Land use transformation by urban informal settlements and ecosystem impact

Abstract

The rapid expansion of informal settlements poses significant challenges to urban ecosystems and their services, a pressing issue that this study addresses by examining its impacts in Addis Ababa. This study delves into the impact of informal settlements on ecosystem services in Addis Ababa, comparing them with formal settlements. Utilizing geographic information systems (GIS) and remote sensing, it employed Landsat imagery, aerial photography, and base maps to track spatiotemporal changes and analyze trends. Through a GIS overlay approach, informal settlements and associated land use changes were identified, while the benefit transfer method assessed ecosystem service values. The findings revealed a significant increase in informal settlements on the city’s outskirts, expanding from 77 ha in 2009 (2% of the total area) to 765.6 ha in 2023 (21% of the total area). Nearly half (48.5%) of these informal settlements were established on previously natural land covers through encroachment. The research highlighted the ongoing conversion of agricultural land, forests, and urban green spaces into informal settlements, particularly on the city’s outskirts, leading to significant encroachment on these areas. This transformation caused an annual loss of $1,665,033.7 in ecosystem services from 2009 to 2023. Significant impacts were identified on food production, climate regulation, and habitat ecosystem services. Overall, the annual loss in ecosystem services due to land use changes amounted to $1,933,320.08. Informal settlements accounted for 86.1% of this total loss, highlighting the urgent need for targeted interventions to mitigate their disproportionate effects on ecosystem services. The study underscores the urgency of addressing the impact of informal settlements on ecosystem services through effective urban planning, sustainable land management practices, prevention of encroachment on natural land covers, and promotion of sustainable ecosystem management and utilization.

Introduction

Land use and land cover (LULC) encompasses the natural and artificial features of the Earth’s surface, including water bodies, vegetation, soil, and built structures, alongside human interventions (Guida Johnson and Zuleta 2013; Patel et al. 2019). Changes in land cover entail modifications to these surface characteristics, while alterations in land use relate to human activities shaping the landscape (Patel et al. 2019). LULC change is a global phenomenon influenced by diverse socio-economic and environmental factors. Globally, rapid urbanization has profoundly reshaped land cover patterns on which three-quarters of the earth’s land surface has been altered by humans with in the last millennium (Winkler et al. 2021). In Africa, notable changes in land use and land cover (LULC) are primarily propelled by population growth and the consequent demand for resources, leading to the loss of vegetation cover, soil erosion, and declining agricultural yields (Assede et al. 2023). Similarly in Ethiopia, LULC change is exacerbated by population growth and urbanization (Mezgebo 2021). In Addis Ababa, Ethiopia’s capital city, rapid urbanization, and informal settlement growth are significant contributors to LULC change, leading to the conversion of natural land covers into built-up areas and informal settlements (Adegun 2017; Tufa 2022; Woldegerima et al. 2017a).

Informal settlements are areas built without abiding by relevant rules (Collier et al. 2018), permission (Nassar and Elsayed 2018), and planning (UN-Habitat 2015). They lack legal titles that occur on public land (Montoya-Tangarife et al. 2017) and are considered illegal or squatter settlements (Soyinka and Siu 2018). Around one billion people, or one-seventh of the global population, live in informal settlements, the most common form of urbanization worldwide (Samper et al. 2020), and one-third of the world’s urban population resides in slums (UN‐Habitat 2019). Ethiopia’s urban areas are characterized by unofficial settlement expansion and legal land reform failure, with cities built without thorough land use plans, ignoring capacity, and anticipated informal settlement expansion (Fetene and Worku 2013). The growth of informal settlements negatively impacts the ecosystem, and results in the loss of numerous natural resources (Bulti and Sori 2017), and the rise in urban land demand and density has also led to the loss of natural resources (Wang et al. 2022). As to Addis Ababa City Directive No. 17/2014, settlements established before 2005 and captured in the aerial photograph of 2005, referred to as the “line map” of 2005, must possess title documents and undergo regularization. On the other hand, settlements built after 2005 that lack title deeds are classified as informal settlements. Furthermore, the UN-HABITAT classification criteria were used on which formal settlements possess legal recognition and secure land tenure, comply with official urban planning and zoning regulations, and residents hold legal land titles, building permits, and documentation. In contrast, informal settlements lack legal recognition and secure land tenure, develop without adherence to official urban planning and zoning regulations, and residents do not have legal land titles, building permits, or documentation (UN-Habitat 2022).

Ecosystem services are the natural resources and circumstances that enable ecosystems and ecological processes to offer humans commodities and services necessary for survival (Costanza et al. 2017; Wang et al. 2019). Ecosystems provide both tangible and intangible services that improve human well-being and provide essential resources for all living organisms (Talukdar et al. 2020). They also encompass various ecological services, both financial and non-financial, crucial for the well-being of urban populations(Chen et al. 2021; Das and Das 2019). The benefits can directly impact individuals through regulation, provision, and cultural services, or indirectly through supporting services (Costanza et al. 2017) Ecosystems sustain human survival, yet human activities have significantly altered them in recent decades (Chen et al. 2019). Numerous anthropogenic and natural factors like land use and land cover change (Akber et al. 2018) and urbanization (Das and Das 2019) have contributed to changes in land use and land cover, which have a considerable impact on ecosystems (Talukdar et al. 2020). Accelerated economic development, industrialization, and urbanization have led to an increase in the prevalence of anthropogenic environmental disruptions, including changes in land use and climate disruption (Liu et al. 2019a; Schröter et al. 2018; Zhao et al. 2018). As urbanization continues, the conversion of ecological lands, including forests, grasslands, wetlands, and water bodies, into urban infrastructure poses significant challenges to conserving the urban environment and ecology (Arowolo et al. 2018; Das and Das 2019). This has significant effects on the supply and distribution of essential ecosystem services (Wu and Fan 2022). Furthermore, several studies found that the encroachment of forest land (Dai et al. 2021; Markos et al. 2018; Msofe et al. 2020), agriculture (Li et al. 2021; Markos et al. 2018), shrublands, and grasslands (Zhou et al. 2018) by built-up areas into altered land uses hurt the ecosystem service values. Land use change is frequent in Addis Ababa, often resulting in the expansion of built-up areas at the expense of natural land covers such as forests (Abebe and Megento 2016), agricultural land (Tufa 2022), and urban green areas (Woldegerima et al. 2017b).

