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Drought Resistance Index Calculator

Compute agricultural stress indices (STI, SSI, MP, TOL) to evaluate crop yield performance under drought conditions vs normal irrigation.

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About

Agricultural research relies on quantitative metrics to determine which crop genotypes possess superior drought resilience. The Drought Resistance Index Calculator allows agronomists and plant breeders to compute standard stress indices based on yield performance. By comparing Yield under Stress (Ys) against Yield under Potential/Normal conditions (Yp), researchers can isolate genetic potential from environmental noise.

This tool computes the Stress Tolerance Index (STI), Stress Susceptibility Index (SSI), Mean Productivity (MP), and Tolerance (TOL). These metrics are critical for identifying varieties that maintain high stability across varying hydrological environments versus those that only thrive in high-input systems. A built-in reference database provides baseline yield data for major global crops to assist in comparative analysis.

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Formulas

The calculation relies on the individual yields and the overall experimental means. The Stress Intensity (SI) of the environment is first calculated as:

SI = 1 − YsYp

Where Ys is the mean yield of all genotypes under stress, and Yp is the mean yield under normal conditions. A higher STI indicates a genotype that performs well in both environments.

Reference Data

Index NameFormulaInterpretation Strategy
Stress Tolerance Index (STI)Yp × YsYp2Higher is better. Selects for high yield in both conditions.
Stress Susceptibility Index (SSI)1 − (Ys / Yp)SILower is better. Indicates stability (less change between conditions).
Mean Productivity (MP)Yp + Ys2Higher is better. Favors high average yield regardless of stability.
Tolerance (TOL)Yp − YsLower is better. Represents the absolute yield loss.

Frequently Asked Questions

For semi-arid regions where drought is frequent but not constant, the Stress Tolerance Index (STI) is often preferred. STI penalizes genotypes that have low potential yield even if they are stable. You want a crop that survives drought but also responds vigorously when rain does occur.
Calculations like the Stress Susceptibility Index (SSI) require the "Stress Intensity" of your specific trial environment. This normalizes your results. A drop of 1 ton/ha might be catastrophic in a mild drought year but excellent performance in a severe drought year; the Mean Yields provide this context.
A high Tolerance (TOL) value indicates a large gap between potential yield and stress yield. This usually means the crop is highly sensitive to stress (low resistance). Breeders typically look for lower TOL values combined with acceptable Mean Productivity.
Yes. The formulas are mathematically agnostic. As long as you have a quantifiable yield metric (biomass kg/ha, fruit count, root weight) for both stress and non-stress conditions, the indices are valid.