An investigation of seasonal precipitation patterns for rainfed agriculture in the Southeastern region of the United States

https://doi.org/10.1016/j.agwat.2019.105728Get rights and content

Highlights

  • Precipitation patterns analyzed for rainfed agriculture in Southeastern United States.

  • Regionalization method combines principal components and cluster analyses.

  • Three precipitation regions are delineated based on statistics and similarity criteria.

  • Probability tables developed for seasonal precipitation totals/events in each region.

  • Results may improve awareness of precipitation deficit or excess relatively to crops.

Abstract

Over the last two decades, signs of precipitation irregularity were frequently reported across the Southeastern United States (US). Even though the region receives a relatively high annual precipitation, the precipitation events are not equally distributed in the time and space. Hence, rainfed agriculture, a common practice in the region is threatened by changes in precipitation frequencies during the crop growing seasons. With this situation, a better understanding of the actual patterns of precipitation irregularity is needed to support the local agriculture. This study uses a spatial regionalization approach to delineate precipitation regions for an area spanning the states of South Carolina, North Carolina, and Georgia. The data used include time-series of seasonal precipitation totals and seasonal numbers of precipitation events >5 mm over the period 1960–2017. A regionalization method which combines principal components and cluster analyses was applied to 208 precipitation stations selected across the study region. Finally, three precipitation regions were delineated based on statistics and similarity criteria. A comparative analysis of these three regions shows significant differences in the seasonal precipitation totals and the seasonal number of precipitation events. In addition, the differences were examined using a probabilistic approach. As a result, tables of probabilities and seasonal precipitation characteristics (precipitation totals and number of events >5 mm) were generated for each region. These tables could provide information about the chances of precipitation deficits or excesses relatively to a crop and henceforth be useful for agricultural water use planning.

Introduction

Worldwide, rainfed agriculture is a very common practice which plays an important role in food and livestock production (Rockström et al., 2010). Rainfed agriculture generally depends on crops, soils, environment, and most importantly, seasonal precipitation totals and their distribution over the crop-growing season. However, rainfed agriculture is vulnerable to climate hazards and its practice does not ensure crop yield stability (Rockström et al., 2010). For instance, when precipitation events are irregular, crops are often subjected to short-term water deficits which cause crop yield losses (Kistner et al., 2018). Indeed, several studies reported the negative impact of short-term water deficit on annual crops yields (Bauer et al., 2009). Particularly, under rainfed conditions, substantial yield gap values (i.e. difference between average and yield potential) are often reported as the consequence of water stress (Lobell et al., 2009). In humid regions such as the Southeastern United States (US), the cumulative annual precipitation totals are relatively high and virtually sufficient to grow a wide range of crops under rainfed conditions. Yet, the sole consideration of annual precipitation amounts may shade critical patterns of precipitation irregularity during the crop growing seasons. This is particularly true in the Southeastern US where short-term precipitation deficits are usual during the crop season (Mo and Schemm, 2008). These short-term precipitation deficits are not necessarily a consequence of a decrease of the total annual or seasonal precipitation as they also seem to be a result of changes in the timely distribution of precipitation events (Kistner et al., 2018). Studies evidenced that changes of precipitation frequency and the subsequent short-term water deficits reduce biomass production, shorten grain filling periods, and lower crop yields (Högy et al., 2013; Katerji et al., 2004). Therefore, an understanding of precipitation patterns (total amount and frequency) is useful for the decision making toward crops management and yields stability.

The frequency of precipitation is critical in rainfed agriculture because it indicates how often the soil water is replenished by natural precipitation events during a given time slice (e.g. month, season, year). In general, the number of precipitation events is assimilated to the number of wet days which can be defined based on a precipitation threshold. Unfortunately, not all precipitation amounts are effective for crops (Rockström et al., 2003; Dastane, 1974). Hence, it is important to define the frequency of precipitation events by referring to daily total thresholds. For instance, the threshold of 5 mm/day (0.2 inch/day) was used in different irrigation scheduling manuals as a minimal daily water need even though the actual need depends on the crop growth stage, the atmospheric water demand, and the antecedent soil moisture condition (Curwen and Massie, 1994). Nevertheless, the 5 mm threshold has been consistently used to study the trend and effects of precipitation events (Goswami et al., 2006; Sala and Lauenroth, 1982). As an example, Mulhouse et al. (2017) considered daily precipitation events of >5 mm to address vegetation response to precipitation timing. Our study also uses the 5 mm threshold to define and address the seasonal number of precipitation events in the Southeastern US.

The climate of the Southeastern US is humid, and the region receives an annual precipitation above 1200 mm. Historically, farmers in the Southeastern US relied on natural precipitations to grow annual crops such as corn, cotton, soybean, peanut, etc. However, the absolute reliance on natural precipitations is nowadays threatened by cases of short-term precipitation deficits occurring during crop growing seasons. Although these precipitation deficits often cause a decrease in crop yield (Rockström et al., 2010), their occurrence is still very unpredictable and therefore needs research attention. To improve the understanding of the occurrence and severity of short-term precipitation deficits, our study had the following three objectives: (i) propose a coherent precipitation regionalization for the Southeastern US, (ii) examine the long-term patterns of precipitation, and (iii) establish a probabilistic framework to support agricultural water management.

Section snippets

Data

The study addresses the part of the Southeastern US encompassing the States of Georgia (GA), North Carolina (NC), and South Carolina (SC). The study aims to regionalize the Southeastern US based on the long-term patterns of precipitations. Hence, data were collected from a total of 422 land-based weather stations distributed across the Southeastern US (Fig. 1). For the 422 stations, all the available daily precipitation records over the period 1960 to 2017 were obtained from the National

Principal components and cluster analysis

The PCA conducted on the seasonal precipitation total and the seasonal frequency of precipitation events >5 mm yielded respectively 19 PCs and 15 PCs with an eigen value greater than one. After the varimax rotation, the 19 PCs obtained from the seasonal precipitation total captured 84% of the total variability in the time-series, while the 15 PCs obtained from the seasonal number of precipitation events >5 mm captured 80% of the variability. The original m by n (i.e. 208 × 232) matrix of

Synthesis, discussion and application

The study analyzed precipitation patterns across the Southeastern US of the United States and outlined implications for agricultural water management. The analyses used 58 years (i.e. period 1960 to 2017) daily precipitation data obtained from 208 synoptic stations distributed across the Southeastern US. The yearly seasons winter (DJF), spring (MAM), summer (JJA), and fall (SON) were considered to generate time-series of seasonal precipitation totals and seasonal numbers of precipitation events

Conclusion

Under rainfed systems, Lobell et al. (2009) indicated that crop yields are in average 50% or less below yield potentials due to water stress. Although this tendency is global, it presumes room for improving yields in regions dominated by rainfed agriculture practices such as the Southeastern US. Indeed, several studies supported the possibility of ceiling yield potential with supplement irrigation (Van Ittersum et al., 2013; Grassini et al., 2011). However, yield gaps vary consistently from one

Disclaimer

Mention of trade names or commercial products in this article is solely for the purpose of providing specific information and does not imply recommendation or endorsement by the U.S. Department of Agriculture.

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