# A Review of Irrigation Information Retrievals from Space and Their Utility for Users
## 5 The User Perspective: Observation Requirements and Current Obstacles
### User Characteristics  
The majority of the contributing organizations belong to an irrigation district or irrigation consortia (7/10), that is, they are farmers or institutions that directly serve the farmers managing or distributing water. The remainder of them were public actors, such as basin authorities or other irrigation-related public actors, who are less focused on the actual distribution of water but are interested in managing and accounting for the whole hydrological cycle of a large area (e.g., a river basin). The size and spatial structure of the irrigated fields and irrigation districts in Mediterranean areas are often tied to complex historical and technical processes. For example, in the Po River valley (Italy), this condition has historical reasons related to the Roman centuration, where the divisions of the land were based on the needs and technical limitations of the ancient society (see Figure 3). In other countries, this might have changed with time due to the influence of the Post-Roman occupation of the land and to the current need to facilitate agricultural practices and to boost production. For instance, in Catalonia (Spain), in modernized irrigation areas, land is often reorganized to ensure a more homogeneous division and thus agricultural plots tend to have larger extents than they used to have, when traditional irrigation methods were used. Despite the change of land use in Europe, the irrigation districts and consortia tend to be organized in many small fields (although this varies from country to country) relative to the size of a satellite footprint. These fields might contain different types of crops close to each other and may use different irrigation systems, which complicate attempts to stratify them based on crop type or the type of irrigation. Furthermore, water use exhibits large field-to-field variability, which cannot be explained fully by differences in weather, soil type, crop choice, or technology [18], but instead depends largely on the farming practices adopted by different farmers. The majority of the contacted organizations have mixed systems. For example, it is not uncommon to grow fruit trees, which often use drip irrigation, close to maize fields that will probably use sprinklers. This highlights that collecting irrigation information can be very challenging with only one type of observation, and combining multiple techniques to retrieve information about irrigation (i.e., thermal, optical, and microwave) may be advantageous. Figure 3: Centuriation near Cesena, Italy, in a late nineteenth century Italian military map—Roman grid system (**a**) and what is left today in the Po River valley with superimposition of the old system (**b**). Source: Wikipedia ([[https://en.wikipedia.org/wiki/Centuriation](https://en.wikipedia.org/wiki/Centuriation)]([https://en.wikipedia.org/wiki/Centuriation](https://en.wikipedia.org/wiki/Centuriation)) (accessed on 13 October 2021)). Concerning the technique used to measure irrigation, the majority of the interviewees stated that the amount of water applied is not measured directly in the field but with water meters placed in the main canal or pipeline, or as a total volume of water extracted from wells. Only two interviewees answered that they check soil status in person or use a rain gauge placed in the field to check the accumulated irrigation at the end of the year. The provided answers demonstrate that the collection of in situ irrigation data can be subject to substantial uncertainties, as also highlighted by [PERSON] et al. [137]. Moreover, as the majority of the interviewees measure irrigation at the entrance of the irrigation district, identifying the plot actually irrigated can be very challenging, especially for the basin authorities who, often, do not have access to the counters. This is a very common situation over developing regions and in many places over the Mediterranean basin.