In kvantas/erosivity: Rainfall Erosivity Calculation

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The R coefficient (MJ.mm/ha/h/yr) is defined as the long-term average of the product of the kinetic energy of a storm and the maximum 30 min intensity [@renard1991rusle]:

$$R = \frac{1}{n} \sum_{j=1}^{n} \sum_{k=1}^{m_j} (EI_{30})_{k}$$

where $n$ is the number of years with rainfall records, $m_j$ the number of storms during year $j$ and $EI_{30}$ the erosivity of storm $k$. The erosivity $EI_{30}$ (MJ.mm/ha/h) is equal to:

$$EI_{30} = \left( \sum_{r=1}^{m} e_r \cdot v_{r} \right) \cdot I_{30}$$

where $e_r$ is the energy of rainfall (MJ/ha/mm), $v_r$ the rainfall depth (mm) for the time interval $r$ of the hyetograph, which has been divided into $r = 1, 2, ..., m$ sub-intervals, such that each one of these is characterized by constant rainfall intensity and $I_{30}$ is the maximum rainfall intensity for a 30 minutes duration. The quantity $e_r$ is calculated for $r$ from the relation:

$$e_{r} = 0.29 \left( 1 - 0.72 e^{-0.05 \cdot i_{r}} \right)$$

where $i_r$ is the rainfall intensity (mm/h). The rules that apply in order to single out the storms causing erosion and to divide rainfalls of large duration are:

1. A rainfall event is divided into two parts, if its cumulative depth for duration of 6 hours at a certain location is less than 1.3 mm.
2. A rainfall is considered erosive:
3. if it has a cumulative value greater than 12.7 mm or
4. during a time period of 15 mins a cumulative value of at least 6.4 mm is recorded.

References

kvantas/erosivity documentation built on May 26, 2019, 5:42 p.m.