# Effects of Precipitation and Fire on Land Surface Phenology in the Brazilian Savannas (Cerrado)
###### Abstract
Using software such as TIMESAT (version 3.3), a package to analyze time-series of satellite sensor data, several phenological metrics can be extracted, including the duration of the season, the changes in the vegetation index over the seasonal cycles, and the rates of vegetation greening and senescence [27; 28; 29]. To address the spatial resolution limitations of the MODIS instrument in monitoring small protected areas of the Cerrado, studies focused on vegetation classification have considered sensors with higher spatial resolution [30; 31; 32]. More recently, the Harmonized Landsat Sentinel (HLS) product, with a 30-m spatial resolution [33; 34], has emerged as a promising alternative for examining LSP in response to precipitation and fire across various savanna physiognomies in the Cerrado biome--an application that remains unexplored. The HLS product offers harmonized time series data from Landsat and Sentinel satellites, with observation frequencies ranging from two to three days during the dry season of the Brazilian savannas (June to September). In the rainy season (October to May), the frequency of observations decreases with increasing cloud cover in Brazil. With its 30-m spatial resolution and high frequency of satellite observations during the dry season, when most wildfires occur, the HLS product also enhances environmental monitoring of such dynamic events. It enables the potential selection of control sites situated near burned areas within the same savanna vegetation type, which is essential to track vegetation recovery after fire disturbance. At the ENP, the Park's Management Plan prioritizes research, monitoring, and fire control activities as essential strategies for conserving native vegetation. For example, firebreaks and controlled burns have been implemented over the past few decades to prevent the occurrence and spread of fires [35]. By reducing the accumulation of dry biomass (fire fuel), these management actions have lowered the likelihood of large wildfire events in the park. Despite these efforts, the ENP has experienced three major wildfire events between 2002 and 2023, which have affected significant portions of the park's area: 45% in 2005, 90% in 2010, and 21% in 2021. At the ENP, characterizing the seasonal behavior of LSP metrics, such as Amplitude (AMP), Base Level (BL), End of Season (EOS), Large Seasonal Integral (LSI), and Small Seasonal Integral (SSI), is essential, as these indicators reflect ecosystem conditions. Long-term trend analysis of these metrics is also crucial for understanding climate-vegetative interactions. However, before evaluating changes in their temporal trends, it is essential to develop a clearer understanding of the variability driven by fire, a key factor in vegetation phenology studies within savanna ecosystems. To address this gap in the literature on the Brazilian savannas, further research is needed to assess the relative influence of fire on the determination of LSP metrics, especially in comparison to the effects of precipitation. In this study, we assessed for the first time the effects of both precipitation and fire on NDVI-derived phenological metrics at the ENP, a protected savanna area in central Brazil. These metrics were calculated using the TIMESAT software, along with the MODIS MOD13Q1 and HLS products, across grassland and woodland areas.