This indicator is expressed as annual groundwater recharge of shallow aquifers in a hydrological year (1 November–31 October) in all groundwater bodies for the entire territory of the Republic of Slovenia.

Groundwater is replenished by aquifer recharge, which is a complex process of water inflow into the subterranean saturated zone. Recharge is assessed by the regional water balance model and expressed as the height of water infiltrated into aquifers (mm) or the annual variability index (the 1981–2010 average = 100).

Droughts can have severe consequences for Europe’s ecosystems and citizens, and for many economic sectors, including agriculture, energy production, industry and public water supply. It is important to distinguish between different kinds of drought. A persistent meteorological drought (i.e. a precipitation deficiency) can propagate to a soil moisture (agricultural) drought affecting plant and crop growth, which may deepen into a hydrological drought affecting water resources, water quality and freshwater ecosystems. A river flow drought is characterised by unusually low river flow, which may result from a prolonged meteorological drought, possibly in combination with socio-economic factors.

The lowest recharged quantities as well as the highest variability in year-to-year groundwater recharge in shallow aquifers were recorded in groundwater bodies of northeastern Slovenia and in the Primorska region (Figure VD15-1). In the recent decade, the average recharge of aquifers in the Goričko region was 10-times lower than that of aquifers in the Julian Alps. Apart from this highly pronounced spatial variability, great variability over the course of time was recorded in the recent decade. Compared to the average for the 1981–2010 period, the index of annual groundwater recharge shows great variability, indicating high sensitivity of shallow aquifers in terms of groundwater quantity.

In the hydrological year of 2018, the total rechargeable groundwater quantity in shallow aquifers of Slovenia was markedly above the 1981–2010 average (Figure VD15-2). The average deviation for the entire territory of Slovenia is 24 %. The largest positive deviations from the average of the period 1981-2010 were in the groundwater body of the Mura Basin, where they also reach a 60% deviation. A larger positive deviation also occurs in the groundwater bodies Obala and Kras with Brkini. Elsewhere in Slovenia, the deviation ranges between 10 and 25 %. A slightly smaller negative deviation occurs in the west of Slovenia (up to -10%) and in the extreme northeast (up to -20%).