ASSESSMENT OF COMPOUND EXTREMES IN INDIA USING STATISTICAL METHODS AND THEIR IMPACT ON TERRESTRIAL ECOSYSTEM

Abstract

Compound extremes are two or more extreme events occurring simultaneously or successively that have a huge impact on the ecosystems. Multiple variables play an important role in causing such events. Assessing the compound extremes is crucial to understanding the hydroclimatic variables and their dependence. This study assesses the compound hot-dry, hot-wet, cold-dry, and cold-wet extremes using the temperature and precipitation datasets in India, and further quantifies the impact of compound hot and dry extremes on terrestrial ecosystem productivity. The ecosystem response to hot-dry events is compared with the responses to hot and dry events to understand the cumulative impacts of compounding of extreme hot and dry conditions. Compound extremes were assessed using the empirical and multivariate distribution analysis for the period 1971-2020. The empirical analysis shows an increase in hot-dry and hot-wet conditions throughout the country, whereas there is a decrease in cold-dry and cold-wet days in the 50 years. The multivariate distribution analysis is done to analyze the dependence between precipitation and temperature using Copula. Six different copulas from two copula families, namely Gaussian, Student t, Clayton, Gumbel, Frank, and Joe, are chosen to study the compound extremes. The comparison of empirical and multivariate approach reveals that the probability of occurrence of compound extremes is found to be higher for empirical analysis than multivariate analysis. Further, the impact of compound hot, dry, and hot-dry extremes on the terrestrial ecosystem was assessed using gross primary production and ecosystem water use efficiency as indicators of terrestrial ecosystem functioning and responses. Among hot, dry, and hot-dry conditions, the dry event shows a maximum negative impact on the productivity of the terrestrial ecosystem, followed by hot-dry and hot conditions. The arid regions experience a decrease in productivity for all three conditions, whereas other climate zones indicated mixed responses to these conditions. The water use efficiency shows an overall positive response to the extremes. These findings can provide a better insight into the impact of compound extremes on the terrestrial ecosystem in India and help the decision makers for better ecosystem management under the projections of increasing compound extremes in the country.