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SJIF IMPACT FACTOR: 5.42 CRDEEP Journals International Journal of Basic and Applied Sciences Tareefa S. Alsumaiti Vol. 7. No. 1 ISSN: 2277-1921

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International Journal of Basic and Applied Sciences. Vol. 7 No. 1. 2017. Pp. 57-61 ©Copyright by CRDEEP Journals. All Rights Reserved. Full length Research Paper Mapping Changes in Mangrove Forests and the Future Impacts of Sea

Level Rise in Abu Dhabi, United Arab Emirates

Tareefa S. Alsumaiti Geography and Urban Planning Department, College of Humanities and Social Sciences, United Arab Emirates University, P.O. Box 15551, Al Ain, United Arab Emirates.

Introduction

Mangroves are littoral trees in the sheltered coastlines within the intertidal zone of tropical and subtropical regions. Mangrove forests

provide a critical habitat and breeding grounds for marine and terrestrial animals. They prevent the coastline erosion caused by waves

and ocean currents. They are considered as a major source of wood and fuel. They also play an essential role in supporting fisheries,

which are the main income source for many coastal inhabitants. Mangrove forests also play an important role in reducing carbon

emissions and lowering the amount of pollution in the coastal environment (Alsumaiti et al., 2017; McLeod et al., 2006; Tamimi,

1999). In addition, they provide a beautiful view of the shores. The fauna and flora associated with the mangrove forests provide

tourism, recreational, educational, and research opportunities, all of which may bring significant income into the economy of many

coastal zones (Ashton & Macintosh, 2002).

Main threats to mangrove ecosystems include trimming and clearing of forests for agricultural, urban, or industrial expansion;

hydrological alterations; toxic man-made chemicals; and eutrophication. In many countries with mangroves, much of the human

population resides in the coastal zones, and their activities impact the integrity of mangrove forests negatively (Alsumaiti et al., 2017).

In addition, various studies have proved that recent changes on climate conditions are also one of the major threats to mangrove

forests. Global warming has significant effects on the growth of mangroves and their areal extent. The primary climate factors that

affect mangrove forests include changes in temperature, precipitation, and sea level. In fact, sea level rise may be the greatest threat to

mangroves. Mangroves cannot survive if water completely covers their aerial roots that provide oxygen for respiration. Mangrove

sediment surface elevations will also be affected with the rising of sea level. (Gilman et al., 2008).

Intergovernmental Panel on Climate Change (IPCC) projected global sea level to rise by 0.09 to 0.88m between 1990 and 2100. The

main two factors causing the volume of oceans water in the world to change are: 1) the thermal expansion of seawater, and 2) the

transfer of ice from glaciers and ice caps to oceans water (IPCC, 2014). A Review of the stratigraphic record of mangrove ecosystems

Article history Received: 03-12-2017 Revised: 05-12-2017 Accepted: 06-12-2017

Corresponding Author: Tareefa S. Alsumaiti Geography and Urban Planning Department, College of Humanities and Social Sciences, United Arab Emirates University, P.O. Box 15551, Al Ain, United Arab Emirates.

Abstract In the last 40 years, there were major changes in the growth and spatial distribution of mangrove forests in Abu Dhabi, United Arab Emirates (UAE). In this study, the changes in mangroves areas were detected using geographic information systems and remote sensing techniques. An Unsupervised Classification using an ISODATA algorithm was employed to Landsat images acquired in 1972, 1989, 2000 and 2014. The classification results detect that mangrove area decreased about 1,018 hectares (32.5%) between 1972 and 1989, while the forests decreased about 394 hectares (17%) from 1989 to 2000. However, between 2000 and 2014 the mangrove area increased about 622 hectares (26%). The visual interpretation of the images shows that urban expansion plays a major role in mangrove reduction from 1972 to 2000. Whereas, the increase after the year 2000 is mainly due to the government efforts to restore and plant new mangroves. Furthermore, a model using ArcGIS Model Builder was created to detect the effect of sea level rise on mangrove forests in Abu Dhabi. This model outputs indicate that by 1 meter see level rise, the current mangrove area (2,456 hectares) will be reduced by 20% and will reach to 1,968 hectares. By 2 meters sea level rise the current mangrove area will be reduced by 67% and will reach to 827 hectares. By 3 meters sea level rise the current mangrove area will be reduced by 95% and will reach to 140 hectares finally, 100% of mangrove forests will extinct if sea level increased above 3 meters. This study provides valuable information about past, current, and future changes in mangrove forests of Abu Dhabi.

