# Explaining and Measuring Social-Ecological Pathways: The Case of Global Changes and Water Security
## 4 Earth Observations for Water Security: The Data Cube
### Avenues for Implementing an Analysis of Water Security Dynamics through Data Cube  
Currently, the most advanced EODC implementation is represented by Digital Earth Australia (DEA) that already developed some interesting information products related to water management. In particular, using the Water Observations from Space (WOfS), they map the presence and extent of surface water over the entire country using 27 years of Landsat observations [89]. It allows for flood risk assessment, agricultural water tracking, and mangrove monitoring. Similarly, Australia has developed an algal bloom early warning alert system informing SDG 6 (clean water and sanitation). This initiative contributes to build common and replicable measurements of the water security ecological system. We argue combinations of these measurements of the ecological system with variables about the social system related to water security, namely institutions and actors, is promising. Moreover, there is a momentum for these combinations as social sciences recently developed new methods for collecting information and coding variables about institutions and actors configurations [65; 31; 66]. For instance, these new methods allow for systematic measurement of polycentricity and policy content with many observations over time and space. It could advantageously be merged with ecological dataset. Then, because the dataset has a time dimension, it becomes possible to analyze patterns of change. For instance, we could appraise the impact of socio-institutional changes in oil and gas regulation [65] on water quality. Regarding the on-going debates about fracking, it would result in substantial added-values for both science and policy-making. More generally, it enables to link fine-grained measurements of polycentricity with water resources and thus to provide new insights into influential water governance paradigms such as the Integrated Water Resource Management. Regarding water security, EODC paves promising avenues in the use of the Water Security Index (WSI) [5]. The WSI results from a quantitative and integrated (e.g., physical and socio-economic) approach to develop a spatial multi-criteria analysis framework. The index combines four criteria, \"availability\", \"availability services\", \"safety and quality\" and \"management\", based on the measurement of ten indicators (Table 2). Indicators about water availability are at the 0.5\({}^{\circ}\) spatial resolution while the other indicators are at the country or river scales, and the time coverage excludes dynamic analysis. Figure 4: Sampling in a data cube (adapted from [88]). A first avenue is to take advantage of EODC versatility to replicate the measure of the WSI and expand its time coverage to several decades. It would allow observing changes in water security situations and in relations between the criteria of WSI (e.g., accessibility to water services with safety and quality). Then, the longitudinal measure of the WSI could be combined with accurate measures about actors and institutions, i.e., under the country scale. Because EODC facilitates spatial matching thanks to disaggregating-reaggregating pixels procedures, one could test our institutional and cognitive model of change for SES (Figure 3). For instance, it allows estimating the association of new regulations with WSI changes to grasp the institutional complexity trap dynamic. This would allow identifying the level of saturation of SESs (see Figure 1). The potential contribution of EODC for water security is wider than expanding the use of the WSI EODC allows measuring an index that corresponds more with the water systems and current use of the resource. For instance, ecological structure is a critical component of any SES. With EODC, it is possible to characterize the river degree of fragmentation and the water extent. EODC allows observing total suspended matter and chlorophyll content in water bodies which will enable for appraising water quality in the past (where no sampling have been made) and in the future reliably.