Regional dynamical and statistical downscaling temperature, humidity and windspeed for the Beijing region under stratospheric aerosol injection geoengineering.

We use four Earth System Model (ESM) to simulate climate under the modest greenhouse emissions RCP4.5, the "business-as-usual" RCP8.5 and the stratospheric aerosol injection G4 geoengineering scenarios. These drive a 10 km resolution dynamically downscaled model (WRF), and a statistically bias corrected (ISIMIP) and downscaled simulation in a 450×330 km domain containing the Beijing province, ranging from 2000 m elevations to sea level. The 1980s simulations of surface temperatures, humidities and windspeeds using statistical bias correction makes for a better estimate of mean climate determined by ERA5 reanalysis data than does the WRF simulation. However correcting WRF output with Quantile-Delta Mapping bias correction removes the offsets in mean state and results in WRF better reproducing observations over 2007-2017 than ISIMIP bias correction. WRF simulations show consistently 0.5°C higher mean annual temperatures than from ISIMIP due both to the better resolved city centers and also to warmer winter temperatures. In the 2060s WRF produces consistently larger spatial ranges of surface temperatures, humidities and windspeeds than ISIMIP downscaling across the three future scenarios. WRF and ISIMIP methods produce very similar spatial patterns of temperature with G4 are always cooler than RCP4.5 and RCP8.5, by a slightly larger amount with ISIMIP than WRF. Humidity scenario differences vary greatly between ESM and hence ISIMIP downscaling, while for WRF the results are far more consistent across ESM and show only small changes between scenarios. Mean windspeeds show similarly small changes over the domain, although G4 is significantly windier under WRF than either RCP scenario. [ABSTRACT FROM AUTHOR]