Stress index

Within WARM_WL a water stress index is calculated in order to estimate the impact of water shortage on both growth and development processes.

The water stress index (ranging from 0 to 1; 1 = no stress) is simply the ratio between the actual and the potential rate of transpiration. The actual rate of transpiration is not calculated within the model, whereas the potential transpiration rate is the minimum between potential transpiration and potential root water uptake, calculated as follows:

where TP is potential transpiration, Kc a crop coefficient used to correct reference evapotranspiration (ET0) for rice, k is the extinction coefficient of solar radiation and GLAI the green leaf area index.

where WUP is potential water uptake, WUPmax the maximum water uptake of full canopy, k is the extinction coefficient of solar radiation and GLAI the green leaf area index.

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