Spatial and Temporal Variability of Drought Patterns over the Continental United States from Observations and Regional Climate Models

The aim of this study is to analyze the spatial and temporal structure of drought over the continental United States (CONUS) and their teleconnection at different timescales from observations and climate models. We use the standardized precipitation evapotranspiration index (SPEI) at 12- and 24-month timescales as the drought index. Spatial patterns of drought regimes are delineated by using the principal component analysis (PCA) while the temporal characteristics of the variability of each drought pattern and teleconnection with climate indices are analyzed by using the wavelet analysis. Wavelet coherence of the drought pattern and four climate indices: El Niño–Southern Oscillation (ENSO), Pacific decadal oscillation (PDO), Atlantic multidecadal oscillation (AMO), and North Atlantic Oscillation (NAO) are analyzed. The results show that major drought patterns are located over the Northwest, South, Upper Midwest, and East regions. The spatial pattern of the drought regimes is similar for the 12- and 24-month timescale drought. ENSO influences the drought over West and South at decadal timescales throughout the study period (1950–2015) while intermittent significant coherence is observed at interannual timescale. The coherence of NAO and PDO with SPEI-12 is decreased during recent decades. Generally, regional climate model (RCM)-simulated drought patterns are more localized in a smaller area over the region compared to the spatial extent of observed drought patterns. Power spectra of seasonal to interannual variability (2–5-yr period) of all four drought patterns from RCM simulations are similar to those from the observations. However, at larger periodicities (decadal variations) among-RCM spread increases with increasing periods.