Nature-based solutions on the coast in face of climate change: The case of Benidorm (Spain)

Abstract

The increase in anthropic activities and floods of coastal and river origin put the proper functioning of coastal cities at risk. Benidorm (Spain), an international tourist destination, is no exception to the effects of climate change. Maritime storms intensified, with an increase in wave height by 61% in the last 10 years. Likewise, changes in atmospheric circulation patterns have maximized the irregularity and torrentiality of rainfall in the study area, finding that 2 of the 3 years with the highest number of days of daily precipitation >30 mm have occurred in recent years (2017 and 2019). All these changes will accelerate the beach erosion process. Therefore, it was necessary to act, implementing natural solutions that increase the resilience of the coastal city. The innovative construction of a vegetated urban dune parallel to the promenade was proposed to protect it from the 3 m flood level during the most unfavourable maritime storm. The dune must favour the drainage of sea water and be compatible with the recreational activities carried out in its surroundings. The solutions proposed here are a recommendation so that Public Administrations in other parts of the world can design their climate adaptation plans using nature-based solutions.

Full text

Urban Climate 53 (2024) 101816
Available online 3 February 2024
2212-0955/© 2024 The Authors. Published by Elsevier B.V. This is an open access article under the CC BY-NC-ND license (http://creativecommons.org/licenses/by-nc-nd/4.0/).
Nature-based solutions on the coast in face of climate change: The
case of Benidorm (Spain)
Ignacio Toledo
a
,
*
, Jos´
e Ignacio Pag´
an
a
, Isabel L´
opez
a
, Luis Aragon´
es
a
,
Jorge Olcina
b
a
Department of Civil Engineering, University of Alicante, Carretera Sant Vicent del Raspeig s/n, 03690 Alicante, Spain
b
Department of Regional Geographic Analysis and Physical Geography, University of Alicante, Carretera Sant Vicent del Raspeig s/n, 03690
Alicante, Spain
ARTICLE INFO
Keywords:
Climate change
Climate extremes
Nature-based solutions
Beach protection
Sand dunes
ABSTRACT
The increase in anthropic activities and oods of coastal and river origin put the proper func-
tioning of coastal cities at risk. Benidorm (Spain), an international tourist destination, is no
exception to the effects of climate change. Maritime storms intensied, with an increase in wave
height by 61% in the last 10 years. Likewise, changes in atmospheric circulation patterns have
maximized the irregularity and torrentiality of rainfall in the study area, nding that 2 of the 3
years with the highest number of days of daily precipitation >30 mm have occurred in recent
years (2017 and 2019). All these changes will accelerate the beach erosion process. Therefore, it
was necessary to act, implementing natural solutions that increase the resilience of the coastal
city. The innovative construction of a vegetated urban dune parallel to the promenade was
proposed to protect it from the 3 m ood level during the most unfavourable maritime storm. The
dune must favour the drainage of sea water and be compatible with the recreational activities
carried out in its surroundings. The solutions proposed here are a recommendation so that Public
Administrations in other parts of the world can design their climate adaptation plans using
nature-based solutions.
1. Introduction
Coastal erosion is a natural phenomenon that is becoming a growing problem on shorelines around the world (Gracia et al., 2018;
Jacob et al., 2021). This problem is the result of multiple factors, and can be classied into those related to anthropic pressure or those
related to the maritime climate of the area (sea level rise, greater storm frequency, increase in sea surface temperature, etc.), many of
them being stimulated in recent decades by global climate change (Reimann et al., 2018; Toimil et al., 2020).
Anthropogenic activities have been extensively reviewed in the literature (Danladi et al., 2017; Foti et al., 2022). We nd actions
such as the construction of dams in the river course (Aragon´
es et al., 2016), massive urban developments in many coastal areas (Pag´
an
et al., 2016) or the construction of dikes and breakwaters to protect the coast from storms (Martin et al., 2021). All this has altered the
natural dynamics of the coast as a consequence of the retention of sediments or the lack of erosion of the hydrographic basins, which
has generated retreats of the shoreline throughout the world (De Leo et al., 2017; Warrick et al., 2019). Another example of these
* Corresponding author.
E-mail addresses: nacho.toledo@ua.es (I. Toledo), jipagan@ua.es (J.I. Pag´
an), lopez.ubeda@ua.es (I. L´
opez), laragones@ua.es (L. Aragon´
es),
jorge.olcina@ua.es (J. Olcina).
Contents lists available at ScienceDirect
Urban Climate
journal homepage: www.elsevier.com/locate/uclim
https://doi.org/10.1016/j.uclim.2024.101816
Received 16 August 2023; Received in revised form 16 November 2023; Accepted 26 January 2024

Urban Climate 53 (2024) 101816
2
anthropogenic actions is the nourishment of beaches. Any spillage of material can cause impacts on the environment, since it will cause
changes in water currents (Truong et al., 2021), turbidity (Chiva et al., 2018) and even the destruction of natural habitats, such as
Posidonia oceanica meadows (Aragon´
es et al., 2015).
Changes in wave direction, as well as in their intensity and frequency, are another aspect that inuences the evolution of the
shoreline (Flor-Blanco et al., 2021; Toledo et al., 2022). The more frequent and intense occurrence of extreme weather events is already
a reality. The increase in sea surface temperature has a direct correlation with the potential of cyclones (Mei et al., 2015; Pytharoulis,
2018). In the same way, the deepening of the storms and the increase in wind speed have a consequence in the increase in the level of
the storm surge and, therefore, in the risk of ooding in coastal areas (Jisan et al., 2018; Vousdoukas et al., 2016). For all these reasons,
it is necessary to continuously monitor the meteorological variables through different instruments with the aim of establishing valid
climate projections for any region of the world (Lemos and Rood, 2010; Susmitha and Sowya Bala, 2014).
All these changes become more important in the event that they occur in urban areas. Currently, half of the largest cities on the
planet are located on the coast, where almost 40% of the world’s population lives (Kummu et al., 2016). Government agencies are
forced to provide coastal cities with protection elements against the erosion of their environment. During the last decades, hard
defence works have played a very important role in coastal protection (Morris et al., 2020; Schoonees et al., 2019). However, these
engineered solutions, such as dikes or breakwaters, are becoming increasingly economical and ecologically unsustainable (Morris
et al., 2018). For this reason, it is necessary to broaden the range of coastal protection interventions to more natural ones.