Keywords: Mangroves; Areal Extent; Sea Level Rise; Impacts; Abu Dhabi.

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during sea level changes of the Holocene shows that mangroves in low land can keep up with a maximum of 12cm of sea level rise per

100 years. While mangroves in high land can keep up with a maximum 25cm of sea level rise per 100 years (Blasco & Saenger,1996).

Several studies have focused on the effects of natural and human-induced changes on mangroves, and how to restore and rehabilitate

the valuable mangrove ecosystems (Wilkie &, Fortune, 2003; Yagoub & Kolan, 2006; Vistro, 2010; Yusuf et al., 2017). However, the

main purposes of this study are to use geographic information systems and remote sensing techniques to detect the major changes on

the growth and the areal extent of mangrove forests in Abu Dhabi from 1972 to 2014; to determine the causes of these changes; and to

predict future changes on these forests due to sea level rise.

Materials and Methods

Site Description

The mangrove forests cover thousands of hectares of land along the United Arab Emirates’ shoreline. The forests occur naturally

along several eastern coastal areas and islands in the country. The UAE eastern coast stretches for more than 400 Miles along the

southern shore of the Arabian Gulf. Abu Dhabi City is located at approximately 23°00' north latitude and 52°00' east longitude

(Embaby, 1993). More than 70% of the Mangrove forests in UAE are present along the near shore islands and lagoons of Abu Dhabi

covering thousands of hectares (Anwahi, 1994]. In this paper, mangrove forests located near several islands were studied, including

Futaisi, Saadiyat, Al Reem, Bisrat Fahid, Sas Al Nakhal and the islands of Khor Faridah. The location of the study area is shown in

Figure 1. Although there are more than 50 species of mangroves found worldwide, the only mangrove species that grows widely in

Abu Dhabi is Avicennia Marina or grey mangrove. The average height of the mangroves trees found in Abu Dhabi is about three

meters (Alsumaiti, 2014).

Fig1: The location of the study area.

Data Acquisition

The satellite datasets used in this study were a set of Landsat MSS images, Landsat TM images, Landsat ETM+, and Landsat 8

acquired on September 30th

1972, August 28th

1989, August 23rd

2000, November 10th

2014 respectively. The satellite datasets were

downloaded from the Earth Science Data Interface (ESDI) of the Global Land Cover Facility (GLCF) (ESDI-GLCF, 2016) which

provides public access to Landsat and other remote sensor data and derivatives. Only the visible and the near-infrared bands were

used in this research to detect changes in mangrove forests after rectification to a Universal Transverse Mercator (UTM) Projection

(WGS 84, zone 40N). A subset images of the area of interest were created using ERDAS Imagine software. The Landsat 8, TM and

ETM+ bands have a spatial resolution of 30 meters, while Landsat MSS has a spatial resolution of 60 meters.

The digital elevation model of Abu Dhabi (23°N, 52°E) was downloaded from the ASTER Global Digital Elevation Model (ASTER

GDEM). The DEM was used to map and to detect the future changes of mangrove forests due to sea level rises [ASTER GDEM,

2016].

Data Analysis

Before classification composite images were created from Landsat bands, then the images were masked to include only areas where

mangrove trees area likely to occur. Masking mangrove areas increases the overall accuracy of the classification, reduce data volume

and the amount of land cover types and spectral variation (Held et al., 2003).

Using an unsupervised classification in ArcMap software, an Iterative Self-Organizing Data Analysis Techniques (ISODATA)

algorithm (Jensen, 2005) was applied to the Landsat images of different periods to detect the changes in mangrove area of Abu Dhabi.

Three classes were created; 1) mangrove, 2) terrestrial non-mangrove, and 3) water. Using the results of the classification, the total

area of mangroves was calculated for the years 1972, 1989, 2000, and 2014 as shown in Figure 2. An accuracy assessment was




conducted to the four images to ensure that no mangrove areas were missed. Additionally, Landsat images were visually interpreted to

study these changes as shown in Figure 3.