Informal settlements, commonly situated in ecologically sensitive and biodiversity-rich zones of urban areas, exert a notable impact on green spaces and natural ecosystems (Adegun 2017). Unfortunately, the misuse and reckless usage of natural resources endanger the welfare of coming generations (Wu et al. 2019). Policymakers need to examine the influence of informal settlements on land use and ecosystem services to address regulatory concerns. Ecosystem service valuation provides a comprehensive understanding of these changes (Kusi et al. 2023). Understanding the importance of ecosystem services at the local and national levels can reduce trade-offs between them (Aryal et al. 2021), which is crucial because the deterioration of all types of ecosystem services globally has been primarily initiated by changes in land use (Chen et al. 2019). Moreover, the efficient collection of spatial and temporal data on the land surface by remote sensing enables prompt identification of spatiotemporal changes in the local eco-environment (Chen et al. 2023; Indrawati et al. 2020; Wang et al. 2021), and the quantification of ecosystem service values in terms of money can sufficiently gauge the advantages that come from ecosystems (Costanza et al. 2014). This research applies a benefit transfer approach developed by (Costanza et al. 2014) to evaluate changes in ecosystem services arising from land use transformations caused by informal settlements.

There has been a long history of research on land use and land cover change in Ethiopia (Gedefaw et al. 2020; Gessesse and Bewket 2014; Zeleke and Hurni 2001). However, little has been done to monitor the spatiotemporal changes in informal settlements in metropolitan areas, with only a few recent works (Abebe et al. 2019). The former study delineated informal settlements, categorizing them as built and non-built areas. In contrast, our research employs a GIS overlay technique with the line map of 2005, a base map of 2023, and satellite images from 2009, 2011, and 2023. Furthermore, we assess the impact of informal settlements on ecosystem services. In addition, there have been notable changes in land cover and use in Ethiopia, which have had an impact on ecosystems. There have only been a few recent studies on urban settings (Degefu et al. 2021; Woldegerima et al. 2017a), with the majority of studies in this field focusing on rural locations. However, this study looked at the spatiotemporal changes in Addis Ababa’s informal settlements and compared their dynamics and effects on ecosystem services to those of formal settlements. Urban areas exhibit greater human population densities in contrast to rural regions, resulting in heightened demand for essential ecosystem services like clean water, air purification, and recreational spaces. Grasping the impact of urban settlements on these services is pivotal for sustainable urban planning and management. Additionally, urban regions experience significant infrastructure development to accommodate the expanding population, often leading to alterations in natural landscapes. These changes can deeply affect ecosystem services. Analyzing urban settlements offers insights into how infrastructure projects influence ecosystems and strategies to mitigate adverse effects. Urban settlements embody intricate socio-ecological systems where human activities interact with natural processes. Understanding these dynamics is crucial for effectively managing ecosystem services in urban environments. Assessing the connection between ecological services and urban growth is crucial for sustainable urban development and policy (Das and Das 2019). Thus, integrating ecosystem services into land use management and policymaking can be aided by understanding the impacts of changes in land cover and use brought about by informal settlements on ecosystem services and how to balance them.

The study assesses how informal settlements affect local ecosystem services, providing insights for city administrators and urban planners. It provides historical analysis for improved ecosystem and land management policies. It addresses the knowledge gap regarding the monetary value of natural capital and offers new perspectives on changes in ecosystem service value due to informal settlements. From a methodological standpoint, it can be valuable to distinguish between informal and formal settlements in the research areas using base maps of the city, aerial photographs, and satellite imagery. This research analyzes the impact of informal settlement-induced landscape transformations on ecosystem services in Addis Ababa and compares them with formal settlements. We looked at how informal settlements affected land usage between 2009 and 2023. The study also quantifies the total value of ecosystem services and the value of individual ecosystem functions in response to land use changes due to informal settlements. Specifically, we estimated the ecosystem service values of land cover classes in from 2009 to 2023 and linked land-use dynamics to changes in ecosystem service values. This study aims to address critical research questions concerning the impact of informal settlements on local ecosystem services in Addis Ababa. Specifically, it examines how these settlements have changed spatially and temporally from 2009 to 2023 and their impacts on ecosystem services compared to formal settlements. Additionally, the study evaluates the monetary value of the loss in ecosystem services due to the expansion of informal settlements and explores strategies to mitigate these adverse effects through sustainable urban planning and land management practices. The specific objectives of the study are (i) land use land cover changes in 2009, 2011, and 2023, (ii) informal settlements from 2009 to 2023, and (iii) ecosystem services from 2009 to 2023.

Materials and methods

Study area

Addis Ababa, Ethiopia’s capital and Africa’s diplomatic center is a rapidly growing city located at 8° 50′ 00ʺ N–9° 06′ 00ʺ N and 38° 39′ 00ʺ E–38° 55′ 00ʺ E, with an average altitude of 2380 m (Fig. 1). Yeka and Lemikura, two outlying suburbs of the city with an expansionist bent, were the study's main areas.

Fig. 1

Location Map of the study site

In 2015, the population was around 3.3 million; whereas, in 2022 the estimated population was around 4 million (Shiferraw 2022). The population is projected to reach about 6 million in 2030 (Central Statistical Agency 2013). From 1990 to 2020, Addis Ababa’s average daily minimum and maximum temperatures were 9.01 °C and 38.75 °C, respectively, with an average annual rainfall of 1255 mm. The city experiences its highest rainfall during the summer season, which occurs from June to August, while the least precipitation occurs in the winter season, spanning from December to February. The average annual temperatures in Addis Ababa range from 12 to 24 °C, with nighttime temperatures between 10 and 15 °C and daytime temperatures ranging from 20 to 24 °C. The city’s administrative hierarchy comprises the city-level, middle-level bodies (Sub city), and local bodies or districts called Weredas.

