The performance of the reformulated Gash rainfall interception model in the Hyrcanian temperate forests of northern Iran

Abstract

• Reformulated Gash Analytical models (RGAM) applied for seven reforestations. • Models need frequent numbers of rainfall to estimate rainfall interception loss. • RGAM is advisable for predicting interception with small numbers of rain storms. • Ecohydrological parameters dramatically differs between studied stands. Modeling rainfall interception ( I ) is fundamental for understanding the forests’ role in ecohydrological processes in local and regional scales. This research examines the Reformulated Gash Analytical Model (RGAM) applicability for estimating I in seven dissimilar plantations ( Acer velutinum , Quercus castaneifolia , Pinus brutia , Picea abies , and Cupressus sempervirens L. var horizontalis ) in the four reforested areas across the Hyrcanian temperate forests, northern Iran. Field measurements were performed from May-2012 to March-2014 for 167 distinct throughfall and gross rainfall observations. According to our results, the effects of inter-species variation on I value was evident, as P. abies might be the most excellent among the five frequently used tree species for planting project in temperate forests if the primary goal of plantation is to decrease erosion and surface runoff as it intercepted and evaporated more rainfall than other species. Our findings showed that in terms of average-based calculation, the mean of free throughfall coefficient ( p ) value in evergreen needle-leaved reforestations (0.47) was lower than those calculated for deciduous broad-leaved reforestations (0.59), and vice versa for the canopy storage capacity ( S ; 1.85 mm vs . 1.36 mm, respectively), and mean of the ratio of evaporation rate to the mean of rainfall intensity during saturated canopy conditions ( E ¯ / R ¯ ; 0.45 vs . 0.38, respectively). The RGAM satisfactorily estimated I for all species (except for A. velutinum stand), because the estimation error of I was lower than 15% and the Nash–Sutcliffe efficiency was equal to or higher than 0.87. In conclusion, using data from a short time study period to derive canopy ecohydrological parameters as well as modeling I by the RGAM is advisable in reforestation areas across the Hyrcanian temperate forests and regions with similar forest and meteorological attributes.