WRF with age-weighted water tracers: implementation, application, and new insights into the regionally accelerated atmospheric hydrological cycle under global warming

<p>Atmospheric water residence time, here defined as time between the original evaporation and the returning of its respective water masses to the land surface as precipitation, is <span lang="EN-US">a</span> measure of the speed of the atmospheric hydrological cycle. Traditional <span lang="EN-US">analytical </span>methods are generally limited by crude assumptions in the coupling between the land surface and the atmosphere<span lang="EN-US">, and hence are not applicable to</span> <span lang="EN-US">regions </span>with complex monsoon systems<span lang="EN-US"> under a changing climate. To this end, we have implemented the age-weighted water tracers into t</span>he Weather Research and Forecasting WRF model<span lang="EN-US">, namely, WRF-age,</span> <span lang="EN-US">to </span>follow the atmospheric water pathways and to derive atmospheric <span lang="EN-US">water </span>residence times<span lang="EN-US"> accordingly</span>. <span lang="EN-US">The newly developed, physics-based WRF-age is used to regionally downscale the reanalysis of ERA-Interim and the </span>MPI-ESM Representative Concentration Pathway 8.5 scenario (RCP8.5)<span lang="EN-US"> simulation for </span>an East Asian monsoon region<span lang="EN-US">, i.e., the Poyang Lake basin, for two 10-year slices of historical (1980-1989) and future (2040-2049) times. In comparison to the historical WRF-age simulation, the future 2-meter air temperature rises by 1.3 &#176;C and precipitation decreases by 38% under RCP8.5 on average. In this context, global warming leads to decreased atmospheric residence times of the column-integrated water vapor (from 22 to 13 hours) and column-integrated condensed moisture (from 26 to 14 hours) in the atmosphere over the basin, but slightly increased atmospheric residence times of surface precipitation (from 12 to 15 hours) in agreement with reduced the precipitation amounts. Our findings demonstrate that global warming increases the complexity of regional atmospheric water cycle, especially the associated changes in the residence times of atmospheric water states of matter.</span></p>