Assessment of ecosystem services in the Tehran metropolitan and analysis of their sensitivity to climate drivers

Introduction

Ecosystem services (ES) refer to the benefits derived from the structure and function of ecosystems and play an important role in human well-being and welfare (Adelisardou et al., 2021). The two interconnected approaches of carbon sequestration and habitat provisioning are ecosystem services that have the potential to mitigate climate change and biodiversity loss caused by the built environment (Varshney et al., 2022). The rapid urbanization of Tehran in recent decades has led to significant disruptions to both the natural and urban landscape. Sustainable population growth, industrialization, and urbanization processes have led to the reduction or destruction of natural vegetation, the development of urban constructions, various human activities (such as transportation and production centres), and drastic changes in land cover/land use (LULC). These factors have also contributed to an increase in energy consumption, which has resulted in elevated surface temperatures in urban environments. Under these conditions, the current research aims to examine two ecosystem services - regulatory services (carbon storage) and support services (habitat quality) - provided by the InVEST model. The research will focus on the role and impact of these two crucial services in enhancing the quality of the environment and analyzing the climate of the Tehran metropolis.

Data and Methodology

The current research aims to investigate the effect of land use/land cover on changes in carbon storage (regulating service) and habitat quality (supporting service) at spatial and regional scales using the InVEST software. The carbon storage model integrates land use and land cover (LULC) data with information on carbon storage inventories in four main carbon storage pools: aboveground biomass, belowground biomass, deadwood, and soil organic carbon. This integration enables calculations and spatial distribution of inventories and carbon storage in the area. To conduct habitat quality modelling, several components are necessary, including the (LULC) map, threat sources, impact weight tables, impact distance for each threat, and the sensitivity of each habitat to the threat source. One of the important inputs of the InVEST model is the land use/land cover map. In the present study, the classification of local climate zones (LCZ) was utilized to calculate and generate a land use and land cover (LULC) map for the city and suburbs of Tehran.

Results and Discussion

The results showed that the highest amount of carbon storage on an annual scale is associated with aboveground biomass and soil organic carbon, while the lowest amounts are found in deadwood and belowground biomass. The aboveground biomass in region 22, specifically the Chitgar Forest Park area and the northeastern areas of the region where trees are densely and sparsely distributed, has the highest carbon storage capacity. It is estimated to be between 218 and 335 tons per hectare per year. After that, the southern and southeastern parts of region 15, as well as the northern and eastern parts of regions 8 and 14, which are characterized by open mid-rise land cover, are ranked next in terms of carbon storage. The results of the Habitat Quality Index also showed that the highest amount of habitat quality, indicated by a 16% coverage (values between 0.7 and 1), was concentrated in the northern parts of the study area. The habitat quality gradually decreased towards the southern and, in particular, the southwestern areas. In 65% of the study area, the habitat quality is extremely low, primarily due to urban development and settlements in the southwest of the city. The central (10, 11, and 12) and western (21 and 22) areas of the municipality have the lowest habitat quality due to the lack of urban green spaces, the destruction of existing ones, and the expansion of settlements and industrial complexes. Finally, to measure the sensitivity of ecosystem services to climate, we analyzed the effect of two primary climate components: temperature and precipitation, on ecosystem services. The results showed that although the correlation coefficients between the studied series were relatively low (temperature and ES=0.221, precipitation and ES=0.234), the regression analysis indicates that both ecosystem services will decrease under conditions of increasing temperature and decreasing precipitation.

Conclusion

In this study, we evaluated the spatial changes of two carbon storage services and habitat quality concerning land use/land cover change in the Tehran metropolis and its surrounding suburbs. The results showed that the land is covered with dense and scattered trees, as well as open mid-rise, sparsely built, open low-rise, and low plants. These areas had the highest absorption values in all four carbon pools. In this sense, Region 22 and the eastern part of the Northern Region had the best conditions for carbon absorption. The output of InVEST habitat quality also indicated that the highest amount of habitat quality, with a coverage of 16% (values between 0.7 and 1), is found in the northern parts of the basin. Gradually, the quality of the habitat decreases towards the southern areas, especially in the southwest. Although the obtained results indicate the favourable ecological potential of some areas in the metropolis of Tehran, climate change and human activities have severely affected this potential. Based on the linear relationship between the normalized series of climatic components (temperature and precipitation) and ES, there was an inverse relationship between temperature and ES and a direct relationship between precipitation and ES. As a result, both regulatory services and ecosystem support will decrease under conditions of increasing temperature and decreasing precipitation.