President’s Column

The vulnerability of Caribbean countries to natural hazards, and particularly climaterelated hazards, is well known The Region’s population is highly and increasingly urbanized, much of the key and critical infrastructure is coastal, and many settlements and the infrastructure serving them are low-lying or located in mountainous terrain Hydrometeorological hazards, such as extreme rainfall events, floods, tropical storms, hurricanes, and landslides, impact the Caribbean with noticeable frequency. The Sixth Assessment Report of the Intergovernmental Panel on Climate Change (AR6) notes that due to their limited size, resource constraints and limited connectivity, the risks from climate change impacts and risks are amplified for small islands, and small islands present the most urgent need for investment in capacity building and adaptation. Strengthening our capacity to manage the effects of high rainfall events is one such urgent need

Understanding rainfall and its likely impact on any location in our physical environment is essential for the safe and efficient provision of infrastructure to serve the social and economic needs of our community This applies to roads, storm drains, housing and any other land development, including for agriculture. Too often, due to a combination of factors, infrastructure is inadequate to manage the volume of rainfall experienced, contributing to flooding and attendant risks to life, health and property.

Updated rainfall intensity-duration-frequency curves (IDF) are not available for most Caribbean countries IDF curves are a basic tool used to provide rainfall parameters appropriate for the design of drains, culverts and other infrastructure, according to applicable building codes or relevant design reference documents IDF curves are prepared from statistical analysis of rainfall data.In their 2011 paper[1] on the challenges experienced in attempting to produce IDF curves for five Caribbean countries, a consulting team comprising specialists from HR Wallingford Ltd. and the Caribbean Institute of Meteorology and Hydrology noted the decreasing number of rainfall stations over past decades, the lack of long records of short-duration rainfall data, and the inability to obtain data from national meteorological and hydrological agencies among the main limitations A recent study[2] of 22 hydromet agencies in the Caribbean found these agencies to have key capacity gaps in the technical production, translation, transfer, and facilitation of the use of climate information, with 17 having low or moderate capacity to perform climate data rescue or data mining

The consequence of the lack of capacity in this particular area can be a lack of confidence and rigour in the design of some of the drainage and flood management systems in the Caribbean because of the use of generic data and assumptions in their design, or the use of IDF curves from other countries or nearby locations for which topography or other critical characteristics might be different. Where IDF curves are not available, engineers engaged on some larger development projects perform the statistical analysis on the data available to determine the design storm parameters for those individual projects, an approach likely to be sub-optimal. With limited financial resources available, it is important to ensure that funds allocated to infrastructure are used efficiently, contributing to increased resilience.

Designs should be based on data and engineering approaches supported by national building and disaster management regulations. In the aftermath of the deaths, damage and losses caused by Hurricane Sandy, the reliance on outdated IDF curves to assess hydrological impacts on infrastructure design in the USA was highlighted as a flaw, as projections in the New York area were for the events then classified as 100-year events to occur once every 35 to 55 years by 2050[3] Similar observations made in Europe have led to adjustments in the engineering design standards to account for climate change, one change being a reduction in the frequency with which flooding from storm drains is permissible in various spatial settings[4]

AR6 did not identify a significant long-term trend in rainfall in the Caribbean over the period 1901 to 2012, but projected the Eastern Caribbean would be slightly wetter over the period to 2100, with more extreme seasonality and significant local variability, with slightly fewer storms continuing to be the main driver of flooding in the Lesser Antilles A number of remote sensing precipitation products are available around the world based on satellite data, atmospheric physics models and other sources

A 2022 study of the performance of five of these datasets when applied to rainfall in the Greater and Lesser Antilles [5] found one dataset, Multi-Source Weighted-Ensemble Precipitation, to perform satisfactorily for hydrological applications on a watershed scale, though when compared to rain gauge data, the correlation was significantly weaker than observed in other parts of the world

The availability of IDF curves for Caribbean countries, and sub-regions of those countries with different rainfall characteristics, is therefore key not only to the efficient performance, by engineers, of routine drainage design, but to strengthening the resilience of communities to the effects of hydrometeorological hazards and climate change Development of IDF curves for countries for which they don’t exist, and updating and refinement of IDF curves in other countries should be seen as a priority in adaptation to the current climate crisis

[1] Lumbroso, D., Boyce, S., Bast, H. and Walmsley, N. (2011) The challenges of developing rainfall intensity-durationfrequency curves and national flood hazard maps for the Caribbean The Journal of Flood Risk Management, 4 (1). pp. 42-52.

[2] Mahon, R., Greene, C., Cox, S.-A., Guido, Z , Gerlak, A K , Petrie, J -A , et al (2019) Fit for purpose? Transforming National Meteorological and Hydrological Services into National Climate Service Centers. Climate Services, 13, 14-23. https://doi org/10 1016/j cliser 2019 01 002

[3] Wagner, M , Chhetri, N , & Sturm, M (2014) Adaptive capacity in light of Hurricane Sandy: The need for policy engagement. Applied Geography 50: 15–23.

[4] Kundzewicza, Z W and Licznar, P (2021) Climate change adjustments in engineering design standards: European Perspective. Water Policy Vol 23 No S1, 85 doi: 10.2166/wp.2021.330

[5] Bathelemy, R , Brigode, P , Boisson, D , Tric , E , (2022) Rainfall in the Greater and Lesser Antilles: Performance of five gridded datasets on a daily timescale. Journal of Hydrology: Regional Studies, doi org/10 1016/j ejrh 2022 101203

In this Issue

In this issue of The Engine Room, we are delighted to bring to you a number of technical articles touching on the broad topic of Stormwater Design & Management

It is our belief that this is an important topic that must be discussed broadly, properly understood, and actioned accordingly

In our Fellow's Corner, Eng Andrew Hutchinson speaks to not only design considerations for drainage, but to analysis and methodology; and does a review of local stormwater drainage practice Eng Justin Jennings-Wray provides timely information that would be useful to our civil engineering design community by delving into three methods for drainage design - rational method, the modified rational method and the TR55 peak flow method (including their advantages and limitations) Importantly, we have crucial input from the Caribbean Institue of Meteorology and Hydrology, through a contribution from their Shawn Boyce and Kayshawn Hall as they discuss the revision of the IDF curves, rainfall data and collection, and limitations of methods used.

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Cover Photo Credit: Floods in St. Vincent https://www iwnsvg com/2016/11/29/housesdestroyed-as-rains-trigger-floods-across-stvincent/

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