Future Changes in Seasonality in East Africa from Regional Simulations with Explicit and Parameterized Convection
Future Changes in Seasonality in East Africa from Regional Simulations with Explicit and Parameterized Convection
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DOI：
10.1175/jcli-d-20-0450.1
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发表时间：
2020-12
影响因子：
4.9
通讯作者：
Caroline M. Wainwright;J. Marsham;D. Rowell;D. Finney;E. Black
中科院分区：
文献类型：
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作者：
Caroline M. Wainwright;J. Marsham;D. Rowell;D. Finney;E. Black
东非降水季节循环具有重要的社会意义，然而，当前一代耦合的全球气候模型未能正确地捕捉到这种季节性。对流参数化方案的使用是此类模式中降水偏差的已知来源。最近，一个高分辨率的区域模式被用来制作第一个明确模拟对流的泛非气候变化模拟。本文将其与相应的参数化对流模拟进行比较，以探讨该参数化对东非降水季节变化的影响。这两个模式都捕捉到了当前的季节性，尽管在参数化模拟中对9-10月的过高估计导致了北方秋季短雨的早期偏差，这与更高的对流不稳定和近地面湿静态能量有关。这种偏见在显式模型中被消除了。在未来气候变化下，两个模型都显示短时降雨变得更晚、更潮湿。对于北方春季长雨，显式对流模拟表现出起始提前，而参数化模拟变化不大。在乌干达和肯尼亚西部，两个模拟都显示1-2月旱季降雨量增加，北部夏季和秋季降雨量大幅增加，特别是在显式对流模式下，改变了季节周期的形状，可能产生显著的社会经济影响。在这两个模型中，年际变化相似。结果表明，对流的参数化可能是全球模式预测季节性时间变化的一个不确定性来源，应该向用户强调季节性的潜在影响变化。
The East African precipitation seasonal cycle is of significant societal importance, and yet the current generation of coupled global climate models fails to correctly capture this seasonality. The use of convective parameterization schemes is a known source of precipitation bias in such models. Recently, a high-resolution regional model was used to produce the first pan-African climate change simulation that explicitly models convection. Here, this is compared with a corresponding parameterized-convection simulation to explore the effect of the parameterization on representation of East Africa precipitation seasonality. Both models capture current seasonality, although an overestimate in September–October in the parameterized simulation leads to an early bias in the onset of the boreal autumn short rains, associated with higher convective instability and near-surface moist static energy. This bias is removed in the explicit model. Under future climate change both models show the short rains getting later and wetter. For the boreal spring long rains, the explicit convection simulation shows the onset advancing but the parameterized simulation shows little change. Over Uganda and western Kenya both simulations show rainfall increases in the January–February dry season and large increases in boreal summer and autumn rainfall, particularly in the explicit convection model, changing the shape of the seasonal cycle, with potential for pronounced socioeconomic impacts. Interannual variability is similar in both models. Results imply that parameterization of convection may be a source of uncertainty for projections of changes in seasonal timing from global models and that potentially impactful changes in seasonality should be highlighted to users.