Rainfall extreme events and socio-physical effects on a temperate hydrographic basin in Argentina

doi:10.21203/rs.3.rs-2591653/v1

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Rainfall extreme events and socio-physical effects on a temperate hydrographic basin in Argentina

https://doi.org/10.21203/rs.3.rs-2591653/v1

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The increase of Rainfall Extreme Events (REE) intensity and frequency is a typical situation in the current context of Global Climate Change. The aim is to identify REE occurrence using modeled daily rainfall (DR) data analysis and quantify its effects on the Surface Soil Wetness (SSW), as a physical feature of the Napostá Grande (NG) hydrographic basin, differentiating by homogeneous units (HU). And to analyze the occurrence of REE and its social effects in the study area, through a press revision. The methodology includes the DR and SSW data analysis through data series provided by the National Aeronautics and Space Administration (NASA) for the period 1981–2022. Results indicated that the characteristics and the effects of the REE were differentiated along the hydrographic basin. Moreover, we could demonstrate a positive relationship between REE, SSW, and their social effects. Although the highest proportion of extreme events was manifested in the sedimentary fills HU and paleodrains HU, those extreme events that had a greater relevance, due to their social effects, were those that occurred in the urban area. Regarding the effects, an increase and a decrease in the SSW were found during the REE occurrences and normal rainfall, respectively. REE between 50–100 mm were more usual in the paleodrains HU and sedimentary fills HU than the others. This research constitutes a case study, which demonstrates how useful the inclusion of climatic REE and SSW data and press revision can be used for an optimal management of water resources/forecasting flood damage.

Rainfall Extreme Events (REE)

Surface Soil Wetness (SSW)

Climate variability

Argentinean Pampean Plain

Homogeneous Units (HU)

Ways to identify Rainfall Extreme Events (REE) occurrence by Homogeneus Units (HU), using modeled daily rainfall (DR) data analysis in temperate hydrographic basins.
Physical and social effects were analyzed and quantify in the Napostá Grande hydrographic basin.
The hydrological studied basin is not spatially and temporally homogeneous from a REE occurrence point of view. The magnitude, intensity, and frequency were not coincident among HU. This point constitutes a preliminary study regarding to the dynamics of the basin, from a physical and social perspective.

Climate variability is an important driver of spatial and temporal changes in hydrometeorological variables (Nobre et al., 2017). Extreme seasonal droughts and floods have been more frequent in the last two decades and have been gaining relevance all over the world, especially for its impact (Marengo et al., 2015; Petpongpan et al., 2020). Globally, increased frequency and magnitude of extreme precipitation events have become a regular phenomenon (Sridhar et al., 2019), producing several impacts on social and economic activities (Wang et al., 2015). The unequal distribution of rainfall intensities leads to an increase in the effects of these extreme events which often generate floods or droughts (Venkata Rao et al., 2020). The hydrological dynamics of the basins, their natural variability, and anthropic changes (Balasch et al., 2019) require complete knowledge of the historical and recent extreme events.

Every year, new record-breaking hydrological extremes affect our society, fuelling the debate between global climate change and natural climate variability (Lehner et al., 2006). There are regions of the world where rainfall will increase and, therefore, floods will be more abundant, while, in others, droughts will last longer and intensify (Chen et al., 2013). Floods endanger lives, damage the built environment, cause disruption and accrue significant economic losses (De Lucca et al., 2017). As a consequence, government authorities must implement strategies to mitigate the damage caused which are generally focused on during the time of the emergency (Giordan et al., 2020). The impact of extreme and frequent precipitation events over urban areas is more significant, as these areas are the centers of human activities (Sridhar et al., 2019). Effects are unevenly distributed in space and time and for this reason, it is necessary to identify and quantify the affected areas and changes in land cover.

It is useful to understand the changes in rainfall characteristics using precipitation data and statistical analysis for making decisions (Venkata Rao et al., 2020). The study of heavy rainfall and soil moisture through the occurrence of a significant extreme event is useful to improve the understanding of the vulnerability of water and soil to climatic fluctuations (Ho-Hagemann et al., 2015). In this context, many studies agree that hydrological approaches in experimental and representative basins are very important for the optimal management of water resources (Montenegro et al., 2014; Balasch et al., 2019).

