Comment by frm88

Sedimentation and low filling levels, hence increasing costs. Also

We found that 93% of studied reservoirs have not been fully filled up at least once during 2010–2022. Our analyses revealed that droughts are the most probable culprits. About 86% of the 398 reservoirs with accessible SPEI data exhibited significant susceptibility to drought, while 43% of the 525 reservoirs demonstrated notable sensitivity to ENSO events.

Worth a read: https://agupubs.onlinelibrary.wiley.com/doi/full/10.1029/202...