Understanding Future Changes in Midlatitude Orographic Precipitation

地形降水指的是由于空气在山区上空被迫上升而形成的雨雪。地形降水取决于许多因素，以及这些因素在未来气候状态下的变化将如何影响与地形相关的降水数量和位置的气候学。气候模拟的一个常见结果是，山体下坡侧的降水将增加，这将对水资源和潜在的洪水产生重大影响。本研究将分析现有的高分辨率数值模拟，并进行新的模拟，以确定这些变化背后的物理机制。这项工作对美国西部的农民、水资源管理者和其他利益相关者有直接影响，研究人员将通过参与气候影响研究联盟与这些群体接触。还将培养多名研究生。研究小组将进行数值模拟研究，以更好地了解未来气候状态下地形降水的潜在变化。先前的模拟提供的证据表明，在山区背风侧的“雨影”区域，降水将增加。研究小组将分析35年高分辨率“伪全球变暖”模拟的现有结果，并进行新的模拟，以解决以下研究问题：1)什么类型的风暴对喀斯喀特山脉和内华达山脉的降水变化模式贡献最大？2)地形降水变化的动力、热力学和/或微物理机制是什么？它们的相对重要性是什么？3)模型参数化的差异对结果有多敏感，尤其是与云微物理相关的差异？4)喀斯喀特山脉和内华达山脉降水变化的模式和机制是否对其他中纬度山脉（如安第斯山脉或南阿尔卑斯山）有借鉴意义？该奖项反映了美国国家科学基金会的法定使命，并通过使用基金会的知识价值和更广泛的影响审查标准进行评估，被认为值得支持。

Orographic precipitation refers to rain and snow that develops due to air that is forced upward over mountainous terrain. Orographic precipitation depends on numerous factors, and how those factors change in future climate states will impact the climatology of the amount and location of precipitation in relation to the terrain. One common result from climate modeling is that precipitation on the downslope side of mountains will increase, which would have a large impact on water resources and potential flooding. This study will analyze an existing high-resolution numerical simulation and perform new simulations to determine the physical mechanisms behind these changes. The work has direct impact on farmers, water-resource managers, and other stakeholders in the Western US, and the researchers will engage with this group through the participation in the Climate Impacts Research Consortium. Multiple graduate students will also be trained.The research team will conduct a numerical modeling study to better understand the potential changes in orographic precipitation in future climate states. Prior modeling has provided evidence that precipitation will increase in the “rain shadow” areas on the lee side of mountainous terrain. The research team will analyze existing output from a 35-year high-resolution “pseudo-global warming” simulation and conduct new simulations to address the following research questions: 1) What types of storms contribute most to the pattern of precipitation change in the Cascades and Sierra Nevada? 2) What mechanisms – dynamic, thermodynamic, and/or microphysical – contribute to orographic precipitation change, and what is their relative importance? 3) How sensitive are the results to differences in model parameterizations, especially related to cloud microphysics? 4) Does the pattern and mechanisms of precipitation change in the Cascades and Sierra Nevada hold lessons for other midlatitude mountain ranges, such as the Andes or Southern Alps?This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.