This is where Nature-based Solutions (NbS) arise, which are dened as approaches, actions or processes that use the principles of
nature to solve different problems related to territorial and urban management such as adaptation to climate change, management of
resources, or the quality of air and the environment (CONAMA, 2022). In the eld of coastal protection, multiple options have been
proposed to be developed in urban environments, including the management and restoration of green infrastructures (Kabisch et al.,
2017). An innovative sand breakwater was proposed for a port built at Lekki in Nigeria (van der Spek et al., 2020). This solution
includes a monitoring program to ensure the navigability and continued safety of the sand breakwater, and to counter the retreat of the
shoreline downstream of the port through sand feeding. On muddy coastlines, mangrove restoration or bamboo fencing is a sustainable
option on eroded shorelines (Dao et al., 2020; Verhagen, 2019). Another alternative is to benet of the vegetation property in
attenuating the strength of the waves, as was done with the plantation of P. oceanica seeds in Calabaia Beach to reduce the degradation
of the coast (Maiolo et al., 2020). On other occasions, a complete project is proposed that involves the restoration of the riparian
Fig. 1. (a) Study area located in Spain and (b) in the province of Alicante, (c) detail of the study area, with SIMAR node and AEMET weather
stations, (d) location of Poniente Beach, Levante Beach and the ravines in Benidorm.
I. Toledo et al.

Urban Climate 53 (2024) 101816
3
vegetation and the mangrove forest, as well as an articially constructed dune, stabilized with native vegetation and a breakwater
(Rivillas-Ospina et al., 2020).
The shoreline of Benidorm (Spain), an international benchmark in the tourism sector, is not an exception to the effects of climate
change. The city has suffered in recent years a series of storms that have jeopardized the infrastructures located on the coast frontline.
The study of maritime storms in the city has already been recorded in the literature (Toledo et al., 2022). However, solutions to contain
these effects have not yet been proposed. This research has two main objectives: a) to analyse the coastal resilience of Benidorm city
(Spain) against coastal erosion and the effects of maritime storms, which are increasing in recent years due to the effect of climate
change in the Mediterranean zone; b) recommend an appropriate Nature-based Solution to address the continuous ooding that oc-
curs, both on the beach berm and on the promenade. Adaptation to climate change requires urgent actions, especially in coastal areas,
due to the high degree of vulnerability and exposure they present to the higher frequency of development of extreme weather events
predicted in climate models (Cramer et al., 2018; IPCC, 2022). The Spanish Mediterranean coast is the Spanish area that already shows
the greatest effects of the warming process and the one that experiences the greatest economic damage from extreme events (Oliva and
Olcina, 2022; Torres et al., 2021). Therefore, carrying out this study is an opportunity to promote Nature-Based Solutions for the
adaptation of its beaches, which is the main natural resource of its economy (Olcina Cantos and Mir´
o P´
erez, 2017).
2. Methodology
2.1. Study area
The study area corresponds to the city of Benidorm (Spain), which is located on the eastern coast of the Iberian Peninsula, on the
shores of the Mediterranean Sea (Fig. 1a). The city is characterized by a powerful economic activity in the tertiary sector, specically in
tourism. Currently, Benidorm represents a fundamental tourist destination both for the Valencian Community and for the rest of Spain
(Femenia-Serra and Ivars-Baidal, 2021), being the third city in Spain by number of hotel beds after Madrid and Barcelona and the most
important tourist centre of the Spanish Mediterranean coast (Rico et al., 2020).
Originally a small shing village, Benidorm is a typical example of the resorts that emerged along the Mediterranean coast in the
1960s during the mass tourism boom that catered mainly to foreign tourists. Within the framework of local urban planning, the au-
thorities planned the categories of land use and buildings and dened growth areas. Specically, an area of adjacent urban expansion
along its shoreline that gave rise to Benidorm’s distinctive image of high-density urbanism and high-rise building (Nolasco-Cirugeda
et al., 2020).
2.1.1. Physical description
Part of the city’s success is due to the two beaches included in its municipal area: Poniente beach and Levante Beach. Both beaches
are characterized by a ne-sized sediment and a unique morphology (length and width). Playa de Poniente is 3 km long and has an
average width of 68 m, while Playa de Levante is 2.3 km long and has an average width of 54 m (Toledo et al., 2022). Regarding the
sediment size, they have a mean size (D
50
) of 0.28 and 0.25 mm, respectively.
Both beaches are included in a closed littoral system (Fig. 1c), forming a promontory inlet. The orientation of both beaches to the
south and the protection provided by the Sierra Helada massif against waves coming from the east (the most frequent direction in this
area) means that the impact of storms is less than in other parts of eastern Spain (Amores et al., 2020). The waves in the area are
conditioned by Sierra Helada to the east and Punta de Gamell to the west, as well as by the Island of Benidorm (Fig. 1c). P. oceanica
abounds on the seabed, a marine phanerogam that forms extensive meadows on sandy and rocky bottoms (Blanco-Murillo et al., 2022).
A series of ravines that outline the topography of the city ow into the study beaches (Fig. 1d). The high degree of urbanization in
the area due to the transformation of land use has modied the course of the ravines (Table 1). By paving and burying the pipelines, the
hydrological and hydraulic behaviour of the basins has been changed, generating more risks, such as the increase in ow speed.
The continuous erosion caused by the waves and by the discharge from the ravines has caused many feeding actions to be carried
out on the two beaches. The most important was the one carried out in the eastern sector of Playa de Poniente in 1991, where an
articial contribution of 710,847 m
3
was made, which made it possible to increase the beach width to 100 m. However, the excessive
dumping of sand buried the present P. oceanica, destabilizing the beach prole and losing beach surface up to the current width of 30 m
(Aragon´
es et al., 2015).
The study area is located in a microtidal zone, where oscillations due to atmospheric pressure are more important than the tides
themselves. Astronomical tides reach a maximum value of 0.3 m, while storm surges can reach values of up to 0.45 m (Ecolevante,
2006).
Table 1
Temporal evolution of CORINE Land Cover in the Benidorm catchment areas.
