Rainfall erosivity variability over the United States associated with large-scale climate variations by El Niño/southern oscillation

Abstract

A comprehensive investigation of the contiguous Unites States rainfall erosivity patterns in relation to the warm and cold phases of El Niño/southern Oscillation (ENSO) was described using a set of empirical and statistical analyses, such as harmonic analysis, annual cycle composites, and cross-correlation analysis. Monthly rainfall erosivity index (REI) composites for the first harmonic, covering 24-month ENSO events, are formed for all climate divisions over the United States spanning up to 29 ENSO episodes. From the harmonic vectorial maps plotted on the study area, each vector reveals both intensity and temporal phase of the ENSO-related REI teleconnection, and the corresponding candidate and core regions are determined using a machine learning technique of Gaussian Mixture Model (GMM) based on magnitude and temporal phase of climate signal, and Köppen climate classification. As a result of vectorial mapping, five core regions were designated as the northwest (NW), the north central (NC), the northeast coastal (NEC), the southeast (SE), and the southwest/middle-inland (SWM) regions. During fall (0) to spring (+) seasons, the results of this analysis show negative (positive) rainfall erosivity response to the El Niño events at the NW and NC regions (NEC, SE, and SWM regions), while the opposite patterns are detected for the cold phase of ENSO. The temporal consistency values were 0.62 to 0.86 (0.73 to 0.82), and spatial coherence values ranged from 0.93 to 0.98 (0.94 to 0.97) for the El Niño (La Niña) events. Comparative analyses of rainfall erosivity responses to both warm and cold ENSO events reveal the high significance level of the ENSO-REI correlation with an opposite tendency in monthly rainfall erosivity anomalies. Above normal rainfall erosivity anomalies during the El Niño thermal forcing are more significant than below normal rainfall erosivity departures during the La Niña events. Consequently, middle latitude rainfall erosivity responses to the El Niño and La Niña phenomena are detectable over the contiguous United States.