# Terminology and Background

## Key Terms and Definitions

### Rainfall Intensity (I)

The rate of rainfall expressed in millimetres per hour (mm/hr). It describes how fast rain falls during a storm event.

### Maximum 30-minute Intensity (I30)

The maximum rainfall intensity recorded over any 30-minute period during a storm. Expressed in mm/hr. This is a key parameter in soil erosion prediction.

### Kinetic Energy (E)

The energy delivered by raindrops to the soil surface. Calculated from rainfall intensity using empirical equations such as Brown & Foster (1987), Wischmeier & Smith (1978), or McGregor & Mutchler (1976).

### Erosivity Index (EI30)

The product of total storm kinetic energy (E) and maximum 30-minute intensity (I30). It quantifies the erosive power of a rainfall event:

`EI30 = E x I30`

### Erosivity

The ability of rainfall to cause soil erosion. Higher erosivity means greater potential for detaching and transporting soil particles.

### Breakpoint Rainfall Data

Rainfall data recorded at irregular or regular time intervals where each record represents the depth of rain (mm) that fell during that interval.

### USLE — Universal Soil Loss Equation

An empirical model used to estimate average annual soil loss from a field. EI30 is the rainfall erosivity factor (R factor) in the USLE.

### RUSLE — Revised Universal Soil Loss Equation

An improved version of the USLE incorporating updated equations and additional factors for better soil loss prediction accuracy.

### Hydrological Analysis

The study of water movement, distribution, and quality in the environment. Rainfall intensity and erosivity are key inputs in hydrological modeling.

## References

- Brown, L.C. and Foster, G.R. (1987). Storm erosivity using idealized intensity distributions. Transactions of the ASAE, 30(2), 379-386.

- Wischmeier, W.H. and Smith, D.D. (1978). Predicting rainfall erosion losses. USDA Agricultural Handbook, No. 537.

- McGregor, K.C. and Mutchler, C.K. (1976). Status of the R factor in northern Mississippi. Soil Erosion: Prediction and Control, 135-142.