ALVARINHO J LUIS
Climate change is no longer a projected future concern but a present and meas urable global phenomenon. Its impacts are increasingly evident through the rising frequency and intensity of extreme events observed over the past decade across multiple regions. Goa’s climate change has transi tioned from a potential threat to an ongoing environmental stressor. The State Action Plan for Climate Change indicates that increasing temperatures, altered precipitation patterns and intensified land-use chang es are contributing to accel erated ecological degradation and heightened socio-economic vulnerability. Climate change is influenced by both natural variability and anthropogenic forcing. Natural drivers include Earth’s orbital variations, fluctuations in solar radiation, and volcanic activity. In contrast, human activities— particularly the combustion of fossil fuels and deforestation— have led to substantial increases in greenhouse gas (GHG) con centrations, resulting in glob al warming. Consistent with broader global trends, Goa has experienced a significant rise in mean annual temperature exceeding 1°C over the period 1901–2018, with the most pro nounced warming occurring after 1990. The India Meteor ological Department’s (2013) analysis indicates that air temperature rise in Goa since 1970 (0.15-0.20°C/decade) surpassed the national average (0.1°C/decade). Annual mean rainfall, a criti cal determinant for agriculture and potable water availability, has exhibited a significant in creasing trend in Goa, rising by approximately 68% alongside enhanced interannual variabili ty since the 1970s. In North Goa, rainfall increased from ~3000 mm in 1901 to nearly 5000 mm by 2015 (~66%). These trends reflect pronounced regional cli matic shifts with implications for hydrological regimes, eco system dynamics, and climate adaptation planning. Long-term analysis (1901 2018) indicates a significant shift in rainfall characteristics in Goa, marked by declining frequencies of light-to-moderate precipita tion and a pronounced increase in extreme events. Rainfall days within Category 1 (2.5–64.4 mm) show a decreasing trend, where as Category 2 events (64.5–124.4 mm) have increased by ~60%. Notably, Category 3 events (>124.5 mm) have risen by over 100%, reflecting a clear intensifi cation of precipitation extremes and associated hydro-meteoro logical risks. Category 1 and 2 rainfall events support ecological func tioning, groundwater recharge, and agricultural productivity. In contrast, Category 3 events (very heavy rainfall) are linked to flooding, erosion, infrastruc ture damage, and ecosystem disruption. Their increasing frequency aligns with climate change projections, reflecting enhanced atmospheric mois ture-holding capacity under warming conditions. In Goa, inherent flood suscep tibility arising from coastal ge omorphology, fluvial networks, and rapid urban expansion is further exacerbated by the in creasing frequency and intensity of extreme rainfall events, there by amplifying flood risk and as sociated socio-economic and en vironmental vulnerabilities. Projected climate change Climate projections for Goa during the 21st century are de rived from high-resolution re gional climate models, assessing future temperature and precip itation under Representative Concentration Pathways (RCPs). Two emission scenarios are commonly evaluated: RCP8.5, representing a high-emission trajectory, and RCP4.5, reflect ing a stabilisation pathway with moderate mitigation. Un der RCP8.5, atmospheric car bon dioxide concentrations are projected to reach ~940 ppm by 2100, whereas RCP4.5 esti mates concentrations of ~538 ppm. These scenarios provide a robust framework for analysing long-term climatic variability, enabling assessment of poten tial impacts on regional hydrol ogy, ecosystems, and socio-eco nomic systems. Mean temperature projec tions (1901–2100), derived from regional climate model outputs, indicate substantial warming under both RCP4.5 and RCP8.5 scenarios relative to the 1901–1950 baseline. Under the high-emission RCP8.5 path way, mean air temperatures are projected to increase in Goa by approximately 4.5°C, whereas under the moderate-emission RCP4.5 scenario, the increase is estimated at ~2.5°C. These projections highlight the strong sensitivity of regional climate to cumulative GHS concentrations. Consistent with the Paris Agree ment, limiting global tempera ture rise to 1.5–2°C is essential; however, projections suggest that localised warming in Goa may exceed global averages. Mean air temperature pro jections for Goa over the peri od 1901–2100, derived from high-resolution regional cli mate model outputs, indicate significant warming under both RCP4.5 and RCP8.5 emis sion scenarios relative to the 1901–1950 baseline. Under the high-emission RCP8.5 pathway, mean temperatures are pro jected to rise by approximately 4.5°C by the end of the century. In contrast, the moderate-emis sion RCP4.5 scenario projects a comparatively lower increase of about 2.5°C. These projections underscore the strong depend ence of regional temperature responses on cumulative green house gas concentrations and highlight the critical importance of mitigation strategies in limit ing warming. In alignment with the Paris Agreement, global efforts aim to limit temperature rise to with in 1.5–2°C above pre-industrial levels to mitigate severe climate impacts. However, regional pro jections indicate that warming in Goa may exceed global aver ages, reflecting spatial heteroge neity in climate responses and associated risks. Coastal vulnerability The present rate of sea-level rise along India’s coast estimat ed from tide gauges is 1.3-1.8 mm/year. Projected sea-level rise is estimated at 20–30 cm by the end of the 21st century, with a global mean rise of 18±5 cm (relative to the 1986–2005 baseline) under the RCP4.5 scenario. In Goa, digital eleva tion model–based vulnerability assessments identify the ta lukas of Salcete, Tiswadi, and Bardez as highly susceptible to coastal inundation. A projected 1 m sea-level rise could affect nearly 7% of the State’s popu lation, posing substantial risks to coastal ecosystems, tourism infrastructure, and regional so cio-economic stability. A multi-hazard coastal vulner ability assessment done by NIO in 2014 using integrated param eters such as shoreline change, relative sea-level trends, coast al elevation, slope, tidal range, wave height, and geomorphol ogy indicates that ~30 km of coastline across Salcete, Bardez, and Tiswadi, particularly areas below 35 m elevation, are high ly susceptible to sea-level rise and coastal flooding. Observed shoreline erosion rates exceed 0.6 m/yr in Bardez and Salcete and ~0.3 m/yr in Tiswadi. Goa’s aquatic ecosystems along the creeks and riverine networks support high biodiver sity and productivity. Although some zones are protected by sluice gates and embankments, others remain vulnerable to saline intrusion, which is like ly to intensify under rising sea levels and altered hydrological regimes. In addition, groundwater extraction in several regions of Goa remains inadequately regulated, increasing the sus ceptibility of coastal aquifers to overexploitation and subse quent saline intrusion. Progres sive sea-level rise is expected to enhance the hydraulic gradient between marine and freshwa ter systems, thereby facilitating inland saltwater encroachment. Furthermore, elevated ground water tables in low-lying areas reduce soil infiltration capacity and impede natural drainage, leading to increased risks of wa terlogging and pluvial flooding. Consequently, urban areas like Panjim are likely to expe rience compounded hydroge ological stress and heightened flood vulnerability under future climate scenarios, driven by the interaction of sea-level rise, al tered hydrological processes, and anthropogenic pressures. [Dr Luis serves as a Sen ior Scientist at the National Centre for Polar and Ocean Research, Ministry of Earth Sciences, Government of India, Headland Sada. In addition to his scientific role, he is active ly engaged in freelance work]
