Evaluating the performance of regional climate models to simulate the US drought and its connection with El Nino Southern Oscillation

The aim of this study is to evaluate the ability of regional climate models (RCMs) to simulate drought pattern, persistence, and the role of El Nino Southern Oscillation (ENSO) on the Continental United States (CONUS) drought. The Standardized Precipitation Evapotranspiration Index (SPEI) at 3-month timescale is used to quantify the drought. We use the Taylor diagram, Hurst exponent, and logistic regression technique to measure regional drought pattern, persistence, and the link between drought occurrences and ENSO respectively. The observational data are from the Climate Research Units (CRU), the University of East Anglia while the RCM-simulated data are from the six RCMs participating in the Coordinated Regional Climate Downscaling Experiment (CORDEX) for 1979-2015. The results show that RCMs with spectral nudging consistently show large correlations of simulated SPEI with observations over all regions. Observed spatial pattern of the persistence, average severity, and trend in the SPEI time series are very similar to the simulations. RCM simulations generally overestimate the persistence and trends in the SPEI time series while the average severity is underestimated over most regions. The observed link between ENSO and US drought is more prominent during the winter. Unlike for correlations, the RCMs with spectral nudging (CanRCM4, CRCM5 (OURANOS), and WRF) do not show better performance in simulating the link between the ENSO and drought occurrence compared to the RCMs without spectral nudging (CRCM5 (UQAM), RCA4, and RegCM4).

Automated summary

This study evaluates the ability of regional climate models to simulate drought patterns and the impact of ENSO on drought in the Continental United States. Results suggest that while RCMs with spectral nudging show strong correlations with observed data, they tend to overestimate persistence and trends in drought, while underestimating severity. The relationship between ENSO and US drought is more pronounced in the winter, with RCMs without spectral nudging performing similarly to those with spectral nudging in simulating this link.