Changes in Gross Primary Production (GPP) over the Past Two Decades Due to Land Use Conversion in a Tourism City  
[PERSON] [PERSON]  
1 Faculty of Agriculture, Udayana University, Kampus Bukit Jimbaran, Bali 80361, Indonesia; [EMAIL_ADDRESS] (I.W.N. ); [EMAIL_ADDRESS] (I.G.A.G. ); [EMAIL_ADDRESS] (I.M.S.)  
[PERSON]  
2 Center for Environmental Research (PPLH), Udayana University, PB Sudirman Street, Denpasar, Bali 80232, Indonesia  
2 Center for Remote Sensing and Ocean Science (CReSOS), Udayana University, Postgraduate Building, Floor 3, PB Sudirman Street, Denpasar, Bali 80232, Indonesia  
huge social and environmental problems, and the main threats to irrigated agriculture and the related livelihoods are land conversion and the transfer of water from agriculture to non-agricultural uses [10]. Most land use changes in Indonesia at the local and regional scales are conversions from agricultural land into residential land and from forest to agriculture [11; 12; 13; 14]. Land use change can have a large impact on ecosystems, altering their composition and structure as well as their function, including matter and energy cycles [15]. Several studies have explained that land use and land cover changes in urban areas produce global consequences, including effects on the climate, e.g., [16], hydrology, e.g., [17], and biodiversity, e.g., [18], and that these changes alter ecosystem services and affect the biological carbon uptake of urban vegetation, e.g., [19]. Land use changes in urban areas play a significant role in determining local, regional, and global carbon emissions [20]. Meanwhile, urban ecosystems can also account for a significant portion of terrestrial carbon storage at both local and regional scales [21]. Human activities are highly dependent on ecosystem goods and services, especially net ecosystem CO\({}_{2}\) exchange (NEE), the balance between gross primary production (GPP) and ecosystem respiration [5]. GPP is a key measure of carbon mass flux in carbon cycle studies, which is the total carbon fixation by terrestrial ecosystems through vegetation photosynthesis [22]. In addition, GPP can be used to quantify vegetation productivity and to understand temporal variability in productivity [23]. The quantification of the magnitude of carbon uptake by terrestrial vegetation and how it varies due to land use changes in urban areas is an important question, as future potential sequestration is influenced by both increased atmospheric CO\({}_{2}\) and the changing climate [24], especially for tourism cities. Therefore, the estimation of GPP in an urban area is essential for the quantification of net terrestrial carbon and thus is of particular importance for global carbon cycle research. Previous studies on GPP impacts from land cover/land use changes associated with urban growth have been documented in Southeastern Michigan [19; 25]. However, changes in GPP due to land use conversion as a result of urbanization in the tourism area have not been reported in previous work. The remote sensing of vegetation GPP is an important step in analysing terrestrial carbon cycles in response to changing climate [26]. Repetitive and systematic satellite remote-sensing observations of vegetation dynamics and ecosystems allow us to characterize vegetation structure, including leaf area index (LAI) and the absorptivity of photosynthetically active radiation (APAR) [27; 28]. Remote-sensing techniques are advantageous because they allow monitoring of the GPP on a regional and local scale through its relationship with the fraction of absorbed photosynthetically active radiation (fAPAR) driven by vegetation indices [29; 30]. Moreover, remote sensing is the best choice for urban areas to provide a better understanding of the effects of land use change on vegetation dynamics [31; 32; 33]. Moderate-resolution Imaging Spectroradiometer (MODIS) satellite remote sensing data are commonly used to calculate GPP, e.g., [34]. However, for urban regions that have heterogeneous landscapes, Landsat data are more frequently used [19; 35].