Long-term trends of net primary production and evapotranspiration in Iran's forest vegetation zones

Climate change significantly affects net primary production (NPP) and evapotranspiration (ET). To estimate NPP and reference ET (ET0), long-term (1986-2017) meteorological data collected by 96 synoptic weather stations located in five of Iran's forest vegetation zones: Hyrcanian, Arasbaran, Zagros, Khalijo-Omanian, and Irano-Turanian were used. The synthetic model and FAO Penman-Monteith combination equation were employed for estimation. Mann-Kendall test detected annual trends of NPP and ET0. The Hyrcanian zone demonstrated the highest amount of NPP at 10.7 t ha-1 y-1, while Khalijo-Omanian displayed the highest annual ET0 at 2099 mm. The NPP of Khalijo-Omanian and Irano-Turanian zones were roughly similar, ranging between 2 and 3 t ha-1 y-1. Out of 96 observed annual trends of NPP and ET0 in diverse vegetation zones, statistically significant trends were found in 22 trends (23 percent) of NPP and 73 trends (76 percent) of ET0. Understanding the impact of climate change on ecosystem function requires trending of NPP and ET.