There are a high number of studies all over the world that have analyzed hydrological regimes in basins, extreme events, and their impact. There can be distinguished studies about extreme floods and droughts occurrence and their effects on the variations in the hydrological regime of basins (Nepal et al., 2015; Bhatla et al., 2019; Petpongpan et al., 2020) and the analysis of hydrologic risks of intense precipitation events records occurred in a very short period (Merino et al. 2017). It is important to point out mention that much of fundamental hydrological knowledge is obtained in small catchment studies that can contribute to solving some practical issues related to the hydrological cycle such as flood protection, groundwater resources replenishment or soil and water conservation (Holko et al., 2015).

The region of interest (Fig. 1), Napostá Grande (NG) hydrographic basin, is located in the southwest of Buenos Aires province, in the Argentinean Pampean Plain. It is characterized by an alternation between wet and dry periods (Bohn et al., 2011). Wet and dry events tend to be more intense and periodic, so it is estimated that this area will be exposed to a high variation in rainfall (Ferreli et al., 2020) with serious repercussions on the development of socioeconomic activities (Brendel et al., 2017). There are different researches that were developed in the study area related to the specific environmental problems of the upper, middle, and lower sub-basins3 (Zapperi, 2014; López et al., 2015; Montico et al., 2019; Fernández et al., 2020); as well as those who studied the effects of extreme events in nearby basins with similar characteristics (Volonté & Gil, 2019). In the study area, extreme events were considered heavy rainfall phenomena that had important repercussions from the physical and social point of view, and, generally, they usually occur in a few hours.

At this point, it is important to consider that the perception that the local community has regarding the occurrence of REE, usually differs from that of the authorities responsible for their planning and management (Mastrandrea, 2021; 2019). In this way, the social perception of water risk becomes valuable information for territorial planning and decision-making, because it allows to the identification of the needs and interests of the inhabitants, according to the incidence of various individual and collective filters.

The aim of this work is, first of all, to identify REE occurrence by means of modeled daily rainfall (DR) data and quantify its effects on the Surface Soil Wetness (SSW), as a physical feature of the NG hydrographic basin, differentiating by HU. And secondly, we analyze and describe the social effects of REE in the basin, through a press revision in local libraries and current news on digital journalism websites.

[3] This classification was considered due to its uneven patterns of precipitation, soil humidity, and topography, making it likely that precipitated moisture here takes on different characteristics (Mastrandrea, 2021)

2.1. Study area: The Napostá Grande (NG) hydrographic basin

This work concerns the NG hydrographic basin, located in the southwest of Buenos Aires province, in the Argentinean Pampean Plain (Fig. 1). Bahía Blanca city is the main urban nucleus of the basin and has the highest population with 301.572 inhabitants (INDEC, 2010). The city is an important center of socioeconomic and cultural interaction due to the relevance it has in the regional context (Urriza, 2018).

According to topography, drainage, and land use criteria, the basin can be divided into three sub-basins (Carrica, 1998). The upper sub-basin is developed from the Napostá Hill (1108 m.a.s.l.) with an abrupt relief of pronounced ridges. This area includes rocky outcrops located above 350 m.a.s.l. that delimit and regulate the drainage network. One of the main tributaries of the NG stream in this sector is the Águila stream. This sub-basin is located in a range system and has several problems related to water erosion and heavy rainfall. The loss of superficial soil, influenced by the scarce vegetation cover, indicates an improper use of lands and slopes, fostering a potential economic and productive downgrading of soil and water (Gaspari & Bruno, 2003). It is an area of interest for water exploitation as an alternative source of water supply to Bahía Blanca city and other urban cities of the region (Carrica & Lexow, 2004).

The middle sub-basin includes from the closure of the upper sub-basin (25 km north of the urban area). This sector develops on a plain with a boxing of the channel (Melo et al., 2013) and the land use is limited to agricultural, livestock, and tourist exploitations in a rural context. The quality of water in the upper and medium sub-basins was found suitable for tourism and recreational use (López et al., 2015) and land uses correspond mainly to agricultural and livestock activity.

Finally, the lower sub-basin covers an urban and peri-urban space from Puente Canessa to the mouth of the stream in the Bahía Blanca estuary (Carrica, 1998). The NG stream crosses into the urban area, causing different problems associated with anthropic changes. The interventions in various infrastructure works and the activities carried out by the inhabitants have modified the natural dynamics of the system. Considering the alternation of wet and dry periods, the lower sub-basin presents the most important problem related to the decrease in slope conditions and to the planned and spontaneous urbanization process. When heavy rainfall is generated the lower sub-basin is the most exposed to damage because the highest population and the main socioeconomic and cultural activities are concentrated there.

