The agricultural systems of the Canterbury plains use surface and groundwater for irrigation. These withdrawals from rivers and aquifers causes an incremental ET, which needs to be considered as an additional ET for which regulations on water use has to be developed. Water permits are in place to control these developments, but the diffusive character of the withdrawals and limited reporting causes an incomplete picture on the irrigation developments and consequences for the sustainability of the groundwater systems.

The main objective of this study is to determine the feasibility of evapotranspiration monitoring using satellite technology. Sub-areas with likely irrigation practices will be identified, and the incremental ET due to irrigation will be assessed. The study will contribute to quantifying the effect of irrigation on the groundwater budget for any particular area (probably a groundwater management zone). Irrigation will refill the root zone with moisture and result in increased percolation to the water table as a result of the reduced potential for storage of rainfall within the soil profile and the inherent inefficiencies of irrigation.  The modified water balances need to be understood for ensuring a controlled exploitation of the aquifers.