The occurrence of a value of a weather or climate variable way above or way below a threshold value normally results in an abnormal weather related event which could be termed as an extreme event. The most commonly occurring extreme events are floods resulting from high precipitation, droughts resulting from deficient rainfall conditions, and heat waves on account of extreme temperatures. India has a long coastline of approximately 8000 km and faces regular threats of cyclones, storm surges and inundation. The extent of regions affected by droughts has also increased as precipitation over land has marginally decreased while evaporation has increased due to warmer conditions. A new global ranking, calculating the vulnerability of 170 countries to the impacts of climate change over the next 30 years, identifies Bangladesh and India as the two countries facing the greatest risks to their populations, ecosystems and business environments (Maplecroft, 2010, ‘South Asia most at risk from climate change, Scandinavia safest’).
Drought: A period of abnormally dry weather long enough to cause a serious hydrological imbalance – drought, is a relative term. Therefore any discussion in terms of precipitation deficit must refer to the particular precipitation-related activity that is under discussion. For example, shortage of precipitation during the growing season impinges on crop production or ecosystem function in general due to soil moisture drought, (agricultural drought) and during the runoff and percolation season primarily affecting water supply due to hydrological drought. Storage changes in soil moisture and groundwater are also affected by increases in actual evapotranspiration in addition to reductions in precipitation. A period with an abnormal precipitation deficit is defined as a meteorological drought. A mega drought is a very lengthy and pervasive drought, lasting much longer than normal, usually a decade or more (IPCC 2012).
It is projected that in the South Asian region, the average temperature would continue to rise resulting in drier conditions. Variability in rainfall with shorter and intense periods of rain is projected to increase (IPCC 2007) which would mean that there will be upward trend in the frequency and intensity of droughts. India being a country with vast arid and semi-arid regions will have to face severe consequences particularly in terms of water availability. It would adversely affect agriculture in the rainfed areas and thereby the livelihoods and food security of the country.
Rajasthan, Gujarat and Andhra Pradesh are India’s most severely drought affected states. P Gore et. al. 2010, in his work ‘Mapping of drought areas over India’, published in a research report of India Meteorological Department; stated that major parts of India show probability of severe drought in the range 1 to 5 per cent. In some parts of India’s northwest, northern hilly and peninsular region, probability of severe drought is in the range of 6 to 10 per cent. Further ahead in parts of northwest region and in small hilly areas, the probability of severe drought is greater than 10 per cent. S Bhattacharya et. al., 2007, in the paper ‘Vulnerability to drought, cyclones and floods in India’, published by Winrock International; has calculated the probability of drought in India between 0.033 (Odisha) to 0.3 (Punjab).
Flood: The overflowing of the normal confines of a stream or other body of water – or the accumulation of water over areas that are not normally submerged – floods, include river (fluvial), flash, urban, pluvial, sewer, coastal and glacial lake outburst floods.
Dwindling number of rainy days and the increase in the intensity of precipitation events has been projected to occur more frequently in India. River basins, mega-deltas and urban areas will be at an increased risk of flooding. This would mean social displacement and increase in loss of lives, damage to infrastructure and economic production. The 2005 floods in Mumbai demonstrated how in a single day, rain could exceed the collective rainfall of the season and offset every projection. The incidence of floods in newer areas such as the arid region of western India reflect the changing face of extreme event related risks expanding their areas of influences to regions not understood as vulnerable before.
Heat Wave: A heat wave is a prolonged period of excessively hot weather, which may be accompanied by high humidity. While definitions vary, a heat wave is measured relative to the usual weather in the area and relative to normal temperatures for the season. The term is applied both to routine weather variations and to extraordinary spells of heat which may occur only once a century. Severe heat waves have caused catastrophic crop failures and thousands of deaths from hyperthermia.
In India, many heat related deaths go unreported as they are taken to be the consequences of existing ailments. A heat wave caused 100 deaths in Bengal in 2012, more than 1200 deaths in 2002 in Southern India and 2042 deaths in 1998 in Odisha. Apart from death, there has been increase in the incidence of sunstrokes, severe dehydration, vomiting and high fever. Heat wave also affects animal health and their productivity.
Cyclone: In meteorological terms, cyclones refer to any low pressure area with winds moving inwards – rotating clockwise in the southern hemisphere and anti-clockwise in the northern hemisphere. A variety of low pressure system types may be referred to as tropical cyclones, hurricanes and tornadoes in various regions of the world.
Basic favourable environmental conditions for tropical cyclone formations are the sea surface temperatures, conditional instability, and relative humidity. Warmer seas, measured as temperatures in excess of 26 to 27o C to a depth of 60 m with abundant water vapour through evaporation, are likely to increase the frequency and intensity of tropical and extra-tropical cyclones. During the past three decades the number of tropical cyclones of Category 4 (wind speed 210/250 km/hr) and above has increased sharply from 8 to 25 per cent in the North Indian Ocean and 18 to 34 per cent in South Indian Ocean basins – the largest among the ocean basins of the world (P J Webster et. al., 2005, ‘Coastal and Marine Risks in South Asia: Key issues and Challenges’, Science). This is likely to intensify hazard exposure in existing cyclone hotspots which are already densely populated, supporting a range of economic activities (P G Chakrabarti 2011, ‘Disaster management and climate change’, Discussion paper series, CSM). In fact studies reveal that the eastern states in India are more adversely affected by cyclonic storms than the western ones (S Tholkappian et. al. 2006 ‘Relative vulnerability of Indian coastal districts to sea-level rise and climate extremes’, International Review for Environmental Strategies), with Odisha being the most frequently affected.
Various studies have shown that the losses due to extreme events are increasing steeply specially in the last decade of the 20th century. Loss of lives, ecosystems, biodiversity and key infrastructures would enormously affect the socio-economic conditions of the nation. Though the increase in extreme events could be attributed to climate variation the impacts are exacerbated by many factors including the poor design of infrastructures and installations – especially in the cities and towns, high density of urban settlements, poor governance, weak institutions and lack of community based approaches.
Management of Extreme Events
Community based disaster risk reduction strategies and adaptation to climate change are the best available response options to manage risks arising out of extreme events. A good starting point would be to conduct vulnerability analysis across the regions to map the vulnerability prone areas for further action. In fact, focus on the underlying causes of vulnerability is very important in designing appropriate risk management strategies. Early warning systems, good and accurate weather forecasting would help avoid / prevent the risks arising out of extreme events, apart from the integration of local knowledge. Monitoring, research, periodic evaluation, planning are critical elements of disaster and extreme events risk reduction as is training and capacity building at grassroot levels.