Prediction of extreme floods in Huaihe River basin under climate change

Predictions of extreme floods from 2010-2099 are made for the Huaihe River Basin using the projected future temperature and precipitation from 22 global climate models under A1B, A2 and B1 emission scenarios in the Fourth Assessment Report of the Intergovernmental Panel on Climate Change (IPCC AR4) and the Xin'anjiang monthly distributed hydrological model. The model is calibrated and validated with the satisfied results. The ensemble method is applied in the model prediction. The result shows that the A2 scenario would most likely result in a highest number of extreme flood events, and then followed by the A1B scenario and the B1 scenario, respectively. Under A1B, there would be an increased possibility of extreme flooding in the latter half of the 21st century; while for the A2 scenario, the extreme floods could be concentrated on the period 2035-2065 as well as after 2085. Under B1, the frequent extreme floods would most likely occur around 2070s. By integrating the diverse definitions of extreme events, we classify the extreme events into three groups based on the flood magnitudes. In the first magnitude group, the extreme flood events predicted under the A2 scenario would be the most with the largest average flood volume; while those under B1 would be the least with the minimum value of flood magnitude in the third group. There could be an increased occurrence of the extreme flood events in the first magnitude group among all three scenarios. The highest increase might be found under the A2 scenario and followed by A1B and B1. The proportion of extreme flood events in each of the three magnitude groups would also vary under different scenarios. The extreme flood events of the second magnitude group could be more frequently encountered under A1B and A2; while B1 could result in more third group extreme flooding. Nevertheless, there would only a small proportion of extreme flood events with the flood magnitude exceeding the great flood of 1954 in the first magnitude group.