Satellite imagery can be used to identify and monitor environmental and social impacts, and help solve human problems around the world. Despite rapid advancements in space-based technologies, not enough people have access to satellite data and all the insights it offers. Satellite imagery provides an objective way of verifying or validating the testimony of communities who are being impacted by social or environmental harms. Satellite data analysis reveals the impact of large developments, such as mining works and large-scale agriculture developments, on local communities - particularly in cases of forced eviction and land grabs. Reports from affected communities, or organisations working to support them, frequently include claims of impact on water sources and water access. Satellite data analysis can provide an additional, objective source of information for use in legal settings (for instance, international arbitration or third-party conflict resolution mechanisms).
Claims of water access problems are typically the result of changes in water quality or quantity, and/or changes in the ability to physically access water due to - for example - road closures or relocations. Changes in the water quantity can be caused by drought, or by changes in the water retention capacity of the soil. The latter is often a result of deforestation and clearance of vegetation to make way for agriculture or developments. Construction of large developments can also result in the water source being destroyed, requiring communities to use alternatives that can be further away, more dangerous to get to, or inaccessible.
Similar changes to physical access to water sources can be caused by restrictions to mobility such as the destruction or blocking of traditional routes to community water sources. Developments can also cause other physical access limitations such as elimination of water collection points due to destruction of river banks and areas of shallow water where it is safe to collect water.
Gender inequality implications
Problems with water access, particularly due to physical access, are often found to have a disproportionate impact on women. In many of the communities that are close to large developments in low infrastructure communities where culturally women are responsible for water collection, large developments that restrict or block mobility can force women to walk long distances to access clean water (Human Rights Watch, 2018).
Evidence of reported problems with water access can often be sought using satellite imagery. Direct observation of the water surface can provide information about changes in the water quality and quantity. With an image resolution appropriate for the size of a surface-water source significant changes in the water level may be visible. For example, the condition of a moderate sized body of water of around 50m across could be monitored using Sentinel 2 optical imagery (10m resolution, see Figure 1), provided free-to-access through the Copernicus Programme (Copernicus, 2021). However, small streams or pools of water of a few metres across would require assessment via commercial satellite imagery such as those provided by the Worldview satellites (around 0.5m resolution, supplied by e.g., Geocento (2021) and Satellite Imaging Corporation (2021). Such high-resolution imagery is expensive, but some is often accessible for free via Google Earth. Many types of water pollution are difficult to identify from optical satellite imagery but changes in colour in optical data can indicate particulate contamination such as increased silt or dust from mining. Similarly, some changes in water colour are characteristic of algal blooms. Read our article on Water Quality Indicators, to learn more.
In many cases the surface of the water body is not visible from space. This can be due to vegetation cover or because the available satellite imagery has a low image resolution for the size of the water source. If the area close to the water source is vegetated, the health of the vegetation can be used as a proxy for the condition of the water source. Indices for the assessment of vegetation health can be calculated using optical satellite imagery. The Normalised Difference Vegetation Index (NDVI) relies on the differential absorption between the red and near-infrared wavebands by chlorophyll, producing high values in regions of healthy vegetation (e.g., trees, crops) and low values where it is lacking. A Normalised Difference Water Index (NDWI) is sensitive to the presence of water. There are two commonly used variants of NDWI: one is used to map the surface of water whereas the other is sensitive to the water content in vegetation. The latter variant of NDWI utilises the different absorptions of shortwave infrared light and near infrared light by vegetation water content to provide a measure of water stress in vegetation. Changes in these indices between different timeframes during nearby development projects can indicate the changing condition of the water source.
Satellite imagery can also be used to visualise changes to mobility of the local communities who live close to large developments and the accessibility of water sources (see Figure 2). For instance, we would conduct visual surveys of features such as roads, tracks, and paths, as well as any obstacles along key routes. Satellite imagery provides information on the changes of land use close to the communities and the progression of nearby developments. Using historical imagery can prove the presence of established community tracks and paths between water sources and villages. Community intelligence obtained through engagement with these local communities provides coordinates of important water sources and villages. Overlay of community data onto historical and recent satellite imagery shows where these access routes have been blocked or disrupted. An example of such an analysis is shown in Figure 2 (grey shows the extent of a bauxite mine, red shows paths and tracks that have been disrupted by the mine, and orange and blue show impacted and intact water sources, respectively), discussed further below.
How does this work in practice?
These techniques and methodologies have been utilised during work for clients who are in support of communities impacted by mining developments, large scale agriculture, and the construction of power plants. For example, in one of our projects we have worked in partnership with an NGO to provide satellite imagery analysis to inform mediation procedures between a large bauxite mining company and the communities of 13 local villages (see Figure 2).
Among the main concerns of these local communities was the impact that the expansion of the mining activity had had on their access to water. There were reports of polluted and dried-up water sources (orange in Figure 2) as well as paths usually taken by villages destroyed and blocked (red in Figure 2), forcing villages to walk for miles to collect water.
Our NGO partners were able to provide extensive participatory data that included the locations of the water sources that were available to the communities prior to the expansion of the mining works (orange and blue points in Figure 2). The vegetation close to each water source was analysed to track changes in vegetation health before and after the mine expansion. Historical satellite imagery was used to identify previously used tracks and paths between the village locations and the water sources, as well as to capture the expanding footprint of the mining activity (grey in Figure 2). Through this project a verification of community testimony and objective visualisations of the impact that the mining activity had had on the local communities could be provided.