Irrigation system water allocations are, most often, based on assumptions about the
irrigated area, crop types, and the near-surface meteorological conditions that determine
crop water requirements. Hydraulic designs for canals are based on the peak flow rate
required to meet some minimum fraction of the crop water requirement. Remote sensing
enables regular updating of irrigated areas that tend to deviate substantially from the
original estimates of irrigation command areas. Cropping patterns may have changed due
to influences of market mechanisms, water logging, or scarcity due to restricted or
unreliable canal water supply. Even in demand-based systems, knowledge from field conditions, including crop stress, can help managers forecast how much water should be
released from the reservoir