Centre for Atmospheric and Oceanic Sciences, Indian Institute of Science, Bangalore, India.
Sci Rep. 2017 Sep 8;7(1):10989. doi: 10.1038/s41598-017-10750-y.
Amazon discharges a large volume of freshwater into the ocean, yet its impact on climate is largely unknown. Climate projections show that a warmer northern tropical Atlantic Ocean together with a warmer equatorial Pacific lead to extreme droughts in the Amazonia, considerably reducing the Amazon runoff. Here we present results from coupled model simulations and observations on the climatic response to a significant reduction in Amazon runoff into the Atlantic Ocean. Climate model simulation without Amazon runoff resulted in cooler equatorial Atlantic, weakening the Hadley cell and thereby the atmospheric meridional cells. Consequently, the extratropical westerlies turned weaker, leading to prevalent negative North Atlantic Oscillation (NAO) like climate, similar to the observed anomalies during Amazon drought years. This study reaffirms that spatial signature of NAO is in part driven by sea surface temperature (SST) anomalies in the tropical Atlantic. Winters of northern Europe and eastern Canada turned cooler and drier whereas southern Europe and the eastern United States experienced warmer and wetter winters without Amazon runoff. Significant warming over the Arctic reduced the local sea-ice extent and enhanced the high latitude river runoff. More importantly, our simulations caution against extreme exploitation of rivers for its far-reaching consequences on climate.
亚马逊河向海洋排放大量淡水，但它对气候的影响在很大程度上是未知的。气候预测显示，北大西洋热带地区变暖以及赤道太平洋变暖，将导致亚马逊地区出现极端干旱，大大减少亚马逊河的径流量。本文介绍了对亚马孙河流入大西洋的径流量显著减少的气候响应的耦合模式模拟和观测结果。没有亚马逊河流入的气候模式模拟导致赤道大西洋地区降温，削弱了哈德利环流，从而削弱了大气经向环流。因此，温带西风减弱，导致北大西洋涛动（NAO）等负向气候盛行，类似于亚马孙干旱年份的观测异常。这项研究再次证实，北大西洋涛动的空间特征部分是由热带大西洋的海表温度（SST）异常驱动的。没有亚马逊河流入，北欧和加拿大东部的冬季变得更冷、更干燥，而南欧和美国东部的冬季则更暖、更湿润。北极地区的显著升温减少了当地的海冰范围，并增加了高纬度河流的径流量。更重要的是，我们的模拟警告不要过度开发河流，因为这将对气候产生深远影响。