Data collection

Satellite images, field observation, and aerial photographs of 2005 (line map of the city), 2011 (line map of the city), and the 2023 base map of the city were used as data sources for identifying the formal and informal settlements and producing the land use and land cover maps of the study area. Google Earth generated ground truth points (training sites) for LULC mapping. Moreover, ecosystem service values were estimated using global ecosystem service valuation coefficients.

Satellite data acquisition

The USGS (http://earthexplorer.usgs.gov) provided the Operational Land Imager/Thermal Infrared Sensor (OLI/TIRS) of 2023 and the Enhanced Thematic Mapper Plus (ETM+) of 2009 and 2011 for the study. The World Geodetic System (WGS 84) datum is applied to pre-georeferenced the obtained Landsat data using the UTM (Universal Transverse Mercator) coordinate system. This work uses ArcGIS 10.3 to apply the supervised maximum likelihood approach for both the identification of matching biomes and the land use/land cover classification (LULC). To examine the changes in LULC and ecosystem services, all of the images were taken with very minimal cloud cover (less than 10%). Table 1 lists the data used in this investigation, along with its source and description.

Table 1 Description of Landsat images

In this study, satellite images underwent rigorous preprocessing steps to enhance their accuracy and establish a robust connection with biophysical phenomena. The preprocessing included geometric correction, georeferencing, mosaicking, and sub-setting based on the Area of Interest (AOI) using ERDAS 2011 software. Subsequently, the land area was categorized into six classes Built-up area, Agriculture, Forest, Water, urban green, and Barren area based on specific Digital Number (DN) values. Training samples for each land cover type were carefully selected, and spectral signatures were recorded to minimize confusion during classification. Supervised classification, employing the maximum likelihood algorithm, was then applied to classify Landsat photos from multiple years (2009, 2011, and 2023) for Land Use and Land Cover (LULC) assessment. The study area’s LULC types were categorized into bare land, urban green space, cropland, built-up regions, and forest land, providing valuable insights into landscape dynamics (Table 2).

Table 2 The land use classification with descriptions

The study’s categorized images’ accuracy was assessed using the confusion/error matrix method, ensuring an unbiased evaluation through an equalized random sample technique. For each land use and land cover (LULC) class, 100 stratified random points were generated to validate the classified land cover distribution. Actual ground truth conditions were confirmed using Google Earth images. Assessment metrics included producer accuracy, user accuracy, overall accuracy, and the Kappa index of agreement (Kappa coefficient). Producer accuracy measured the correctly classified pixels in the error/confusion matrix diagonal relative to the total classified pixels in the respective column category. User accuracy determined the correctly identified pixels in the row category relative to the total identified pixels in the error matrix diagonals. Overall accuracy represented the ratio of all correctly identified pixels to the total number of pixels in the error matrix. Arc GIS software (version 10.3) was used to construct the land use and land cover classifications for the research region using the Supervised (Maximum Likelihood) Image Classification Technique (SICS). More than 20–30 spectral signatures have been selected as typical signatures for each type of land use and land cover. A few common reference sites from Google Earth images were used to evaluate the accuracy. A total of 100 reference locations for each of the years 2009, 2011, and 2023 have been acquired using Google Earth pictures to assess the accuracy. The accuracy grade for satellite images obtained in 2023 is 95%; for images taken in 2009, it is 93%; and for images taken in 2011, it is 94%.

Aerial images and base map of Addis Ababa

Line maps from aerial photographs taken in 2005 and 2011 were used to map land use and land cover to discriminate between informal and formal settlements. The line maps were collected from the Addis Ababa City administration’s Urban Planning and Development Commission. The line map from 2011 was used to cross-check the settlements established after 2005, and the aerial photo from 2005 was used to compare settlements that existed before and after 2005.

The Addis Ababa city land development and administration office provided a base map of legal settlements, which the study used to identify informal settlements. The aerial photograph of Addis Ababa from 2005 was used as a point of reference for any informal settlements that were classified as such after that year by Directive No. 17 of 2014, while the most recent base map for 2023 served as a point of reference for the formal settlements. The line maps from 2005 and 2011 provide detailed parcel-level information, featuring fences and buildings with a resolution of 0.1 m. These maps are derived from aerial photographs captured directly from aircraft, offering a top-down view. Moreover, the base map incorporates surveyed data for each formal settlement parcel, incorporating essential details such as title deeds.

Ecosystem service values

The study applied the valuation coefficients for ecosystem services globally, as reported by Costanza et al. (2014) who valued 17 ecosystem services from 16 distinct biomes using the benefits transfer approach. This method calculates the overall value by multiplying the unit value per hectare assigned to each land use category by the appropriate area (Costanza et al. 1998). The global coefficients that have been chosen by Costanza et al. (2014) have been extensively utilized by scholars in areas like Africa where data availability is scarce. This study also used global coefficients since there are no localized values, especially in urban settings in Ethiopia. Additionally, while taking into account significant objections, the coefficients have been revised from those provided by Costanza et al. (1998). The values of ecosystem services for Addis Ababa were calculated by comparing them with the 16 biomes that were identified by Costanza et al. (2014) and used in other studies.

The most suitable biome was selected for each land use type, with grassland/shrubland for urban green, cultivated land for agriculture, tropical forest for forest land, built-up for urban areas, and deserts for bare land (Costanza et al. 2014) which is stated in Table 3.

Table 3 LULC categories, corresponding equivalent biomes, and ESV coefficients

Table 3 provides a classification of land use and land cover (LULC) categories, along with their corresponding biomes and ecosystem service value (ESV) coefficients based on Costanza et al. (2014). The table lists six LULC categories: Agriculture, Forest land, Built-up (Formal and Informal), Water bodies, Urban green, and Bare land. Each category is matched with an equivalent biome and a description. The ESV coefficients, expressed in 2011 USD per hectare per year, represent the total ecosystem service values: Agriculture (Cropland) at $5567, Forest land (Tropical forests) at $5382, Built-up areas (Urban) at $6661, Water bodies (Lakes/Rivers) at $12,512, Urban green (Grassland/shrubland) at $4166, and Bare land (Desert) at $0. These values reflect the global coefficients used to quantify the economic benefits provided by different ecosystems.

