Storm-wave trends in Mexican waters of the Gulf of Mexico and Caribbean Sea

Abstract

Thirty-year time series of hindcast wave data were analysed for 10 coastal locations along the eastern Mexican coast to obtain information about storm events occurring in the region, with the goal of examining the possible presence of interannual trends in the number of storm-wave events and their main features (wave height, duration and energy content). The storms were defined according to their significant wave height and duration, and the events were classified as related to either tropical cyclones or Norte events. The occurrence and characteristics of both types of events were analysed independently. There is no statistically significant change in the number of storm-wave events related to Nortes or their characteristics during the study period. However, there is a subtle increase in the number of events related to tropical cyclones in the western Caribbean region and a more evident increase in wave height and energy content of these events.

Introduction

Over the past decades, there has been increasing awareness of the effects of climate change in coastal regions, with numerous studies focused on possible implications of sea-level rise (Nicholls, 2002; Wong et al., 2014) and on the modification of the intensity, frequency and location of storms worldwide (Kossin et al., 2014), which represent a more immediate consequence of climate change. Despite these numerous studies, there is still low confidence in the results of large-scale trends in storminess over the last century (IPCC, 2013), mainly due to changes in the capabilities of observing techniques, which confound the possible presence of trends. One region with reliable data is the North Atlantic, where a robust increase in the frequency and intensity of the strongest storms has been observed since the 1970s, although there is still debate over the cause of this increase (IPCC, 2013; Webster et al., 2005).

Contrary to the meteorological effects of storms, where the main interest is focused on the location of the storm strike (e.g. Resio and Irish, 2015; Needham and Keim, 2014; Keim et al., 2007; Elsner et al., 1999; Simpson and Lawrence, 1971), wave conditions related to a storm event can be observed along distant coasts, well beyond the region of wind stress. Hence, a modification in storm characteristics will be associated with inherent changes in wave height and the storm surge reaching the coastline, which are the two main factors responsible for considerable economic losses in coastal and offshore areas (Mendelsohn et al., 2012; Neumann et al., 2014). This makes the investigation of changes in storminess trends a major concern for coastal management, even more so when taking into consideration that possible storm effects might be enhanced by the effect of sea-level rise and the increase in coastal development.

Wave conditions are commonly obtained from in situ observations (buoys, tide gauges, ships), satellite altimeter data or wave models. In the U.S. Gulf of Mexico (GoM) region, Komar and Allan (2008) analysed a 28-year register of measured buoy data in the central region of the Gulf of Mexico but did not find long-term changes in wave height during the summer months, which, according to the authors, would be attributable to an increase in wave heights caused by tropical cyclones (TCs). This dataset was also included in a study by Bromirski and Kossin (2008) which extended the analysed data to three deep-water (> 1000 m) buoy registers in the northern GoM, each covering a period of 28 years. Their study demonstrated the relationship of such long-term registers with shorter-term coastal registers, making their findings applicable to near-coastal regions. In their study, TC waves were separated from the rest of the register using the National Hurricane Center best-track record, and an increase in the number of TC-related events over the last decades was found. However, this increase was associated neither with increases in significant wave height (SWH) related to the TC events nor with the duration of the TC events. Their study also found a shift in the intra-annual distribution of TC-related events between the first and second parts of the register, with the majority of events taking place during August and September in the first half of the register and during September and October in the second half of the register.

Along the coast of the Mexican GoM, extreme storm-wave events are mainly caused by tropical cyclones and Nortes. Nortes are anticyclonic cold surges that enter the Gulf of Mexico from North America, generating strong northern winds and, therefore, presenting ideal conditions for fetch causing mature wind waves. The study of the occurrence and interannual trends of extreme storm-wave events related to both TCs and Nortes must be regarded separately, given that possible long-term changes in the behaviour of TCs and Nortes and their responses to climate change are not expected to be analogous (Komar and Allan, 2008).

