Rainfall Interception in a Pinus eldarica Plantation in a Semiarid Climate Zone: An Application of the Gash Model

Abstract

Forest canopy rainfall interception loss (I), canopy water storage (S), and the ratio of mean evaporation to mean rainfall intensity ( E / R ) are important components of the water balance in arid and semi-arid climate zones. The goal of this project was to quantify I and S and to evaluate the Gash interception model for rainfall interception in a mature semi-arid Pinus eldarica Medw afforestation planted in the Chitgar Forest Park near Tehran city, Iran. Measurements of gross precipitation (PG) and throughfall (TF) were recorded on an event basis from September 2009 to April 2010. For the measurement period, PG totaled 164.8 mm and I totaled 61.2 mm. I was calculated as the difference between PG and TF. On the event scale, the ratio of I:PG ranged between 0.195 and 1, and averaged 0.614. There was a strong logarithmic correlation between I: PG and PG (R2 = 0.861; P value≤ 0.01). As the size of rainfall events increased, I:PG decreased. The mean method estimated S to be 1.8 mm. The Gash model accurately estimated I to be within 1.1 mm of the total measured value. The results demonstrate that intercepted rainfall represents a considerable portion of PG in P.eldarica afforested regions of the semi-arid climate zone of Iran where soil moisture is a limiting factor for plant growth and productivity. Keywords: Afforestation, Canopy water storage, Iran, Mean method, Throughfall.