The total ecosystem service values for each land use category were used as proxy indicators for the impact of landscape change induced by informal settlements on ecosystem services in Addis Ababa.

Table 4 illustrates the values of individual ecosystem service value function (ESVf) per unit area for individual land use categories (US$/ha/year) which were generated by Costanza et al. (2014). Each land use category offers unique and valuable ecosystem services, with agriculture excelling in provisioning services, forest land in regulating services, grassland/shrubland in supporting services, and buit-up in cultural services. Waterbodies notably provide significant regulating and cultural services.

Table 4 The values of individual ecosystem service value function (ESVf) per unit area for individual land use categories (US$/ha/year)

Sampling techniques

Weredas and sub-cities were selected using a purposive sample technique that considered the areas' propensity for expansion and their outlying location, which is expected to support natural ecosystems. Weredas are administrative districts that fall under sub-city governance. Yeka and LemiKura were chosen from among the eleven available sub-cities. From each sub-city, two Weredas or Districts were selected based on their potential for growth and the existence of natural ecosystems on their periphery. Thus, Yeka Subcity Wereda 10 and 11, as well as Lemi Kura Sub city Wereda 2 and 14, were selected as representatives.

Methods of analysis

Methods of evaluating land use change induced by informal settlements

ArcGIS 10.3 and ERDAS Imagine 2010 were employed to assess Addis Ababa's informal settlements. The GIS overlay technique was applied using the line maps of 2005 and 2011, along with the base map of 2023, to distinguish informal from formal built-up areas. Then, the informal settlements were identified and drawn for each year under consideration and superimposed with the land sat images to examine the land use land cover changes The percentage land use land cover (LULC) change equation was then used to determine the change in the extent of informal settlements on which many studies use it and ensure its reliability (Chen et al. 2020; Hu et al. 2023; Moisa and Gemeda 2021; Treitz and Rogan 2004). Using particular formulas, the yearly rate of change (Eq. 1), the amount of landscape change (Eq. 2), and the proportion of landscape change for informal settlements (Eq. 3) were also examined.

The LULC change rate was computed using the formula suggested by Puyravaud (2003):

$$r = \left( {1/\vartriangle t} \right)ln\left( {{\raise0.7ex\hbox{${A_{f} }$} \!\mathord{\left/ {\vphantom {{A_{f} } {A^{1} }}}\right.\kern-0pt} \!\lower0.7ex\hbox{${A^{1} }$}}} \right) \times 100$$

(1)

where r is the annual rate of change in %; Δt is the time interval in years during the LULC change being assessed; ln is the base of the natural logarithm function; and Ai and Af are initial and final LULC areas respectively.

The magnitude of landscape change will be analyzed with

$$MC\left( {ha} \right) = A_{f} - A_{i}$$

(2)

The percentage of landscape change in informal element

$$P\left( \% \right) = \frac{{A_{f} - A_{i} }}{{A_{i} }} \times 100$$

(3)

where A_i is the class area (ha) at the initial time, and A_f is the class area (ha) at the final time.

Using Landsat data from 2009, 2011, and 2023, the study compared and analyzed the land cover of informal settlements with other land uses, including formal settlements, using GIS and remote sensing tools such as ArcGIS 10.3 and ERDAS Imagine 2010. The land use conversion matrix analyzed changes in land use types, determining transformation directions between 2009 to 2011, 2011 to 2023, and 2009 to 2023, revealing impacts on ecological areas by informal and formal settlements using Eqs. 1,2, and 3.

An assessment of ecosystem services

The values of services provided by the 17 individual ecosystem service functions were estimated to determine the impacts of land use change induced by formal and informal settlements on ecosystem service values using the following Eq. (4).

$$ESVf = \sum Ak \times VCfk$$

(4)

where ESVf is the ecosystem service value of function f, Ak is the area (ha) of land use category k and VCfk is the value coefficient of function f (US $/ha/year) for land use category k. The value coefficients were obtained from Costanza et al.(2014).In this study k can be agricultural land, forest land,water body, urban green, built up (formal) and built up (informal) from the land use land cover analysis.

The average ecosystem services value (ESVavr) was computed with the help of the following Eq. (5)

$$ESVa\nu r = \frac{{ESv_{t} }}{Ua}$$

(5)

where ESVt is the total ecosystem services value for a certain study year for each land use class and Ua is the total geographical area of the urban area in hectare.

The analytical framework of the study is depicted in Fig. 2.

Fig. 2

Analytical framework of the study

Figure 2 illustrates the analytical framework investigating whether informal settlements negatively affect ecosystem services by analyzing their spatiotemporal changes and comparing them to formal settlements. This involves a geospatial analysis that includes detecting informal settlements using aerial photography from 2005 and 2011, a base map of 2023, and satellite imagery from Landsat ETM+ (2009, 2011) and Landsat OLI (2023). The data undergoes image pre-processing and accuracy assessment before applying a supervised Maximum Likelihood Image Classification Technique. This generates land cover maps for 2009, 2011, and 2023. Using these maps, the total ecosystem service value (ESV) and individual ecosystem service (ES) values are computed, employing ecosystem service value coefficients from Costanza et al. (2014). The framework examines trends in informal settlements from 2009–2011 and 2011–2023, and the resulting land use conversion matrix. It assesses the impact of informal settlements on land cover changes and their effect on ESV, and finally, compares these effects with those from formal settlements to determine overall impacts on ecosystem services.

Results

Land use land cover changes from 2009 to 2023

The land use and land cover change analysis of Lemi Kura, and Yeka Sub-city from 2009 to 2023 shows significant changes in various land use categories especially the proliferation of informal settlements (Fig. 3).

