National assessment of throughfall sensitivity to changes in storm magnitude for the forests of Iran.
Aim: of study: To understand throughfall (TF) sensitivity to variability in rainfall amount (Pg) for typical forest sites across the main climate types of Iran. Area of study: Nine forest stands of several common native and introduced tree species situated in all common Iranian climate types, but located primarily in northern Iran. Material and methods: A nondimensional relative sensitivity coefficient was employed to predict responses of TF to Pg changes. Projected Pg changes over the measurement sites for the period 2020-50 were estimated using one of the Coupled Model Intercomparison Project phase 5 (CMIP5) known as HadGEM2-ES under low and high emission scenarios (RCP 2.6 and 8.5). Main results: TF displayed strong positive linear relationships with Pg at all sites [TF=0.66 Pg-0.16; R2=0.91]. The sensitivity coefficient ranged from 0.96-2.35 across the nine forest sites and large sensitivity coefficient differences were found between small (< mean annual Pg) and large (> mean annual Pg) storms for arid and Mediterranean plantations. Shifts in Pg and increased small storm frequency are predicted for these regions (2020-50) under low and high emission scenarios. Research highlights: TTF sensitivity may be a useful variable when selecting tree species for afforestation to buffer expected shifts in Pg due to climate change.