The urban space is an example of the superposition of the natural and the human system (Liu et al., 2007). There the effects of heavy rainfall and other process linked to the urban space, like erosion, accumulation of water, transport of sediments, and drainage changes, among others are produced (Zapperi, 2014; Neumann et al., 2021). This area configures a zone subject to future land management located in a flooded valley of the NG stream where a recreational piece of land is developed (Santamaría & Aldalur, 2014).

The study area is latitudinally included in the zonal area of temperate climates characterized by a seasonal heterogeneity that presents well-defined wet winters and dry summers and moderate springs and autumns. The average rainfall varies between 841.1 mm from the East and 380 mm to the West (Campo de Ferreras et al., 2011). The annual average temperature oscillates between 14º C and 20º C and the rains give it a sub-humid character (Casado & Campo, 2019). With respect to soil characteristics, two large orders predominate: the Molisoles (in Spanish), of the Udoles and Ustoles suborder in the Ventania system, and the Aridisoles (in Spanish), of the Ortides suborder (Gaspari & Bruno, 2003). Mostly, soils in the basin are developed on loess materials (recent sediments of the Pampean Plains, affected by eolian action) (INTA, 1990).

In this research, the analysis of the REE is related to the HU of the NG hydrographic basin, previously delimited by Mastrandrea and Ángeles (2021). Those units were delimited based on their location, altimetry, slope, vegetation type of soil, and uses. According to them, the studied hydrographic basin involved the following HU (Fig. 1): rocky outcrop, sedimentary fills, paleodrains, urban area, coastal area, and piedmont. The two latest were not considered in this research due to their dynamics caused by marshes in the coastal area case and due to the particular dynamism of the piedmont area associated with is associated with the abrupt change in slope that affects the torrentiality of the rains.

Historical and recent REE have impacted the study area due to their environmental and socio-economic consequences. We can mention REE that occurred in 1884 and in 1914, which produced an increase in the flow of the stream and caused several impacts for the occurrence of floods and waterlogging (La Nueva Provincia, 1978). Then, in 1933 in the lower sub-basin an intense rainfall produced the flooding of the main streets of the city, at the same time that it flooded the houses located on the banks of the stream (La Nueva Provincia, 1933). Another significant flood event arose in 1944 causing floods, overflows, and waterlogging with important repercussions for the inhabitants of the study area, many of them had to evacuate their homes (La Nueva Provincia, 1944). It is important to note that although hydraulic infrastructure works have been carried out to mitigate the damage caused by REE, the water risk persists (Mastrandrea, 2021). The reasons that explain this situation derive on the one hand, from the intensity of rainfall in short periods of time and on the other hand, from the characteristics of the urbanization process that has modified the natural dynamics of the NG hydrographic basin.

2.2. Methodology and datasets

Daily Rainfall Extreme Events (REE) and Surface Soil Wetness (SSW) (Januar, 1981 – March, 2022 period) were statistically analyzed in relation to normal values and previous works to determine and characterize (i.e.: occurrence, duration) the REE occurrence. The data was obtained from the National Aeronautics and Space Administration (NASA) Langley Research Center (LaRC) Prediction of Worldwide Energy Resource (POWER) Project funded through the NASA Earth Science/Applied Science Program. It provides solar and meteorological data from NASA research for support to agriculture, sustainability of natural resources, and others. The POWER Data Archive is a curated dataset and not static. Data were obtained from the website of the NASA POWER Project in a punctual way, introducing a representative geographic coordinate for every HU of the NG hydrographic basin. We analyzed 4 data sets since, for every parameter (a total of 8 data sets) a statistical perspective in which the data period involved 1981 (from January 2nd ) – 2022 (since 30th, March) years, for daily rainfall (DR) and SWW parameters. We analyzed the data in relation to their frequency of occurrence, intensity (i.e. mm/day), and the relation between the punctual data and the normal values, among others. Rainfall data has a daily frequency and they are expressed as mm/day. Regarding SSW parameters, the percent of soil moisture shows a value of 0 indicating completely water-free soil. When the value is equal to 1, it indicates completely saturated soil. This parameter is referred to the soil layer from the surface 0 cm to 5 cm below grade.