1990 2000 2006 2012 2018
Agricultural area 32.24% 22.24% 22.24% 9.87% 9.87%
Articial surface 25.77% 37.64% 37.64% 41.21% 41.21%
Natural environments 41.99% 40.12% 40.12% 48.92% 48.92%
TOTAL 100.00% 100.00% 100.00% 100.00% 100.00%
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Urban Climate 53 (2024) 101816
4
2.1.2. Natural hazard in Benidorm
Benidorm city has a Mediterranean climate. This climate stands out for a regime of mild temperatures in winter (10 ◦C on average)
and high temperatures in summer (25 ◦C on average), and for a low annual rainfall, of the order of 400–450 mm. However, this
precipitation tends to be concentrated on a few days a year, especially during the autumn. During this season, deep low-pressure
systems tend to form, associated with the presence of a ‘cold drop’ in height. The ‘cold drops’ have the potential to cause heavy
rains and storm surges simultaneously, as demonstrated by the storm ‘Gloria’ of January 2020 on the Spanish Mediterranean coasts
(Amores et al., 2020).
The appearance of one or several of these meteorological elements simultaneously can cause substantial damage to coastal in-
frastructures (Bevacqua et al., 2017). These natural hazards and their consequences have been recorded over time for Benidorm city
(Tros De Ilarduya and Fern´
andez, 2013). The Benidorm promenade is subject to frequent ooding. Those of a maritime nature are
striking, where sea water oods the entire beach berm and the waves hit the wall of the promenade, causing overows (Fig. 2a-b). In
bays anked by promontories, as is the case in Benidorm, water levels can rise more than in open areas (McInnes et al., 2003).
Pluvial oods are caused by large rainfall discharged in a short space of time. The high intensity that rainfall can reach often
generates large oods in ravines that can overow and cause ooding in the city (Fig. 2c). Many of these situations are caused by a
decient catchment system, causing the ow velocity to increase and eroding the beach berm once it drains on the beach (Fig. 2d-e).
2.2. Study of climatic phenomena
2.2.1. Waves
Wave data (height, period and wave direction) were provided by Puertos del Estado, based on SIMAR series (data simulated from
Fig. 2. (a-b) State of Levante Beach during ‘Gloria’ storm in January 2020 in which the waves hit the promenade, (c) Floods in the centre of
Benidorm on 11 November 2022, (d-e) Damage caused to Levante Beach by the storm on 18 September 2022. Source: UA Climatology Laboratory.
I. Toledo et al.

Urban Climate 53 (2024) 101816
5
numerical models). This is hourly data collected over 65 years, during the period 1958–2022.
For this work, the SIMAR Node 2,082,102 database (0.167◦W, 38.500◦N), located about 5 km south of the study area, was used
(Fig. 1c). The data from this locality were processed by CAROL v1.0 software (developed by IH-Cantabria), obtaining for each of the
study periods the wave height H
s,12
(wave height with a 0.137% probability of be exceeded), and their corresponding periods, di-
rections and probabilities of occurrence. Wave diffraction was not considered given the low inuence that the island has on the change
of direction of the wavefront, since it only eliminates 5% of the waves on the beaches of Benidorm (Fig. 3).
Finally, a key point was the analysis of storms. This study was carried out from the SIMAR Node records. There is no universally
accepted climate denition for the term “storm”. In our study, it was considered storm when a signicant wave height of 1.35 m was
exceeded for Poniente Beach and 1.15 m for Levante Beach (corresponding to the 95th percentile) for a minimum period of 6
consecutive hours and with a delimitation of at least 24 h without exceeding said threshold (Harley et al., 2014; Valiente et al., 2019).
This study focused on the average duration of the maritime storm, and its maximum height.
2.2.2. Precipitation
Rainfall data (daily precipitation, hourly precipitation and maximum hourly intensity) have been provided by Agencia Estatal de
Meteorología (AEMET). For this work, data from various meteorological stations have been used (Fig. 1c), since the period of operation
of these has not been continuous over time. The characteristics of the stations used are attached in Table 2 below:
For the analysis of rainstorms, only days with a daily rainfall >30 mm have been considered, due to the limited availability of
hourly data. On the other hand, only hourly maximum intensity data is provided from 2005, since only station 8036Y has hourly data.
Based on this information, the different rain parameters are analysed (number of days with P >30 mm, maximum daily precipitation
and maximum hourly intensity) in different periods of time (month, weather seasons, years and decades) to know their evolution
throughout time.
2.3. Flood level calculation
This section determines the ood level as the maximum sea level in the beach prole under the action of the most unfavourable
storm produced in the study area since records are available. The estimation of the ood level was made as the combined action of the
Storm Surge (SS), the Astronomical Tide (AT), and the run-up (R
u,2%
). For the calculation of the run-up, the formulation of section
5.2.2 and 5.4.6 proposed in EurOtop was used (Van der Meer et al., 2018).
Ru2%
Hm0
=1,00 ⋅ γf⋅γβ⋅(4−
1,5

γb⋅ξm−1,0
√)(1)
For a maximum value approach, run-up is expressed as in Eq. 1: where R
u2%
is the wave run-up height exceeded by 2% of the
Fig. 3. (a) Bathymetry and incident wave range in the study area, (b) Distribution of wave height and wave direction for the most unfavourable
storm. Source: SMC (Gonz´
alez et al., 2007).
I. Toledo et al.

Urban Climate 53 (2024) 101816
6
incoming waves (m), γ
b
is the inuence factor for a berm (−), γ
f
is the inuence factor for roughness elements on a slope (−), γ
β
is the
inuence factor for oblique wave attack (−) and ξ
m-1,0
is the breaker parameter (−).
Sea level data (astronomical tide and storm surge) have been obtained through the Gandía Tide Gauge, from the Puertos del Estado
Tide Gauge Network (REMPOR). Located in the Port of Gandía (0◦9
′
5“ W, 38◦59’ 43” N). This data point is the closest to the study
area. This is hourly data collected over 15 years, over the period 2007–2022. The Storm Surge, a random variable caused by atmo-
spheric pressure and wind, is estimated as a residual or difference between the starting data (total sea level) and the Astronomical Tide,
a deterministic variable resolved by harmonics analysis (Tapia et al., 2016).