Fig. 3

The dynamics of the land use land cover of LemiKura sub-city Wereda 2 and 14 from 2009 to 2023

Figure 3 shows that the Weredas ecosystem is being encroached upon by built-up areas, particularly informal settlements, with a significant increase in these areas between 2009 and 2023, indicating a decrease in agricultural and urban green spaces. In 2009, settlements encroached so closely on river buffers, wetlands, and ponds that water bodies were used for settlements by infilling quarry sites and wetlands. However, following the demolition of these settlements, the water bodies began to flourish especially the wetlands and ponds. But it may also be a spatial resolution problem.

The results of Table 5 were calculated using Eqs. 1, 2 and 3. Table 5 shows the agricultural land cover in Lemi Kura Sub city Wereda 2 and 14 decreased from 646.6 ha in 2009 to 98.3 ha in 2023, a decrease of − 368.5 ha while informal built-up increased from 26.8 ha in 2009 to 277.8 ha in 2011, and decreased to 231.4 ha in 2023. The forest land category increased from 12.1 ha in 2009 to 44.7 ha in 2023. However, urban green land cover decreased from 655.14 ha in 2009 to 129.3 ha in 2011, and further down to 175.9 ha in 2023. Formal built-up increased from 161.1 ha in 2009 to 731.57 ha in 2023, with a percentage change of 317.1% from 2009 to 2011. These changes reflect evolving land use and land cover patterns in the city.

Table 5 Land use Land cover change of Lemi Kura Sub city Wereda 2 and 14 from 2009 to 2023

Figure 4 shows how built-up areas, especially informal settlements, are encroaching on the natural land covers. In contrast to 2009, when the image mainly showed urban greenery, farms, and forests, a significant amount of the Weredas in 2023 was covered in settlements, especially informal settlements. Furthermore, between 2009 and 2023, there was a decline in the quantity of land used for urban green spaces, agriculture, and forests. On the other hand, settlements significantly rose. Due to settlements encroaching on river buffers, water bodies were hidden in 2009 and 2011; however, after these settlements were demolished, the water bodies were visible.

Fig. 4

The dynamics of the land use land cover of Yeka sub-city Wereda 10 and 11 from 2009 to 2023

Table 6 shows that agricultural land expanded by 213% between 2009 and 2011, then decreased by − 65.7% between 2011 and 2023. Bare land increased by 12.5% between 2009 and 2011 and 96% between 2011 and 2023. Forest land increased by 47.5% between 2009 and 2011, but fell by 36.9% between 2011 and 2023, resulting in a 7% reduction in forest land cover. Informal built-up land increased significantly between 2009 and 2023, reaching 451.09 ha in 2011 and 534.26 ha in 2023, while urban green areas decreased from 1229.11 ha in 2009 to 339.21 ha in 2011, and formal built-up land increased from 121.32 ha in 2009 to 284.47 ha in 2023.

Table 6 Land use land cover change of Yeka Sub-city Wereda 11 and 10, from 2009 to 2023

Table 7 shows the change in land use and cover in Yeka and Lemi Kura sub-cities between 2009 and 2023. The amount of bare land increased by 135.3%, from 337.9 ha in 2009 to 795 ha in 2023 and the overall amount of forest land increased by 4.7%, from 286.8 ha in 2009 to 300.2 ha in 2023, however, urban green space shrank by 70.9% between 2009 and 2023, from 1884.2 ha to 547.5 ha, and between 2009 and 2023, the amount of agricultural land drastically fell, from 785.4 ha to 247.4 ha, a shift of 68.5%. In contrast, the informal built-up area grew by 888.6%, from 77.4 ha in 2009 to 765.6 ha in 2023 and formal settlement increased by 72.2% from 2009 to 2023.

Table 7 Land use land cover change of the Yeka and Lemi Kura sub-cities, from 2009 to 2023

Thus, informal settlements increased significantly between 2009 and 2011, and continued to rise from 2011 to 2023 and the natural land covers decreased drastically especially agricultural and urban green areas. In aggregate, natural land cover decreased by -169%, but built-up areas grew by 79.8% between 2009 and 2023, mainly because of informal settlements, which account for 57.5% of the total increase.

Comparison between formal and informal settlements’ encroachment on ecosystems

Land use land cover conversion in LemiKura sub-city

The conversion of different natural land covers into built-up (formal) and built-up (informal) structures occurred in all land use categories, and the results showed this in most of cases.

Based on Fig. 5, it is evident that informal settlements have encroached upon various ecosystems in LemiKura sub-city Wereda 2 and 14. In the period between 2009 and 2011, informal settlements accounted for a conversion of 0.08 ha of land from different ecosystems, with 0.02 ha from agriculture and 0.06 ha from water bodies being affected. This encroachment indicates a concerning impact on the ecosystems.

Fig. 5

Land use and land cover conversion of LemiKura sub-city Wereda 2 and 14 from 2009 to 2011

Figure 6 reveals a more extensive encroachment during the period between 2011 and 2023. Informal settlements have converted a total of 28.76 ha of land from various ecosystems in LemiKura sub-city Wereda 2 and 14. Among these, 15 ha from agriculture, 0.9 ha from forests, 12.3 ha from urban green areas, and 0.56 ha from water bodies have been affected. This significant increase in encroachment reflects the detrimental impact of informal settlements on the ecosystem. Therefore, a total of 28.8 ha of the natural land cover was changed into informal settlements from 2009 to 2023 in the two Weredas of the Lemi Kura sub-city.

Fig. 6

Land use and land cover conversion of LemiKura sub-city Wereda 2 and 14 from 2011 to 2023

Land use land cover conversion in Yeka sub-city

The conversion of different natural land covers into built-up structures occurred in all land use categories, and the results showed this in the majority of cases.

