Rainfall size and interception of a Pinus eldarica afforestation in a semi-arid climate zone (Chitgar Forest Park)

Rainfall interception loss (I) is an important component of water balance in arid and semi-arid climate zones. The goal of this project was to quantify interception of different seasons and to determine the role of rainfall size in controlling interception in a mature semi-arid Pinus eldarica Medw. afforestation in Chitgar Forest Park near Tehran, Iran, where mean annual precipitation, and air temperature are 267.6 mm and 17.2˚C, respectively. The gross rainfall (GR) was measured based on average records of six manual collectors installed in an open area adjacent to the stand and throughfall (TF) was collected by means of forty five manual collectors, similar to GR collectors, placed randomly beneath the canopy. Interception was calculated as the difference between GR and TF. Measurements were recorded based on rainfall events from September, 2009 to May, 2010. For the study period with 30 recorded rainfall events, GR and rainfall interception loss (I) totaled 164.8 and 61.2 mm respectively. The ratio of I:GR had a range of 19.5% to 100%, with 61.4% as the average value. During this period, the cumulative GR depths of 11, 10, and 9 rainfall events in autumn, winter, and spring were 43.6 mm (I= 65.8%), 72.6 (I= 55.1%), 48.6 mm (I= 62.9%), respectively. On the event scale, there was a strong logarithmic correlation between I:GR and GR in all seasons. As the size of rainfall events increased, the ratio of I:GR decreased. The results demonstrated that intercepted rainfall represents a considerable portion of GR in P.eldarica afforested regions of the semi-arid climate zone of Iran where soil moisture is a limiting factor in plant growth and productivity.