# Mapping Rice Fields in Urban Shanghai, Southeast China, Using Sentinel-1A and Landsat 8 Datasets
## 1 Introduction  
Urban and peri-urban agriculture (UPA) has gained much recognition as a major source of livelihoods for inhabitants within cities and those along the rural-urban fringe, especially in developing countries [1; 2; 3]. The increasing trends of rural-urban migration have triggered a population explosion in cities. Migrated rural surplus labor is mostly unskilled. As a result, migrant populations mainly engage in primary economic activities, prominent among which is farming [4]. The concept of UPA is fraught with definitional challenges as it involves a diverse range of agricultural activities involving crops, livestock, and aquaculture at scales ranging from roof-top gardens to larger cultivated open spaces [5]. Additionally, the boundary between the urban andperi-urban is along a land-use continuum which exhibits considerable heterogeneity [6]. Various definitions of UPA have been put forward by scholars, and at the center of all these definitions is the understanding that urban agriculture is farming practiced in inner city areas. On the other hand, peri-urban agriculture is a residual form of farming at the fringes of growing cities, though a commonly agreed spatial definition is missing [5]. The peri-urban is a transition zone between rural and urban areas, which on the one hand is characterized by lower population density and inadequate infrastructure compared to cities, and therefore not \"urban\", and on the other hand a limited amount of agricultural and natural land, and therefore not \"rural\" [7, 8]. While urban agriculture primarily meets food demands at household levels, peri-urban agriculture provides larger quantities with broader distribution pathways, giving it a separate status in terms of food security planning [5]. Food security is one major objective in the millennium development goals. Urban agriculture is an important land-use and economic activity central to millions of people in the world. It contributes significantly in meeting the nutritional requirements of urban dwellers and hence, improves urban food security [9, 10]. According to [11, 12], urban agriculture supplies food to about one-quarter of the world's urban population. Apart from enhancing food security and urban incomes, urban farming also contributes to flood control, land reclamation and city greening [13, 14]. Hence, the economic and environmental significance of urban agriculture are enormous. However, despite the enormous social, economic and environmental benefits provided by urban agriculture, land is increasingly becoming scarce for the sustainability of this vital sector [3, 15]. Residential and industrial land-uses are ever expanding into arable land at the fringes of urban centers [4]. The unprecedented population increase in cities, especially in the developing world, means more living space will be required for housing and other social infrastructure. This has led to a gradual loss and fragmentation of agricultural land-use in urban and peri-urban areas [16, 17], and one of the most important agricultural crops affected by this socio-economic transformation is rice [18]. Rice is one of the most important food crops and accounts for 20% of the world's calorie supply. Rice is regarded the most important food for the poor as it serves as staple for about a billion people subsisting on less than a dollar a day [19]. The rice crop is extensively grown in upland and lowland ecologies found in the tropics, sub-tropics and temperate regions in Asia, Africa, Australia, Europe and the Americas. Irrigation is often practiced in places where rain-fed agriculture is infeasible [20]. The continuous increase in the world's human population has triggered an increase in the demand for rice especially in developing countries, where rice is a major component of the daily diet. In response to such food demands, several calls have been made over the years to increase rice production [21].