Regional Assessment and Mapping of Groundwater Runoff in the Aral–Syrdarya Water Management Basin, Republic of Kazakhstan

Water scarcity and the degradation of natural ecosystems in the Aral–Syrdarya Basin remain among the most critical environmental challenges throughout the region. Within the framework of the United Nations Convention to Combat Desertification, this territory is recognized as highly vulnerable, requiring targeted and scientifically grounded approaches to sustainable water and land resources management.

The Aral–Syrdarya Water Management Basin comprises the Syrdarya River Basin and its tributaries and is associated with the Syrdarya Complex Hydrogeological Basin formed within a large tectonic depression. Groundwater resources are mainly confined to Quaternary alluvial and alluvial–proluvial deposits, Pliocene–Quaternary sandy formations, and Cretaceous aquifer systems, which are hydraulically separated by a regionally extensive Paleogene aquitard.

The regional assessment of groundwater runoff was conducted for major hydrogeological units within the basin, including river valleys, near-surface aquifers, and extensive sandy massifs. The use of several complementary assessment methods allowed for a reliable estimation of groundwater runoff and provided a solid scientific basis for its spatial representation. This approach is particularly important for the support of long-term planning and sustainable water resources management in the Aral–Syrdarya Basin.

The selection of the applied methodology is based on a critical review of national and international practices, while also accounting for the specific geological, hydrogeological, and hydrometeorological conditions of the study area. Renewable groundwater resources are characterized by using long-term average groundwater runoff values over periods of 10 to 30 years. This allowed for the assessment of groundwater availability and for the evaluation of the relationship between groundwater and surface runoff components.

Groundwater runoff is quantified using discharge values, runoff depth, and the runoff modulus, ensuring the consistency and comparability of results across different spatial units. According to estimates reported for different periods, renewable groundwater resources of the Syrdarya Complex Hydrogeological Basin range from 37.9 to 93.44 m³/s. Updated calculations based on recent hydrometeorological data and groundwater regime observations indicate an average groundwater runoff depth of approximately 14.8 mm/year and an average runoff modulus of 0.47 L/s·km².