Minimum Rainfall Inter-Event Time to Separate Rainfall Events in a Low Latitude Semi-Arid Environment

José Bandeira Brasil,Jacques Carvalho Ribeiro Filho,Maria Simas Guerreiro,Eunice Maia De Andrade,Helba Araújo De Queiroz Palácio,Pedro Henrique Augusto Medeiros

doi:10.3390/su14031721

Abstract

Water scarcity in dry tropical regions is expected to intensify due to climate change. Characterization of rainfall events is needed for a better assessment of the associated hydrological processes, and the proposition of adaptation strategies. There is still no consensus on the most appropriate method to separate rainfall events from a continuous database, although the minimum inter-event time (MIET) is a commonly used criterion. Semi-arid regions of low latitudes hold a distinct rainfall pattern compared to their equivalent at higher latitudes; these seasonally dry tropical forests experience strong spatial–temporal variability with intense short-duration rainfall events, which, in association with high energy surplus and potential evaporation, leads to an atmospheric water deficit. In this study, we identified the most adequate MIET based on rainfall data continuously measured at 5-min intervals over the last decade (2009–2020) in the semi-arid northeast of Brazil. The rainfall events were grouped according to different MIETs: 15 min, 1 h, 2 h, 3 h, 6 h, 12 h, and 24 h to determine rainfall depth, duration and intensity at intervals of 5, 30, and 60 min, time between events, and respective temporal distribution, with and without single tip events. Including single tip events in the dataset affected the number of rainfall events and respective characteristics up to a MIET of 3 h. A MIET of 6 h is the most appropriate to characterize the rainfall distribution in this tropical semi-arid region. Three classes were defined based on rainfall depth, duration, and intensity: I-small events (77% below 40 mm and 32 mm/h), II-high intensity events (3% between 36 and 76 mm/h), III-longer events of higher depth (20%). This study is useful for understanding how the MIET relates to other ecohydrological processes and provides more precise information on the rainfall characteristics at the event scale.

Highlights

The dynamics of the rainfall events indicate that careful attention should be given to studies that adopt data analysis based on the scale of events [21,22,24,28,42], considering that these characteristics influence the assessment of interception [3,4,5,6,7,8], water infiltration in the soil [9], runoff [10,11,12], soil loss [13,14,15], kinetic energy [43], soil moisture content [16,17,18], and ecosystem services [19,20]
The 6 h minimum inter-event time (MIET) is the most appropriate to characterize the rainfall distribution, and the Weibull distribution is the best fit for total event rainfall, duration, and inter-event time in this tropical semi-arid region of Brazil
Our study brings insights on the definition of rainfall events based on the minimum inter-event time (MIET) criterion, for semi-arid environments where continuous long-term rainfall records are usually scarce

Summary

Introduction

Dry regions lie on approximately 47% of the earth’s surface [1] and are concentrated at latitudes above 25◦ , they exist in almost all biomes and climatic zones of the globe.In the northeast of Brazil, an extensive area of approximately 1 Mkm , extending from latitudes −3◦ to −16◦ , represents the main tropical semi-arid ecoregion in South America and is home to over 26 million inhabitants [2].Rainfall depth, duration, and intensity have an impact on hydrologic processes such as interception [3,4,5,6,7,8], infiltration [9], runoff [10,11,12], soil loss [13,14,15], soil moisture [16,17,18], and an impact on ecosystem services [19,20]. Dry regions lie on approximately 47% of the earth’s surface [1] and are concentrated at latitudes above 25◦ , they exist in almost all biomes and climatic zones of the globe. In view of the challenging climate change scenarios projected for semi-arid regions, the spatial and temporal variability of rainfall 4.0/). Sustainability 2022, 14, 1721 need to be characterized on an event basis for a better understanding of the associated hydrological processes and in order to cope with water scarcity. Most rainfall event separation methods are defined based on runoff [21], despite its importance for other hydrological processes as well [22,23]. There is no consensus on the most appropriate method to separate rainfall events from a continuous database [21,22,24]

Objectives

Methods

Results

Conclusion