Sensitivity Analysis of MPSIAC Model

Document Type: Research and Full Length Article

Authors

1 Islamic Azad University, Science and Research Branch-Tehran

2 Faculty member, Research Institute for Water Scarcity and Drought in Agriculture and Natural Resources (RIWSD), Tehran

3 Head of Soil Science Department, Islamic Azad University, Science and Research Branch-Tehran

Abstract

MPSIAC is currently known as an appropriate method to measure sediment of
Watershed basins of the country while there has not been any sensitivity analysis so far for
this method. In this study, required data for MPSIAC model were gathered from six basins;
Amame-Kamarkhani, Kand-Golandok, Tang Kenesht (from two different references), Nojian
(from three different references), Pegahe sorkh katvand (from one reference) and Ivanaki
(authors’ research). Eleven sensitivity analyses were conducted and the amount of sediment
was calculated using the sum of nine factors. Each input parameter was increased or
decreased by 20% using a computer program in Visual Basic in Excel. Then sensitivity of the
model for the parameters was analyzed. The less sediment has the basin, the less sensitivity
has the input parameters in the model. MPSIAC model has twenty input variables that
resulted in nine main factors. Erosion parameter (R) was calculated by adding nine main
factors and the quantity of sediment was calculated by an exponential function. By evaluation
of nine main factors, it was concluded that land use and Gully development were the most
sensitive factors. As a result, based on the area and sensitivity of main factors, more
investments must be done on the most sensitive factor to reduce soil erosion. In the
assessment of nine main factors occurred errors are reduced due to adding operation.
Regarding all items, each factor that has more input quantity has the highest sensitivity. As a
result, if score of each factor grows more than six, more attention must be paid to score
assignation. If occurred errors in assessment of nine factors did not neutralize each other and
have additive or decreasing on the R, by addition of 20% to R, it showed that this factor was
the most sensitive factor to run the model. If R is equal to 60 and 20% related to the error
occurred in calculation of it, 54% error occurs in estimating the amount of sediment and
sensitivity reaches to 2.7. This evaluation indicated that MPSIAC model for evaluation of
basins with the amount of sediment more than 2.2 ton/hectare must be used more preciously
because the model is so sensitive in this status and possible error may get over 50%.

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