The Millennium Drought (southeastern Australia) provided a natural experiment to challenge the assumption that watershed streamflow always recovers from drought. Seven years after the drought, the runoff (as a fraction of precipitation) had not recovered in 37% of watersheds, and the number of recovered watersheds was not increasing. When recovery did occur, it was not explained by watershed wetness. For those watersheds not recovered, ~80% showed no evidence of recovering soon, suggesting persistence within a low-runoff state. The post-drought precipitation not going to runoff was found to be likely going to increased evapotranspiration per unit of precipitation. These findings show that watersheds can have a finite resilience to disturbances and suggest that hydrological droughts can persist indefinitely after meteorological droughts.

千年干旱（澳大利亚东南部地区）提供了自然实验，以挑战流域水流总是从干旱中恢复的假设。干旱七年后，流域（占降水的一部分）没有恢复到37％的流域，恢复的流域数量也没有增加。当恢复确实发生时，分水岭的湿润并不能解释这一点。对于那些尚未恢复的流域，约80％的流域没有迹象表明很快会恢复，这表明低径流状态持续存在。发现干旱后的降水不会径流，这很可能会增加每单位降水量的蒸散量。这些发现表明，分水岭对干扰具有一定的抵抗力，表明水文干旱可以在气象干旱后无限期地持续下去。