A desalination plant would be an ideal standby solution for extreme droughts, ideally powered by photovoltaic cells, as in drought conditions, it is highly likely there will be less cloud cover. When the de-salination plant was not in use , the power supplied by the solar cells could be sold off to the national grid.
Depending on the scale of size of the solar arrays, top up from the grid may be necessary. However this would provide a green solution to the problem..