The Third Pole (TP), which refers to the Tibetan Plateau, is the highest and most extensive upland region in the world. The Tibetan Plateau is termed as the Third Pole given its ice fields contain the largest reserve of freshwater outside the two polar regions (Arctic and Antarctica). Changes in the water cycle over the TP may affect more than 20% of the world population since several major Asian rivers originating from the TP.
The TP has experienced a warming rate of twice as fast as the rest of the world. Under the warming, the number of lakes, with an area larger than 1 km2, has increased to ~1,400 in 2018 from ~1,000 in the 1970s over the western TP. Associated with the increase in the number and area of lakes, wetlands are also expanded due to the increase in precipitation. It is of great interest to investigate the feedback of changes in lakes and wetlands on precipitation over the TP.
Because of its complex terrain and harsh environment, ground-based observations are scarce. The horizontal resolution of prevailing global reanalysis datasets is generally coarser than 30 km, which is not sufficient to examine the impact of changes in lakes and wetlands on precipitation. A high-resolution (< 4 km) regional downscaling project focusing on the TP region has the potential to vastly improve the understanding of physical processes in this region and beyond, paving the way for future physically plausible climate projections. This project aims to enhance our understanding of the water cycle over the TP, with a focus on the impact of changes in surface conditions, such as lakes and wetlands.
The Advanced Research version of the Weather Research and Forecasting model (WRF-ARW) will be used in this project. The targeted resolution is 1-4 km through which the feedback of lakes with an area larger than 1 km2 can be captured. This resolution often referred to as “convection-permitting” or “convection-resolving” scales, the need for parameterizations of deep convection is no longer a requirement, thus greatly reducing model uncertainties and parameter sensitivities. The fifth generation of global reanalysis from the ECMWF, ERA5, with a horizontal resolution of 31km, will be used to drive the WRF-ARW simulations. Impacts of different parameterizations of cloud microphysics and boundary layer turbulence on the simulation of precipitation will be evaluated to finalize the model set up. Then, changes in lakes and wetland areas based on satellite observation and the convective permitted modeling will be jointly used to examine the impact of changes in lakes and wetlands on precipitation over the TP.
The outcomes of the project are expected to enhance our understanding of recent changes in precipitation and water resource over the TP. Studies on the water cycle will also benefit tremendously from the results of this project.
This project is the Swedish contribution to a new endorsed WCRP-CORDEX Flagship Pilot Studies (FPS) about high-resolution climate modeling over the TP (http://rcg.gvc.gu.se/cordex_fps_cptp/).