Collaborative Research: Evaluating the Past and Future of Mississippi River Hydroclimatology to Constrain Risk via Integrated Climate Modeling, Observations, and Reconstructions

密西西比河排干了一块大陆，从宾夕法尼亚州和蒙大拿州收集水，然后排放到墨西哥湾。向一条河流输送如此多的水自然会增加洪灾的风险，而这条河拥有世界上最广泛的防洪系统之一。但目前的制度提供的保护是有限的，我们不知道随着气候变暖，这种保护是否足够。变暖对洪水风险的影响取决于相互竞争的影响之间的平衡：变暖本身可能会通过增加从陆地蒸发的水分而不是流向溪流来减少排放。气候变暖还会减少积雪，导致积雪融化导致的春季径流减少。另一方面，温暖的空气通常含有更多的水分，这导致平均降雨量和极端降雨量增加，从而增加了洪水风险。该项目试图确定这些相互竞争的影响对密西西比河流量的净影响，密西西比河流量是洪水风险的概括性指标。许多工作涉及在气候模型中评估密西西比河的流量，特别是社区地球系统模型(CESM)，该模型使用密西西比河的河流传输模型(RTM)。初步结果显示，在高温室气体排放情景(RCP8.5)下，河流排放量在21世纪大幅增加(可能增加130%)，但在低排放情景(RCP4.5)下仍保持在历史正常水平。这一对比表明，降水导致的径流增加与蒸发和积雪融化导致的径流减少之间的平衡可能与温度有关，降雨量在较高的变暖水平上占上风。该项目还结合天气和径流观测网络、古气候重建以及现代和上个千年气候模型模拟组合，考虑了过去1000年密西西比州排放量的驱动因素。首席调查员(PI)最近的工作表明，中世纪气候异常的暖期的流量低于小冰期，这一结果通常被上个千年的CESM模拟所捕捉到。这一结果也符合21世纪温和变暖的情景。由于对洪水风险的关注，这项工作具有社会利益，PI正在与包括美国陆军工程兵部队和密西西比河城镇倡议在内的利益相关者合作，以了解其结果的实际意义并提供决策支持。该项目还包括教育和外联，支持高中生的暑期研究体验，并与美国女童子军合作，鼓励女孩和年轻女性考虑从事科学工作。该项目为一名博士后研究员和两名研究生提供支持和培训。该奖项反映了NSF的法定使命，并通过使用基金会的智力优势和更广泛的影响审查标准进行评估，被认为值得支持。

The Mississippi River drains a continent, gathering water from as far as Pennsylvania and Montana and discharging it into the Gulf of Mexico. The channeling of so much water into a single river naturally raises the stakes for flooding, and the river has one of the most extensive flood mitigation systems in the world. But there are limits to the protection afforded by the current system and we do not know if it will prove adequate as climate warms. The effect of warming on flood risk is determined by a balance between competing effects: warming by itself would likely reduce discharge by increasing the amount of moisture that evaporates from the land rather than running off into streams. Warming also reduces snowpack, leading to a reduction in the springtime streamflow resulting from snow melt. On the other hand warmer air generally holds more moisture, which leads to increases in both mean and extreme precipitation, thus increasing flood risk. This projects seeks to determine the net effect of these competing influences on Mississippi River discharge, which serves as a broad-brush proxy for flood risk. Much of the work involves assessments of Mississippi discharge in climate models, particularly the Community Earth System Model (CESM), which uses a River Transport Model (RTM) for the Mississippi. Preliminary results show river discharge increasing dramatically (by perhaps 130%) over the 21st century under a high greenhouse gas emissions scenario (RCP8.5) but remaining within historical norms under lower emissions (RCP4.5). This contrast suggests that the balance between streamflow increases from precipitation and decreases from evaporation and snow melt could be temperature dependent, with precipitation winning out at higher levels of warming.The project also considers the factors driving Mississippi discharge over the last millennium using a combination of weather and streamflow observing networks, paleoclimate reconstructions, and ensembles of present-day and last millennium climate model simulations. Recent work by the Principal Investigators (PIs) suggests that the warm period of the Medieval Climate Anomaly featured lower discharge than the Little Ice Age, a result that is generally captured by CESM simulations of the last millennium. The result is also in keeping with the moderate warming scenario for the 21st century.The work is of societal interest due to the focus on flood risk, and the PIs are working with stakeholders including the US Army Corps of Engineers and the Mississippi River Cities and Towns Initiative to understand the practical significance of their results and provide decision support. The project also involves education and outreach, supporting summer research experiences for high school students and working with the Girl Scouts of America to encourage girls and young women to consider careers in science. The project provides support and training to a postdoctoral researcher and two graduate students.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.