Irrigation water requirement of rice

Irrigation water requirement (IWR) of rice is the depth of water that must be supplied by irrigation to rice fields during the crop period, after deducting the effective rainfall, to meet crop evapotranspiration, seepage and percolation, land preparation (puddling) and standing-water needs:

$$\begin{aligned} IWR = ET_c + S\&P + WL + LP - P_e \end{aligned}$$

It is expressed in mm per period, or as a flow rate (l/s/ha).