Collaborative Research: Connecting the Past, Present, and Future Climate of the Lake Victoria Basin using High-Resolution Coupled Modeling

维多利亚湖是非洲最大的湖泊，也是世界第二大湖泊，它大到足以形成自己的天气。湖对天气的影响在降雨总量上是明显的，因为湖上的降雨量比它周围的集水区多得多，在降雨的日循环中，因为湖产生了陆海微风效应，导致降雨在白天落在陆地上，晚上落在湖上。考虑到该湖对天气的巨大影响，人们自然会问，它将在维多利亚湖盆地的气候变化中扮演什么角色。维多利亚在气候变化中所扮演的角色的问题是具有挑战性的，原因有几个，其中包括缺乏对该地区的观测，以及很难进行模拟，以捕捉影响该地区天气和气候的尺度和过程的范围。在空间尺度上，范围从提供大部分降雨的中尺度雷暴复合体的大小延伸到控制降雨季节性的区域尺度环流模式。该地区还可能受到印度洋和大西洋表面温度变化的影响。这里进行的研究采用嵌套建模策略来应对维多利亚盆地气候变化的挑战，其中一个区域模型，即天气研究与预报（WRF）模型，在三个嵌套网格中运行，以捕获相关的尺度范围。外部网格覆盖了整个非洲以及大西洋和印度洋的大部分地区，网格间距为27公里，而最内部网格覆盖了维多利亚湖盆地，网格间距为3公里，分辨率足以捕捉雷暴综合体。WRF与社区土地模型（CLM）耦合，CLM包括维多利亚湖及其与上覆大气相互作用的表示。这项工作包括对该盆地过去、现在和未来气候的模拟。过去的气候模拟集中在1.7万年前湖泊完全干涸的时期，pi假设湖泊的干燥是由于地球轨道周期（这也导致了冰河时代）引起的入射太阳辐射变化的结果。该项目还考虑了更普遍的问题，即区域气候如何取决于维多利亚湖的大小，这可以在模型模拟中改变。湖泊大小的变化可能会驱动降水变化，进而导致湖泊大小的进一步变化，因为湖泊的水输入可能有80%来自当地降雨（流入湖泊的河流提供了另外20%）。考虑到大约有4000万人生活在维多利亚湖盆地，并依赖其水资源，这项工作具有社会和科学意义。降雨既是一种危险，也是一种资源，因为大部分降雨都是在强风暴中发生的，这对渔船队来说是一种特别的危险。这些机构通过在贝勒大学梅伯恩博物馆和肯尼亚国家博物馆举办巡回展览，向公众宣传该地区的气候变化。此外，该项目还为德克萨斯大学奥斯汀分校的两名研究生和贝勒大学的一名研究生提供支持和培训。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。

Lake Victoria, the largest lake in Africa and the second largest in the world, is big enough to make its own weather. The lake's influence on weather is evident in rainfall totals, as considerably more rain falls over the lake than the catchment around it, and in the diurnal cycle of rainfall, as the lake creates a land-sea breeze effect which causes rain to fall during the day over the land and at night over the lake. Given the lake's outsized influence on weather it is natural to ask what role it will play in climate change over the Lake Victoria Basin. The question of Victoria's role in climate change is challenging for several reasons, among them the lack of observations over the region and the difficulty of making simulations which capture the range of scales and processes that matter for the region's weather and climate. Regarding the spatial scales the range extends from the size of the mesoscale thunderstorm complexes the deliver much of the rain to the regional-scale circulation patterns that control the seasonality of rainfall. The region could also be influenced by changes in surface temperature over the Indian and Atlantic Oceans.Research conducted here takes up the challenge of Victoria Basin climate change using a nested modeling strategy in which a regional model, the Weather Research and Forecasting (WRF) model, is run with three nested grids to capture the relevant scale range. The outer grid covers all of Africa and much of the Atlantic and Indian Oceans with a 27km grid spacing while the innermost grid covers the Lake Victoria Basin at 3km, sufficient resolution to capture thunderstorm complexes. WRF is coupled to the Community Land Model (CLM), which includes a representation of Lake Victoria and its interactions with the overlying atmosphere.The work involves simulations of past, present, and projected future climate over the basin. Past climate simulations focus on a period 17 thousand years ago when the lake dried out completely, and the PIs hypothesize that the dessication of the lake was the result of changes in incoming solar radiation due to Earth's orbital cycle (which also caused the ice ages). The project also considers the more general question of how regional climate depends on the size of Lake Victoria, which can be varied in the model simulations. Changes in lake size could drive precipitation changes that cause further lake size change, as the lake receives perhaps 80% of its water input from local rainfall (rivers flowing into the lake provide the other 20%).The work is of societal as well as scientific interest given that about 40 million people live in the Lake Victoria Basin and are dependent on its water resources. Rainfall is a hazard as well as a resource given that much of the rain falls in severe storms, a particular hazard for the fishing fleet. The PIs conduct public outreach regarding climate change in the region through a traveling museum exhibit to be presented at the Mayborn Museum at Baylor University and at the National Museum of Kenya. In addition, the project provides support and training to two graduate students at the University of Texas at Austin and one at Baylor University.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.