2.4. Hydrological study
The objective of this section consists in the elaboration of a basic hydrological study in order to identify the hydrological ow of the
different basins that ow into Poniente and Levante beaches (Benidorm). To carry out this analysis, the HEC-HMS hydrological
modelling program has been used, which is designed to simulate the precipitation-runoff processes of dendritic drainage basins. The
analysis of the catchment basins and the main ows has been carried out using the ArcMap 10.6 software. Data on elevation, land use,
hydrography, sub-basins, and permeability were collected (Table 3).
The data used to calculate the design precipitation have been obtained from the AEMET 8036Y – Benidorm weather station (Parc
Les Foietes), as can be seen in Fig. 1c. An analysis of maximum rainfall has been carried out using the Gumbel function, an adjustment
function required by Highway Instruction 5.2-IC (de Fomento, 2019). For this, a design rainfall of 24 h duration has been taken using
the alternating block method with a time interval of half an hour (Δt =0.5 h). This calculation has been made for different return
periods (50, 100 and 500 years). To determine the time of concentration, the T´
emez model for rural basins has been used (MOPU,
1987).
The inltration method used has been the Runoff Curve Number (CN) method developed by the Natural Resources Conservation
Service - USDA (formerly SCS), widely used in predicting the approximate amount of runoff from a given rainfall event. It is mainly
based on soil properties, land use and hydrological conditions (Ajmal et al., 2015). GIS was used to map the Curve Number (CN). In this
study, the classication proposed by the Spanish Highway Instruction 5.2-IC (de Fomento, 2019) was used, which depends on i) the
slope of the study area classied into two groups (<3% or greater than or equal to at 3%), ii) hydrological group of the soil (four
categories based on inltration speed: A, B, C and D) and iii) the use of the soil. The transformation method used has been that of the
SCS Unit Hydrograph, in which a unit hydrograph is dened by rst establishing a percentage of 37.5% of the unit runoff that occurs
before the maximum ow (Natural Resources Conservation Service, 2007).
Finally, the characteristics of the considered scenario are dened:
•It has been considered that there is no retention of rainwater by the treetops due to the signicant scarcity of these in the study area.
•The precipitation that can be retained in small supercial retentions, to inltrate or evaporate later, has also been considered zero.
•Initial abstraction (mm) has not been considered, since it has little inuence on the outlet ow.
•A delay time (T
lag
) of 40% of the concentration time of the basin has been considered.
•Finally, the base ow method has not been considered, since in none of the channels that cross the city of Benidorm there is a
continuous base ow prior to the rainy episode.
Table 2
Characteristics of the AEMET weather stations in Benidorm.
Code Name Start date End date Series Next series UTM X UTM Y
8036 BENIDORM 1972 1981 1972–1972 1980–1981 749,964 4,269,170
8036B BENIDORM (AQUAGEST) 1996 2022 2000–2003 2009–2022 749,812 4,270,925
8036Y BENIDORM (PARC LES FOIETES) 2005 2022 2011–2019 2020–2022 749,453 4,270,018
8037 BENIDORM MEDIA LEGUA 1954 1968 1955–1957 1959–1961 753,601 4,272,186
8036C BENIDORM-TERRA MITICA 2002 2003 2002–2002 2002–2003 747,260 4,271,956
Table 3
Type, date, format, resolution and source of data used in this study.
Data type Date Format Resolution Source
Digital Elevation Model 2016 Raster 2 m/pixel IGN
https://centrodedescargas.cnig.es/
Land uses 2018 Vectorial 1:100.000 CORINE
https://land.copernicus.eu/en/products
Hydrography 2007 Vectorial 1:25.000 IGN
https://centrodedescargas.cnig.es/
Sub-basins 2013 Vectorial 1:25.000 DGA-CEDEX
https://aps.chj.es/down/html/descargas.html
Permeability 2015 Vectorial 1:200.000 IGME
https://mapas.igme.es/
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Urban Climate 53 (2024) 101816
7
3. Results
3.1. Study of climatic phenomena
In both Poniente Beach and Levante Beach, a large increase in H
s,12
was detected in the period 2013–2022 for almost all incoming
directions (Fig. 4). The cases of waves coming from the west (SSW, SW, WSW) stood out. The SSW swell at Poniente Beach increased its
wave height by 44% in the last period compared to the previous one (2.13 m vs. 3.06 m), while at Levante Beach the wave height for
SSW directions, SW and WSW increased by 18%, 38% and 31%, respectively. Waves originating from the west also increased with
respect to incident waves for the period 2013–2022 compared to the period 1993–2002. Through a linear regression analysis, we can
know the inuence of climate change in Benidorm. A growing trend in wave height can be seen on both beaches, especially in Levante,
where the average wave height has experienced an increase of 62% in the last 50 years. At Poniente Beach, the frequency of SSW wave
direction increased by 11%, while the frequency of ESE and S decreased. Likewise, an increase of 13% could be observed for Levante
Beach and 4% for the SSW and SW directions, respectively, while 15% is lost in the S direction.
In addition, the incoming storms on Poniente and Levante beaches since 1958 were analysed (Fig. 5). Poniente Beach presented a
similar average duration, but a higher wave height of the storms, compared to Levante Beach. In Poniente, it has remained relatively
stable between 15 and 25 h due to storms until 2005, where from that year a slight downward trend is observed, marking a minimum of
10 h in 2007. In the case of Levante, there is greater instability in the average duration and, therefore, a greater number of peaks.
However, this small decrease observed in the trend of the average duration on both beaches was not reected in the same way in the
storm H
max
. As in the H
s,12
study, H
max
has shown a signicant increase since the 1960s on both beaches, especially in the last 15 years,
with a maximum of 3.58 m in 2017 on Poniente Beach (Fig. 5b) and 3.31 m in 2018 on Levante Beach (Fig. 5d). A more detailed study
Fig. 4. Wave height (H
s,12
) and frequency for each direction and period in (a) Poniente Beach and (b) Levante Beach.
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Urban Climate 53 (2024) 101816
8
of storms in the study area was carried out by (Toledo et al., 2022).
