Sensitivity of net primary production to climate change in the Hyrcanian region

Net primary production (NPP) is an important indicator of ecosystem production potential, which is heavily affected by climate change. The purpose of this study was to investigate the effect of climate change on-trend and sensitivity of NPP in the Hyrcanian region of northern Iran using long-term (31 years, 1987-2017) meteorological data recorded in Gorgan, Ghaemshahr, Babolsar, Nowshahr, Ramsar, Bandar Anzali, and Astara synoptic stations. The synthetic climate-based model was used to estimate NPP and Mann-Kendal test was employed to test the trends of NPP and other meteorological parameters. We observed that the trends of annual temperature were statistically significant in all stations, whereas the annual precipitation trends were not statistically significant. The average annual NPP in the Hyrcanian region was found to be 10.6 t. ha-1 per year on average (SD: ±1.91), in which the maximum and minimum NPPs were corresponded to Bandar Anzali (13.42 t. ha-1 per year; SD: ±1.38) and Gorgan (7.6 t. ha-1 per year: SD: ±1) stations, respectively. The amount of NPP showed an increasing trend from the eastern to the western Hyrcanian region up to Bandar Anzali. Furthermore, the sensitivity of the NPP coefficient was estimated at 0.5 throughout the Hyrcanian region in response to changing temperature. This indicated that a 0.6 °C increase in temperature could approximately increase annual NPP by 0.2 t. ha-1 per year. Conclusively, understanding the temporal change of NPP in response to changing climate is necessary for the utilization of ecosystem services and benefits.