**2. Materials and methods**

#### **2.1 Study area**

This assessment covered the whole of Somalia (**Figure 1**). The country extends from the equator to the north of Gulf of Aden. It is one of the Horn of African countries and borders Kenya and Ethiopia to the west, Indian Ocean to the east and Djibouti to the northwest. The country's population was estimated at 14.74 million in 2017 by the World Bank. The population increased from 8,872,254 in 2000 to 15,442,905 in 2019 (**Figure 2**). This is equivalent to an increase of 6,570,651 (74.06%).

#### **Figure 1.**

*Map of the study area. Somalia is part of the horn of Africa and the eastern-most country in the African continent.*

**Figure 2.**

*Population variations between 2000 and 2019 (source: The World Bank database).*

Somalia covers a total land area of 637,660 km2 most of which may be classified as either arid or semi arid. Its administrative and commercial capital is Mogadishu. According to [30], at least 50% of the country's economy is dependent on pastoralism.

Topographically, the country is divided into several physiographic zones. The northern part of the country receives high annual temperatures and forms the driest zone. Plateaus cover the central and southern parts bordering the coastline. The two main perennial rivers (Webe Shebele and Jubba), whose source is Ethiopian plateau, are found in southern Somalia. Between these two rivers is a highly productive plain which is occasionally affected by floods. Somalia's coastline covers 3,025 kilometers and is the longest in Africa.

Generally, the country is hot throughout the year with an annual average day temperature of 27°C. This is attributed to country's close proximity to the equator and the low rainfall amounts received. The northern parts experience highest temperatures of 45°C around Karkaar Mountain in summer while the lowest temperatures are experienced to the south of Somalia along the coastline largely due to the effect of the sea breeze. Somalia received little amount of rainfall throughout the study period with an average of 20.96 mm per year. The lowest (18.5 mm) and highest (25.6 mm) amount of rainfall was received in 2010 and 2019 respectively. Although there is a generally upward trend in the amounts of rainfall received over the years from 2000 to 2019, the total annual amount of rainfall is still small as shown in **Figure 3**.

Somalia has two climate zones, arid and semiarid zone. The semiarid zone covers the northern and southwest parts of the country and the arid zone covers the central and the northernmost parts [31]. The semiarid zone receives medium rainfall and is suitable for rain fed agriculture whereas the arid zones receiving low rainfall are preferably used for pastoralism. The most common tree species is *Acacia commiphora* [32] which covers about 50% of southern Somalia. Others include: Apple ring acacia (*Acacia albida*), Egyptian thorn (*Acacia nilotica*), Gum arabic (*Acacia senegal*), Umbrella thorn (*Acacia tortilis*), soapberry tree (*Balanites aegyptiaca*), Myrrh tree (*Commiphora myrrah*), common tug tree (*Conocarpus lancifolius*), Yihib nut tree (*Cordeauxia edulis*), Spiny desert tree (*Terminalia spinosa*), Pencil cedar (*Juniperus excels*), Tamarisk (*Tamaria aphylla*) and Tamarind (*Tamarindus indica*).

#### **2.2 Dataset and the analysis platform**

This study adopted the word wide forest data that was developed by Hansen [4]. The dataset was created from the annual 30 m resolution Landsat data. The *Remote Sensing Based Quantification of Forest Cover Change in Somalia for the Period… DOI: http://dx.doi.org/10.5772/intechopen.99365*

**Figure 3.** *Annual rainfall trends from 2000 to 2019 (source: The World Bank database).*

products being global forest cover at year 2000 and annual forest cover loss and gain. In this dataset, vegetation above 5 m in height is defined as trees. Trees are expressed as '2000 Percent Tree Cover' percentage per output plot cell. Forest Cover Loss is defined as a change from forest to non-forest status in the period 2000–2019. Forest gain is defined as the opposite of loss, that is, the change in non-forest to forest in the period 2000–2019.

Google Earth Engine (GEE) enables cloud computing processing of Landsat images through its online system. This helps to navigate the challenge of processing Landsat images at global scale which is normally expensive in terms of time and resources [4]. Landsat images are ideal for monitoring environmental changes at local scale because of the 30 m spatial resolution [33]. Since 1972, Landsat have been used for land cover change analysis [34–37]. Due to its ability to analyze large volumes of remotely sensed datasets, GEE was preferably selected for Landsat data analysis in this study. For ease and fast workflow, a web-based JavaScript API was developed in the GEE Code Editor Feature.
