Planting · 15 Dec
Allocation · 4.5 ML/ha

Rooting depth and depletion factor come from the crop, and change when you pick a different one. The two below control irrigation scheduling and bare-soil evaporation.

Basin Futures · Explorable models

How Basin Futures grows crops

Basin Futures grows crops with the FAO crop water model — crop water use from FAO Irrigation and Drainage Paper 56, yield from Paper 33. Rain and irrigation fill a store of soil water, the crop draws it down, and the days it runs short set the yield. This page runs that calculation against real weather from 1998 to 2020, on a paddock in the Namoi valley of New South Wales.

It is the standard method, not a Basin Futures invention: the same crop coefficients, the same soil water balance and the same yield response an agronomist would use by hand. Australia is the worked example because the yield and water-use records there are good enough to check the model against. Pick a different crop at the top and the weather stays put.

Namoi River at Wee Waa, New South Wales
reach 12515707 · 10,691 km² · Basin Futures Namoi model

Settings sit at the top of the page and drive every chart on it.

One season, day by day

The soil store holds a fixed amount of water the roots can reach. Depletion is how far below full it has fallen. Each day the crop takes Kc × evaporative demand, rain and irrigation put water back, and anything past the root zone drains away. While the store is wet the crop transpires freely; once depletion passes the readily available water the crop starts closing down, and that shortfall is what costs yield at picking.

Five seasons are offered below, picked from the record by how wet they were. Press play, or drag anywhere on the charts.

season
Rainfalldark = effective rain, the part the soil keeps
Irrigation applied
Soil water depletionshaded = below readily available water
Water stress

With and without an allocation

Basin Futures runs rainfed crops through the same equations as irrigated ones — they simply get no access to the river. Here is the same paddock twice, same soil and same weather, with and without the allocation set at the top.

Irrigated

—

Rainfed

no allocation, rain only

irrigation adds— per megalitre— rainfed failures—

Every season in the record

Twenty-two seasons of the same paddock. For cotton, the line is what New South Wales actually averaged; it mixes irrigated and dryland crops, so it sits above a thirsty paddock and below a fully watered one. Click any bar to open that season above.

Yield by season

Irrigation water appliedband = industry average for irrigated cotton, 6–7 ML/ha
Show the numbers as a table
mean yield— worst season— water applied— per megalitre—

Planting date and allocation

These two interact. An early crop meets the summer peak with a full profile but asks for more water; a late one cannot be rescued by irrigation whatever the allocation. Each cell is a complete twenty-two-season run. Click one to move the paddock there.

Mean yield

planting date →

1,512 full simulations, about a second.

Spreading a fixed volume

A district with a set volume of water can grow a small area well or a large area thinly. Because the yield–water curve bends, thin and wide produces more in an average season and less in the worst one.

District production against planted area

About this page. The model is FAO-56 crop coefficients with a daily soil-water balance, and yield from the FAO-33 water production function — the same calculation Basin Futures runs for every irrigated crop in every basin, checked against the simulator here.

Weather is MSWEP rainfall and CRU evaporative demand over the Wee Waa reach of the Basin Futures Namoi model, 1998 to 2020: 574 mm of rain and 1,610 mm of demand a year. Crop coefficients, planting calendars and yield ceilings are the simulator's own defaults. Observed yields are NSW cotton production and yield by season (NSW Department of Primary Industries), which mixes irrigated and dryland crops; the benchmarks — 10.9 to 11.9 bales per hectare fully irrigated, about 4 raingrown, 6 to 7 ML/ha applied — come from CRDC grower surveys and NSW DPI water-productivity benchmarking. One Australian bale is 227 kg of lint.

This is one paddock with a seasonal allocation, where the full model solves a whole district against river flow, on-farm storage and groundwater alongside every other water user. Two of Rooting depth, depletion factor and the irrigation schedule follow FAO-56, which is what the simulator now uses: water is ordered once the crop has used its readily available water, rather than topping the profile up every day. Models built before that change carry 500 mm, a depletion factor of 0.50 and daily watering for every crop; setting the trigger to zero above reproduces them.