Finally, the evolution of the main wave parameters on the two beaches of Benidorm has been studied (Table 4). As previously
mentioned, the signicant wave height has suffered a signicant increase in the period 2013–2022 in both locations, with Levante
Beach standing out with an increase of 14% compared to the previous period. The periods, both average and peak, have not shown
major changes over time, with rises and falls in the last two analysed periods. However, the average wave direction stands out among
all, with a signicant clockwise rotation since the period 1983–1992. Since then, the waves have rotated 7.2◦at Poniente Beach and
5.3◦at Levante Beach.
The behaviour of the precipitation variables in Benidorm city was also studied. First, the number of days per year in which a daily
rainfall of 30 mm is exceeded was analysed (Fig. 6a). This value is highly variable given the Mediterranean climate in which the
Benidorm is located with irregular rainfall over time. However, the three years with the highest records have already occurred in the
21st century, 7 days with daily precipitation >30 mm in 2007 and 6 days in 2017 and 2019. Despite this, the trend over time remains
stable on 2 days per year. Grouping the years by periods of 5 years (lustrum) and by season, the characteristic irregularity of the
Benidorm climate is once again observed, where in periods of 5 contiguous years the number of days with P >30 mm can double or
halve with relative frequency (Fig. 6b). An example of this is the 5 days with P >30 mm in the 1998–2002 period, going to 12 days in
2003–2007 and subsequently dropping to 7 days in the 2008–2012 period. The ve-year period with more days of precipitation >30
mm occurs in the last period analysed (2018–2022) with up to 15 days. The days with the highest precipitation accumulate in the
autumn period, concentrating more than half of these in many cases. In addition, there is a slight increase in this type of rain in spring,
becoming in the last 15 years the second season with the highest number of days with P >30 mm, surpassing winter. Next, maximum
daily precipitation per year is analysed (Fig. 6c). Once again, an increase in precipitation can be seen in the last years analysed. 7 of the
8 years in which the maximum daily rainfall exceeds 75 mm have occurred since 1996, which determines a signicant change in the
current climate, making it more torrential (Olcina, 2020). The year with the highest daily rainfall occurred in 1997 with 136.5 mm. In
Fig. 5. Evolution of storms in the study area: (a) Storm duration average in Poniente, (b) Storm H
max
in Poniente, (c) Storm duration average in
Poniente, (d) Storm H
max
in Levante.
Table 4
Evolution of wave parameters in Poniente Beach and Levante Beach: signicant wave height (H
m,0
), average period (T
m
), peak period (T
p
), average
wave direction (AWD).
Poniente Beach Levante Beach
H
m,0
(m) T
m
(s) T
p
(s) AWD (◦) H
m,0
(m) T
m
(s) T
p
(s) AWD (◦)
1963–1972 0.525 3.684 5.225 147.85 0.461 3.462 5.064 173.00
1973–1982 0.508 3.669 5.178 147.65 0.441 3.448 5.032 172.67
1983–1992 0.519 3.687 5.194 145.86 0.434 3.434 5.002 172.84
1993–2002 0.527 3.651 5.197 148.00 0.454 3.416 5.028 173.09
2003–2012 0.512 3.356 5.038 151.68 0.477 3.135 4.932 176.85
2013–2022 0.568 3.551 5.429 153.02 0.546 3.319 5.317 178.12
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Urban Climate 53 (2024) 101816
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this case, an increase in this parameter is notable, with an upward linear trend of 15 mm in the last 68 years (47 mm in 1954 and 62 mm
in 2022). Analysing the maximum daily precipitation by lustrums and by seasons, a common pattern can be seen (Fig. 6d). The
maximum rains usually occur during the autumn given the climatic conditions. During the spring, although it has become the second
rainiest season, the maximum precipitation is considerably lower than in autumn or winter, with records that rarely exceed 50 mm in
one day. Finally, the maximum daily intensity of precipitation was analysed. Given how short the series is, it is difcult to obtain a
trend in the behaviour of the rain. However, it can be seen how in recent years there have been higher hourly intensities, such as in
2018 with 80.4 mm/h or in 2022 with 79.2 mm/h (Fig. 6e). Regarding the maximum hourly intensities by lustrum and weather season,
it is evident that the highest precipitation intensities occur in autumn given the type of rain that occurs at this time of the year (Fig. 6f).
It is striking, comparing the gures of precipitation and maximum intensity, how winter presents maximum daily precipitations higher
than spring and close to those of autumn in many cases, however, the intensities are clearly lower.
3.2. Flood level calculation
The most unfavourable wave conditions in the study area (H
m,0
=2.83 m, T
m,0
=7.53 s and SWL =63 cm) generate a ood level of
1.71 m at Levante Beach. This sea water level covers the entire berm beach surface during the most unfavourable storm in the historical
series. However, at specic times the ood level can reach 2.49 m (Fig. 7). The low level of the promenade in some points, of the order
of 2.3–2.4 m, causes ooding in part of the promenade, and causing material damage to urban roads and businesses located on the
waterfront.
Fig. 6. (a) No. days with precipitation >30 mm, (b) No. days with precipitation >30 mm per lustrum/season, (c) Maximum daily precipitation
(mm), (d) Maximum daily precipitation per lustrum/season (mm), (e) Maximum hourly intensity (mm/h), (f) Maximum hourly intensity per
lustrum/season.
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Urban Climate 53 (2024) 101816
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3.3. Hydrological study
The process of delimiting basins and obtaining main ows using ArcMap determines that the Lliriet basin is the one with the
greatest urbanization, with a curve number of 64.92 (Table 5). In addition, this basin is by far the one with the greatest difference in
height, with a difference of almost 800 m in just 11.94 km.
The design rainfall for each return period and basin has been simulated in HEC-HMS (Table 6). The basin with the highest outow is
Lliriet for all return periods. 58.9 m
3
/s are reached for a return period of 500 years. This basin, despite not being the largest (the
Barcel´
o basin is), has a lower runoff threshold than the rest due to the high level of urbanization in the area (Table 5). Also noteworthy
is the high outow in the l’Aigüera basin. This basin only has an area of 4.53 km
2
. However, being a fundamentally urban basin and
having a short time of concentration, outows of up to 30 m
3
/s are reached for T =500 years.
