Using Convective Available Potential Energy (CAPE) and Dew-Point Temperature to Characterize Rainfall-Extreme Events in the South-Central Andes

Abstract

The interactions between atmosphere and steep topography in the eastern south–central Andes result in complex relations with inhomogenous rainfall distributions. The atmospheric conditions leading to deep convection and extreme rainfall and their spatial patterns—both at the valley and mountain-belt scales—are not well understood. In this study, we aim to identify the dominant atmospheric conditions and their spatial variability by analyzing the convective available potential energy (CAPE) and dew-point temperature ( T d ). We explain the crucial effect of temperature on extreme rainfall generation along the steep climatic and topographic gradients in the NW Argentine Andes stretching from the low-elevation eastern foreland to the high-elevation central Andean Plateau in the west. Our analysis relies on version 2.0 of the ECMWF’s (European Centre for Medium-Range Weather Forecasts) Re-Analysis (ERA-interim) data and TRMM (Tropical Rainfall Measuring Mission) data. We make the following key observations: First, we observe distinctive gradients along and across strike of the Andes in dew-point temperature and CAPE that both control rainfall distributions. Second, we identify a nonlinear correlation between rainfall and a combination of dew-point temperature and CAPE through a multivariable regression analysis. The correlation changes in space along the climatic and topographic gradients and helps to explain controlling factors for extreme-rainfall generation. Third, we observe more contribution (or higher importance) of T d in the tropical low-elevation foreland and intermediate-elevation areas as compared to the high-elevation central Andean Plateau for 90th percentile rainfall. In contrast, we observe a higher contribution of CAPE in the intermediate-elevation area between low and high elevation, especially in the transition zone between the tropical and subtropical areas for the 90th percentile rainfall. Fourth, we find that the parameters of the multivariable regression using CAPE and T d can explain rainfall with higher statistical significance for the 90th percentile compared to lower rainfall percentiles. Based on our results, the spatial pattern of rainfall-extreme events during the past ∼16 years can be described by a combination of dew-point temperature and CAPE in the south–central Andes.

A Model for the Relationship between Rainfall, GNSS-Derived Integrated Water Vapour, and CAPE in the Eastern Central Andes

“…TRMM rainfall data are interpolated at the station location using nearest neighbour interpolation method. TRMM data have been indicated to be a reliable dataset for investigating rainfall in South America [4,38,39].…”

“…Fourth, we analyse the correlation between the daily mean of rainfall and CAPE at both station locations (TUCU and CATA) using a power-law relationship as described in previous research based on parcel theory [4,26,27]. Based on parcel theory, we expect the rainfall intensity to be commensurate to √ CAPE (β = 0.5), if CAPE is efficiently transferred to parcel kinetic energy [26,27].…”

“…ln rain f all = c + α * GNSS-IWV + β * ln CAPE (6) where α and β are the regression coefficients for GNSS-IWV and CAPE, respectively. Our approach and the formulations are based on previous studies for extreme rainfall [4,26,27]. Sixth, we compare the contribution of each variable to the rainfall extreme events in the presence of each other by joint regression of both variables using quantile regression [47].…”

“…The south-central Andes is an area that is affected by hydrometeorological extreme events, e.g., [1][2][3][4][5][6][7]. The combination of topography and climate forms the most important driver for generating deep convective storms along the eastern central Andes, e.g., [8][9][10][11].…”

“…Furthermore, Murugavel et al [29] have shown a high contribution of CAPE to heavy rainfall during the monsoon season over the Indian region. A different study suggested that the spatial pattern of extreme-rainfall events can be described by a combination of the dew-point temperature and CAPE in the south-central Andes [4].…”