Page - 246 - in Book of Full Papers - Symposium Hydro Engineering

4.2. INCREASES OF EXTREME DROUGHT AND FLOOD Through summing up the reservoir inflow in recent years, it shows that the extreme dry event occurred 3 times and the extreme precipitation event occurred 1 time in less than 5 years， (1)In the late September and early October in 2013, the precipitation in the upper reaches of TGP reservoir reduced 30% and 73% respectively compared with the same period in history. In the flood season in 2015, the runoff in the overall upper reaches of Yangtze River are less than 34% and 38% respectively over the average annual runoff in history. The extreme drought occurs again in 2016, the inflow of the TGP reservoir in the early-September is only 11700 m3/s, ranking the least in the data series. (2)The strong flood occurred in non-flood season in 2017. The heavy rainfall from October 2nd to 4th ranked second in the historical strong flood series. Affected by this, the inflow of the TGP reservoir freshened the maximum record in the same period in history. Under the same prediction accuracy range, the extreme runoff can increase the forecast flow error which is proportional to the size of flood or drought. Frequent extreme drought and flood bring difficulties to forecast work. With the increase of unforeseeable degree in the forecast dispatching, the flood control operation in super flood will be at greater risk, and the difficulty of water storage work will be increased. 4.3. THE DEMAND IN EMERGENCY SCHEDULING IN THE MID-LOWER REACHES OF THE YANGTZE RIVER Frequent extreme weather events also has different influence in the middle and lower reaches of the Yangtze River, and mainly manifested in the disaster caused by severe convective weather and extreme strong rainfall. Through the analysis of extreme weather events in the middle and lower reaches of the Yangtze River, this paper demonstrates that the extreme weather events bring great challenges to the coordination of flood control and water storage work, and put forward higher requirements for emergency operation. During the May in 2011, the precipitation in the middle and lower reaches of the Yangtze River decreased 50% compared with the same period of many years, resulting in the worst drought in 60 years. The water level of some lakes dropped even close to the dead water level. The TGP reservoir increased the discharge by 10000m3/s to ease the drought. In the flood season in 2015, the tornadoes occurred in the middle and lower reaches of the Yangtze River, resulting in the overturn of "Star of the East". The discharge in the TGP reservoir is gradually reduced by 10000m3/s in 3 hours, and helped to rescue the capsized ship in time. In 2016, after the heavy sustained precipitation in the middle and lower reaches of the Yangtze River, the water level in the downstream of Yangtze River are almost all over the warning level. In the same period in 2017, the heavy storm occurred again in the middle and lower reaches of the Yangtze River, the water level in some tributary stations have reached the highest in history. The TGP reservoir intercepted water and reduced flood peak timely and effective control of danger. 246