The MABIA Method is a daily simulation of transpiration, evaporation, irrigation requirements and scheduling, crop growth and yields, and includes modules for estimating reference evapotranspiration and soil water capacity. It was derived from the MABIA suite of software tools, developed at the Institut National Agronomique de Tunisie by Dr. Ali Sahli and Mohamed Jabloun. The algorithms and descriptions contained here are for the combined MABIA-WEAP calculation procedure.
The MABIA Method uses the ‘dual’ Kc method, as described in FAO Irrigation and Drainage Paper No. 56 (Spanish version of FAO 56), 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. In this way, MABIA is an improvement over CROPWAT, which use a single Kc method, and hence, does not separate evaporation and transpiration. This method can be used to model both agricultural crops as wells as non-agricultural land classes, such as forests and grasslands.
Although the timestep for MABIA is daily, the timestep for the rest of your WEAP analysis does not need to be daily (although it can be daily). For each WEAP timestep (e.g., monthly), MABIA would run for every day in that timestep and aggregate its results (evaporation, transpiration, irrigation requirements, runoff, and infiltration) to that timestep. For example, in January, MABIA would run from January 1 to 31, and sum up its results as January totals, including most importantly, the supply requirement for irrigation. WEAP would then solve its supply allocations, using this monthly irrigation requirement from the MABIA catchments. In the case where the supply delivered to the catchments was less than the requirement, MABIA would rerun its daily simulation, this time using only the reduced amount of irrigation to determine actual evaporation, transpiration, irrigation requirements, runoff, and infiltration.
The steps in the MABIA calculations are as follows:
Reference Evapotranspiration (ETref)
Soil Water Capacity
Basal Crop Coefficient (Kcb)
Evaporation Coefficient (Ke)
Potential and Actual Crop Evapotranspiration (ETc)
Water Balance of the Root Zone