Irrigation

Two water management systems are implemented for agricultural land: irrigation and rain-feeding. The percentage of total agricultural land under irrigation is a non-linear function of GDP per capita:

FeliX formula for irrigated area σ, expressed as a fraction of agricultural area. σMIN and σMAX represent lower and upper (a priori) limits on irrigated area, and are defined to be 0 and 1, respectively. GDPpc is global productivity per capita (variable), and GDP† is a reference value calibrated to 120,000 (US$2005 per capita).

FeliX formula for irrigated area σ, expressed as a fraction of agricultural area. σMIN and σMAX represent lower and upper (a priori) limits on irrigated area, and are defined to be 0 and 1, respectively. GDPpc is global productivity per capita (variable), and GDP† is a reference value calibrated to 120,000 (US$2005 per capita).

The plot below traces the expansion of irrigation systems through 2100, explicitly displaying the percentage of agricultural land under irrigation (σ). This high-efficiency water management strategy is predicted to expand over 300% by the end of the century. Also shown is rain-fed area, which oscillates within a smaller range over the same period.

water_Agricultural_Water_Demand.png

For simplicity, average areal water consumption is primarily dependent on management system (binary) and secondarily linked to GDP per capita. Water use is not dependent on agricultural land subclassifications. Areal water demand is parameterized by GDP, growing with agricultural intensification according to the following equation:

FeliX formula for areal water demand (ω) of irrigated (I) and rain-fed (R) land. Demand is scaled between ω MIN (I,R) = (0.005, 0.005) and ωMAX (I,R) = (0.05, 0.1), representing minimum and maximum water demand, respectively.  GDP†(I,R) are reference values calibrated to (4,000, 8,000) (US$2005 per capita).

FeliX formula for areal water demand (ω) of irrigated (I) and rain-fed (R) land. Demand is scaled between ω MIN (I,R) = (0.005, 0.005) and ωMAX (I,R) = (0.05, 0.1), representing minimum and maximum water demand, respectively.  GDP†(I,R) are reference values calibrated to (4,000, 8,000) (US$2005 per capita).

otal demand through 2100 is in the lower half of the plot above. Over this period, intensification and expansion lead to a 60% increase in total agricultural water demand.