Figure 7 showed how informal communities in Yeka sub-cities Wereda 10 and 11 are encroaching on ecosystems. Of these, 65.36 ha were once used for agriculture, 16.04 ha for forests, and 237.16 ha for urban green spaces before becoming informal settlements. Between 2009 and 2011, there was an encroachment of informal settlements on 318.56 ha of land from different ecosystems. This suggests that informal settlements are altering the landscape, thereby impacting the ecology. The fragmentation of habitats can disrupt ecological connections, isolating populations of plants and animals and decreasing gene flow, ultimately resulting in reduced biodiversity.

Fig. 7

Land use and land cover conversion of Yeka sub-city Wereda 10 and 11 from 2009 to 2011

Figure 8 illustrates the encroachment of informal settlements on ecosystems in the Yeka sub-city, namely in Weredas 10 and 11. Of those 16.71 ha of land were turned into informal settlements from farming, 0.33 ha from forests, 6.79 ha from urban green areas, and 0.32 ha from water bodies. In all, 24.15 ha of land from various ecosystems were taken over by built-up (Informal) between 2011 and 2023. This suggests that the ecology is being impacted by the development of informal settlements. Between 2009 and 2023, the two Weredas of the Yeka sub-city witnessed 342.71 ha of informal settlement encroachment on ecosystems.

Fig. 8

Land use and land cover conversion of Yeka sub-city Wereda 10 and 11 from 2011 to 2023

Between 2009 and 2023, a total of 371.51 ha of the two sub-cities study areas' natural land cover was transformed into informal settlements. This indicates that 48.5% of all informal settlements are located on prior natural land cover, encroaching upon urban green spaces, forests, water bodies, and agricultural land. The data reveals that a significant portion of informal settlement encroachment in urban areas is concentrated on green spaces, accounting for 33.5% of the total encroachment. In comparison, encroachment on agricultural land constitutes 12.7%, while forests are affected to a lesser extent at 2.2%. Water bodies experience the least encroachment, with only 0.1% affected.

The physical structure has been encroaching on natural land covers, with informal settlements causing more significant damage to agricultural, forest, and urban green areas.

Table 8 shows that between 2009 and 2023, informal settlements encroached on 97.1 ha of agricultural land, accounting for 76.5% of total encroachment. In former forest regions, informal settlements occupied 17.2 ha, accounting for 83.1% of total incursion. In urban green zones, informal settlements occupied 256.1 ha, covering 93.7% of the overall encroachment. Water bodies were less harmed by encroachment, with informal settlements only invading 1 hectare rather than formal settlements encroaching 2.5 ha. In general, informal settlements exhibit a higher degree of encroachment on natural land covers, accounting for 87.5% of the total encroachment of physical structures on such areas. Furthermore, it was rendered a chi-square test for independence to analyze the relationship between land use categories and the type of settlement (formal or informal) concerning encroachment.

Table 8 Comparison between formal and informal settlements’ encroachment on ecosystems due to land use change from 2009 to 2023

The Chi-square test indicates a significant association between the type of settlement (informal vs. formal) and the land use categories they encroach upon, as the p-value is much lower than the conventional threshold of 0.05 (Table 9). The analysis underscores that informal settlements have a substantially greater impact on ecosystem encroachment relative to formal settlements, as evidenced by their higher χ² contributions across all land use categories (Table 9). This suggests that informal settlements play a crucial role in altering ecosystems, particularly in areas such as agriculture and urban green spaces. Consequently, effective management strategies are imperative to mitigate the adverse environmental impacts associated with informal settlements and ensure sustainable land use practices.

Table 9 Chi-square calculation results for comparison between formal and informal settlements' encroachment on ecosystems

The impact of informal settlements on ecosystem services

Change in individual and grouped ecosystem service values due to the land use change induced by informal settlements

Informal settlements’ land use changes between 2009 and 2023 significantly impacted ecosystem service values. They affected provisioning, regulating, supporting, and cultural services across various categories.

The analysis of ecosystem service losses due to land use changes induced by informal settlements from 2009 to 2023 reveals significant impacts across various service categories (Table 10). The results are based on Eq. 4. In the provisioning category, food production suffered the most substantial loss at $56,478.4 annually. Genetic resources also experienced a significant loss of $436,428.2 annually. Regulating services faced notable losses, totaling $196,900.6 annually. Climate regulation, waste treatment, and erosion control were the most affected. Supporting services incurred a loss of $ 375,653.7 annually, primarily driven by habitat/refugia loss. Cultural services saw a total loss of $74,502.3 annually, mainly attributed to recreation and cultural services. Overall, the total loss in ecosystem service values amounted to $1,665,033.7 annually (Table 10). Provisioning services accounted for the highest percentage (60.6%) of the total loss, followed by supporting services (22.6%), regulating services (11.8%), and cultural services (4.5%). Land use change associated with informal settlements can alter ecosystem functions such as nutrient cycling, water purification, and carbon sequestration. These changes can have cascading effects on biodiversity. They affect the abundance and distribution of species that rely on specific ecosystem functions for survival.

Table 10 Individual and grouped ecosystem service value loss due to informal settlements from 2009 to 2023

Comparison between the impact of formal and informal settlements induced landscape transformation on ecosystem services values

The formal settlements in most cases reside on the lands preserved for built-up structures but some settlements encroached on the environmental spaces by abusing the proposed land for ecosystems.

The comparison between formal and informal settlements’ impact on ecosystem services due to land use change highlights distinct patterns. Table 11 shows that informal settlements predominantly contribute to ecosystem service value loss, especially in agriculture (98.2%), forests (54.4%), and urban green areas (87.2%). Conversely, formal settlements have a greater impact on water bodies, accounting for 68.4% of the total loss. Overall, informal settlements contribute to 86.1% of the total loss, emphasizing the need for targeted interventions to mitigate their disproportionate effects on ecosystem services. Yet, differences between formal and informal settlements generate a positive impact on ecosystem services, notably in cultural services. Informal settlements exhibit a positive value of $2,129,540, likely attributed to community activities or cultural diversity, while formal settlements show $304,794, potentially reflecting contributions such as cultural events or historic preservation.

