Recent intensification of hydroclimatic change in the middle reaches of the Yangtz River Basin driven by PDO, ENSO and WPSH

How hydroclimate will change in the future has been of great interest with the increasing concern of global warming. Acquirement of ample high-resolution proxy-based reconstructions will aid to answer such question by increasing the accuracy of climate prediction models. However, discrepancies among existing reconstructions in the southeast part of China (SEC) has aroused great uncertainty about the hydroclimatic conditions. Here we present an annually-resolved June-August scPDSI reconstruction and a June-July relative humidity reconstruction from 1876 to 2015 in the middle reaches of the Yangtz River, based on accurately-dated tree-ring materials. The reconstructions well reproduce the instrumental records, with explained variance of 48.82% and 46.79%. A secular wetting trend is found in the study area from 1876 to 2000, then it dried quickly. The driest (2006-2015) and wettest (1943-1955) periods both occurred after 1940, and 40% of the top 10 driest years occurred in the twenty-first century. Overall, an increasing intensified hydroclimatic variation is identified, especially significant in the recent decade. The historical summer hydroclimatic fluctuations, which were found closely related to the concurrent temperature variations, show broadly large spatial and temporal synchronicity with existing hydroclimatic reconstructions in SEC, while the intensity of variation is intermittently different. Hydroclimatic variation in the study area might be a comprehensive effect of Pacific Decadal Oscillation (PDO), Western Pacific Subtropical High (WPSH) and El Nino-Southern Oscillation (ENSO) variations. Our reconstruction provides additional support not only for a comprehensive understanding of the spatiotemporal characteristics of hydroclimatic variations, but also for the diagnosis and prediction of hydroclimatic anomalies.