Monitoring the the Impacts of Climate Change and Variability on the Phenology of Natural Vegetation Using 250m MODIS-NDVI Satellite Data: Cace Study of the Dryland Ecosystem of Sokoto, North-Westrn Nigeria. Abubakar Magaji Jibrillah 1 , Nathanial Bayode Eniolorunda 1 , Garba Abdulmumin Budah 2 , Dalhatu Ahmad 2 1 Usmanu Danfodiyo University, Sokoto , Nigeria, 2 National Space Research and Development Agency (NSRDA) Abuja, Nigeria ISSN 2354-9114 (online), ISSN 0024-9521 (print) Indonesian Journal of Geography Vol 55, No 1 (2023): 51-58 DOI: 10.22146/ijg.61697 website: htps://jurnal.ugm.ac.id/ijg ©2023 Faculty of Geography UGM and Te Indonesian Geographers Associaton Submit : 2020-11-27 Received: 2020-07-26 Accepted: 2023-01-02 Keywords: Phenology; Vegetation; Climate Change; Dryland; Ecosystem Correspondent email: ajibrillah@gmail.com Abstract. Recent climate change and variability together with other anthropogenic drivers have exerted tremendous pressure on the fragile dryland ecosystem of Sokoto, North-western Nigeria. Vegetation phenology is one of the active indicators of the impacts of climate change on the ecosystem. This study aimed to monitor how the ecosystem of the area responds to the challenges associated with climate change in order to provide baseline information for policies and programmes geared towards addressing these challenges. It explored the applications of remote sensing data (MODIS-NDVI), GIS and statistical analyses in achieving this aim. Image processing operations such as data extraction, raster calculations, geometric transformations and creation of the region of interest were conducted using ArcGIS 10.5 model builder while TIMESAT software was used determined the vegetation phenological events such as the start, end and length of the growing seasons. The results indicated a persistent decline in the length of the growing seasons of the major vegetation classes in the area due to late onset and early cessation of the growing season which is positively correlated with rainfall distribution. From the year 2001 to 2016, 36% and 33% declined in the length of the growing season were recorded for shrubs and grasses respectively. These are positively correlated with the annual rainfall distributions in the area, with the correlation coefcient of r = 0.40 and r = 0.36 for the shrubs and grasses respectively. Implications of these on the ecosystem and livelihoods of the people in the area were discussed and ways forward suggested. ©2023 by the authors. Licensee Indonesian Journal of Geography, Indonesia. Tis article is an open access article distributed under the terms and conditions of the Creative Commons Attribution(CC BY NC) licensehttps://creativecommons.org/licenses/by-nc/4.0/. 1. Introduction Te term phenology refers to the timing of repeated biological events in plants such as the emergence of leaf, leaf coloration, fowering and leaf fall (Ibrahim et al., 2021; Ma et al., 2013; Tian et al., 2021). It deals with the variations in the timing of vegetation growth stages such as the start, the peak, the end and the length of the growing season and how these are related to the prevailing climatic conditions (Adole et al., 2016; Jiao et al., 2015; Vintrou et al., 2014). Vegetation Phenology therefore is an expression of the response of vegetation to the intra and inter-annual variations in climatic parameters such as rainfall and temperatures and also a key indicator of terrestrial ecosystem functioning (Adole, Dash, & Atkinson, 2018; Filipponi, Smiraglia, Mandrone, & Tornato, 2021; Tian et al., 2021; Vrieling et al., 2019). Vegetation phenology can be studied either using ground- based techniques or by application of remote sensing satellite data. However, while the ground-based phenological studies ofer a more detailed and fne temporal resolution information on diferent vegetation types, the technique is time consuming, limited in spatial coverage and only applicable in areas accessible to man (Adole et al., 2018; Rodriguez-Galiano, Dash, & Atkinson, 2015). On the other hand, remote sensing satellite-based techniques ofer a wider spatial coverage, longer temporal dimension including the ability to monitor the phenology of the past years and is applicable even in areas with limited accessibility or inaccessible to man (Adole et al., 2018; Richardson et al., 2018; Tian et al., 2021; Ugoyibo, Joy, & Chinwe, 2021). In the more developed countries of Europe, North America and Australia, the study of vegetation phenology has received much attention with scholars exploring detailed characteristics and trends in the phenology of diferent vegetation type, at diferent spatio-temporal resolutions and employing both ground-based and remote sensing-based techniques (Adole et al., 2016; Ibrahim et al., 2021; Igboabuchi, Echereme, & Ekwealor, 2018; Osunmadewa, Gebrehiwot, & Csaplovics, 2018). In the African continent however, there are limited studies in vegetation penology. Tis is in spite of the fact that, Africa accounts for 17% world forest, and forest covers 23% of the Africa’s total land surface area. Te continent is also endowed with diverse range of vegetation types with complex dynamics ranging from tropical rainforest, mangrove forest, to deciduous forest, savannah woodland, mountain vegetation, savannah grassland, semi-desert and desert vegetation (Adole et al., 2016, 2018; FAO, 2010). Again, Africa Indonesian Journal of Geography, Vol 54, No. 3 (2022) 463-470 RESEARCH ARTICLE