Mesoscale rainfall patterns observed around wetlands in sub-Saharan Africa
Mesoscale rainfall patterns observed around wetlands in sub-Saharan Africa
复制标题
撒哈拉以南非洲湿地周围观察到的中尺度降雨模式
DOI：
10.1002/qj.3311
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发表时间：
2018
影响因子：
8.9
通讯作者：
Taylor C
中科院分区：
文献类型：
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作者：
Taylor C
湿地是景观的动态组成部分，对当地和上游的降雨、河流流量和地下水的变异性以及水管理做出反应。同时，在蒸发需求强烈的地区，湿地可以对大气表现出很强的陆面非均质性，驱动感热和潜热通量的显著梯度。因此，在一年中的某些时间，湿地可能会对降雨提供陆面反馈。在这里，我们评估湿地对撒哈拉以南非洲(SSA)降雨量的影响。使用一个成熟的基于多卫星的湿地面积产品，我们发现在15年的数据集中，大约22%的SSA出现了显著的湿地覆盖率(>；10%)。我们利用卫星数据分析了主要湿地附近的降雨模式，发现与附近干旱地区相比，在SSA上湿地上局部抑制的降雨信号是一致的。这一信号与简单的大气水分平衡观点形成了鲜明对比，后者表明，由于局部蒸发量增加，降雨量增加。观测到的信号在下午最强，夜间减弱。利用萨赫勒地区的云顶温度资料，我们发现午后对流的启动更有利于湿地附近，这与感热通量梯度的热诱导环流的强迫是一致的。我们还发现，在该地区，绝大多数降水与远程触发的中尺度对流系统(MCS)有关，当这些系统经过湿地时，对流减弱。从这项研究中，我们得出结论，横跨SSA的气候带范围内的湿地影响当地的降雨模式，而MCS是降水的重要组成部分，这种影响可以延伸到更大的区域，与长期MCS的轨迹有关。
Wetlands are dynamic components of the landscape, responding to local and upstream rainfall, river flow and groundwater variability, and to water management. At the same time, in regions of strong evaporative demand, wetlands can present very strong land surface heterogeneity to the atmosphere, driving marked gradients in sensible and latent heat fluxes. At certain times of year, wetlands can therefore potentially provide a land surface feedback on rainfall. Here we assess the influence of wetlands on rainfall across sub‐Saharan Africa (SSA). Using a well‐established multi‐satellite based product of wetland extent with monthly temporal resolution, we find significant wetland coverage (>10%) occurs at some point in the 15‐year dataset for about 22% of SSA. We analyse rainfall patterns in the vicinity of major wetlands using satellite data, and find a consistent signal across SSA of locally suppressed rainfall over the wetlands as compared to nearby drier areas. This signal contrasts with a simple atmospheric water balance perspective which would suggest increased rain in response to increased local evaporation. The observed signal is strongest during the afternoon and weakens overnight. Using cloud‐top temperature data from the Sahel, we find that afternoon convective initiation is favoured close to wetlands, consistent with forcing by a thermally induced circulation from gradients in sensible heat fluxes. We also find that in this region, where the vast majority of rainfall is associated with remotely triggered Mesoscale Convective Systems (MCS), convection weakens when these systems pass over wetlands. From this study, we conclude that wetlands across the range of climate zones spanning SSA influence rainfall patterns locally, and where MCS are an important component of rainfall, this influence can extend over a larger region, associated with the tracks of long‐lived MCS.