Effects of Climate Internal Variability on the Drought Characteristics over China and U.S

Climate change is due to the internal variability and external forcing. The external forcing, such as volcano eruption and anthropogenic greenhouse gas emission, can be observed or relatively accurately quantified. But the climate internal variability (CIV), induced by the interaction of intrinsic non-linear dynamical processes within the earth system, is difficult to be obtained. Drought, as an extreme phenomenon of the climate change, is also a regional event. Studies have shown that the CIV may be as important as anthropogenic climate change at the regional scales for a few decades, in particular, at middle and high latitudes. In order to better understand drought characteristics and mechanisms, the relationship between CIV and drought needs to be addressed. The Community Earth System Model (CESM) Large Ensemble (CESM-LE) project provides a 30-member ensemble for the period 1920–2005 using the historical forcing, and 2006-2080 under the Representative Concentration Pathway 8.5(RCP8.5) scenario. All ensemble simulations are different only slightly in initial conditions. The ensemble mean represents the response of simulation to the external climate forcing, while the spread among ensemble members may represent the CIV. The products in CESM-LE contain various meteorological and hydrological variables, which facilitate to investigate the drought characteristics. In this presentation, we will inter-compare the drought over continental China and U.S. The land surface variables (e.g., precipitation, land surface air temperature, radiation, wind, soil moisture etc.) are used to construct drought indices. The drought characteristics (e.g. frequency, severity, and duration) and its relationship with CIV will also be investigated.