sensitivity analysis of mpsiac model

mpsiac is currently known as an appropriate method to measure sediment ofwatershed basins of the country while there has not been any sensitivity analysis so far forthis 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 sedimentwas calculated using the sum of nine factors. each input parameter was increased ordecreased by 20% using a computer program in visual basic in excel. then sensitivity of themodel for the parameters was analyzed. the less sediment has the basin, the less sensitivityhas the input parameters in the model. mpsiac model has twenty input variables thatresulted in nine main factors. erosion parameter (r) was calculated by adding nine mainfactors and the quantity of sediment was calculated by an exponential function. by evaluationof nine main factors, it was concluded that land use and gully development were the mostsensitive factors. as a result, based on the area and sensitivity of main factors, moreinvestments must be done on the most sensitive factor to reduce soil erosion. in theassessment 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 aresult, if score of each factor grows more than six, more attention must be paid to scoreassignation. if occurred errors in assessment of nine factors did not neutralize each other andhave additive or decreasing on the r, by addition of 20% to r, it showed that this factor wasthe most sensitive factor to run the model. if r is equal to 60 and 20% related to the erroroccurred in calculation of it, 54% error occurs in estimating the amount of sediment andsensitivity reaches to 2.7. this evaluation indicated that mpsiac model for evaluation ofbasins with the amount of sediment more than 2.2 ton/hectare must be used more preciouslybecause the model is so sensitive in this status and possible error may get over 50%.