The hydraulic capacity of the existing drainage pipes must be used to the maximum. To this end, it has been hydraulically proven
that the ow circulating through the ravines can be absorbed by the existing pipes once it enters the urban nucleus of the city. The
dimensions of the pipes provided by the Benidorm City Council are shown below (Table 7). Only the Murtal drainage system, for all
return periods studied, and that of Lliriet, only for T =500 years, present drainage problems. In the case of Murtal, the hydraulic
capacity is very small, so the resulting ow circulates on the surface once the hydraulic section is completed, ooding part of the
Poniente Beach promenade.
Finally, the water level that affects the streets has been estimated from the ow that is not conducted by the storm pipes, as the
difference between the ow for each return period and the maximum drainage capacity (Table 8). This ow in Murtal varies from 0.18
m for a T =50 years to 0.34 m for a T =500 years. As for Lliriet, the maximum draft reaches 0.31 m for the return period of 500 years.
3.4. Recommendation of solutions to adopt
The solutions shown in this subsection are solely recommendations of the authors based on the literature reviewed with the aim of
addressing the increase in the frequency and intensity of extreme weather events derived from climate change in Benidorm. In no case
are they the result of an exhaustive analysis of different solutions based on pre-established criteria.
3.4.1. Urban dune for defence against waves
The design of an urban wave containment dune is proposed on the backshore of the Benidorm beach with the aim of avoiding
ooding on the promenade during maritime storms. The sea defence dune should be designed in such a way that the amount of
overow is limited. When the waves ood the beach berm in its entirety, the front slope of the dune will begin to erode, which will
eventually add sand to the beach, recovering part of the volume lost during the strong waves. The dune will be destroyed and must be
rebuilt once the storm period ends. The proposal is to articially maintain the sand supply cycle, now interrupted by anthropic actions
in the study area. This dune must be vegetated with autochthonous shrub planting to prevent sand mobility when the wind blows with
a maritime component (wind from the south).
Since the main function of the dune is to contain the waves, when establishing the design conditions, the design is considered as a
vegetated sand dike. For classical dike design, a dike is safe enough when <2% of the waves break over it. The dune height must be
sufcient to contain the ood level, but minimizing the visual impact that it may generate on people walking along the promenade. As
in Section 2.3. Flood level calculation, the ood level has been calculated again (Van der Meer et al., 2018), but this time with the dune
design included. The most unfavourable waves generate a ood level of 3 m at its maximum point (Fig. 8). For this reason, the dune
crest elevation must be higher than this value, that is, have a maximum height of 3.2 m.
In this research, the urban dune will be built as an ‘inverse breakwater’. The core of the dike will be made of a thicker and more
permeable material than the armour layer, with the aim of facilitating the outow of inltrated water, as well as being a reservoir for
the beach itself. Therefore, the dune will be composed of two layers of different size of sediment (Fig. 8). The core will be formed by
Fig. 7. Most unfavourable situation with oods around the promenade.
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Urban Climate 53 (2024) 101816
11
sand washed from quarry and free of ne sediments, while the armour layer will be covered with the size of the current sand, which
according to laboratory tests carried out on the study beaches is 0.27 mm (Toledo et al., 2022).
Gentler slopes generally provide a greater ecological benet because they do not have stability problems (Verhagen, 2019), but are
more expensive due to the larger volume of sand required. A frontal slope of the dune of 25% (1:4) is proposed, with the aim of
Table 5
Main physical characteristics of the study basins.
Features/Basin Murtal Xix ´
o Aigüera Lliriet Barcel´
o
Area (km
2
) 6.62 1.26 4.53 10.74 13.10
X coordinate discharge point (m) 747,930.62 748,950.97 750,460.91 751,490.26 751,856.15
Y coordinate discharge point (m) 4,268,862.58 4,269,270.22 4,269,153.91 4,269,128.94 4,269,074.61
Curve number 54.12 58.92 59.40 64.92 46.67
Runoff threshold 42.38 34.86 34.18 27.02 57.14
Main water ow length (km) 6.30 3.34 4.48 11.94 6.38
Difference in maximum height of the main water ow (m) 332 179 190 798 184
Time of concentration (h) 2.13 1.31 1.71 3.30 2.41
Table 6
Calculated outlet ow for all basins and for all return periods.
Q
output
(m
3
/s)
Basin name T ¼50 years T ¼100 years T ¼500 years
Murtal 11 15.4 27.8
Xix´
o 4.3 5.6 9.3
Aigüera 13.5 18 29.9
Lliriet 30.4 38.4 58.9
Barcel´
o 8.2 13.1 28.2
Table 7
Dimensions and slopes of the pipes when the basins enter the urban area of Benidorm.
Dimensions (mm) Area (m
2
) Slope
Murtal Ø4500 GS → 2Ø600 MC 15.9 → 0.6 1.8% → 2.9%
Xix´
o 4ØØ1500x2000 MC 12 5%
Aigüera ØØ2300x2600 MC 6 2.1%
Lliriet 2ØØ1850x2450 MC 9.1 0.6%
Barcel´
o ØØ1700x4450 MC 7.6 0.3%
GS → Galvanized steel
MC → Mass Concrete
ØØ → Rectangle frame
Table 8
Water level produced as a result of the lack of capacity of the drainage pipes.
Water level (T ¼50 a˜
nos) (m) Water level (T ¼100 a˜
nos) (m) Water level (T ¼500 a˜
nos) (m)
Murtal 0.18 0.23 0.34
Lliriet – – 0.31
Fig. 8. Future situation with the dune protecting the promenade from ooding.
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Urban Climate 53 (2024) 101816
12
achieving greater stability and minimizing the volume of sand required. Below is a 3D reconstruction of the urban dune of Benidorm
(Fig. 9).
3.4.2. Drainage network maintenance
In case of ooding events, despite the fact that the pipes full hydraulically, it is necessary to review the surface water collection
system and properly direct it to the rainwater pipe network. For this, it is recommended to improve the design of inlets, increase their
number and distribution along the urban road.
The Benidorm sewage system has a powerful network of large pipes for the evacuation of rainwater. However, rainfall in the study
area frequently generates ooding in some localized points of the city, as has been observed through the images and videos collected in
the press and social networks (Fig. 2). There are points in the drainage system that prevent all the precipitated water from being
collected, even with precipitation that is signicantly lower than the design rainfall obtained in this section. Improving the surface
water collection system of the city, which currently consists of 6000 storm drains, would make the most of the hydraulic capacity of the
existing collectors, especially in Barcel´
o basin.
