Rainfall-Runoff Simulation Using Grey System Theory (Case Study: Lighvan Watershed)

Grey system theory plays a role in prediction of events which have less observational statistics noting its mathematical basis, and in hydrology it might remove the problem of data insufficiency. In this study, the simulation of rainfall-runoff process was done by Grey system theory with the Mathematica software using the data of six corresponding events of rainfall-runoff hyetographs and also hydrometric data of Tabriz station in Lighvan zone. We used the least sum of squares method to calculate the differential and hydrological Grey Model equation (DHGM) and Grey parameters (and and). We found the mean values of those parameters as 0.1012365, -0.07836 and 0.200251 respectively. Simulated results were evaluated for the events that had happened in the dates of 25 May 2003 and 21 June 2003 and we obtained (R2, RMSE, VE %) parameters as (0.89, 0.22, 42%) and (0.75, 0.12, 38%) respectively. Using the obtained parameters, the model was tested for two additional events. The comparison between the obtained results by the correlation coefficient index and the least-squares error indicated good efficiency of the Grey model in simulation of rainfall-runoff process.