Daily REE have been classified and defined in two categories depending upon rainfall received in a day: Category I rainfall, which includes moderate and rather heavy rainfall events, has been defined as days receiving rainfall of 50–100 mm. Category II rainfall is defined as rainfall that is above 100 mm in one day and includes heavy rain. This classification was made taking as reference previous studies related to climate data analysis (Bhatla et al., 2019). The REE were classified by those categories and differentiated long the hydrographic basin for a period of 41 years (1981–2022). For a shorter period (2002–2022), the REE effects in the basin were described based on newspaper and press archives recopilation.

The search of historical archives in local libraries (Rivadavia newspaper library) and current news in local digital journalism websites was carried out considering keywords referring to the date of the event, its main effects, and the physical and social repercussions. The information was recorded in a summary table that contains the following categories of analysis: event date, duration (days), effects (physical and social), and main affected areas. The selection of these extreme events was made from the results of the statistical analysis of the modeled data and a revision of the news corresponding to the events that had the greatest social impact in the hydrographic basin. The boundaries, for the HU of the studied basin, were previously delimited by Mastrandrea & Ángeles (2021) and they were based on the identification of units with a certain internal homogeneity with respect to biotic and physical characters, such as, for example, in terms of their location, altimetry, slope, vegetation type of soil and uses, among others in a GIS setting. The objective of the delimitation was to establish diagnostic units as a basis for environmental planning, intending to make a synthesis of the most relevant aspects (Camino Dorta et al., 2014). A summary of methodological steps as well as the used database in this research is described in Fig. 2.

3.1. Daily (REE) identification and its relation with the SSW (1981–2022) at the NG hydrographic basin

For the study of the daily REE and SSW at the NG hydrographic basin, we analyzed the data by HU (Table 1), using the daily rainfall data obtained, free of charge, from the Power Project. Daily rainfall temporal patterns and REE has statistically studied over the study area for 41 years (1981–2022) as shown in Fig. 3.

A total of 15065 daily rainfall (DR) and SSW data were considered for the period 1981–2022. As a result, 10779 events of DR surpassed the normal value and 49459 events of DR were below than normal value, which on average was 1.9 mm in the 4 HU analyzed. It was observed that of the total DR data, 82.1% did not surpass the normal value, and 17.9% of events surpassed that value. This first analysis allows us to identify the extreme events that were located within those values that surpassed the normal value (Fig. 3).

One of the extreme events that we found in all the HU, during the study period, was the one that occurred on May, 7th, 1994 (101.89 mm/day in rocky outcrop; 89.44 mm/day in paleodrains and sedimentary fills and 74.79 mm/day in the urban area). Another REE that can be mentioned in all HU, was that occurred on November 26th, 2018 (90.7 mm/day in rocky outcrop; 113.33 mm/day in paleodrains and sedimentary fills, and 123,51 mm/day in the urban area) (Fig. 3).

In relation to the extreme events that were located between 50 and 100 mm, the number of 22 events were determined in rocky outcrops (17% of the total REE); 38 events in paleodrains (29%); 39 in sedimentary fills (30%); and 32 in the urban area (24%) Regarding this distribution, it is important to mention that the sedimentary fills and paleodrains HU represent the largest area (km²) of the basin (Fig. 4, near here). Considering the REE that became relevant in each HU, it is important to mention those that occurred on October, 14th, 2002 (77.35 mm/day) in rocky outcrop; on September 27th, 2019 (89.30 mm/day) in paleodrains and sedimentary fills respectively; on October 14th, 2002 (74.59 mm/day); on September 27th, 2019 (98.7 mm/day); and on March 5th, 2021 (80.63 mm/day) in the urban area (Fig. 3).

Table 1 is presented below, which summarizes the average, maximum, minimum, and data higher and lower than the normal Rainfall data collected for the studied period.

Social effects of REE at the NG hydrographic basin (2002–2022)

Regarding the evolution of DR and SSW data, during the years which contain the most relevant REE (2002–2022), 7396 data were analyzed (Fig. 5). Of this total, 15.3% of DR surpassed the normal value (1.75 mm) and the 84.7% was below. Although a less representative percentage of DR was the one that exceeded the normal value, extreme events were detected within that range that had important social effects on the residents of the urban area.

