Assessing how accumulated precipitation and long dry sequences impact the soil water storage

Abstract

Precipitation or no precipitation persistent over time often became extreme weather conditions with greater regional economic impact. The temporal and spatial variability of these variables, together with the evapotranspiration, is crucial in the east‐northeast of Argentina, where rain‐fed agricultural production is carried out. In this work, the frequency of precipitation was studied from dry spells and complemented with an analysis of the accumulated precipitation and evapotranspiration. In particular, dry sequences longer than 15 days, return period and severity, were the focus of this study. Finally, the impact of the amount and frequency of precipitation on soil water storage was assessed through a decadal analysis. The region of study is characterized by northeast‐southwest gradient in accumulated precipitation and east–west gradient in winter long dry sequences. During summer, higher and more frequent precipitations (lower probability of long dry sequences and lower return period of 15 days and severity) were presented whereas the opposite was found in winter. However, the stations located to the west presented the highest probability of long dry sequences with higher severity and lower accumulated precipitation. This result highlights the vulnerability of the agriculture activity in the western stations. Regarding the impact of long dry sequences over soil water storage, the seasonality of evapotranspiration is also involved. The impact is stronger during austral summer because of higher values of evapotranspiration and it is lower during winter, in spite of the higher probability of long sequences. Decadal analysis suggested that soil water storage responds to precipitation amount or frequency depending on the magnitude of the anomalies. In this sense, the impact of precipitation over soil water storage depends on how it is distributed.

El Niño–Southern Oscillation incidence over long dry sequences and their impact on soil water storage in Argentina

“…When analysing Severity Index (Figure 8), higher values are found in drier regions (western stations), with stronger east-west gradient during spring (more details in Pántano et al, 2017). During La Niña events, autumn anomalies present drier conditions (more severe long dry sequences), except for some stations in the northeast and west, whereas, during El Niño, wetter conditions prevail (less severe long dry sequences).…”

“…The most noticeable response during autumn is the occurrence of three long dry sequences in Concordia during 2009, when La Niña conditions affected southeastern South America with a prolonged drought (Arndt et al, 2010). Three long dry sequences also occurred in Córdoba in 1994 and 1987, although this station is located in a drier region characterized by a higher percentage of long dry sequences (Pántano et al, 2017). Between 1 or 2 long dry sequences are presented in Concordia during any of the phases during spring whereas in Azul, the occurrence of more than one long dry sequence is absent under El Niño.…”

“…A dry day was considered when the accumulated precipitation of two consecutive days was lower than 5 mm. This rainfall amount was established taking into account the crop requirements and water losses from evapotranspiration and run-off (Pántano et al, 2017).…”

“…In order to complement the previous analysis, accumulative precipitation and soil water storage responses are analysed. Figures 11 and 11 presents the anomalies of seasonal accumulative precipitation and the anomalies of each soil water storage condition, under different ENSO phases with respect to the climatology analysed in Pántano et al (2017). Under La Niña phase (Figure 11), lower seasonal precipitation prevails during summer and spring.…”

“…Fixed thresholds are useful as indicators for specific impacts independently from the climate characteristics, whereas the variable ones, such as percentiles, are useful to define the climate extreme with low probability of occurrence. In the region of interest, different fixed thresholds were used to characterize daily dry sequences (Penalba and Llano, 2008;Llano and Penalba, 2010;Pántano et al, 2017).…”