Furthermore, using ASTER Global Digital Elevation Model (GDEM) and ArcGIS software, a sea level model was created to detect

the mangrove forests that are susceptible to sea level rises of one to four meters. The model classified DEM to map 1, 2 ,3 and 4

meters sea level rises by using 4 conditions. The four outputs of the DEM were combined to one raster layer using mosaic to new

raster function. The mosaic output and the classification results of mangroves in year 2014 were both converted to a vector layer using

raster to polygon function, and intersected together to calculate total mangrove forests that are susceptible to extinct due to sea level

rises. However, the accuracy of mapping the coastal areas that are potentially inundated by rising sea levels depends on the accuracy

of current mean sea level measurements as well as the accuracy of models that project sea level rises. The model outputs are shown in

Figure 4.

Fig 2: The outputs of classifying Landsat images.

Fig 3: Satellite images show changes in mangrove forests in Al Reem Island due to urban development.

Results

The results of the unsupervised classification show that the total area of mangrove forests in Abu Dhabi was 3,226 hectares in 1972,

2,208 hectares in 1989, 1834 hectares in 2000, and 2,456 hectares in 2014. This means that mangrove area decreased about 1,018

hectares (32.5%) between 1972 and 1989, while the forests decreased about 394 hectares (17%) from 1989 to 2000. However,

between 2000 and 2014 the mangrove area increased about 622 hectares (26%) as shown in Figure 5. Visually interpreted satellite

images of the area illustrate that the great urban and industrial expansion has the essential role in this decrease between 1972 to 2000.

For example, thousands of hectares of mangrove forests on Al Reem Island totally disappeared and were replaced by urban features as

previously shown in Figure 3. The increase of the area of mangrove after 2000 to 2014 is mainly due to the government efforts to

restore and plant new mangroves around Aljubail, Zeraa, and Saadiyat islands.

The results of the sea level rise model indicate that the coasts of Abu Dhabi will be affected by sea level rise associated with climate

change as shown in Figure 6. The ArcGIS model outputs show that by 1 meter see level rise, the current mangrove area (2,456

hectares) will be reduced by 20% and will reach to1,968 hectares. By 2 meters sea level rise the current mangrove area will be reduced




by 67% and will reach to 827 hectares. By 3 meters sea level rise the current mangrove area will be reduced by 95% and will reach to

140 hectares finally, 100% of mangrove forests will be extinct if sea level increased to 4 meters.

Fig 4: The model outputs show projections of inundation area in Abu Dhabi due to sea level rises of 1, 2, 3 and 4meters. The images

combined to one mosaic image showing the 4 classes.

Fig 5: Unsupervised classification results show the changes of mangrove area in Abu Dhabi from 1972 to 2014.

Fig 6: Total area of mangroves that are susceptible to extinct due to sea level rises of 1, 2, 3 and 4 meters.




Discussion

Mangrove forests are one of the most vital ecosystems in Abu Dhabi. Yet, there were major changes in their areal extent and spatial

distribution along the coastlines. This study used geographic information systems and remote sensing techniques to map the areal

changes in mangrove forests in Abu Dhabi for the following years; 1972, 1989, 2000, and 2014. The results indicated that a 49.5% of

mangrove areas decreased between the years of 1972 to 2000, mainly due to urban expansion. While between 2000 to 2014, the

mangrove areas increased by 26% due to government rehabilitation and conservation efforts. This study also indicated the impacts of

sea level rise between 1 to 4 meters in mangrove areas by creating a model using ArcGIS Model Builder. The model results estimated

that the mangrove will extinct if sea level rises over 3 meters. This poses significant risk for mangrove forests in coastal zones and

emphasizes sea level rise will have a significant impact on mangrove forests in Abu Dhabi.

Conclusion

This study provides important information about past, current, and future changes in mangrove forests of Abu Dhabi. In the past

century, almost half of the total area of Abu Dhabi mangroves was wiped off due to urban and industrial projects. However, by the

beginning of the twenty first century, Abu Dhabi government starts to implement mangrove restoration and rehabilitation projects; and

increased the community awareness related to the ecological and environmental benefits of this valuable ecosystem. This study also

illustrates that sea level rise is the main future threat to mangrove ecosystems in Abu Dhabi through sediment erosion and inundation

stress. The measures of coastal accretion and erosion can change in the shoreline dynamics and modify the coastal area for mangroves.

Thus, the most important aspect in analyzing the impacts of sea level rise is the detailed monitoring and various measures of these

changes. The information of shoreline changes can help in predicting future changes. It can also help in preparing the management and

adaptation policies for sea level rise.

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