Groundwater recharge in arid areas is crucial for managing water resources. Researchers in SE Iran used various methods to estimate recharge into the Birjand aquifer with low rainfall. They found that rainfall and irrigation return flow contribute to groundwater recharge. The total recharge rate was estimated at 37.5 mm/year, with 7.0 mm/year from rainfall and 30.5 mm/year from irrigation return flow. This study suggests using stable isotopes and water-table fluctuation methods to estimate rainfall and total recharge in arid regions.