Assessing the Impacts of Climate and Land Use Change on Sustainability and Productivity in the Village Tank Cascade Systems of Sri Lanka

Abstract

<p>Changes in climate and changes in land use and land cover (LULC) are the two most pressing threats to sustainability and productivity in Social-Ecological Systems (SESs). </p> <p>The Village Tank Cascade Systems (VTCSs) in Sri Lanka are among the oldest SESs in the world. Human populations began developing these systems during the 4th century BCE (Before the Common Era) to sustain their livelihoods and well-being in the face of climatic uncertainties in the dry zone of Sri Lanka. For more than two millennia, VTCSs operated in harmony with nature, preserving unique biodiversity and ecosystem services. Over time, further human interventions saw the VTCSs evolve into sustainable agroecosystems. In the 21st century, VTCSs are vulnerable to adverse global environmental changes. Ecological health in the system has deteriorated as a result, threatening the food security and livelihood of rural farming communities. Currently, about 16,500 village tanks are operational. Approximately 90% of these form part of clusters called VTCSs.</p> <p>Measures to build resilience and adaptive capacity to the threats posed by impacts of climate and LULC change stressors on sustainability and productivity in VTCSs are urgently required. However, little is known or understood about the spatial and temporal aspects of changes in climate and LULC in VTCSs. Research is required to better understand how to manage critically-threatened VTCS landscapes. This study quantifies climate and LULC changes in VTCSs and evaluates the risk these changes pose to the sustainability and productivity of VTCSs. The study incorporates transdisciplinary approaches combining various research methods, tools and techniques: i) biophysical assessment using quantitative modelling techniques for climate and LULC data, and ii) community perception assessment using standardised participatory tools and techniques within the community and with other stakeholders and experts involved in the management of the VTCSs.</p> <p>The thesis consists of nine chapters. An introductory chapter is followed by a review of current research into SESs (Chapter Two), focussing specifically on VTCSs in Sri Lanka. An extensive and in-depth review of research literature was carried out to identify existing knowledge with respect to sustainability and productivity dimensions of VTCSs. This was then subjected to bibliometric analysis and knowledge mapping to assess the status, statistical trends, terminological clusters and emerging concepts of VTCS research. It also offers some insight into the research hotspots and neglected areas of research into VTCSs.</p> <p>Chapter Three presents a comprehensive, logical framework for analysing causal factors and processes that result in reduced system productivity. It seeks to identify factors that reduce the ecological productivity of VTCSs by examining the social-ecological nexus between system elements, the way these factors impact productivity and the challenges for restoration. The study makes use of i) spatial data and analysis techniques to differentiate spatial components and identify significant spatial patterns, and ii) participatory field assessment and key informant interview data to determine the social-ecological nexus.</p> <p>Chapter Four investigates trends of climate variability and their potential impacts on VTCSs especially with respect to future paddy cultivation. Paddy is the staple food in Sri Lanka and paddy cultivation is the main livelihood of people in VTCS areas. Rainfall and temperature data of the VTCS area were used to evaluate past variability trends (1970 to 2020). Modelled data was used to project future trends (from the present to 2100). The modelled data indicates that future rainfall and temperature variability are likely to deviate considerably from past trends across the VTCS zones. </p> <p>In addition, modelled data projects a continuous warming trend. Warming is likely to increase variability in rainfall resulting in longer/shorter seasons and the increased likelihood of extreme weather events in the future. The area of land suitable for paddy farming is also likely to change over time in response to future climate change scenarios. The changes projected in this study are likely to negatively impact paddy farming in the future.</p> <p>Chapter Five examines changes in land use and land cover (LULC) as well as landscape patterns and the impacts of these changes on the productivity of VTCS zones. Satellite imagery and GIS techniques were used to map LULC in VTCS landscapes in 1994 and 2021. These maps were then used to create a LULC change matrix and calculate spatial pattern metrics to examine LULC and landscape pattern change dynamics over the time period. The results reveal transformations of the LULC and gradual changes of landscape patterns from natural forest to agriculture. Landscape patterns were analysed at both the landscape and LULC class levels. At the landscape level, the structure became more complex and fragmented, while at the class level, increased fragmentation of forest habitats was observed. The study concludes that VTCSs are undergoing a gradual loss of environmental sustainability as a result of these changes. Assessment of LULC, including fragmentation, can help to monitor the spatial pattern impacts. Thus, the study provides scientific guidance for the ecological restoration of degraded VTCSs.</p> <p>Chapter Six of the thesis assesses ecosystem services in VTCSs using a participatory research approach, involving the integration of local knowledge, experts’ judgments and land use system attribute data. The study develops an ecosystem services supply and demand matrix model. This model shows that the current overall ecosystem services demand for regulating and supporting ecosystem services exceeds supply. The model highlights that land degradation and biodiversity deterioration reduce the capacity to provide ecosystem services. The study concludes that ecological restoration of VTCSs depends on the extent to which integrated effort addresses the levels of ecological complexity, as well as the social engagement of communities and other stakeholders. The study provides a scientific basis to guide future land use decisionmaking in VTCSs.</p> <p>In Chapter Seven, the thesis describes a household survey that was conducted in a VTCS to investigate farmers’ perceptions of the impacts of changing climate and land use on food production. The majority of farmers felt that the climate of the VTCS areas had changed over time. They reported a notable increase in the variability of rainfall patterns. The increased cost of production, damage caused by wildlife, and land degradation were regarded as the factors that most impacted food production. Farmers rated deforestation and land clearing—encroachment of natural habitats as the most impactful on LULC. Farmers’ perceptions of the severity of both climate and land use changes were influenced by the following determinants: level of training, household size, farm size, level of income/profit, level of adaptation and the location of the farm. The study findings will help to formulate localised land use policies and climate change adaptation strategies in VTCSs with a combination of both top-down and bottom-up approaches.</p> <p>Chapter Eight undertakes a comprehensive assessment and characterisation of underutilised, neglected, and wild food plants found in Sri Lanka, with special attention to SESs. Plant species were identified and documented on the basis of six plant-food groups. The work involved: field surveys, field observations, community interviews, herbarium records, key informant interviews and expert validation. Particular attention was paid to the ecosystem services provided by these food plants in the SESs of SriLanka. The chapter also provides data concerning the nutritional values of these plants. Policies to enhance climate resilience and adaptive capacity of VTCS food systems are recommended</p> <p>In conclusion (Chapter Nine), the findings of this research demonstrate that climate and LULC changes significantly impact the productivity and sustainability of the VTCSs in Sri Lanka, particularly with respect to ecosystem health and food production. Through a participatory approach, the study integrates community perceptions with other aspects of the SES phenomenon of tank cascades (VTCSs), including ecosystem services, spatial changes, vulnerability, adaptive capacity, resilience, and restoration strategies, decision-making, and plant life. In so doing, it offers a range of new insights into the ways in which these challenges can be met. Although the findings of this study are specific to the VTCSs of Sri Lanka, they may be applicable to SESs in other tropical regions with similar climatic and LULC conditions.</p>