Climate change has been unequivocally known to be real, and its impacts are recognized as one of the most pressing global issues in the current decade. Evidences from a variety of different studies show that the impacts of climate change have become a major threat to agriculture and the food security in both the developed and developing countries across the world. With unabated increase in the anthropogenic atmospheric greenhouse gas emission that is known to interfere with `the regional and global circulation systems, global warming, and climate change in the twenty first century and beyond, would continue to be the most important agenda of debate and scientific discourses. Moreover, the negative impacts of climate change have been observed to be more pronounced in the high latitude areas, such as the mountainous countries in the Himalayas and elsewhere. Studies have also strongly postulated that the adverse impacts of climate change are most likely to be more severe in the developing countries in south Asia, Southeast Asia, Sub-Saharan Africa, and Latin America, due to their low adoption of farming technologies and lack of capacity to respond.

As many developing countries in the region report the negative impacts of climate change, Bhutan—an agrarian country located in the Eastern Himalayas, is no exception. The country has experienced increasing incidences of risks and disasters associated with climatic variabilities in the recent years. There have been pervasive issues of changing weather patterns that make farming a highly risky and vulnerable occupation. Apart from this, there are other pre-disposing factors that make Bhutan an even more sensitive and vulnerable to the climate variabilities. The highly rugged mountainous topography is one of the most important factors that make farming very challenging, as farmlands are concentrated in the river valleys with scattered land parcels in the mountain slopes. Thus the farms are highly prone to natural disasters that are triggered by weather and climatic events. The dramatic rise in elevation even over a small distance is another factor, which influence the orographic effects of mass air-flow systems, contributing to sudden changes in weather, thus negatively impacting crops and farms. Moreover, the Himalayan Mountains are considered to be geologically fragile, with inherently infertile soils for farming. This further makes farming prone to the destructive natural events, including those of weather phenomena. All of these, contribute to the challenging and subsistence nature of farming in the Bhutanese agricultural system. Therefore, this research was undertaken to study climate change and its impacts on various aspects of agriculture across different agro-ecological zones in Bhutan. The study used a combination of farmers’ perception analysis, geo-spatial techniques and modelling approaches to fill the much-needed knowledge gap on the issues of climate change faced by the Bhutanese farmers, and provides insights into the past, present and future climate change impact scenarios. Much of the climate and impact reports on Bhutan were based on hearsay, and scientific studies are few and far between.

As part of this research, a thorough review of agricultural production management system and pertinent issues of climate change impacts in Bhutan was undertaken. It was found that agriculture in Bhutan and the study region have been largely affected by the rising temperature, droughts and precipitation changes, which in turn have led to many other issues, ranging from water availability, crop and infrastructure damage to land degradation. Moving further, assessment of land cover changes in Punatsang Chhu Basin of Bhutan indicated large scale changes, especially in the high elevation areas. The findings from this study show that there is an increased rate of glacier retreat, with repercussions of Glacial Lake Outburst Floods (GLOF) and erosive activities of rivers and streams that directly and indirectly affect farming downstream in the river valleys. This indicates that mountain agriculture is highly vulnerable to the impacts of climate change and is at high risks of food insecurity. Likewise, the results from the analysis of farmers’ perceptions across the various agro-ecological zones in Bhutan indicated that farming has become more and more challenging. The extreme weather events, such as untimely rains, droughts and windstorms have become frequent occurrences, thus inflicting between 1-19% crop damages. The monsoon rains were assessed to be highly unpredictable, and untimely, which were perceived to have impacted the decisions of farmers, due to drying up of water sources, crop losses, land fallowing and cropping pattern changes. Farmers have also perceived issues of the emergence of diseases and pests, which together with aggressive incursion of invasive species (Parthenium hysterophorus, for example) would herald uncertainties and rising pressure on Bhutan’s limited arable land. Further, based on the projections of the Intergovernmental Panel on Climate Change (IPCC), MaxEnt modelling of rice distribution indicated large changes in crop suitability shift. Such a crop suitability change, especially from high to low suitability in the major rice growing areas, indicates decline in crop area and yield under the impact of climate change in the near future. Therefore, for improving the resilience and sustainability of the Bhutanese farms, a comprehensive climate change adaptation plan, backed up by in-depth research and policy instrument must be put in place.

