elevation and planting date. It will also vary with cultivar (crop variety). Generally, once the effective full cover for a plant canopy has been reached, the rate of further phenological development (flowering, seed development, ripening, and senescence) is more dependent on plant genotype and less dependent on weather.

The end of the mid-season and beginning of the late season is usually marked by senescence of leaves, often beginning with the lower leaves of plants. The length of the late season period may be relatively short (less than 10 days) for vegetation killed by frost (for example, maize at high elevations in latitudes > 40°N) or for agricultural crops that are harvested fresh (for example, table beets and small vegetables).

High temperatures may accelerate the ripening and senescence of crops. Long duration of high air temperature (> 35°C) can cause some crops such as turf grass to go into dormancy. If severely high air temperatures are coupled with moisture stress, the dormancy of grass can be permanent for the remainder of the growing season. Moisture stress or other environmental stresses will usually accelerate the rate of crop maturation and can shorten the mid and late season growing periods.

These values are useful only as a general guide and for comparison purposes. The listed lengths of growth stages are average lengths for the regions and periods specified and are intended to serve only as examples. Local observations of the specific plant stage development should be used, wherever possible, to incorporate effects of plant variety, climate and cultural practices.


The MABIA Method uses the ‘dual’ Kc method, whereby the Kc value is divided into a ‘basal’ crop coefficient, Kcb, and a separate component, Ke, representing evaporation from the soil surface. The basal crop coefficient represents actual ET conditions when the soil surface is dry but sufficient root zone moisture is present to support full transpiration.  The crop coefficient curve represents the changes in Kcb over the course of the growing season, depending on changes in vegetation cover and physiology. During the initial period, shortly after planting of annuals or prior to the initiation of new leaves for perennials, the value of Kcb is often small.  Only three values for Kcb are required to describe and construct the crop coefficient curve: those during the initial stage, the mid-season stage and at the end of the late season stage.  A typical curve is illustrated below.

Many crops grown for forage or hay receive multiple harvests during the growing season. Each harvest essentially terminates a “sub” growing season and associated Kcb curve and initiates a new “sub” growing season and associated Kcb curve. The resulting Kcb curve for the entire growing season is the aggregation of a series of Kcb curves associated with each sub cycle.  To handle this situation, the crop library has different entries for the first cutting and subsequent cuttings.  (Search for alfalfa in the crop library to see an example.)  Specify multiple crops (in the Crop Scheduling Wizard) for a particular branch, where the first crop chosen is that for the first cutting, and the second (and third) crop is for the crop specifying the subsequent cutting's parameters.

Depletion Factor

The depletion factor is the fraction of total available water (TAW) that a crop can extract from the root zone without suffering water stress.  The depletion factor normally varies from 0.30 for shallow rooted plants at high rates of ETc (> 8 mm d-1), to 0.70 for deep rooted plants at low rates of ETc (< 3 mm d-1). A value of 0.50 is commonly used for many crops.

Yield Response Factor (Ky)

The response of yield to water supply is quantified by the yield response factor (Ky) which relates relative yield decrease (1-Ya /Ym) to relative evapotranspiration deficit (1-ETa /ETm), where Ya, Ym, ETa and ETm represent actual and maximum yields and evapotranspiration. Hence, the Ky values for most crops are derived on the assumption that the relationship between relative yield (Ya /Ym) and relative evapotranspiration (ETa /ETc) is linear and is valid for water deficits of up to about 50% or 1 - ETa /ETc = 0.5.  The higher the yield response factor, the greater the decrease in yield for a given evapotranspiration deficit.

The yield response will vary according to the individual growth periods in which it occurs; these growth periods, ordered from least to most sensitive to evapotranspiration deficit, are: ripening, vegetative, yield formation, and flowering.  Although these growth periods do not exactly correspond to the four crop growth stages (initial, crop development, mid-season and late season), for the sake of simplicity they are considered the same.  If you do not have data on Ky for individual growth periods, enter it in the column labeled "Overall."

Maximum Height

The maximum height of the crop, which will occur in the mid-season stage.

Minimum Root Depth

Initial depth of roots.

Maximum Root Depth

Maximum depth of roots, which will occur in the mid-season stage.  The rooting depth determines the total available water for evapotranspiration.

See also: MABIA Calculation Algorithms

Menu Option: General: Crop Library (only available if there is at least one catchment on the schematic whose method is "MABIA.")