Document Type : Research Paper
Authors
1 Dept of Irrigation and Reclamation Engineering, Faculty of Agriculture, University of Tehran Karaj, Iran
2 Dept of Irrigation and Reclamation Eng, Faculty of Agriculture,University of Tehran, Karaj,Iran
Abstract
Keywords
Main Subjects
Phenology is the study of the annual life cycles of plants, animals, and other living organisms, particularly the timing of cyclical patterns of major events driven by changes in weather and climate. Phenology is both biological and meteorological, thus providing a key perspective for investigating biosphere–atmosphere interdependence in spatial, temporal, and specific ecological contexts. The timing behaviors of plant and animal species are coordinated with the annual changes of sunlight, temperature and precipitation in different weather conditions. Land Surface phenology is the study of plant phenology at a regional to global scale, derived from data obtained from space-based optical sensors. The most common vegetation indices are NDVI and EVI index, which are examples of reflectance-based greenness information. The time of SOS, LOS and EOS of plant growth season are the most important phenological parameters that can be extracted from the time series of satellite vegetation indicators. In this study, using TIMESAT software and EVI index, the phenology stages of Gorgan city forest have been extracted and the sensitivity of these stages to climate fluctuations was investigated.
In this article, the land use map of Golestan province was retrieved using the global land cover product of the European Space Agency (ESA) with a resolution of 10 meters in the Google Earth Engine software, and drawn in 9 classes. To obtain temperature and precipitation data, agrometeorological data of AgERA5 database were obtained using a Python programming code. Then these data (, and P) were prepared seasonally and during the statistical period of 2001-2022 in the four seasons of winter, spring, summer and autumn. To extract the time series of the EVI index, the 16-day data of the MODIS sensor with a resolution of 250 meters was called in the Google Earth Engine system, and the SOS, EOS and LOS phenology stages of vegetation growth were calculated using TIMESAT software version 3.3 and they were prepared with three smoothing methods of Gaussian, Double Logistic and Savitzky-Golay. Then the relationship between EVI index and meteorological variables of temperature and precipitation in winter, spring, summer and autumn seasons was calculated by Pearson correlation method.
Results showed that in all three smoothing methods, an increase in and in the 10-day period prior to SOS phenology stage, it would be delayed, similarity any decrease in and in a 10-day period before the EOS, this stage is also delayed. In Gaussian and Savitzky-Golay (p < 0.05) and Double Logistic (p < 0.01) methods, correlation between LOS and and in spring; and in all three smoothing methods, the correlation of SOS and EOS with in the summer season was significantly positive (p < 0.05), and the correlation of SOS and EOS with in the summer season was weak and positive. Also, SOS, EOS and LOS phenological stages have not shown any significant relationship with precipitation in different seasons. According results, temperature is the most important factor in the variability of SOS, EOS, and LOS occurrence time in study forest. Any increase and decrease of and cause daily shifts in the time of occurrence of these phenology stages.
The results indicate that the annual shift in of SOS and EOS occurrence date has an increasing trend in all three smoothing methods, which indicates the high sensitivity of these phenology stages to meteorological variables and climate variations during the study period. Satellite LSP monitoring is directly driven by meteorological variables, and among them, temperature plays the most important role. It should be noted that some limitations such as the distinct phenology of plant species in a pixel, affect the change in timing of LSP criteria. Therefore, it is necessary to perform frequent field monitoring of plant species in the region. Availability of high-quality meteorological data within the forest region and finer spatial resolution of satellite images are also quite important to achieve reliable results. Therefore, it is suggested to use other satellite images with higher resolution in order to increase the accuracy in the time series of satellite spatial greenness information and consider the asymmetric effects of and in satellite vegetation phenology simulations.
Conceptualization, N.G. and H.M.; methodology, N.G and H.M.; software, H.M.; validation, H.M.and N.G.; formal analysis, H.M.; investigation, H.M.; resources, H.M.; data curation, H.M.; writing—original draft preparation, H.M.; writing—review and editing, N.G.; visualization, H.M.; supervision, N.G.; funding acquisition, N.G. All authors have read and agreed to the published version of the manuscript.”
All authors contributed equally to the conceptualization of the article and writing of the original and subsequent drafts.
The authors confirm that the data supporting the findings of this study are available within the article
The authors would like to thank Iran Meteorological Organization and Iran Forest and rangeland organization for providing some of required datasets
The study was approved by the Ethics Committee of the University of Tehran (Ethical code: IR.UT.RES.2024.500). The authors avoided data fabrication, falsification, plagiarism, and misconduct.
The author declares no conflict of interest.