3.4.3. Channelling of the ravines that ows into the beach
A more efcient storm drain system would increase the peak ow at the drainage point of the basin, causing greater beach erosion
and damage to urban infrastructure. Therefore, solutions must be taken to reduce these effects.
The implementation of a natural channelling solution for the nal section of the ravines that drain to the beach is proposed
(Fig. 10). Sand defence dikes will be placed on both sides of the drainage in order to channel the ow and prevent other areas of the
beach from being eroded, as well as preventing the unbalance of access walkways to the beach and footbaths. These dune ridges, which
will be located perpendicular to the shoreline, will have the same technical characteristics as the urban dune proposed in the Section
3.4.1. Urban dune for defence against waves.
On the other hand, a cobblestone will be designed at the exit of the ravines that drain to the beach in order to reduce the speed of the
ow of the discharged water and with it, the erosion of the beach berm. It will be necessary to lower the ground level to favour the
outow of water towards the sea. The cobblestone will only be exposed when the drainage of the rain runoff occurs, and must be
covered by a layer of sand of the existing size on the beach, thus facilitating the passage of bathers in safety conditions.
Finally, to avoid the concatenation of simultaneous ooding events of uvial and maritime origin, the design of a vertical wall in
the upper part of the drains is proposed. This wall will be equipped with a bullnose to contain the overow that may be produced by the
reection of the waves (Fig. 10c). In times of atmospheric stability, this infrastructure will serve as a long bench for the enjoyment of
citizens (Fig. 10d).
4. Discussion
Like any coastal place in the world, Benidorm is no exception to the changes that occur in its territory over time. The city has
suffered signicant anthropogenic pressures, especially as a result of the urbanization process carried out during the 1960s, which
caused, for example, changes in land use (waterproong the land) or channelling of ravines (increased ow speed). This circumstance,
together with the construction of maritime infrastructures, such as the Port of Benidorm, causes a decrease in the contribution of
sediments to the beaches, causing their erosion (Aragon´
es et al., 2015; Toledo et al., 2022). The beaches, in addition to their tourist
importance, are elements of coastal defence, which protect all the infrastructures (buildings, urban roads…) located on their backside
from maritime storms. However, if climate change increases the storm effects, both in frequency and intensity, they will accelerate the
eroding process of the beaches.
Fig. 9. (a) Urban dune at low points of the promenade, (b) Urban dune where the height of the promenade is sufcient to contain mari-
time ooding,
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Urban Climate 53 (2024) 101816
13
In this study, the evolution of waves and sea storms in each of the study beaches has been analysed. The protection offered by Sierra
Helada protects the study beaches from easterly storms. However, they present a high risk of deterioration compared to storms coming
from the south (Tros De Ilarduya and Fern´
andez, 2013). These are precisely the waves that occur most frequently and have increased
their intensity the most during the last 2 periods analysed (Fig. 4). For example, in Poniente Beach, the SSW swell increased its wave
height by 44% in the 2013–2022 period compared to the 2003–2012 period (2.13 m vs. 3.06 m), while its frequency increased by 11%.
The intensication of storms in the study area, enhanced by climate change, is a pattern that is also detected in other parts of the
western Mediterranean (Amarouche et al., 2020; Amarouche and Akpinar, 2021). Despite the fact that the average duration of the
storm remains stable or has even decreased in recent years, a greater increase in wave height has been detected, marking a maximum of
3.18 m at Poniente Beach and 2.59 m at Levante Beach (average of the previous 5 years), both in 2019 (Fig. 5). This exceptional
situation of maximum regime will be the one that denes the design criteria when proposing solutions to contain the waves and protect
the promenade. Therefore, it will be necessary to monitor the evolution of the parameters that dene storms (average duration, SPI,
H
max
, direction…) and thus obtain trends that allow us to know their behaviour over time.
The irregularity of rainfall is a feature that identies the Mediterranean climate, but this has worsened in recent years, maximizing
the extremes (Benabdelouahab et al., 2020; Olcina Cantos, 2021). Two of the three years with the highest number of days with daily
rainfall >30 mm have occurred in the last 5 years, with a total of 6 days per year (Fig. 6). On the other hand, in the period 2010–2014
there have not been years in which this type of precipitation has occurred on more than one occasion. In the same way, 7 of the 8 years
in which the maximum daily precipitation exceeds 75 mm have occurred since 1996. During the last few years, changes have been
detected in the atmospheric circulation that have caused a greater number of detachments of ‘cold drop’, assuming a greater increase in
the days with the greatest amount of rain and torrentiality (Olcina, 2020). However, these changes in the jet-stream also increase the
possibility of generating more frequent dry periods over time (Morote et al., 2022). This irregularity in the climate is also observed
within the annual cycle. The maximum rainfall usually tends to be concentrated during the autumn season in the study area (Fig. 6).
However, given the current climate change context, with higher sea temperatures and changes in atmospheric patterns, it is likely that
in the future these intense precipitations will also extend beyond autumn, as occurred on 19 January 2017 (winter), when a daily
precipitation of 88 mm occurred.
On the other hand, the analysis of the maximum daily intensity of precipitation will give us clues about what type of rain is
occurring in each case. Comparing the precipitation and maximum intensity gures, it is striking how winter presents higher daily
maximum precipitation than spring and close to autumn in many cases. However, the intensities are clearly lower (Fig. 6f). This fact is
Fig. 10. (a) General view of the intervention area in Levante Beach, (b) Sand dikes for channelling the ravines, (c) Design of the bullnose seen from
the outlet of the drainage pipes, (d) Design of the long bench equipped of a bullnose on the seafront.
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Urban Climate 53 (2024) 101816
14
a consequence of the different genesis that exists behind the rainy episodes in each season of the year. During winter, the presence of
precipitation events linked to weather fronts is more common, with a greater magnitude both in the temporal and spatial framework
(Pe˜
na-Angulo et al., 2020). In these cases, the maximum intensities are not excessive and can rarely exceed 50 mm/h, but the total
accumulated precipitations can be, and the presence of daily accumulated values >60 mm is usual. At the other extreme, precipitation
events are linked to convective weather phenomena. These phenomena are much more frequent at the end of summer, when there is a
context with a high moisture load (as a consequence of the evaporation produced during the summer period), their spatial extension is
usually much smaller compared to weather front processes, and the maximum intensities produced can reach very high values (around
100 mm/h) and present extraordinary spatial heterogeneity, with totally different maximum data at very close points (Maier et al.,
2020; Peleg et al., 2018). This last type of rain is the one that commonly causes problems in the rainwater drainage system of cities,
causing ooding and increasing erosion in ravines and on beaches, such as the one that occurred on 18 September 2022 in Levante
Beach, Benidorm (Fig. 2).
