Estimation of the canopy storage capacity and free throughfall coefficient by a Pinus eldarica afforestation using the regression-based methods

The study aims to estimate the canopy storage capacity (S) and the ratio of mean evaporation rate from the wet canopy to the mean rainfall intensity (), and the free throughfall coefficient (p) of Pinus eldarica (44 years-old-age) afforestation using three regression-based methods (Minimum, Gash and Morton and Mean methods) in the Chitgar Forest Park, near Tehran, with a semiarid climate zone. To measure gross rainfall (GR), 10 rain gauges were fixed in an open space nearby to the stand and throuhgfall (TF) was measured during a year using the 50 rain gauges randomly placed underneath the canopy cover. Rainfall interception (I) was computed as the difference between GR and TF. Fifty rain storms were recorded with a cumulative depth of 262.5 mm. The TF and (TF:GR)% were recorded 69.5% and 53.2% of the rainfall event on the cumulative-based, and event-based (each GR), respectively. Positive logarithmic correlations were observed between (TF: GR)% and GR during the study period (TF:GR = 16.598 ln GR + 35.494; R² = 0.630). For dry (from May to November) and wet periods these values corresponded to 0.988 and 0966 by positive linear correlations. The mean value of S,, and p were estimated 1.23 mm, 0.10, and 0.19, respectively. Since measurements of the amount of GR and I are expensive and time-consuming in semiarid and arid regions, and attended measurements in the field are currently carried out, thereto, regression models for estimating I and its components, e.g., S, p, and  coefficients can successfully been applied.