Contribution of soil moisture variability to summer precipitation in the northern hemisphere

Abstract

The variability and impacts of spring soil moisture (SSM) over the Northern Hemisphere (NH) in the recent 30 years are investigated. The results show that there are two maximum regions of interannual variability of SSM, which are located in the central region of North America (Region 1), and Europe and West Asia (Region 2). These two regions are crucial areas of land-atmosphere interaction; SSM in these two regions is closely connected with subsequent summer precipitation in NH. Four simulation experiments show that compared to the oceanic effect, the SSM has a positive contribution to summer precipitation over northern Europe, central Asia, and the southern region of North America but a negative contribution to the central region of North America, Arabia, and India, which accounts for 5%-10% of the summer precipitation based on the regional average. The SSM has significant impacts on subsequent summer precipitation in the midlatitudes, while the oceanic impact is dominant over tropical continents. The regions with remarkable variability of SSM are the areas where the coupling between SSM and summer precipitation is relatively strong. The anomalous SSM over NH primarily influences the general circulation through diabatic heating anomalies and changes the low-level moisture condition, leading to the anomalies of summer precipitation.