Contribution of precipitation and potential evapotranspiration to long-term changes in aridity in Argentina over recent decades

Abstract

In recent decades, aridity in Argentina has intensified because of an imbalance between water availability and atmospheric water demand. Nevertheless, the relative role of these factors in driving changes in aridity remains poorly explored. This study quantifies and analyses the contributions of precipitation (PRE) and potential evapotranspiration (PET), the latter derived from mean temperature (TEMP), to changes in aridity across the country during 1961 ~ 2020. Monthly PRE and TEMP data from the Climatic Research Unit (CRU) were used to estimate PET using the Thornthwaite method and to calculate the United Nations Environment Programme (UNEP) aridity index (AI) at annual and seasonal scales. Subsequently, linear and nonlinear trends, climatic shifts, and the contributions of PRE and PET to AI changes were evaluated. The results show a widespread decrease in annual AI across much of Argentina (1–10% per decade), driven by PRE reductions and slight PET increases. Seasonally, AI increases prevail in summer and autumn (locally > 30% per decade), decreases dominate in winter (1–30% per decade), and a mixed pattern emerges in spring (-20 to 10% per decade), with PRE acting as the main controlling factor. Moreover, AI nonlinear variability is also controlled by PRE, which determines the direction, magnitude, and occurrence of low-frequency oscillations and abrupt shifts, whereas PET plays a secondary and regional role by modulating the intensity of these signals through amplification or attenuation of index changes. In the Northwest, Subandes, and Transition regions, long-term oscillations and abrupt shifts were mainly controlled by PRE, with summer AI increases of up to 0.417 and decreases associated with PRE reductions reinforced by minor PET increases; in Andean and Extra-Andean Patagonia, variability was weaker and more gradual, with PRE explaining low-frequency oscillations and PET amplifying annual aridification; and in the East, nonlinear AI structures were less defined, although abrupt changes were relatively more modulated by PET increases, whose contribution exceeded that of PRE (0.034 versus 0.009). Overall, aridification in Argentina is primarily governed by changes in PRE, while PET acts as a regional and seasonal amplifier, highlighting the need to adopt an integrated water-balance perspective to assess aridity and its impacts.