Historical and future changes of atmospheric precipitable water over China simulated by CMIP5 models

Abstract

Atmospheric water vapor has not only been reported to increase in the real world, but is also expected to increase in climate models. Correctly simulating water vapor and its relationship with temperature is thus vital for climate models. In this study, atmospheric precipitable water (PW) from phase 5 of the Coupled Model Intercomparison Project (CMIP5) is evaluated over China during 1970–2005, and then the future changes of PW and their correlation with near-surface air temperature (Ts) are further investigated. The results show that the PW biases in the model simulations are within ~ 20% for most of eastern China, but have larger root-mean-square error over southeastern China. Most models are able to simulate the observed PW upward trends since 1970, but with large inter-model spread. CanESM2, GFDL-CM3, HadGEM2-ES and MIROC5 are relatively better at reproducing the observed long-term variations and trends for the whole of China and its subregions. An empirical orthogonal function (EOF) analysis shows that the model simulations reproduce the first observed leading modes well, but barely capture the temporal variation revealed by the second observed EOF. The model simulations project ubiquitous increases in PW in the twenty-first century, resulting from an increase in the mean and a flattening of the probability distribution functions of the PW anomalies. In particular, the increases in PW under the most severe future emissions scenario (RCP8.5) are nearly twice as much as those under the low–mid emissions scenario (RCP4.5) for most of China by the late twenty-first century. The model simulations suggest that the changes in PW are largely consistent with the changes in Ts during 1970–2005, with a dPW/dTs slope of ~ 4.6–6.0% K−1, which roughly agrees with the observed results but is slightly lower than the 7% K−1 implied by the Clausius–Clapeyron equation with a constant relative humidity. In the twenty-first century, the dPW/dTs is projected to be about 5.5–7.0% K−1 under the RCP4.5 scenario, but may reach ~ 7.4% K−1 or higher under the RCP8.5 scenario.