Contribution of transpiration and evaporation to precipitation: An ET-Tagging study for the Poyang Lake region in Southeast China

Abstract

In this study, a regional climate model-based evapotranspiration tagging (ET-Tagging) algorithm has been applied for the first time over Southeast China. Fifteen month simulations (October 2004 to December 2005) were performed to investigate where and to which extent the tagged evapotranspired water from the Poyang Lake region returns to the land surface as precipitation. The contributions of direct evaporation and transpiration were estimated separately using an extended ET-Tagging partitioning algorithm. In 2005, the contribution of moisture originating from the Poyang Lake region to the local annual precipitation in Southeast China reaches a value of up to 1.2%. A maximum contribution of 6% is found near the Poyang Lake region in August. In 2005, 69% of total tagged precipitation originates from direct evaporation of water whereas 31% from transpiration. In winter, precipitation originating from transpired moisture only accounts for around 10% of the total tagged precipitation, but in the summer season the contribution of transpiration increases up to 50%. To explore the source-target relations under consideration of the respective precipitation regime, we introduce source-specific precipitation efficiencies. For the period under investigation, the efficiency for direct evaporation generally dominates, except during the comparatively dry August and in the winter months. Our study shows that the location and the magnitude of tagged precipitation show large spatial and temporal variations. The comprehensive interactions between land surface characteristics and synoptic weather conditions control the annual cycle of the individual contributions to precipitation, emphasizing the important impacts of vegetation cover and land use on the atmospheric hydrological cycle.