IMPACT OF CLIMATE VARIABILITY AND CHANGE ON DROUGHTS OVER INDIA

Abstract

Drought is a state of environment which represents the de ciency in the water availability for a prolonged period in comparison to its normal availability. Each year many parts of the world experience drought. Hazard caused by drought costs more than any other natural calamity. However, the negative impacts of drought can be alleviated with careful monitoring and e cient planning. India faces one drought in approximately every three years. The frequency of drought is likely to increase, however, not much emphasis has been given previously toward the assessment of future droughts. Therefore, in the present study an attempt has been made to develop a comprehensive methodological framework for drought modelling to understand the spatiotemporal variation of drought conditions and to analyse the impacts of changing climate under di erent development pathways on drought characteristics over di erent parts of India. The broad objectives of the present study are: (i) To analyse the impacts of climate variability on precipitation characteristics and droughts and to investigate the causal teleconnections between large scale coupled ocean-atmospheric process and droughts in India. (ii) To study the spatiotemporal variation of drought using a multi-indices approach using multiple regional climate models using two di erent Representative Concentration Pathways (RCPs). (iii) To study the probabilistic characteristics of droughts and the Severity-Area-Frequency and Severity-Duration-Frequency relationships. (iv) To analyse the univariate and bivariate joint return periods of severity, duration and intensity using copulas. These goals have been designed such that the gaps in the current state of the research literature can be bridged. The methodologies to achieve each objective and the brief outcomes from each objective are as follows: Analysis of causative factors of precipitation extremes The dependence of precipitation extremes on climatic factors such as El-Ni~no Southern Oscillation (ENSO) and global warming, and topographical factors such as land surface elevation has been investigated using seven di erent precipitation extreme indices along with four di erent large scale coupled ocean-atmospheric circulation-based indices. Most of the extreme precipitation indices (EPIs) exhibited a positive and statistically signi cant correlation of high magnitude with land surface elevation for the elevation band above 1500 meters. A spatial heterogeneity of teleconnections between precipitation extremes and the ii large-scale climatic indices was revealed. Most EPIs, except Consecutive Dry Days (CDD) and CWD, showed higher positive association with extreme events in contiguous region of Rajasthan, Madhya Pradesh, Uttar Pradesh and West Bengal. Investigation of causal teleconnections between ENSO and droughts The co-variation of ENSO and Indian drought conditions were studied using an advanced causality-based Granger causality test (GCT) which provides insights into the causal teleconnection relationship and the direction of information transfer. The results of the nonlinear approach were also compared with the traditional Granger causality test to elucidate the potential of the non-linear approaches in analysing the teleconnections. Results suggest signi cant potential of nonlinear Granger causality approach for examination of teleconnection of ENSO and Indian dry/wet conditions. Assessment of Impact of Climate Change on Drought Characteristics An assessment of impacts of climate change was performed for projected droughts over 21st century for India using data obtained from Regional Climate Model (RCMs) under Representative Concentration Pathways (RCPs) 4.5 and 8.5. The Standardized Precipitation Index (SPI), Standardized e ective Precipitation Evapo-Transpiration Index (SP*ETI) and Standardized Precipitation-Evapotranspiration Index (SPEI) were used for drought characterization. Analysis revealed that the increase in evapotranspiration due to the projected rise in temperature could play a major role in a ecting the future drought dynamics in most parts of India. North India is likely to be more vulnerable to increase in drought severity and frequency in the near future. However, in the far future, most parts of India, except few south-eastern states, are likely to face an escalation in drought severity and frequency. Further, change in periodic cycles of drought due to climate change was found to be insigni cant. Multivariate Modelling of Projected Drought Frequency and Hazard over India The multivariate dependence of various drought characteristics was examined by analysing the spatiotemporal characteristics of drought occurrence, frequency, and hazard. Copulabased improved methodology for developing SDF curves which uses Markov Chain Monte Carlo (MCMC) simulation for parameter estimation under the Bayesian framework is proposed. Moreover, an improved fuzzy clustering-based drought hazard assessment measure, iii named as the Modi ed Drought Hazard Index (MDHI), is also proposed. Analysis reveals that with the progression of time, drought severity associated with various durations is expected to increase signi cantly with increase in the duration for most of the regions. Modi ed drought hazard index performed better than the traditional drought hazard index. Copula-based Probabilistic Characterization of Drought over River Basins An analysis of drought characteristics over 22 river basins of India was performed for the historical and the projected periods. Dependence of drought characteristics was analysed using copulas. Several univariate distributions and bivariate copulas were tested to model the drought severity, duration and intensity, and their interdependence. An analysis of the uncertainty in the projection of precipitation, temperature and drought characteristics was also performed. Results indicate that the temperature exhibit signi cant increasing trend of high magnitude for the future period over all river basins in India. The Joint Return Periods (JRP) for the Severity-Duration, Duration-Intensity and Severity-Intensity were indicating more frequent occurrence of exceedance of 5, 10- and 50-year return values of any two characteristics in the same year during the NF than the FF. Most basins were projected to face extreme droughts in the far future; therefore, India needs better preparedness to mitigate these extremes. Future, attempts could incorporate the non-stationarity in assessment of drought indices. Moreover, impact of Atlantic and paci c based oscillation on droughts over India may also be studied. Hydrologic evaluation of drought for projected future may help us to assess the changing risks related to hydrological droughts over different basins over India.