Water Resources - Total Internal Renewable

Total Internal renewable water resources (IRWR): long-term average annual flow of rivers and recharge of aquifers generated from endogenous precipitation. Double counting of surface water and groundwater resources is avoided by deducting the overlap from the sum of the surface water and groundwater resources. Surface water is the water of rivers and lakes; groundwater is the water captured in underground reservoirs. Surface water flows can contribute to groundwater replenishment through seepage in the river bed. Aquifers can discharge into rivers and contribute their base flow, the sole source of river flow during dry periods. Therefore, the respective flows of both systems are not wholly additive.