WaterCROP

Introduction

WaterCROP is an evapotranspiration model to estimate the crop water demand by source (rainfall plus irrigation) as a function of the soil moisture available in the soil and the potential for irrigation expansion (by source, surface water or groundwater bodies) based on current yield gap. Originally introduced in Tuninetti et al. (2015) and written in the Matlab scientific computing programming language, WaterCROP performs separated water footprint computations by rainfed and irrigated production conditions and by growing season of multiple crops at the spatial resolution of 5 × 5 arc min.

WaterCROP performs spatially-explicit estimates of daily crop-specific actual evapotranspiration (ETa,j) that a crop consumes via evapotranspiration throughout the growing season. For rainfed production, WaterCROP computes the water stress coefficient (ks,j) through a daily steady state water balance. In this case, every time water from precipitation is not sufficient for optimal evapotranspiration, the crop becomes stressed and the water stress coefficient drops below 1. For irrigated production, the model assumes that the crop receives all the water required to optimally evapotranspire via irrigation, even when water is not available from precipitation. Hence, the water stress coefficient is equal to 1 throughout the growing period. Taking the sum of the daily ETa,j values for the entire growing season gives the annual actual evapotranspiration (ETa) estimate for a crop in a grid cell. Therefore, ETa is evaluated over different time intervals and for each study crop, thus providing multiple scenarios of crop water requirement. Furthermore, WaterCROP computes the green (ETRa,g and ETIa,g) and blue (ETIa,b) shares of the crop actual evapotranspiration over the growing period, in order to evaluate the distinct contributions of precipitation (green) and irrigation (blue) water to the crop water footprint. Thus, the crop water footprint is provided as disaggregated in its green (uWFg), blue (uWFb), rainfed (uWFrf), irrigated (uWFirr) components and it is evaluated both in volume (m3) (WF) and per unit of production (m3·ton-1) (uWF).

Model structure

WaterCROP has two modules:

1. Main module WaterCROP1_ETactual.m estimates crop-specific actual evapotranspiration in its rainfed, irrigated, blue and green components.
2. WaterCROP2_Irrigation_requirements.m module computes the irrigation requirements associated with all the scenarios for closing the water gap on rainfed areas and the respected crop yield achieved

• WaterCROP1_ETactual.m - parameters to be inputted manually:

in line 3 input the working directory (i.e. the folder path containing the WaterCrop database downloaded from Zenodo).

in line 10 input the Potential evapotranspiration data folder path (available in the official Zenodo repository of the RE4AFAGRI platform).

in line 27 input the Precipitation data folder path.

in line 61 input the working directory.

in line 63 select the desired crops to be included in the run and define, for each of them, the data folder path and the results folder path.

in line 387 input the working directory.

• WaterCROP2_Irrigation_requirements.m - parameters to be inputted manually:

in line 12 input the working directory.

in line 17 input the folder path to the outputs of module 1.

in lines 23, 58, 72 input the folder path to the outputs of module 1, taking care of preserving the different sub-folders indicated in the code.

in line 217 define results folder.

Input data and scenarios

WaterCROP accomodates 5 arc minute (1/12°; ∼ 10 km) input data and crop-specific information. Precipitation and reference evapotranspiration data are required as input data to the model, as well as crop yields (ton·ha-1) and harvested areas (ha), crop coefficients, water stresss coefficient, planting date, length of growing period, soil available water content, root zone depth and the depletion fraction.

The ETa,j estimate is equal to the product of: the daily water stress coefficient (ks,j), that is a proxy for the daily water deficiency in the unsaturated soil layer; the daily crop coefficient (kc,j), that integrates the effects of crop height, crop-soil surface resistance, and albedo of the crop-soil surface; and the daily ET0 from a hypothetical well-watered grass surface with fixed crop height, albedo and canopy resistance

Running the model

Analysing the outputs

Runtime, frequent issues, and FAQs

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Preparing a new country analysis and designing a new scenario

Refer to the Examples and exercises page for details