Groundwater analysis to prevent a water crisis in Yemen

Yemen is facing a severe water crisis, where groundwater—the country’s main source of water for drinking, agriculture, and sanitation—is under increasing pressure due to over-extraction, climate variability, and the impacts of prolonged conflict. At the same time, damaged infrastructure and limited monitoring capacity have made it difficult to track water resources and respond effectively to emerging risks.

To address this gap, GMV, in collaboration with the World Bank under ESA’s Global Development Assistance program, developed an Earth Observation-based approach to monitor groundwater conditions across the country. Using satellite data, the project provides a consistent picture of groundwater storage, recharge, abstraction, and availability over the past two decades.

The results show a clear long-term decline in groundwater resources, driven by an imbalance between limited natural recharge and sustained water use, particularly in agricultural areas such as the Aden–Tuban Basin. While occasional intense rainfall events provide temporary relief, they do not reverse the overall trend of depletion.

By translating complex data into accessible indicators of groundwater availability, the project supports early identification of water stress and improves the ability of decision-makers to anticipate and respond to water scarcity. This contributes directly to managing risks that affect water access, food production, and public health in one of the world’s most fragile contexts.

Yemen is currently experiencing one of the world’s most severe and complex water crises, driven by a combination of chronic water scarcity, excessive groundwater depletion, and the impacts of the armed conflict. Groundwater represents the backbone of the country’s water supply, sustaining drinking water provision, sanitation systems, and agricultural livelihoods. However, it is being systematically over-extracted, leading to widespread depletion and long-term degradation of water resources.

Since the escalation of the conflict in 2014, the situation has been further exacerbated by extensive damage to water and sewage infrastructure, as well as pollution linked to conflict-related activities. These impacts have significantly reduced the functionality and safety of water supply systems across large parts of the country. As a result, many water sources have become unsafe for human consumption, increasing reliance on alternative and often lower-quality sources.

The deterioration of water infrastructure and quality has had direct and severe public health consequences, including recurrent outbreaks of waterborne diseases. Among the most serious was the cholera epidemic between 2016 and 2022, which affected more than two million people and highlighted the strong interconnection between water insecurity, infrastructure fragility, and public health emergencies.

In this fragile context, water scarcity is not only a resource management issue but a humanitarian and health risk driver. Declining groundwater availability directly affects access to safe drinking water, increases exposure to contaminated sources, rises water costs, and reduces agricultural productivity, all of which contributes to worsening food insecurity and vulnerability.

In this context, decision-makers face critical constraints due to the lack of reliable and up-to-date information caused by the disruption of the monitoring networks which has hindered the ability to track groundwater conditions, assess risks, and plan effective interventions.

This project delivered an integrated set of groundwater services that transform satellite data into practical information to support sustainable groundwater resources management in Yemen. The framework integrates three complementary components covering groundwater monitoring, quantification, and management. Combined, they provide an extensive view of how groundwater resources have evolved in the past two decades. Together, these components describe long-term changes in groundwater storage, the occurrence of drought episodes, the spatial distribution of recharge processes, and the intensity of groundwater use at basin level.

The results show a clear long-term decline in groundwater resources at national level, reflecting increasing stress on a resource that millions of people depend on for drinking water, agriculture, and sanitation. A distinct west–east gradient emerges, with relatively higher groundwater variability and availability in western regions, particularly along the Tihama coastal plain. These areas experience strong fluctuations driven by both rainfall variability and intensive human use.

At basin scale, the Aden–Tuban system shows a slightly different behaviour. While it also shows an overall declining trend, recent years present short periods of recovery associated with extreme rainfall events and cyclonic activity. However, these improvements are temporary and insufficient to offset the longer-term pressure on the system.

This spatial pattern is closely mirrored in groundwater recharge, confirming that precipitation is the dominant driver of groundwater replenishment in Yemen. Only a limited number of areas, mainly in the western highlands, receive meaningful recharge, while most of the country experiences very low natural replenishment making groundwater systems highly vulnerable to drought and prolonged dry conditions.

On the other side of the balance, the analysis of groundwater abstractions conducted for the Aden-Tuban basin shows that these are consistently high. The strongest pressure is detected during dry periods when rainfall is lowest. This mismatch between when water is available and when it is most heavily used is a key driver of long-term depletion.

To make these results more accessible for decision-makers, groundwater conditions were also translated into a simple indicator of groundwater availability, showing how much groundwater remains compared to the historical maximum and minimum levels. This reveals a clear shift over time: conditions that were once moderate have increasingly moved into low and, in some years, very low levels at national level. These conditions directly affect the reliability of water supply for households, farming, and essential services.

Overall, the results highlight a system under sustained stress, where natural replenishment is no longer keeping pace with human demand. While extreme rainfall events can temporarily ease pressure, they do not reverse the long-term trend of depletion. From a practical perspective, these EO-based insights provide critical support for identifying areas under the greatest water stress and for understanding how groundwater scarcity is evolving in ways that directly affect food security and public health in one of the world’s most fragile environments.

The analysis is based on a combination of satellite observations and global hydrological datasets designed to ensure consistent monitoring in a data-scarce environment.

At the core of the assessment are data from the GRACE and GRACE Follow-On satellite missions, which measure changes in the Earth’s gravity field to detect variations in total water storage. To improve reliability, data from two different processing centers were combined, reducing uncertainties and strengthening the robustness of the results.

Since GRACE data capture overall changes in total water stored across the water cycle, the groundwater component needs to be separated by removing the contribution from soil moisture, surface water and vegetation. This information is obtained from the GLDAS global land surface models, which simulate hydrological processes based on satellite observations and meteorological inputs. As in the case of the GRACE processing, three different GLDAS models were used to generate an ensemble, enhancing the estimation’s robustness and reducing uncertainty.

Precipitation data are derived from the CHIRPS dataset, which combines satellite imagery with ground observations to provide rainfall estimates. In this study, rainfall patterns are also compared with groundwater changes to better understand how the two are linked over time and across space.

Evapotranspiration estimates were obtained from MODIS to carry out the abstractions quantification assessment. The combination of all datasets and analysis make it possible to estimate how water moves through the environment and to quantify the balance between water inputs and outputs.

The findings demonstrate the value of Earth Observation in fragile and conflict-affected contexts, where water crises are often compounded by the breakdown of monitoring systems and limited access for field-based surveys. The Yemen case shows that EO can provide scientifically robust and policy-relevant insights at both national and basin scales, even when conventional data sources are unavailable. This approach offers a replicable framework that can support evidence-based water management in other constrained environments facing similar data and capacity limitations.

Overall, the results highlight that Earth Observation is not a substitute for in-situ monitoring, but a practical and scalable solution to bridge critical information gaps where ground systems are weak or disrupted. In contexts such as Yemen, combining EO-based monitoring with gradual efforts to rebuild local observation capacity represents a pragmatic pathway toward more resilient and informed water resource management.