# Effects of Precipitation and Fire on Land Surface Phenology in the Brazilian Savannas (Cerrado)
###### Abstract  
In protected areas of the Brazilian savannas (Cerrado), Land Surface Phenology (LSP) is influenced by both precipitation and fire, but the nature of these relationships remains unexplored. Here, we assessed the impacts of precipitation and fire on LSP metrics derived from the Normalized Difference Vegetation Index (NDVI) at Emas National Park (ENP). Using TIMESAT, along with the 250-m Moderate Resolution Imaging Spectroradiometer (MODIS) MOD13Q1 and 30-m Harmonized Landsat Sentinel (HLS) products, we investigated these effects in both grassland and woodland areas. To evaluate the effects of precipitation, we identified the driest and wettest seasonal cycles between 2002 and 2023 and analyzed the relationships between accumulated rainfall during the rainy season and each of the 13 TIMESAT metrics. To assess the effects of fire, three major events were examined: 1 September 2005 (affecting 45% of the park's area), 12 August 2010 (90%), and 10 July 2021 (21%). The burned grassland area and the subsequent vegetation recovery following the 2021 event were analyzed in detail using a non-burned control site and LSP metrics extracted from the HLS product, covering both pre- and post-disturbance cycles. The results indicated that the metrics most positively correlated to precipitation were Amplitude (AMP), End of Season (EOS), Large and Small Seasonal Integrals (LSI and SSI), and Rate of Increase at the Beginning of the Season (RIBS). The highest correlation coefficients were found in woodland areas, which were less affected by fire disturbance than grassland areas. Similar trends were observed in the behavior of AMP, EOS, and SSI in response to both precipitation and fire, with fire exerting a stronger influence. By decoupling the fire effects from rainfall influence using the control site, we identified Base Level (BL), SSI, EOS, AMP, and Values at the End and Start of the Season (VES and VSS), as the metrics most sensitive to fire and subsequent vegetation recovery in burned areas. The effects of fire were evident for most metrics, both during the disturbance cycle and in the post-fire cycle. Our study underscores the importance of combining MODIS and HLS time series to understand vegetation phenology in the Cerrado. Cerrado; vegetation phenology; time series; HLS; burned areas; TIMESAT 2025 17, 2027 17 2025 17 17 2025 17 17 2025 17 2025 17 2025 17 2025 17 climate, with similar maximum monthly temperatures during both summer and winter. This ecosystem experiences a well-defined rainy season from October to May, and a dry season from June to September [3]. The native vegetation varies in composition, with increasing vegetation cover ranging from savanna grasslands (lacking trees) to woodland savannas [4; 5]. Small scattered trees (open canopies) are typically observed in most woodland areas, where soil exposures and herbaceous vegetation on the ground are detectable by satellite sensors [6]. The rapid expansion of crops and cultivated pastures, driven by the adoption of soil and crop management practices in the Cerrado, has led to the clearing of approximately half of its native vegetation, according to the Action Plan for the Prevention and Control of Deforestation and Wildfires in the Cerrado Biome (PPCerrado). The Cerrado has therefore become one of the world's most important regions for grain production and livestock farming. Thus, in this fragmented landscape, the presence of various protected areas of savanna native vegetation provides a valuable opportunity to investigate vegetation phenology in response to seasonal and interannual patterns of precipitation. In the Brazilian savanna, the phenology of native vegetation is heavily influenced by changes in precipitation, which affect the timing of seasonal cycles or phenophases [7; 8; 9]. Phenological changes in the Cerrado are therefore highly sensitive to climatic fluctuations across the different seasonal cycles.