The impacts of climate change on tea production systems may be very variable, at both the national and global levels. In particular, Sri Lanka is considered vulnerable to climate fluctuations due to a variety of geographic, socioeconomic, and political factors. The predicted effects of climate change could have serious and irreversible consequences for tea production, quality, and habitats. Therefore, the consequences of climate change on Sri Lanka's tea industry should be extensively researched to determine its impact on production and quality, which in turn related to export revenues and employment for rural populations. However, information is exiguous on how climate change could affect climate/land suitability and tea quality under rainfed conditions in Sri Lanka. To narrow this gap, this study aimed at evaluating the effects of climate change on climate/land suitability for tea and its quality using a case study of Sri Lanka, a well-known high-quality black tea producer, as a classic example of a susceptible region. The study used species distribution techniques, geographic information system (GIS), remote sensing (RS)–based applications, and chemical analysis of tea leaves. The systematic review suggested that the impacts of the current and future climate on tea production systems outweigh the beneficial impacts, having multidimensional and multifaceted consequences. Tea yield increases when CO₂ levels rise, but this positive effect could be hindered by rising temperatures. Further, tea yield would be negatively impacted by drought, uneven rainfall, and extreme weather events. For tea quality attributes, climate change can serve as both a boon and a bane, leaving questions and giving research priority to quantifying the thresholds of biochemicals to define tea quality, according to customer satisfaction. Climate change affects tea habitats by causing losses, gains, and shifts in climate suitability. Further review suggested the scarcity of appropriate method to model impacts of future climate changes on tea quality and for determining climate suitability for tea. It also highlighted the importance of implementation of adaptive and mitigation measures in tea production to alleviate the undesirable impacts of climate change. At regional scale climate modelling for Sri Lanka's tea sector, indicated that precipitation seasonality, annual mean temperature and annual precipitation are the three most important bioclimatic variables of tea habitat distribution in Sri Lanka. Land suitability classes for tea cultivation comprised of low suitability (42.1%), unsuitable (28.5%), moderate (12.4%), highly suitable (13.9%), and very highly suitable (2.5%). There is a chance of decrease in optimal and medium suitability areas in low-elevation regions in the future, with overall decline assessed to be between 8-17% for all suitability areas. This indicating that climate change will have a negative effect on the habitat suitability of tea in Sri Lanka by 2050 and 2070. Further, the refinement in land suitability classification through inclusion of other climatic and environmental variables (solar radiation, temperature, rainfall, topographic and soil) in climate model made two suggestions namely (1) there is a noticeable difference between tea- and non-tea-growing areas in terms of all above factors" (2) under future climate change scenario, tea-growing regions in Sri Lanka could expand to a range of locales, if some key variables are carefully managed.

For tea quality assessment, model showed a significant interaction effect of weather conditions, cultivar, and geographical location over the concentrations of major tea quality biochemicals (total polyphenol content (TPC), free sugar, protein, and theanine) in tea leaves. The bioclimatic variables present seasonality (monthly range in temperature and precipitation), monthly trends (mean monthly temperature, monthly total precipitation), and extreme environmental variables (temperature of the coldest and warmest month, and precipitation of the wettest and driest months). They particularly caused changes in the four tested biochemicals of tea. The thresholds of all tested biochemicals are likely to increase with future climate change as temperatures and rainfall intensities are likely to increase. The distribution class with "very high" concentrations of TPC and theanine is expected to increase by 10% and 14%, respectively, in the future, while protein and free sugar classes are expected to decrease by 14% and 12%, respectively. For tea quality assessment, model showed a significant interaction effect of weather conditions, cultivar, and geographical location over the concentrations of major tea quality biochemicals (total polyphenol content (TPC), free sugar, protein, and theanine) in tea leaves. The bioclimatic variables present seasonality (monthly range in temperature and precipitation), monthly trends (mean monthly temperature, monthly total precipitation), and extreme environmental variables (temperature of the coldest and warmest month, and precipitation of the wettest and driest months). They particularly caused changes in the four tested biochemicals of tea. The thresholds of all tested biochemicals are likely to increase with future climate change as temperatures and rainfall intensities are likely to increase. The distribution class with "very high" concentrations of TPC and theanine is expected to increase by 10% and 14%, respectively, in the future, while protein and free sugar classes are expected to decrease by 14% and 12%, respectively.