In arid, semi-arid and dry sub-humid areas water supply relies heavily on groundwater. In dryland catchments the recharge water comes from the component of rainfall that drains below the root zone and  percolates to the water table. Average recharge rates over dryland catchments are typically 3-10% of average rainfall. 

Pressure on limited resources in these areas is intensifying due to rising demand linked to population growth, tourism, urbanization and expansion of agricultural land under irrigation. Excessive groundwater withdrawals have led to groundwater depletion in many regions. Substantial uncertainty remains in recharge projections under climate change.