Irrigation Water Demand for Crops

This model simulates the daily Crop Coefficient (Kc) for one or more crops throughout their respective growing seasons. The resulting Kc time series can be used, typically by multiplying with Reference Evapotranspiration (ETo), to estimate Crop Evapotranspiration (ETc) for irrigation scheduling or water resource management studies.

The model implements the single crop coefficient approach as described in the FAO Irrigation and Drainage Paper 56. It simulates the four standard crop growth stages:

1. Initial Stage: Germination, to 10% ground cover
2. Crop Development Stage: Rapid vegetative growth, increasing ground cover to around 70-80%
3. Mid-Season Stage: Full canopy, maximum ground cover, peak physiological activity, and maximum evapotranspiration
4. Late Season Stage: Maturation and Senescence, fruit ripening, grain filling completion and drying, leaf senescence, general decline

Kc values are determined based on user-defined inputs for the initial (Kc_ini), mid-season (Kc_mid), and end-of-late-season (Kc_end) stages.

• Kc remains constant during the Initial (Kc_ini) and Mid-Season (Kc_mid) stages.
• Kc is linearly interpolated between Kc_ini and Kc_mid during the Crop Development stage.
• Kc is linearly interpolated between Kc_mid and Kc_end during the Late Season stage.

A key feature of this model is the use of stochastic durations for each growth stage (Dur_Init, Dur_Dev, Dur_Mid, Dur_Final). Instead of fixed average values often cited in literature, durations are sampled from user-defined probability distributions (e.g., Normal). This approach allows the model to represent the natural variability and uncertainty inherent in crop development timing while ensuring robust sequential progression through the stages across multiple simulation realizations (Monte Carlo runs). While conceptually aligned with the FAO 56 framework, this method explicitly incorporates uncertainty in stage length.

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