Simulation of hydrological cycle changes over China during Mid-Holocene

Present and Mid-Holocene climates are simulated with a global climate model CCM3 nested with a regional model MM5. From the model results, it is found that in Mid-Holocene, the center of the effective precipitation variation changes with season. A maximum of 3 mm/d effective precipitation variation occurs over Northeast China and the eastern part of Inner Mongolia in summer. Meanwhile, precipitation between the Huanghe River and the Yangtze River decreases with a maximum of 2 mm/d. Cloud cover in North China increases while that over the middle and downstream of the Yangtze River basin reduces. Changes of low cloud amount are the most in three types of clouds with a maximum of more than 0.2, but high cloud changes are the least among them. Temperature between the Huanghe River and the Yangtze River rises the most due to the cloud cover reduction in summer. Water vapor and relative humidity over this region decrease, in accordance with the cloud cover reduction. Water vapor changes in South China are different with seasons. Water vapor and relative humidity in Northeast China increase, which results in cloud cover and precipitation increase. The model results illustrate that the relative humidity isn't a conservative factor, the maximum change of which is more than 15%. Moreover, temperature increases in some regions while water vapor decreases. However, in Last Glacial Maximum, when temperature decreases, water vapor consistently reduces. These indicate that temperatures decrease can result in water vapor reduction, but temperature increase does not always bring about water vapor enhancement. This is different from the fact that at the global scale the relative humidity is conserved. In MidHolocene, the Yangtze River basin became warmer and drier in all seasons except spring. Meanwhile, Northeast China and the eastern part of Inner Mongolia became more rainy and wetter.