How is climate change impacting net primary production and reference evapotranspiration in the Zagros region of western Iran?

We assessed how climate change may impact net primary production (NPP) and reference evapotranspiration (ET۰) from the Zagros region of western Iran covered extensively by oak, -Quercus branti Lindl. forests. The daily meteorological parameters of temperature (T), precipitation (P), relative humidity (RH), wind speed (WS), and sunshine hours were obtained from ۲۰ meteorological stations throughout the region over a ۳۰-year period (۱۹۸۸-۲۰۱۷). Net primary production and ET۰ were estimated by the synthetic and the FAO Penman-Monteith models, respectively. A non-dimensional relative sensitivity coefficient was used to examine the sensitivity of NPP and ET۰ to changes in the meteorological parameters. The sensitivity analyses were carried out for T, P, and WS within a possible range of ± ۱۰%, ± ۳۰%, and ± ۱۰%, respectively, from the long-term mean. Except for the P with no notable trend, other meteorological parameters exhibited upward or downward trends. The mean NPP and ET۰ values were estimated to be ۶.۵ t ha-۱ y-۱ and ۳.۹ mm d-۱ across the Zagros region, respectively. Net primary production was found to be more sensitive to precipitation with a sensitivity coefficient of ۰.۶۶ and less sensitive to temperature with a sensitivity coefficient of ۰.۴۰. The ET۰ sensitivity coefficients in response to T changes doubled relative to WS (۰.۳۳ against ۰.۶۳). Identifying the contributing factors in NPP and ET۰ trends is important for understanding the relative impacts of climate change and human activities in arid and semi-arid regions.

Keywords:

FAO Penman-Monteith model , Sensitivity analyses , Synthetic model