Table 11 Comparison between formal and informal settlements’ impact on ecosystem services due to land use change from 2009 to 2023

Discussion

The study underscores the need for urgent conservation and management efforts to preserve ecosystem services, integrating valuation into decision-making to prioritize conservation and raise awareness and to culvert the expansion of informal settlements.

The dynamics of informal settlements and the land use land cover changes

The observed land use and land cover changes in Lemi Kura and Yeka Sub-cities from 2009 to 2023 indicate a significant transformation of the urban landscape, with a notable proliferation of informal settlements. These changes have been accompanied by a decline in agricultural land and urban green spaces, as well as an increase in built-up areas, particularly informal settlements. From 2009 to 2023, the overall built-up area increased by 79.8%, with significant growth in both formal and informal developments. Meanwhile, natural land covers, including urban green spaces, water bodies, and agricultural areas, decreased by 169%. Over time, the area occupied by non-formal buildings has grown dramatically. There has been a periodic increase in the number of informal settlements, particularly in the study's scenario from 2009 to 2011, when a sizable portion of the two sub-cities was covered by these settlements. This suggests that there are issues with land management. The trend of increasing informal settlements persists, but the most significant changes occurred between 2009 and 2011, with large-scale informal settlements established before 2011. This surge was due to the lack of a land lease proclamation and political conflict in 2005, which allowed many informal settlements to emerge rapidly. Despite this, the number of informal settlements continues to rise afterward. Other studies also concluded the increasing magnitude of informal settlements in urban areas. An unprecedented increase in informal settlements is occurring, and peri-urban location serves as a useful indicator of this growth (Samper et al. 2020). In a similar vein, research conducted in Osogobo, Nigeria, finds that the built-up area, or informal settlement, has expanded quickly over time (Oyinloye et al. 2018). Informal settlements cause land encroachment, negatively impacting agriculture, forests, and urban green areas. The study focused on spatiotemporal results of informal and formal settlements to foresight sustainable development interventions.

In peri-urban areas with significant ecological value, there is an increase in informal human settlements, and there are difficulties in preventing the negative effects (Aguilar and Santos 2011; Benítez et al. 2012). The problem of land use changes is in place due to improper executions of the land use plan in Addis Ababa (Hailu et al. 2023). It is crucial to address this issue through sustainable urban planning, community engagement, and awareness-raising to ensure a more harmonious coexistence between human settlements and the environment. The study revealed that a significant number of agricultural lands were converted into built-up structures mainly informal settlements. The conversion of agricultural land to informal settlements is a significant concern as it reduces food production, disrupts farmers’ livelihoods, and negatively impacts the local economy(Oyinloye et al. 2018). Furthermore, forest lands were also changed into built-up structures and the loss of trees has detrimental impacts on ecosystem services like carbon sequestration and water management, as well as biodiversity. Though urban green spaces improve the general well-being of its population, and their influence on these regions is especially significant, informal settlements significantly encroached on them hence the benefits of urban green spaces for leisure opportunities, enhance mental and physical well-being, and help lessen the effects of climate change deteriorated. Such regions can have long-term social and environmental repercussions if they are lost to invasion. Similarly, another study concluded that informal settlement encroachment on ecologically sensitive areas is highly prevalent in urban areas (Andreasen et al. 2022).

Several studies have highlighted the detrimental impact of informal settlements on ecosystems. A study conducted by Abebe et al. (2019) continued the conversion of different land uses into unofficial settlements, which encroach on open space and agriculture, especially on the outskirts of cities. The informal settlements have been growing, consuming dense forests, gallery forests, agriculture, and water bodies, which affects the ecosystem negatively (Oyinloye et al. 2018). Additionally, there is a significant expansion of informal settlements onto agricultural lands (Nassar and Elsayed 2018). However, this study further supplements by comparing informal and formal settlement encroachment on natural land covers to suggest and indicate case-specific measures on which the informal settlements' invasion of natural land covers is much higher than the formal settlements.

The impact of informal settlements on ecosystem services

Informal settlements’ land use changes have led to significant ecosystem service losses, emphasizing the need for sustainable land management practices to mitigate environmental impacts. Understanding ecosystem service loss from settlements can guide sustainable practices, policies, and initiatives to conserve and restore ecosystems, ensuring vital services for society and the environment. The overall ecosystem services were occasionally declining due to built-ups, especially informal settlements, converting natural land covers. This suggests that ecosystems that would otherwise benefit the city and its citizens were being lost particularly in light of the growth of informal settlements. The decreasing ecosystem service values due to land use changes unveiled in the studies of Abebe et al. (2019) and Oyinloye et al. (2018).

The study found that the individual ecosystem service functions' contributions to the overall ecosystem service values in the study area had decreased. The most significant losses occurred in food production, habitat, and climate regulation. These losses not only affect the natural environment but also impact human livelihoods and well-being. A consistent study by Oyinloye et al. (2018) and Tufa (2022) revealed the loss of food production due to the transformation of agricultural lands into settlements. Moreover, the studies of (Markos et al. 2018; Msofe et al. 2020) asserted the loss of climate regulation and habitat functions of ecosystem services due to land use changes, thus, it is crucial to consider the consequences of land use change and promote sustainable practices to minimize the negative impacts on ecosystem services.

There was a significant loss in providing services, indicating that the majority of agricultural lands were turned into settlements, mostly informal settlements. There was also a significant loss in supporting and regulating services, indicating issues with habitat creation, gas regulation, climate regulation, and flooding control. Several studies have confirmed the negative impacts of land use changes on ecosystem services. For example, Das and Das (2019) found that urban settlements caused significant losses in supporting services, which aligns with the findings of this analysis. Additionally, studies by González-García et al. (2020) and Wang et al. (2019) also highlight the negative impacts of land use change on regulating and supporting services, respectively. Another study conducted by He et al. (2021) revealed significant land use changes in Guangzhou’s main metropolitan area between 1987 and 2017, primarily due to built-up growth and degradation of forest and cultivated land, impacting ecosystem services like food production, and water supply, nutrient cycling, and gas management. Some studies suggest informal settlements can enhance cultural services by promoting community diversity (Shafqat et al. 2021) but it's crucial to evaluate and balance their impact on ecosystem services.

