Calculation of Rainfall erosivity index(R)

I am working on SDR model in India. It will be immensely helpful if anyone suggests any way for calculating Rainfall erosivity index (R) for India.

Thanks in advance.

Manas

Comments

  • swolnyswolny Member, NatCap Staff
    Hi Manas -

    When we did a project in India, we used an equation from Singh et al that uses annual precipitation values, and is referenced in this paper, among others. You might also try looking for USLE studies that have been done in your area, which may give similar equations that are more tuned to that particular place.

    ~ Stacie
  • Thank you very much swolny 
  • And one more clarification. Can I use SDR model on yearly basis if I use equation for calculating R value which uses annual rainfall values?
  • swolnyswolny Member, NatCap Staff
    The SDR model is intended to be used with long-term average annual climate data, and will produce corresponding annual average sediment export and retention results. It is not generally intended to predict erosion in a particular year. So when you are creating the erosivity layer, you should use rainfall data that is calculated from at least 10 years of continuous rainfall data. WorldClim and others provide this on a global scale. If you are calculating annual rainfall from local rain gauges, you should look closely at the gauge data to see how many years it covers, are there any major gaps in reporting, etc.

    ~ Stacie
  • PerrinePerrine Moderator, NatCap Staff
    Hi both,

    One clarification point: the erosivity layer *can* be used at the annual time step if you have precipitation data at a fine time step (<30min). 

    As Stacie mentioned, in practice, many regression equations at the annual time step are derived for the average annual erosivity, so I wouldn't necessarily use those to derive annual erosivity layers. 
    However, if you have the 30min precipiation data in your region, you can calculate the rainfall "Energy Intensity" factor, following the procedures given in the RUSLE manual (Renard et al. 1997). This would give you values for your annual erosivity.

    Best,

    Perrine

    Ref:
    Renard, K., Foster, G., Weesies, G., McCool, D., Yoder, D., 1997. Predicting Soil Erosion by Water: A Guide to Conservation Planning with the revised soil loss equation. Agriculture Handbook No. 703
  • manasmanas Member
    Thanks to both of you for your clarification.
     I have total suspended sediment value in gm/L unit and corresponding discharge data in cumec unit. So if I want to calculate the amount of sediment transported per day, then can I do this in the following way? suppose Q= 1 m^3/sec and TSS(total suspended sediment load)=2 gm/L.  Then total sediment transported per day =  1*2*24*3600 kg/day=172800 kg/day=172.8 ton/day. Have I done any mistake? please help
  • PerrinePerrine Moderator, NatCap Staff
    Hi manas,

    Assuming gm means gram in the above, you are right. 
    (I initially thought there was a typo and that you meant mg/L (milligrams per liter), which is common for TSS). If that's the case, you are missing a factor 0.001.)

    Cheers
  • manasmanas Member
    Thanks Perrine.

    Is the unit of sed_export in ton/ha/yr in the output shape file?

    Please clarify.

    Manas
  • PerrinePerrine Moderator, NatCap Staff
    Hi manas,
    sed_export is in tons per watershed: see User's guide: section Interpreting results for details.
    Best,
    Perrine
  • manasmanas Member
    edited March 2016
    Hi Perrine,
    The unit of total exported sediment (E) is ton/ha/yr as mentioned in the User's guide. so we need to multiply by the area of the watershed(ha) to get the exported sediment amount in ton/yr. so  keeping in mind the unit of E, I want to know whether area is already considered in generating the sed_export output  value in tons per watershed because I am getting very less value of sed_export from the model.  
    Please help.
    Post edited by manas on
  • PerrinePerrine Moderator, NatCap Staff
    Hi, 
    Sorry if this wasn't clear. 
    The shapefile output for sediment export is in ton per watershed, and the raster provides values of ton per pixel.
    To obtain these values, the model multiplies the USLE values (in ton/ha/yr) by the pixel size in ha.
    Hope this helps!
Sign In or Register to comment.