Does elevation-dependent warming hold true above 5000\u2009m elevation? Lessons from the Tibetan Plateau

Yanhong Gao,Jianwei Xu,Linhong Xiao,Dennis P Lettenmaier,Fei Chen,Xia Li

doi:10.1038/s41612-018-0030-z

Abstract

Available observations below 5000 m altitude suggest that some mountain regions are undergoing accelerated elevation-dependent warming (EDW) in response to global or regional climate change. We address the question of whether EDW exists above 5000 m altitude, which is the elevation of much of the mountainous portion of the Tibetan Plateau, and headwaters to most of Asia’s major rivers. We analyzed four data sources: in situ observations, gridded observations, ERA-Interim reanalysis, and Weather Research and Forecasting (WRF) regional climate model output over the portion of the Tibetan Plateau above 5000 m elevation. We also analyzed the relative contributions of changes in water vapor, diabatic heating, snow, and surface energy changes to EDW in WRF simulations and ERA-Interim. Gridded observations over the Tibetan Plateau show EDW below 5000 m, in apparent consistency with studies elsewhere. However, the gridded observations above 5000 m are essentially entirely extrapolated from lower elevations. Despite differences in details, neither ERA-Interim nor WRF indicate EDW above 5000 m. The WRF simulation produces more realistic temperature profiles at elevations where observations exist, which are also consistent with the simulated profiles of factors contributing to vertical heating. Furthermore, WRF projects no EDW above 5000 m in future climate projections (with CCSM4 boundary conditions) for RCP 4.5 and 8.5 global emission scenarios. Therefore, we conclude that EDW above 5000 m over the Tibetan Plateau is not occurring, nor is it likely to occur in future decades.

Highlights

Observations and modeling efforts for several mountain regions in the world indicate that greater surface warming occurs at higher altitudes.[1,2,3,4,5,6,7] Rangwala and Miller[8] examined elevation-dependent warming (EDW) over four mountain regions: the Swiss Alps, the Colorado Rocky Mountains, the Tibetan Plateau/Himalayas, and the Tropical Andes
Based on observations obtained from China Meteorological Administration (CMA) stations, a clear signal of EDW below 5000 m has been reported in recent decades over the Tibetan Plateau (TP).[1,2,3,9]
Having established that there are no observations above 5000 m and the extrapolation beyond 5000 m in the gridded data likely is not reliable, we focus on analyzing the physical processes that may contribute to differences in EDW between dynamical downscaling (WRF) and ERA-Interim below and above 5000 m

Summary

INTRODUCTION

Observations and modeling efforts for several mountain regions in the world indicate that greater surface warming occurs at higher altitudes.[1,2,3,4,5,6,7] Rangwala and Miller[8] examined elevation-dependent warming (EDW) over four mountain regions: the Swiss Alps, the Colorado Rocky Mountains, the Tibetan Plateau/Himalayas, and the Tropical Andes. The glacier and snow meltwater from high elevations in the Tibetan Plateau/Himalaya region feed the headwaters of nine of Asia’s major rivers including the Yangtze, Huang He (Yellow), Indus, Ganges, Brahmaputra, Irrawaddy, Salween, and Mekong Rivers The headwaters of these rivers are all located above 5000 m and provide, in part or whole, the water source for approximately 10% of the world’s population.[13] Lacking adequate observations, it is a challenge to assess whether these high-mountain headwater areas have warmed at a higher rate than the rest of the regional land surface.

RESULTS

DISCUSSION

Findings

METHODS