According to the analysis carried out on the basis of the modeled data of DR and SSW, we can distinguish the following days with rainfall > 50 mm, which means that they are REE, Category I: first of all, the registered rainfall in the urban area of September 27th, 2019 (R = 98.75 mm/day); then, March 5th, 2021 (R = 80.63 mm/day); October 14th, 2002 (R = 74.59 mm/day); February, 3rd 2010 (R = 66.67 mm/day); May 14th, 2011 (R = 65.36 mm/day); October 12th, 2012 (R = 64.5 mm/day), April 20th, 2007 (R = 62.82 mm/day), August, 29th, 2002 (R = 52,71 mm), as the most representative of the period studied. In all cases, those days correspond to the maximum rainfall of a short period, which is developed along 3, 4–5 days. On this way, for example, the REE cited for October 14th, 2002 involved a total of 5 pluvious days: from 12th to 16th October, 2002 (Table 2); the event of April 20th, 2007 involved a total of 4 pluvious days: form 17th to 20th April, 2007, etc. The totality of the aforementioned events was found in the press and the description of their social-physical effects is shown at Table 2.

Based on DR data, various news of regional and local journalism had been consulted. Most of them included physical and social effects, especially for the most populated areas, where intense rainfall produced relevant impact related to the concentration of the population and of socioeconomic and cultural activities. One of the potentialities of working with the regional and local journalism is the description of what happened by mentioning the characteristics and effects on the population as well as obtaining a type of information that cannot be obtained from official sources (Table 2).

According to the previous analysis, during the months of August and October, 2002, high relevant events of heavy rainfall occurred. The first of them, which was cited on August 27th, had important repercussions, generating the evacuation of 300 affected people in the upper sub-basin (in the rock outcrop HU) and in the lower sub-basin (in the urban HU). The second event, which was cited on October 12th of that same year, involved (according to the rainfall modeled data) a total of 5 days with rainfall register (Fig. 6). It also had important effects generating the evacuation of 150 people and serious problems related to the generation of floods and waterlogging. In this way, 2002 has already been approached as a very wet year in various studies (Bohn et al., 2011; Campo de Ferreras et al., 2011; García & Piccolo, 2006).

It is important to note that, according to the analysis of climatic data, the maximum value of DR corresponds to October 14th, 2002 (74.59 mm/day). Regarding the behavior of the SWW, an upward trend is observed from the month of April, with a relevant increase from September, considering that the maximum value of the year was registered on August 29th (0.92).

Then, in an event cited by the press on April 18th, 2007, problems related to the flooding of access and rural roads, especially in the upper sub-basin (rocky outcrop HU) were described (Fig. 7). According to the analysis of climatic data, it can be observed that the maximum value of DR corresponds to April 20th, 2007 (62.82 mm/day) and that day was involved in a short period of 4 pluvious days (from 17 to 20th April, 2007. The maximum value of SSW also occurred on 20th April.

The event of DR > 50 mm occurred on 1st April 2017 (R = 61.05 mm), cited by the press on March 31st, 2017, and involved a pluvious period of 8 days (according to modeled data). For this event, according to the press (Table 2), problems related to flooding and overflows in the neighborhoods located in the lower sub-basin (Bahía Blanca district) and in the upper sub-basin (Tornquist district), were described (Fig. 8).

Considering the statistical climate data analysis, on March 25th the maximum value of rainfall (77.45 mm/day) and SSW (0.9) was recorded. This event, which involved 5 days (from 22 to 26th March, 2022) caused, according to the press, adverse environmental consequences such as: evacuation of 111 people, destruction, falling trees, flooding, overflow of the homonymous stream, water ingress into homes and commercial and sports enterprises, among others. Given this situation, the local authorities implemented a series of measures aimed at mitigating these consequences derived from the heavy DR. Among them, assistance to the most vulnerable groups through evacuation systems, the interruption of public activities during the day after the maximum DR, continuous monitoring of the situation by the local authorities and continuous communication with authorities at the regional level due to the floods that occurred in the upper sub-basin (Fig. 9).

