The 2014 severe drought over northeast China and its comparison with droughts over the southern regions: A perspective from synergic effects of water vapour and cold air

Northeast China (NEC) is an agricultural base of the country. It suffered a severe drought in 2014. During the drought, the western Pacific subtropical high is stronger than normal and stretches to the west. The warm and moist air in the southwest edge of the high transports northwestwards and thus cannot affect NEC. Over high latitudes, in the regions west and east to NEC, there are large anomalies in geopotential height, which favour meridional exchange and may lead to stronger-than-normal cold air intrusions. Because of the lack of warm and moist air supply from the south while the invasion of the cold and dry air from the north, the atmosphere over NEC is finally drier and colder than normal in saturation levels. Based on the physical relation between seasonal precipitation and relative humidity, along with the defined C-q and C-T, indicators for measuring the changes in moisture and temperature, the effects of water vapour and air temperature on the drought can be linearly separated, and thus compared. Results reveal that, at middle and high levels, the dryness of the air, which plays a positive role in the drought, can offset the negative effect of the coldness, and the atmosphere over NEC then maintains a lower-than-normal relative humidity. In the near-surface level, the air is drier and warmer than normal, which facilitates the drought.