فرامقياس‌سازي ويژگي‌هاي هيدروليكي خاك در مقياس منطقه‌اي بر اساس توپوگرافي

Upscaling soil hydraulic properties at locall scale through topography

برآورد ويژگي­هاي هيدروليكي مؤثر خاك در مقياس بزرگ به­عنوان يك چالش مهم در مدل­سازي هيدرولوژيك مطرح است. هدف از اين پژوهش، محاسبه مقادير مؤثر پارامترهاي هيدروليكي مدل ون­گنوختن-معلم از طريق فرامقياس­سازي توابع انتقالي خاك (PTFs) و توابع انتقالي طيفي (STFs، SPTFs) در مقياس منطقه­اي و بر اساس توپوگرافي بود. منطقه مورد مطالعه بخشي از زيرحوزه آبخيز زنجان­رود به وسعت 250 كيلومتر مربع بود. بدين منظور، با استفاده از روش عملگر متوسط توان (PAO) پارامترهاي ، ، و در مقياس نقطه­اي به پيكسل­هايي به ابعاد يك كيلومتر فرامقياس شدند. بر پايه نتايج به­دست آمده، همبستگي زياد و معني­داري (50/0p) با ميانگين CTI نشان داد. نتايج اين پژوهش نشان داد كه توپوگرافي عامل مهمي در شناسايي مقادير مؤثر ويژگي­هاي هيدروليكي خاك در مقياس منطقه­اي است

Estimating effective soil hydraulic properties for largescale is an outstanding challenge in hydrologic modelling. The aim of this study was to provide effective van Genuchten-Mualem hydraulic parameters at localscale through topography-based Upscaling Pedotransfer functions (PTFs) and spectrotransfer functions (STFs, SPTFs). The Zanjanrood sub-watershed with an area about 250 Km2 was selected as the study area for this research.hereby, a topography-based aggregation scheme, the so-called power average operator, PAO, was used to upscale (1Km×1Km) point scale parameters of , , and . With respect to the results, considerable and significant correlations (R>0.50) were obtained between measured and estimated hydraulic parameters. Upscaled STFs showed the largest and significant correlations with upscaled measurements of (0.65), (0.70), (0.86), while upscaled PTFs performed best for (0.55). The PAO performed best in the pixels which have the highest topographic index (CTI). The biggest R values were obtained between shape parameters (i.e., and ) andthe standard deviation CTI as well as between and with the average CTI. The ASAR estimated soil moisture values appeared to be significantly (p<0.005) correlated (-0.453) with the average CTI. The results of this study indicate that the topography is an important factor in characterization ofeffective soil hydraulic properties at localscale.