Future changes in precipitation and water availability over the Tibetan Plateau projected by CMIP6 models constrained by climate sensitivity

Abstract

Precipitation projections over the Tibetan Plateau (TP) show diversity among existing studies, partly due to model uncertainty. How to develop a reliable projection remains inconclusive. Here, based on the IPCC AR6–assessed likely range of equilibrium climate sensitivity (ECS) and the climatological precipitation performance, the authors constrain the CMIP6 (phase 6 of the Coupled Model Intercomparison Project) model projection of summer precipitation and water availability over the TP. The best estimates of precipitation changes are 0.24, 0.25, and 0.45 mm d⁻¹ (5.9 %, 6.1 %, and 11.2 %) under the Shared Socioeconomic Pathway (SSP) scenarios of SSP1–2.6, SSP2–4.5, and SSP5–8.5 from 2050–2099 relative to 1965–2014, respectively. The corresponding constrained projections of water availability measured by precipitation minus evaporation (P–E) are 0.10, 0.09, and 0.22 mm d⁻¹ (5.7 %, 4.9 %, and 13.2 %), respectively. The increase of precipitation and P–E projected by the high-ECS models, whose ECS values are higher than the upper limit of the likely range, are about 1.7 times larger than those estimated by constrained projections. Spatially, there is a larger increase in precipitation and P–E over the eastern TP, while the western part shows a relatively weak difference in precipitation and a drier trend in P–E. The wetter TP projected by the high-ECS models resulted from both an approximately 1.2–1.4 times stronger hydrological sensitivity and additional warming of 0.6 °C–1.2 °C under all three scenarios during 2050–2099. This study emphasizes that selecting climate models with climate sensitivity within the likely range is crucial to reducing the uncertainty in the projection of TP precipitation and water availability changes.

摘要

青藏高原是气候变化敏感区, 可靠的气候预估对气候变化应对至关重要. 青藏高原夏季降水变化的预估结果在CMIP6气候模式间存在较大的不确定性, 原因部分地和这些模式对温室气体强迫的敏感度不同有关. 作者在对CMIP6模式性能进行评估基础上, 选择了具有较高气候态降水模拟技巧的模式用于预估研究, 并根据IPCC AR6估算的平衡态气候敏感度 (ECS) 的可能性范围, 对青藏高原夏季降水的中远期 (2050–2099) 变化进行约束. 结果表明, 在SSP1–2.6, SSP2–4.5 和 SSP5–8.5情景下, 青藏高原夏季降水将分别增多0.24, 0.25 和 0.45 mm d⁻¹ (5.9 %, 6.1 %, 和 11.2 %), 水资源可用性 (P–E) 将分别增加0.10, 0.09和0.22 mm d⁻¹(5.7 %, 4.9 % 和13.2 %) . 与约束预估相比, 高ECS模式预估的水文敏感度约为约束后的1.2–1.4倍, 升温幅度偏高0.6 °C–1.2 °C, 这二者共同导致高ECS模式预估的高原降水增幅约为约束预估的1.7倍. 本文指出气候敏感度是影响未来青藏高原水资源预估不确定性的重要来源, 同时基于IPCC AR6对ECS的最佳估算, 给出了高原夏季降水和水资源的最佳预估结果.