Seasonality of East African Rainfall

东非降雨的季节性

• 批准号: 1701520
• 负责人: Kerry Cook
• 金额: $ 68.36万
• 依托单位: University of Texas at Austin
• 依托单位国家: 美国
• 项目类别: Standard Grant
• 财政年份: 2017
• 资助国家: 美国
• 起止时间: 2017-08-01 至 2022-07-31
• 项目状态: 已结题
• 来源: https://www.nsf.gov/awardsearch/showAward?AWD_ID=1701520&HistoricalAwards=false
• 关键词: Seasonality; East; African; Rainfall

The seasonality of rainfall in East Africa from Ethiopia in the north to Malawi and Mozambique in the south is complex, including bimodal and unimodal rainy seasons. Regions with bimodal rainy seasons, with precipitation maxima and agricultural growing seasons in the spring and fall, occur generally within about 7 degrees of the equator in Kenya, southern Somalia, southern Ethiopia, and northern Tanzania. This rainfall distribution is traditionally explained as being related to having two overhead passes of the sun each year. However, this explanation is not complete since regions 10 or 15 degrees from the equator have one rainy season each year despite two overhead passes of the sun at these latitudes. In addition, equatorial central and western Africa experience humid climate with rainfall throughout the year. This suggests that a more complete understanding of the seasonality of East African rainfall should consider such factors as the roles of the Indian Ocean, topography, and near-equator atmospheric dynamics (with a small or absent Coriolis force) in addition to the solar forcing. This research project is aimed at advancing our understanding of how the seasonality of rainfall in East Africa is determined, and to apply that improved understanding to issues of climate variability and change, including impacts. Analysis of observations, comparing multiple datasets in this data-poor region, and output from high-resolution model simulations will be used to investigate these physical processes to produce a more comprehensive understanding of how the seasonality of rainfall is distributed across East Africa.It is crucial to understand the seasonality of rainfall to improve our ability to predict change and variability, especially in regions such as East Africa where the population is highly vulnerable. Variations in rainfall, including its seasonality, strongly impact the region's agriculture, economy, and water resources which, in turn, affect livelihoods and political stability. These issues will be directly addressed within the project by relating observed and simulated variations and trends in climate variables to variables more directly related to impacts. Changes in climate variables will be used to calculate changes in natural vegetation using a model that relates vegetation type to climate conditions. Changes and trends in growing season days and surface water availability will also be evaluated. These representations will provide direct input for impacts analysis. The research project benefits the climate modeling field more generally in contributing to the development of regional-scale climate simulation, including high-resolution models that can explicitly resolve convection within the governing equations. This is important since the parameterization of convection in models with coarser resolution, such as global climate models, is known to degrade simulations. Broader impacts of the research program also include the education of graduate students in STEM fields.

从北部的埃塞俄比亚到南部的马拉维和莫桑比克，东非降雨的季节性是复杂的，包括双峰和单峰雨季。在肯尼亚、索马里南部、埃塞俄比亚南部和坦桑尼亚北部，降水量最大和农业生长期在春季和秋季的双峰雨季地区，通常出现在赤道7度以内的地区。这种降雨分布传统上被解释为与每年有两次太阳从头顶经过有关。然而，这种解释是不完整的，因为距离赤道10或15度的地区每年只有一个雨季，尽管这些纬度的太阳在头顶经过两次。此外，赤道中非和西非全年都有降雨，气候湿润。这表明，要更全面地了解东非降雨的季节性，除了太阳强迫外，还应考虑印度洋、地形和近赤道大气动力学（科里奥利力很小或不存在）等因素的作用。该研究项目旨在提高我们对东非降雨季节性是如何确定的理解，并将这种改进的理解应用于气候变率和变化问题，包括影响。观测分析、比较这一数据贫乏地区的多个数据集以及高分辨率模式模拟的结果将用于调查这些物理过程，从而更全面地了解降雨的季节性如何在东非分布。了解降雨的季节性对于提高我们预测变化和变异的能力至关重要，特别是在东非等人口非常脆弱的地区。降雨的变化，包括其季节性，严重影响该地区的农业、经济和水资源，进而影响生计和政治稳定。通过将观测到的和模拟的气候变量的变化和趋势与与影响更直接相关的变量联系起来，这些问题将在项目内直接解决。气候变量的变化将被用于利用一种将植被类型与气候条件联系起来的模式来计算自然植被的变化。还将评估生长季节天数和地表水可用性的变化和趋势。这些表述将为影响分析提供直接输入。该研究项目有利于气候模拟领域更广泛地促进区域尺度气候模拟的发展，包括可以在控制方程中明确解决对流的高分辨率模型。这一点很重要，因为众所周知，在分辨率较粗的模式（如全球气候模式）中对流的参数化会降低模拟效果。该研究项目的更广泛影响还包括STEM领域研究生的教育。

项目成果

Observed relationship between the Turkana low-level jet and boreal summer convection

图尔卡纳低空急流与夏季北方对流之间的观测关系

• DOI: 10.1007/s00382-019-04769-2
• 发表时间: 2019
• 期刊: Climate Dynamics
• 影响因子: 4.6
• 作者: Vizy, Edward K.;Cook, Kerry H.
• 通讯作者: Cook, Kerry H.

Interannual variability of East African rainfall: role of seasonal transitions of the low-level cross-equatorial flow

• DOI: 10.1007/s00382-020-05244-z
• 发表时间: 2020-04
• 期刊: Climate Dynamics
• 影响因子: 4.6
• 作者: E. Vizy;K. Cook

Influence of Indian Ocean SST regionality on the East African short rains

• DOI: 10.1007/s00382-020-05265-8
• 发表时间: 2020-04-28
• 期刊: CLIMATE DYNAMICS
• 影响因子: 4.6
• 作者: Liu, Weiran;Cook, Kerry H.;Vizy, Edward K.
• 通讯作者: Vizy, Edward K.

Influence of Walker circulations on East African rainfall

• DOI: 10.1007/s00382-020-05579-7
• 发表时间: 2021-01
• 期刊: Climate Dynamics
• 影响因子: 4.6
• 作者: Siyu Zhao;K. Cook

Contemporary Climate Change of the African Monsoon Systems

• DOI: 10.1007/s40641-019-00130-1
• 发表时间: 2019-09-01
• 期刊: CURRENT CLIMATE CHANGE REPORTS
• 影响因子: 9.5
• 作者: Cook, Kerry H.;Vizy, Edward K.
• 通讯作者: Vizy, Edward K.