Throughout this study, different solutions have been recommended to deal with the problems of beach erosion and ooding on the
shoreline. The construction of a sand dune as a protection element is a solution that has already been proposed in other parts of the
world (Rivillas-Ospina et al., 2020; van der Spek et al., 2020). However, the design of a vegetated urban dune is a novel alternative
applicable to cities with a risk of coastal ooding in the vicinity of their promenade. The dissipative power of the waves that the dune
vegetation possesses would decrease its speed, reducing its erosive capacity (Feagin et al., 2019; Maiolo et al., 2020), in addition to
naturalizing the area. The design of the dune must be such that it allows a climate of harmony with the environment in which it is
located, but also that it is compatible with the recreational activities that take place around it. The dune ridge must have a sufcient
height to contain, or at least limit, the overow of the waves to its back (Fig. 8), but also to allow a direct view of the beach from the
promenade, given the importance of this ecosystem in the city (Fig. 9). The use of 2 sizes of sand is due, on the one hand, to the ease of
drainage from the interior of the dune to the sides, and, on the other hand, to the low availability of marine sediment deposits for the
extraction of sand, generating environmental problems with it (Dan Gavriletea, 2017).
The Benidorm rainwater pipe system is sufcient to evacuate the outlet ows that occur in the ravines that cross the city in most of
the cases studied (Table 6). Despite this, ood events continue to occur in certain areas with lower than design rainfall. The continuous
oods of uvial origin that occur in Benidorm are caused by an insufcient storm drain network, this being a common problem in cities
(Nanía-Escobar et al., 2006; Othman et al., 2015). It is recommended to improve the design of the storm drains, increasing their
number and distribution. In the latter case, it is also proposed to integrate high-capacity collection elements into the urban landscape
(Campisano et al., 2017; Morote, 2017), without ruling out the possibility that water can circulate in a timely manner on the surface.
Far from being an impediment, this alternative should be understood as an opportunity to create spaces that can be ood-prone linear
green areas, that is, infrastructures that allow recreation for people and, in turn, the transit of water during ood events. Some ex-
amples can be found in the Marjal Park in the city of Alicante; or without going any further, in the last section of the Lliriet ravine, once
it ends at Levante Beach (Fig. 11).
The images of ooding, both on the beach and inland, and of the damage caused to the shoreline will be repeated more frequently in
the current and future context of climate change (Olcina Cantos, 2021; Olcina, 2020). This type of damage will limit the proper
functioning of the city, reducing its resilience against future storms. That is why the Public Administrations must design action plans to
limit this damage, especially during the prevention stage. Throughout this work, several alternatives have been described to deal with
the consequences that these storms may cause. These solutions must be based on nature, that is, they must be in harmony with the
ecosystem in which they are going to be implemented, and they must also be sustainable over time (Castelle et al., 2019; Kabisch et al.,
2017). Here the particular case of the city of Benidorm (Spain) is presented, with some beaches of natural origin, but in a fully ur-
banized environment. Despite the local focus, the solution recommended here is fully exportable to any part of the world, especially to
those cities whose main economic activity (tourism) depends on the adequate maintenance of the beaches and the shoreline.
Fig. 11. High-capacity rainwater harvesting elements integrated into the urban environment, (a) Marjal Park in Alicante, (b) the last section of
Lliriet Ravine in Benidorm.
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Urban Climate 53 (2024) 101816
15
5. Conclusions
The coastal regions of the world are part of the most vulnerable ecosystems that exist. The strong urbanization of the territory and
extreme weather events driven by climate change put the normal functioning of the cities in these areas at risk. In this study, the danger
of coastal and river ooding in the city of Benidorm (Spain) has been analysed, and solutions have been proposed to minimize it,
increasing its resilience.
The climate in Benidorm has undergone signicant changes. The average duration of maritime storms has remained stable over
time. However, these have intensied, with wave heights 60% higher than the previous 10 years. Furthermore, the behaviour of
rainfall has worsened, maximizing the extremes: 7 of the 8 years in which the maximum daily rainfall exceeds 75 mm have occurred
since 1996.
Thus, the design of a vegetated urban dune on the backshore of the beach is proposed to contain the ood level of 3 m, minimizing
overows on the promenade. To protect the beach from erosion caused by river ooding, the implementation of vegetated sand dikes is
proposed to channel the water outow from the ravines. A cobblestone is laid out to reduce the speed of the ow and the promenade is
provided with a bullnose to limit the combined action of uvial and coastal ooding. In Benidorm there is a problem of collecting
rainwater that does not allow the total capacity of the pipes that drain to the beach to be used. In addition to increasing the number and
distribution of storm drain, it is planned to integrate high-capacity elements into the urban landscape, such as oodable green spaces.
Author contribution statement
Conceptualization: L. Aragon´
es conceived the presented idea, the formulation and the general goals and aims of the research.
Methodology: I. Toledo designed the methodology of this reseach.
Software: I. Toledo was responsible for managing the software used.
Validation: I. Toledo and I. L´
opez took care of the reproducibility of results.
Investigation: I. Toledo carried out the statistical analysis.
Resources: I. Toledo collected data from Aemet and Puertos del Estado website.
Writing - Original Draft: I. Toledo.
Writing - Review & Editing: I. L´
opez, J. Olcina and L. Aragon´
es.
Visualization: I. Toledo.
Supervision: J.I. Pag´
an.
Declaration of competing interest
The authors declare that they have no known competing nancial interests or personal relationships that could have appeared to
inuence the work reported in this paper.
Data availability
No data was used for the research described in the article.
Acknowledgments
The authors thank AEMET, Instituto Geogr´
aco Nacional (IGN) and Puertos del Estado for facilitating access to their data.
This work has been funded by the European Commission through the project Smart Control of the Climate Resilience in European
Coastal Cities (SCORE).
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