3.2. Discussion

During the last few decades, REE have increased in a global as well as regional scale in frequency and intensity (Sridhar et al., 2019; Bahtla et al., 2019). An increase in the air temperature has caused changes in the hydrologic cycle, which have been followed by several emergencies of natural extreme events around the world (Petpongpan et al., 2021). Rainfall is one of the most important climate variables that vary both in space and time (Venkata Rao et al., 2020), and, for this reason, it is important to consider the study of REE, in the context of climate change for water resources management in a river basin.

In the regional context of the study area, extreme events have been determined using climatic data, in a similar way as Campo de Ferreras et al, (2011); Gentili et al., (2013); Moretto (2018) & Ortuño Cano et al. (2019) whose identified them, for a portion of the studied basin, based on press revision. In those works, databases were designed and articles were inventoried in relation to extreme events that occurred in locations of the Buenos Aires province (Argentina). News revision becomes an important tool to analyze the genesis, evolution, and characteristics of extreme events, as well as their effects on society (Campo de Ferreras et al., 2011). Unlike what has been done in these works, in our case, the press review was used to characterize the social effects of REE, but also, this information was complemented with the statistical analysis of climatic modeled data, just like Casado & Campo (2019) and Ferrelli (2020) have done to determinate physical effects of extreme events in the southwest region of Buenos Aires province. Other works have focused on applying grid data for the spatiotemporal analysis of precipitation in areas subject to a marked discontinuity of climatic records in space and time (Casado & Piccone, 2018).

The NG hydrographic basin is characterized by presenting an alternation between dry and humid periods (Mastrandrea, 2021). In this work, extreme events were determined including the analysis of climatic data (rainfall, mm/day). Daily REE have been defined and classified into two categories depending on rainfall received in a day, as Bhatla et al. (2019) did. In other works, extreme events have been determined according to their duration including a methodology based on different methods and techniques (hydrographic, geomorphologic, biogeographic) (Volonté & Gil, 2019). According to the IPCC (2014), an extreme weather event is an average of a series of weather events in a particular period. In our case, daily REE and SSW (1981–2022) were statistically analyzed in relation to average values and previous works to determine and characterize the extreme rainfall events occurrence and their physical and social effects.

The study area has been studied from different points of view. Carrica & Lexow (2004) analyzed the natural recharge to the aquifer of the upper sub-basin of the NG stream, concluding that the pluvial recharge, located in the mountain foothills, is the main source of aquifer feeding.

Fernández et al. (2017) studied the water quality of the NG stream and determined a decrease in the surface water quality downstream. For this reason, we consider it a priority to continue deepening the analysis of the processes that manifest themselves in the lower sub-basin, corresponding to the urban space, totally modified by the urbanization process (Zapperi, 2014). Other authors identified the urban ecosystem services of Bahía Blanca city to analyze its potential in recognizing the aspects associated with water security (Montico et al., 2019). In addition, Mastrandrea & Ángeles (2021) determined areas exposed to the danger of floods due to the intensity of rainfall, using Multicriteria Evaluation (MCE) techniques and map algebra. They determined that the areas that present high and very high danger levels are located mostly in sectors near the stream, in the middle and lower sub-basin. There are studies that have focused on the analysis of the social perception of water risk, especially in the urban area of the lower sub-basin. In the southern sector of the urban space, residents perceive with greater intensity those socio-environmental problems that occur as a consequence of the occurrence of floods and waterlogging, due to the generation of intense rains in short periods of time (Mastrandrea, 2019). In this way, we agree that the social effects reported by the press are recorded mostly in the south and southeast of the urban space of the lower sub-basin.

Given the latest REE, it is important to consider that, in the urban fluvial environment the lower sub-basin, the local authorities decided to carry out mechanical cleaning of the NG stream. This intervention had already been considered and, faced with the resistance of different social organizations, it had not come to fruition. Among the headlines of the local digital press that reported on this intervention, the controversies generated by the sudden decision of the local municipality can be recognized: "The cleaning of the Napostá stream began to relieve the Maldonado Canal" (Telefé Bahía Blanca, 2022); “Despite the controversy, the cleaning of the Napostá stream continues” (Channel 7 Bahía Blanca, 2022); Controversy over the cleaning of the Napostá: "It was the best option and the only one" (Telefé Bahía Blanca, 2022) and "Discomfort among environmentalists over the intervention in the Arroyo Napostá” (Telefé Bahía Blanca, 2022), among others. In this way, the occurrence of an extreme event exposes the environmental conflicts that manifest in the study area, which are communicated by the press according to the social effects that they cause for the residents.

