How shrinkage of Lake Chad affects the local climate
How shrinkage of Lake Chad affects the local climate
复制标题
DOI：
10.1007/s00382-022-06597-3
复制
发表时间：
2022-11-27
期刊：
影响因子：
4.6
通讯作者：
Vizy，Edward K.
中科院分区：
文献类型：
--
作者：
Zhao，Siyu;Cook，Kerry H.;Vizy，Edward K.
对流允许集合模拟被用来了解乍得湖的面积变化如何影响降水。乍得湖从25，000平方公里缩小到现在的1300平方公里，使得下午的降雨量增加。在一个大的湖泊降水减少与浅的行星边界层，这减少了触发对流的湍流和削弱垂直水分混合的可能性。因此，大湖不会成为下午对流的水汽来源，但会减少中低层的湿度，从而使白天的环境更加稳定。白天的湖风也通过诱导低层水分发散和下沉来抑制大湖上空的对流。在衰退为一个小湖期间，乍得湖部分被湿地取代，湿地也减少了当地下午的降雨量，但程度不像大湖。这种影响主要与异常沉降和白天湿地表面温度低于邻近土地有关。湿地上的边界层高度远高于大湖上的边界层高度，这是湿地抑制白天降雨的作用较弱的原因。乍得湖和邻近湿地的损失影响当地和中尺度气候通过修改白天湖泊/湿地微风影响的空间区域。在具有积云对流参数化的模型中，降雨对湖泊/湿地环流扰动的响应可以被忽视。
Convective-permitting ensemble simulations are used to understand how areal changes of Lake Chad affect precipitation. Shrinkage of Lake Chad from about 25,000 km2to its current size (~ 1300 km2) increases rainfall over the lake basin in the afternoon. Reduced precipitation over a large lake is associated with a shallow planetary boundary layer, which decreases the likelihood of triggering convection by turbulence and weakens the vertical moisture mixing. As a result, the large lake does not act as a moisture source for afternoon convection, but lessens the low to mid-level humidity leading to a more stable daytime environment. Daytime lake breezes also act to inhibit convection over the large lake by inducing low-level moisture divergence and subsidence. During the recession to a small lake, Lake Chad is partially replaced by wetlands which also reduce local afternoon rainfall but not to the same extent as the large lake. This effect is primarily associated with anomalous subsidence and cooler surface temperatures over the wetlands than over the adjacent land during the day. Boundary layer heights over the wetlands are much higher than over the large lake, accounting for the wetlands’ weaker effect in suppressing daytime rainfall. Loss of Lake Chad and adjacent wetlands impacts the local and mesoscale climate through modification of the spatial area influenced by daytime lake/wetland breezes. The rainfall response to the circulation perturbation of the lake/wetlands can be overlooked in models with cumulus convective parameterization.