In summary, the shift in land use caused by informal settlements has resulted in significant losses in ecosystem service values, particularly in providing, regulating, sustaining, and cultural services. Not only does the ecology suffer from these losses, but human livelihoods and general well-being are also impacted. Addressing the effects of shifting land use and promoting sustainable practices are essential to reducing negative effects on ecosystem services. The literature has acknowledged the detrimental effects of land use change on ecosystem services, even though various research may give differing perspectives and findings (Basu and Das 2021; Liu et al. 2019b; Tolessa et al. 2021). However, this study explains in detail how informal settlements affect ecosystems through changes in land use, and it also compares this effect with formal settlements. This is because categorizing and assessing the impact of informal settlements helps policymakers and implementers understand where attention should be focused to safeguard ecosystems and maintain sustainable cities.

The limitations of the study and directions for future research.

The effect of informal settlements on environmental services is examined in this study. While the study notes that more research is necessary, it substantially contributes to our understanding of how to detect informal settlements geographically and compare their impact on ecosystems with formal settlements beyond aggregate land use change. The study prefers the use of globally accessible coefficients due to the absence of local value coefficients. While this study provides valuable insights into the impact of informal settlements on ecosystem services, several methodological limitations should be acknowledged. The use of globally accessible coefficients, rather than locally specific ones, limits the accuracy of ecosystem service valuations, potentially leading to generalized results that may not fully capture local conditions. The reliance on historical aerial photographs and satellite images, despite being comprehensive, may not always offer the highest resolution needed for fine-scale analysis, possibly overlooking smaller informal settlements or subtle land use changes. Additionally, the study primarily focuses on land cover changes from a spatiotemporal perspective without fully integrating socio-economic data, which is crucial for understanding the drivers of informal settlement growth. Future research should incorporate localized value coefficients, higher resolution imagery, socio-economic variables, and ground-truthing efforts for a more detailed and accurate assessment of the impacts of informal settlements on ecosystem services.

Implications of the study

The findings of this study have significant implications for regions worldwide, especially those experiencing rapid urbanization and informal settlement growth. The demonstrated impact of informal settlements on ecosystem services highlights the urgent need for integrated land use planning and sustainable urban management practices. Other regions facing similar challenges can draw valuable lessons from this study to mitigate environmental degradation and promote sustainable development. Firstly, the study underscores the necessity of conserving and managing ecosystem services through proactive measures. Regions experiencing the proliferation of informal settlements should prioritize the valuation of ecosystem services in their decision-making processes. This approach can help raise awareness among policymakers and the public about the importance of preserving natural resources, thus supporting the implementation of conservation strategies. Secondly, the analysis of spatiotemporal changes in informal settlements provides a framework for understanding how land use dynamics affect ecosystem services. Other urban areas can adopt similar geospatial analysis techniques to monitor and manage the spread of informal settlements. By detecting changes over time, regions can implement timely interventions to protect valuable ecological areas and prevent further degradation. Moreover, the study emphasizes the importance of sustainable urban planning and community engagement. Regions facing informal settlement encroachment should invest in sustainable urban development plans that integrate green spaces, maintain river buffers, and promote environmental stewardship. Engaging local communities in these efforts is crucial for fostering a sense of ownership and responsibility towards environmental conservation. The negative impacts of informal settlements on food production, climate regulation, and habitat functions observed in this study are relevant to many rapidly urbanizing areas. Other regions can benefit from adopting policies that balance urban growth with the preservation of agricultural lands, forests, and other natural resources. By doing so, they can ensure food security, enhance climate resilience, and protect biodiversity. Finally, this study highlights the need for further research tailored to local contexts. While global coefficients provide a starting point for understanding the impact of informal settlements, local studies are necessary to capture the specific environmental and socio-economic dynamics. Regions should invest in localized research to develop targeted strategies that address the unique challenges posed by informal settlements.

In summary, the implications of this study extend beyond the specific context of Addis Ababa, offering valuable insights for urban areas worldwide. By integrating the lessons learned from this study into their urban planning and environmental management practices, other regions can better navigate the challenges of informal settlement growth and work towards sustainable and resilient urban futures.

Conclusion

From 2009 to 2023, Lemi Kura and Yeka sub-cities experienced significant land use and cover changes, with a notable increase in informal settlements at the expense of natural ecosystems. The growing number of informal settlements is primarily due to their encroachment on natural ecosystems, causing significant losses on ecosystem services. This highlights the potential consequences of environmental degradation, such as habitat destruction, pollution, and climate change. Informal settlements have a higher tendency to encroach on agriculture, forests, and urban green spaces compared to formal settlements. This highlights the need for effective urban planning and management strategies to mitigate these losses, including preventing encroachment on agricultural and forested lands and conserving urban green spaces. Sustainable land management practices and policies are crucial to preserve and sustainably utilize ecosystem services. Policymakers and planners must consider these findings when making decisions about land use management, aiming to balance the needs of settlements with the preservation of ecosystem services for sustainable development. The study’s methodology, which uses ArcGIS, base maps, aerial photographs, and satellite images, can be replicated in other urban areas with similar characteristics and challenges. The study recommends integrating ecosystem service valuation into urban planning to prioritize conservation and raise awareness about the environmental impacts of informal settlements. To curb the expansion of informal settlements, especially in ecologically valuable peri-urban areas, it is crucial to implement sustainable urban planning and effective land management practices. Engaging communities and raising awareness are essential for fostering a harmonious coexistence between human settlements and the environment. Future research should concentrate on understanding local value coefficients, the socio-economic drivers behind the growth of informal settlements, and exploring ecological restoration methods to balance urban development with environmental preservation. Addressing these challenges requires a multifaceted approach involving policymakers, urban planners, and the community to ensure sustainable urban growth and the preservation of vital ecosystem services.