Understanding the terrestrial biosphere’s functioning requires an assessment of the magnitude and distribution of Green-Blue Ecosystems (GBE) (Crowther et al., 2015). Green Ecosystems (GE) support a considerable amount of global biodiversity, playing an important role in biogeochemical cycles, and providing several Ecosystem Services (ES) such as water quantity and quality regulation, food production, raw materials provisioning, genetic resources, and carbon storage and sequestration (Mulatu et al., 2017). Forest density influences soil and water retention rates, flood regulation, as well as competitive dynamics and habitat suitability for a variety of plant and animal species (Rijal et al., 2021). Blue Ecosystems (BE) provide the backbone of ecosystems, enabling agriculture, and influencing urban development decisions (Newbold et al., 2015). As forests are intricately connected to rainfall and water availability, changes in vegetation cover, as well as poorly planned and managed forests, have significant impacts on the carbon and water cycles, leading to pressures on the environment (Liquete et al., 2011). Extreme weather events and soil and water contamination are perceived as the top risk, directly impacting natural capital and biodiversity, and consequently decreasing human well-being (Lundqvist & Unver, 2018). Knowledge of the interactions between carbon and water cycles is vital for predicting ecosystem responses to climate change, as well as the influence on natural capital (Seddon et al., 2021). Despite significant advances, the coupling mechanisms of these cycles under socio-economic and climatic pressures remain poorly understood (Keith et al., 2021).
Ecosystem Accounting (EA) encompass a statistical framework for quantifying and valuing the interactions between nature, society, and the economy, providing physical and monetary measurements of ecosystem assets (Bateman & Mace, 2020). In March 2021, the United Nations Statistical Commission adopted the System of Environmental-Economic Accounting Ecosystem-Accounting (SEEA-EA) as a baseline to inform policy development by countries. It represents a huge milestone in the history of accounting as “it moves beyond GDP and takes better account of biodiversity and ecosystems in national economic planning” (Edens et al., 2022). Thus, it is susceptible to shaping the future of the national statistic apparatus toward the inclusion of natural capital (Edens et al., 2022; Lange et al., 2022). Among the challenges still to be overcome is the substantial wide variety and amount of data required to produce comprehensive accounts (Bordt, 2018; Hein et al., 2020). Besides, extending locally generated ES models to other locations or scales has constraints due to the necessity for parameterization, calibration, and validation, which is sometimes hampered by a lack of ground truth data (Cord et al., 2017; Gosal et al., 2022).
The opportunities associated with technological innovations include the potential for gathering, processing, analyzing and visualizing different types of data, and integrating socio-economic and environmental information (Fleming et al., 2022). Advancements in geospatial techniques, such as satellite imagery, geospatial mapping, drones, and sensors, are viewed as highly promising to improve decision-making on both individual and cross-sectoral levels facilitating the deployment of EA (Farrell et al., 2021). Besides, the increased computational power and the transition towards open-access data and open-source technologies are significantly contributing to enhancing natural capital accounting (del Río-Mena et al., 2023).
Satellite Earth Observation (SEO) data and technologies, coupled with Geographic Information Systems (GIS), provide advantages such as synoptic and repeated coverage, historical spatial data analysis, and cost-effectiveness (Ramirez-Reyes et al., 2019). Therefore, where data is unavailable, imputation data techniques through statistics and Machine Learning (ML) are employed to fill in missing or incomplete data (Fleming et al., 2022). Additionally, data fusion is commonly applied, integrating information from diverse sources such as monitoring, statistics, modelling, or interviews (Braun et al., 2018). These approaches enable more frequent, and consistent assessment of ecosystem dynamics, regardless spatial scale of analysis (Hossain & Hashim, 2019).
In developing models for quantifying natural stocks, accurate and timely data on the extent and status of ecosystems are critical and challenging to gather particularly due to the dynamic and intricate interactions between water/groundwater and vegetation (Ellison et al., 2017). Significant efforts have been made to unveil the potential of SEO in ES assessments (Willcock et al., 2018), such as the European Copernicus programme powered by the European Spatial Agency (2023). The platform yields free and open access to SEO imagery and datasets, providing insights into the status of natural resources not only for Europe but also on a global scale (Almeida & Cabral, 2023). Among the various products, it provides the Water & Wetness Probability Index (WWPI) and the Tree Cover Density (TCD) to assist in building policy-relevant ecological accounts. The WWPI is a biophysical indicator for freshwater and wetland ecosystems (Ludwig et al., 2019) utilized as a spatial proxy to support environmental mitigation, wetland protection, erosion control, flood monitoring, and streamflow regulation (Vargas et al., 2019). The dataset provides information on the status of BE reflecting their overall quality and conditions (Copernicus Programme, 2023). The TCD is an indicator describing forest ecosystem conditions through a continuous spectrum of crown cover information, population numbers, densities, and wood stocks (Crowther et al., 2015). It is acknowledged as an effective method for environmental analyses, forest management, supporting decision-making, and tracking changes in tree cover losses and gains (Chen et al., 2020). Therefore, these products have some limitations due to: a) the availability and quality of SEO data, b) the availability and quality of in-situ data, and c) the influence of climatic and topographic conditions (European Environment Agency, 2023). Satellite mission launch dates restrict SEO data availability, and the quality of imagery is influenced by the atmospheric effects on the light reflected off the Earth's surface and captured by the sensor. Another challenge is the lack of ground-truth data, which is expensive to acquire (Mairota et al., 2015).
Some studies have demonstrated improvements with the integration of climate and topographic variables when assessing GBE. Crowther et al. (2015) demonstrated the strong associations between climatic variables and forest density in their research. Ludwig et al. (2019) combined multi-temporal optical imagery, topographic data, and spectral indices to build an automated wetland mapping detection, based on the WWPI. Madrigal-González et al. (2023) used climatic and topographic characteristics to investigate the relationship between tree density and water availability. Han et al (2021) estimated carbon stock in forests by considering temperature, precipitation, elevation, and soil type as factors. Alqadhi et al (2022) demonstrated the impact of landscape and topographic characteristics on ES capacity provisioning, considering: elevation, slope, aspect, drainage density, and precipitation. However, none of these studies used Reverse Engineering (RE) to reproduce TCD and WWPI taking into consideration climatic and topographic factors to estimate inland GBE at the national level. RE refers to the process of extracting knowledge or design information from products and subsequently reproducing or recreating them based on the acquired information (Nieves-Chinchilla et al., 2018). Through RE, it is possible to learn about the products, search for inconsistencies, or overall vulnerabilities, and assess whether there is a more efficient way to improve them (Wood, 2009).
In this study, the WWPI and TCD will be modelled within Portugal's mainland in ArcGIS Pro (ESRI, 2023) using the Random Trees Regression algorithm, and spatial associations will be analyzed through geographical detectors utilizing the geodetectors package (version: 1.0–4) in R software (Wang et al., 2016). EA baselines (Kienast et al., 2009) will be followed to assess the climate-driven stock accounts of forests, water, and wetlands at the national level. The aim is to develop more integrated and updated versions of TCD and WWPI contributing to the broader scientific community by exploring the potential of SEO data and technologies combined with global climatic and topographic open-access data. Furthermore, this research will shed light on the interplay between aquatic and terrestrial ecosystems and foster innovative solutions for assessing the status and conditions of inland GBE. Advancing our understanding of the development of Copernicus products will deepen our knowledge of the replicability and applicability of such datasets in EA.