As for the western Caribbean Sea (WCS), storminess trend studies based on wave datasets are absent to the authors' knowledge. Projected changes in wind shear suggest a decrease in the number and intensity of TCs in the region (Biasutti et al., 2012), although studies suggest an intensification of wind speed of higher-category events on a global scale (Holland and Bruyère, 2014). Wave hindcast results from Appendini et al. (2014) do not project increases in wave height, although a recent analysis indicates more intense waves in the future climate for the WCS as a result of tropical cyclones (Appendini et al., 2017).

Along the eastern coast of Mexico (Gulf of Mexico and western Caribbean Sea), in situ and satellite data are scarce and temporally discontinuous. This contribution analyses a 30-year time series of hindcast wave data, covering the period of 1979 to 2008 (Appendini et al., 2014). The selection of this time interval allows for comparison to previous work in the region and is considered the standard period by the World Meteorological Organization to characterize climate, although the use of shorter time periods has been suggested to characterize non-stationary climates, e.g. under climate change conditions (Arguez and Vose, 2011). Appendini et al. (2014) did not find any significant trend in time series of extreme wave heights (using the 99th percentile) along the eastern Mexican coast, but their research examined the entire time series without regard of the type of extreme event.

i.

Time series of the number of TC events, SWH${}_{\mathrm{mean}}$ and SWH${}_{max}$, mean duration and$E_{\mathrm{s},\mathrm{mean}}$ for the Holbox, Cancun and Tulum nodes.

[Figure omitted. See PDF]

Conclusions

In the GoM region, Nortes are responsible for the majority of extreme wave events occurring from 1 November to 30 April, while TCs are responsible for the majority of extreme wave events occurring during August. During the months of September and October, both Nortes and TCs can be responsible for extreme wave events. The TC season in the Mexican GoM starts and ends later than in the North Atlantic; it lasts from August to December instead of June to October.

There is not a general statistically significant change in the number of storm-wave events related to Nortes or their characteristics in the GoM and the WCS during the study period. The time series of events related to Nortes and their characteristics do not show consistent behaviour in the study area. Although there are a few time series where the presence of a trend in the data is corroborated by the Mann–Kendall test at the 90 % significance level, the available evidence is not sufficient to conclude that there is variation in storminess related to Nortes.

For most of the GoM time series of events related to TCs and their characteristics, the presence of a trend in the data cannot be corroborated by the Mann–Kendall test at the 90 % significance level. However, the basin shows a certain consistency, with no trends (or trends close to zero) for the Coatzacoalcos and Paraiso nodes and increasing trends with increasing distance from these nodes. Overall, with the exception of the Bay of Campeche, the results for TC-related events show an increase in wave height in the WCS and the GoM.

In the WCS, the data confirm the presence of positive trends in the number, SWH, duration and energy of storm events. There is a subtle increase in the number of storms related to TCs, which will result in an increase of one TC-related event every 10 years in Cancun and every 20 years in Tulum. Considering the mean SWH, the estimated trends show an increase of 2.2 m in both Cancun and Tulum during the entire study period. The obtained trends result in a more evident increase in mean SWH associated with TC events in the second half of the study period.

The IBTrACS record (Knapp et al., 2010) was downloaded from the NCDC website (https://www.ncdc.noaa.gov/ibtracs) in May 2016. The 10 nodes from the wave hindcast used in this work are available in the Supplement. The entire wave hindcast and the Norte dataset are available upon request to Christian M. Appendini.

The Supplement related to this article is available online at https://doi.org/10.5194/nhess-17-1305-2017-supplement.

The authors declare that they have no conflict of interest.

Acknowledgements

The Mexican National Council for Science and Technology (CONACYT) and the Universidad Nacional Autónoma de México provided financial support through projects INFR-2014-01-225561 and Proyectos Internos Instituto de Ingeniería 5341 and 6602. Elena Ojeda is a Cátedras CONACYT researcher under project 1146, Observatorio costero para estudios de resiliencia al cambio climático. The authors would like to thank the technical support from José López-Gonzaléz, Gonzalo Martín-Ruiz, Edgar Escalante Mancera and Iván Adrián Moreno. Edited by: Nadia Pinardi Reviewed by: three anonymous referees