erosivity fournier index

amontanaamontana Member
edited February 2014 in Freshwater Models
I have a question on the test data erosivity model soil retention, raster values ​​ranging from 2646-1004, however the quoted text in the user manual indicated values ​​ranging from 100 to 200 (aprox.) for that area (Salem Oregon) (page 50)

Does anyone know how to pass value index modified fournier (in hundreds) raster values ​​in thousands?

my study area in southern Chile, has similar values ​​aggressiveness Oregon rain

excuse my English by google translator
Post edited by amontana on


  • ArcGIS version requires the R (erosivity) values given in the table should each be multiplied by 1000??
  • swolnyswolny Member, NatCap Staff
    No, the erosivity values should not be multiplied by 1000. Erosivity is a raster layer, not specified in the coefficient table.

    ~ Stacie
  • Erosivity for the the InVEST model should be MJ*mm*(ha*h*yr)-1. The USDA publication gives erosivity in United States imperial units (ft*tonf*in*(ac*h*yr)-1) so the values would need to be converted to the metric unit equivalent.



  • edited February 2014
    For future reference, the conversion rate is 17.02 if going from imperial units using (hundreds of foot*tonf*inch)/(acres*hour*year) or 100*(ft*tonf*(in))*(ac*h*yr)-1 to metric units. Some agencies in the United States will report units in (foot*tonf*inch)/(acres*hour*year) or (ft*tonf*in*(ac*h*yr)-1) so the conversion in this situation should be 0.1702. Jess Silver recently found a useful conversion document and I have attached it here. Thanks Jess!


    Post edited by mlacayo on
  • For reference, the citation for the conversion document is actually Appendix A of Predicting soil erosion by water, a guide to conservation planning in the Revised Universal Soil Loss Equation. 1997. USDA Agricultural Research Service, Agricultural handbook no. 703

  • Thanks to all!

    In Chile the data available for the whole country are the Modified Fournier Index for trasnformarlos to R (erosivity) expressed in hJ/meter2 * cm / hr * r must divide the rainfall intensity in 30 minutes by a constant which is 173, 6 (it is assumed that the intense rainfall of 30 minutes is equal to the Modified Fournier Index)

    Now I have to convert hJ/meter2 * cm / yr in hr * MJ * mm / ha * yr * hr * ft or tonf * in (ac * yr * hr)

    I hope to find the answer here:
  • Hi amontana,
    I am also working with the MFI and I don't know how to convert that into R (erosivity), have you managed to do it?
    I speak Spanish if that's easier for you.
  • PerrinePerrine Moderator, NatCap Staff

    To convert from hJ m^-2 cm h^-1 yr^-1 to MJ mm ha^-1 h^-1 yr^-1, you need to multiply by 10,000.
    This is: /10 to convert hJ to MJ; then *10,000 to convert m2 to ha; then *10 to convert cm to mm.

    The document attached in amontana's post is the study by Renard et al. (1994) with the conversion from MFI to erosivity R (note that it is supposed to be for the US only but the paper reports alternative relationships for other regions).

    Hope this helps,
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