High Resolution Climatological Simulations for South and Southeast Asia and the Tibetan Plateau

The extreme concentration of population over South and Southeast Asia makes it critical to accurately understand the global warming impact on the South and Southeast Asian monsoon (SAM and SEAM) while the complex orography of the regions makes future projections of monsoon intensity technically challenging. Here we describe a series of climate projections constructed using the Weather Research and Forecasting (WRF) Model to dynamically downscale a global warming simulation generated using the Community Earth System Model. All projections are characterized by a consistent increase in average monsoon precipitation and daily extreme precipitation. A regional ocean model based upon the Coastal and Regional Ocean Community model system was then incorporated into the dynamical downscaling pipeline and this has also contributed to significantly improving the simulations of both sea surface temperature and rainfall. Since the Tibetan Plateau (TP) is widely considered to act as an elevated heat source which contributes to driving the Asian monsoon system, a coupled dynamically downscaled simulation with flattened plateau has also been performed so as to investigate the role of TP in the SEAM at a higher spatial resolution than has previously been investigated. We also have completed a series of regional paleoclimate simulations using the coupled modeling system to dynamically downscale global simulations during the mid-Holocene (MH), a time period featuring generally warmer summers than present in the Northern Hemisphere. In the global model, we have taken care to incorporate Green Sahara (GS) boundary conditions so as investigate the interactions between the GS and the Asian monsoon circulations. SAM and SEAM precipitation is greatly enhanced by the inclusion of a GS. Data–model comparisons with downscaled simulations outperform those with the coarser global model, highlighting the crucial role of downscaling in paleo data–model comparison. The TP also contains the headwaters of major Asian rivers and understanding the characteristics and changes of the hydrological regimes on the TP during the MH will help understand the expected future changes. Thus, an analysis of hydroclimates in three major river basins in the TP are also presented, based on dynamically downscaled climate simulations constructed using coupled WRF-WRF-Hydro. 由于南亚和东南亚是世界上人口最稠密的地区之一，因此准确了解全球变暖对南亚和东南亚季风（SAM 和 SEAM）的影响至关重要，而该地区复杂的地形对未来季风强度的预测提出了技术上的巨大挑战性。本研究使用了天气研究和预报模型 (WRF) 对地球系统模型 （CESM）生成的全球变暖情况下的气候模拟进行动力学降尺度，以构建一系列对南亚和东南亚季风的气候预测。所有预测均显示出平均季风降水和极端降水的增加。我们随后将基于沿海和区域海洋社区模型系统的区域海洋模型 （CROCO）纳入动力学降尺度系统，这显着改善了对海面温度和降雨的模拟。由于青藏高原（TP）被广泛认为是推动亚洲季风系统的抬高的加热源，本研究因此还进行了无高原情况下的动力学降尺度模拟，从而得到了具有比以前研究更高的空间分辨率的对TP在SEAM中的作用的研究。本研究还使用了此耦合模式系统完成了一系列区域古气候模拟，对全新世中期 (MH) 的全球模拟进行了动力学降尺度。在该时期的夏季北半球通常比现在更温暖。在全球模式中，我们同时加入了绿色撒哈拉 (GS) 边界条件，以研究 GS 和亚洲季风环流之间的相互作用。加入 GS 后，SAM 和 SEAM 降水大大增强。对比使用更粗分辨率的全球模式，我们的动力学降尺度的模拟效果明显更优，这也突显了更高分辨率在古气候模拟中的关键作用。青藏高原还是亚洲很多主要河流的源头，了解 MH 期间青藏高原水文状况的特征和变化将有助于了解气候变暖情况下的未来变化可能。因此，本研究最后使用基于耦合 WRF-WRF-Hydro模式的动力学降尺度模拟，对 TP 上三个主要河流流域的水文气候分析。

Keywords: Asian monsoon
Dynamical downscaling
Extreme climate events
Global climate change
High-resolution global regional simulation
Hydroclimate
Advisor: Peltier, W. Richard