The irrigation water demand model describes one or more
irrigation districts or units, that can range in size and
complexity from a single field to an entire regional irrigation
The model output is the daily or monthly irrigation water demand
in terms of river diversion or extraction/pumping requirements, which provides direct input
as a time series of water demand for a demand node of type "irrigated agriculture"
in the central water resources demand/supply, allocation and dynamic budgeting model
that provides the basis for the water management optimization.
The model input includes basic hydro meteorological data (precipitation and temperature
as well as humidity, wind speed and solar radiation depending on the evapotranspiration model used,
wind size and crop pattern of the irrigation object,
irrigation technology used, transmission, local (buffer) storage capacity and and pumping/conveyance
constraints, as well as soil characteristics and a linkage to the dynamic groundwater table.
The model uses tabulated physiological water demand values of major crops from an embedded data base of
Irrigated Crops over the vegetation period, similar to the
FAO CROPWAT approach to estimate weather dependent plant crop water requirements
and thus supplementary irrigation water demand in the growing season and computes
supplementary irrigation water requirements from that,
The model covers a range of irrigation technologies, their capacity constraints and
efficiencies (loss terms) including rice paddy cultivation. Local storage capacity
within the irrigation system can be used to smooth the water demand (extractions or diversion
from the water resources system) for the irrigation system. Return flow (drainage)
is also computed and can be fed back into the water resources network.
In parallel to the water requirement, the model can generate a simple cost-benefit analysis
for the irrigation operation (based on optimal, heuristic water allocation rules
with or without constraints, or more complex (multi-criteria) optimization scenarios.
The model output is presented in graphical format as
time series of the various components of the water budget,
which supports the calculation of multiple and overlapping
growing seasons for multiple crops.
The model can be structured for hierarchies of irrigation operations,
so that it can aggregate the output from numerous individual fields
and plots into large irrigation districts.
This possibility of a hierarchical representation makes it
possible to configure complex irrigation schemes at a high level of detail and realism.
The output, the dynamic supplementary irrigation water demand,
can be exported to be used in the overall water resources model (WRM)
where the respective irrigation district is represented as a demand node,
extracting water from the main system, and adding its return flow (drainage)
downstream of the irrigation district.
Irrigation districts can be included in the overall optimization model
to determine optimal size, crop distribution, irrigation technology, and/or local storage capacity.