Houston - Just when it seemed the situation in the eastern parts of the US state of Texas could not get any worse, more extreme rainfall is expected in the coming hours.More than one metre of rain has fallen over the last few days in the metropolitan Houston area. Much of that rain has flowed into people's homes and cut off their roads and highways.That rain, which has been held back in reservoirs and bayous, is threatening to overtop earthen dams which would cause rapid life-threatening flooding.Emergency services are struggling to cope with the ongoing situation, but there is every chance that there will be just as much rain still to fall. In the last 24 hours, Harvey has drifted back over the Gulf of Mexico, allowing it to garner more moisture and energy from the warm surface waters. A second bout of record rainfall could well befall many parts of eastern Texas and Louisiana in the next 24- to 48 hours. The National Weather Service continues to issue warnings of "catastrophic" flooding as computer models show the potential for another 350- to 1 300mm - this would clearly mark Harvey the biggest rain-making storm system in US history.Predicted rainfall totals are based on computer models. There is no precedent for such an active weather system in this region, so there is some margin for error.But if another 1 300mm of rain was to fall in any area already under a metre of floodwater, it is difficult to see how the death toll will not increase dramatically.