Hydroclimatic intensity change in China during the past decades and its future trend based on CMIP5/6

• Hydroclimatic Intensity Intensified in China except for northwest in last decades. • An alleviated/intensified hydrological cycle in northwest/elsewhere is projected. • Rainfall frequency/intensity dominates Hydroclimatic Intensity in northwest/elsewhere. Changes in the hydrological cycle have far reaching impacts on agricultural productivity, transport availability, energy supply. For example, increasing intensity and declining frequency of rainfall in China have led to a prolonged period of drought as well as more floods, with serious impacts on economics and environment. Different hydrological indices, for instance the accumulated precipitation, the Palmer drought severity index etc., which can reflect the intensity of precipitation or drought, have been proposed to understand the change of hydrological cycle. However, they lead to obvious disagreements in case of China's hydrological cycle because various indices emphasis mainly on either wet or dry feature of the hydrological cycle. The disagreements interfere our ability to manage environmental assets, drought risks, and flood hazards. To reconcile these disagreements, this study has utilized a hydroclimatic intensity index (HY-INT) which is proposed innovatively by previous study with advantages in quantifying the intensity of hydrological cycle. HY-INT integrates and amplifies the signals of precipitation intensity and dry spell length, viewing the response of these two metrics to warming as deeply interconnected. An increase of HY-INT represents the accelerated hydrological cycle and the increased risks of wet and/or dry extremes. Based on the daily gauged precipitation at 540 stations within mainland China, this study has assessed the change of HY-INT in China during 1961–2017. The results show an increasing trend of HY-INT in central-east China, indicating the increasing intensity of hydrological cycle (i.e., more severe droughts and/or rainfall events). While a decreasing trend of HY-INT is observed in northwestern China which implies less wet-dry extremes. Future change of HY-INT is further assessed based on the outputs from climate models in the Coupled Model Inter-comparison Project phase 5 and phase 6 (CMIP5 and CMIP6) under the more realistic medium stabilization emission scenarios. The models are weighted by the performances in reproducing both spatial distribution and inter-annual variability of observed HY-INT. Results of weighted multi-model ensemble suggest an increased hydrological cycle over most part of China, especially in the Yangtze River Basin, indicating more wet-dry extremes. While an exception is seen in northwest China where the HY-INT will decline due to the dominance of the decreased dry spell length over the increased precipitation intensity. This reveals an alleviated intensity of hydrological cycle and fewer wet-dry extreme events therein, similar to the change in recent decades. The changes of HY-INT are attributed to the different variation patterns in the precipitation probability, which are associated with the change in atmospheric instability and moisture content.