Finally, we consider that the present work constitutes a contribution regarding the combination of quantitative and qualitative techniques for the knowledge of the physical and social effects of the daily REE on an intermediate-sized hydrographic basin. The results presented in this work can constitute an important diagnosis and starting point for the knowledge of the physical and social dynamics of the study area.

Considering the analysis of DR and SWW data in the study area for a period longer than 40 years, it is important to note that, in general, the maximum values of DR and SWW have not represented high percentages, which feature allows us to infer a low frequency of REE in the study area, in a daily resolution. However, which this information, it was possible to identify the context in which extreme events are located in relation to those values that surpassed the normal value in each HU, and analyze the most important physical effects. This analysis has provided us with the possibility of making a diagnosis of the occurrence of extreme events in the NG hydrographic basin.

From the press analysis, we detected that the main social effects of the REE in the study area were the evacuation of people, infrastructure damages, and social and educative activities suspension. It was observed that the main affected areas corresponded to the southern sector of the urban space, in the lower sub-basin. The most representative event occurred on March 2022, 25th with serious physical and social effects, that should be taken into account to implement optimal management of water resources/forecasting flood damage.

The statistical analysis of REE and SSW has allowed having more detailed knowledge of the maximum, minimum and average values in the analyzed units, as well as those that surpassed normal values and those that were below. On the other hand, the search for news alluding to the occurrence of REE has allowed us to analyze the main effects that such events caused in society, as well as the areas most affected and conceived as potentially dangerous, especially in the last twenty years in which the urban growth has affected the generation of floods and waterlogging.

Finally, we can define that the hydrological studied basin is not spatially and temporally homogeneous from a REE occurrence point of view. The magnitude, intensity, and frequency were not coincident among HU. This point constitutes a preliminary study regarding to the dynamics of the basin, from a physical and social perspective.

Acknowledgments

The authors thank the Rivadavia Library of Bahia Blanca city, for the advice provided regarding the consultation of historical news and archives and the National Aeronautics and Space Administration (NASA) Langley Research Center (LaRC) Prediction of Worldwide Energy Resource (POWER) Project funded through the NASA Earth Science/Applied Science Program, for the information provided on modeled climate data. The authors thank to Consejo Nacional de Investigaciones Científicas y Técnicas and Universidad Nacional del Sur (UNS). This research is developed within the framework of the investigation project: Hydrological vulnerability and environmental problems in hydrographical basins of plains (Pampean region, Argentina), Universidad Nacional del Sur.

Competing interests

Not applicable

Authors' contributions

The first draft of the manuscript was written by Aldana Mastrandrea, and both authors commented on previous versions of the manuscript. Supervision, validation and review were performed by Vanesa Yael Bohn. Both authors read and approved the final manuscript

Funding

This work is supported by the Project: Hydrological vulnerability and environmental problems in lowland hydrographic basins (Pampean region, Argentina)”, PGI-UNS Project directed by Vanesa Yael Bohn, Universidad Nacional del Sur, Bahía Blanca (Buenos Aires, Argentina).

Availability of data and materials

Daily precipitation and Surface Soil Wet products data were provided by the National Aeronautics and Space Administration (NASA) Langley Research Center (LaRC) Prediction of Worldwide Energy Resource (POWER) Project funded through the NASA Earth Science/Applied Science Program, 2.x.x version on 2022/12/19for the period 1981-2022 and the administrative boundaries used in the cartography elaboration were obtained from the Instituto Geográfíco Nacional (IGN) (https://www.ign.gob.ar/). Data were obtained from the website of the NASA POWER Project (https://power.larc.nasa.gov/).

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Table 1 and 2 are available in the Supplementary Files section.

No competing interests reported.

TableI.jpg
Table 1 Descriptive statistics for rainfall (mm/day) and SSW data by HU (1980-2022), NG hydrographic basin
TableII.jpg
Table 2 Social and infrastructure effects of the REE at the NG hydrographic basin based on press revision (2002 – 2022)

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Rainfall extreme events and socio-physical effects on a temperate hydrographic basin in Argentina

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1. Introduction

2. Study Area, Methodology And Datasets

2.1. Study area: The Napostá Grande (NG) hydrographic basin

2.2. Methodology and datasets

3. Results And Discussion

3.2. Discussion

4. Conclusions

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