mrwater Assumptions

Overview

The following document provides an overview of assumptions that the mrwater library is based on.

Zero Irrigation Water Requirements

The allocation of potentially irrigated areas (PIA) is based on the total volume of water requirements (sum of water requirements over all crops grown under the selected cropmix) that is compared to the available water (see calcRiverDischargeAllocation). For the case that crop-specific irrigation water requirements are reported to be 0 in the input data, no irrigation area is assigned to these crops in the algorithm that derives PIA because the assumption is that irrigation is not required there and therefore rainfed production takes place (see calcPotIrrigAreas).

print(paste0("Total rainfed area is, ",
              round(sum(rfArea), digits = 2),
              " Mha."))
print(paste0("Of these, ",
             round(sum(rfArea[cropIrrigReq == 0]), digits = 2),
             " Mha have 0 water requirements."))
print(paste0("That is, ",
             round(sum(rfArea[cropIrrigReq == 0]) / sum(rfArea) * 100, digits = 2),
             " % of rainfed land."))

However, for the scenario of ‘committed agricultural uses’ where areas that are already irrigated are reserved for irrigation before the allocation of additional potentials, areas that are reported to be irrigated but show 0 irrigation water requirements (ca. 0.43 Mha, i.e. 0.18% of irrigated area), areas are assigned to be irrigated (see calcIrrigAreaActuallyCommitted) to avoid data mismatches in the area accounting.

print(paste0("Total irrigated area is, ",
             round(sum(irArea), digits = 2),
             " Mha."))
print(paste0("Of these, ",
             round(sum(irArea[cropIrrigReq == 0]), digits = 2),
             " Mha have 0 water requirements."))
print(paste0("That is, ",
             round(sum(irArea[cropIrrigReq == 0]) / sum(irArea) * 100, digits = 2),
             " % of irrigated land."))