Comparison of different Gash physically-based models for estimating stemflow in Elder pine stand in Chitgar Forest Park

In plant ecohydrology studies, stemflow considered as point input of rainfall into plant ecosystems. To date, due to field measurement, time-consuming and high cost of stemflow measurements, models are used to estimate the stemflow amounts. The aims of this study were to test the performance of three physically-based model of Gash and revised versions (Gash-1 and Gash-2) to estimate the stemflow in an elder pine (Pinus eldarica Medw.) stand in the Chitgar Forest Park for three-years study period. Rainfall magnitude and throughfall was measured with 10 and 60 rain-gauges, respectively. Stemflow was measured for 9 trees in each stand that were considered representative of the stand. According to the validation step, Gash and Gash-2 models were found to be the best models to estimate the stemflow, respectively, however the performance of each model was different at each rainfall magnitude class. For the very small rainfall class (lower than 2.50 mm), estimation of all models was incorrect. For the small (2.51-5.00 mm) and medium (5.01-7.50 mm) rainfall classes, Gash-2 was the best model, while Gash model estimated very well for the large (7.51-10 mm) and very large (more than 10.00 mm) rainfall classes. In conclusion, Gash model requires few input variables, hence would be more applicable than to other models. Due to the climate change, which is affected by the frequency of rainstorms in different rainfall magnitude classes, it is necessary to use appropriate models to estimate the amount of stemflow.