Acceleration of the hydrological cycle under global warming? An
age-weighted regional water tagging approach
Abstract
Global warming is assumed to accelerate the global water cycle. However,
quantification of the acceleration and regional analyses remain open.
Accordingly, in this study we address the fundamental hydrological
question: Is the water cycle regionally accelerating/decelerating under
global warming? For our investigation we have implemented the
age-weighted regional water tagging approach into the Weather Research
and Forecasting WRF model, namely WRF-age, to follow the atmospheric
water pathways and to derive atmospheric water residence times
accordingly. Moreover, we have implemented the three-dimensional online
budget analysis of the total, tagged, and aged atmospheric water into
WRF-age to provide a prognostic equation of the atmospheric water
residence times. The newly developed, physics-based WRF-age model is
used to regionally downscale the reanalysis of ERA-Interim and the
MPI-ESM Representative Concentration Pathway 8.5 scenario (RCP8.5)
simulation exemplarily for an East Asian monsoon region, i.e., the
Poyang Lake basin (the tagged moisture source area), for two 10-year
slices of historical (1980-1989) and future (2040-2049) times. In
comparison to the historical simulation, the future 2-meter temperature
rises by +1.4 °C, evaporation increases by +6%, and precipitation
decreases by -38% under RCP8.5 on average. In this context, global
warming leads to regionally decreased residence times for the tagged
water vapor by 8 hours and the tagged condensed moisture by 12 hours in
the atmosphere, but increased transit times for the tagged precipitation
by 4 hours over the land surface that is partly attributed to a slower
fallout of precipitating moisture components in the atmosphere under
global warming.