STUDY OF REGIONAL DROUGHT CHARACTERISTICS AND ENVIRONMENT

Abstract

Water is regarded as the important natural resource for the well-being of Society and existence of life on the earth. Increasing population and industrialization reduces the water supply for agricultural and domestic purposes. Major reason of reduced water supply is lack of precipitation, which leads to effect the usual social, economic and developmental activities of that region. When there is prolonged shortage of water supply or the occurrence of rainfall lower than the average for a given region then it is said to be drought. Among all the natural hazards droughts are the most severe around the globe, occurring in every region and spreads over lager area than earthquake and floods. The recent studies on hydrologic extremes indicate that even after advancement in technology every region in the world is susceptible to ill-effects of droughts. In India droughts are very frequent which results in loss of about ten millions of lives over the period of 18th, 19th, and 20th centuries. The agriculture in India is heavily dependent on the rainfall especially the rainfall from the south west monsoon. The monsoon failure leads to the reduced water supply and reduction in the crop yield. Keeping this in mind, the study focuses on the behavior of regional meteorological drought characteristics (i.e. frequency, severity and its duration) across the different climatic regions of India and its relationship with the various climatic parameters. In this study, long-term rainfall data of 113 years (1901-2013) of 516 districts of India located in different climatic regions has been used. In India, mean annual rainfall (P) ranges from 100 mm at Jaisalmer in Rajasthan to 4700 mm at Tamenlong in Manipur and the mean potential evapotranspiration varies from 1340 mm in Kottayam, Kerala to 2664 mm at Jaisalmer (in Rajasthan). In India, about 80-90% of the annual rainfall occurs during the monsoon (rainy) season and the deficit during the monsoon season of a year usually continue till the arrival of next monsoon season. Therefore, in this study the seasonal rainfall departure from corresponding long term mean has been used to identify the drought years and its severity. The analysis revealed that the average return period of drought can be described using the climatic parameters in terms of ratio of average annual potential evapotranspiration to average annual rainfall (PET/P). The average return period of drought and its severity have notable related to the PET/P ratio. The average return period of drought increases gradually from dry to wet regions, from 2-3 years in the arid regions (12 > PET/P  5), 4-6 years in the semiarid regions (5 > PET/P  2) and 6-9 years in the sub-humid regions (2 > PET/P  3/4) and 10 years or more in humid regions. The arid and semiarid regions are more vulnerable to severe and frequent drought events than the areas in the sub-humid and humid regions. The areas with PET/P ratio of less than or equal ii to 1.5 has much rare chance of occurrence of severe drought events. In the regions with PET/P ratio less than 1.5, the occurrence of extreme droughts are almost none. Further, the more frequent and persistent droughts occur in arid and semi-arid regions than in the other climatic regions. This study can be used as a sensible tool for prediction of regional drought characteristics and to sensitize the drought response system for proactive planning based on long term regional pattern. The study has been also carried out to explore the relationship of drought frequency and severity with the range of annual temperature variation. From the analysis of a large set of meteorological data in India from various climatic regions, the frequency and severity of meteorological droughts are found to be strongly related with the range of annual normal temperature variation (θR). The average drought frequency and severity increase with increase in θR, and vice versa. Specifically, parts of Gujarat and of Rajasthan and Gujarat States falling under arid climatic region (where θR varies in the range of 40 °C to 35 °C) faced droughts once in every three years and the maximum rainfall deficiency had been 70% or more. The semiarid regions which include central and south-west parts of India where θR varies from 35 °C to 30 °C have the average drought frequency of once in 4-6 years with more number of severe drought events. The places with θR ranging from 30 to 25 °C and 25 - 20 °C experienced droughts once in 6-9 and 9-14 years with maximum severity in the range of 57% to 45% and 45% to 35%, respectively. Regions θR < 20 °C generally experienced moderate droughts once in 14 years or more. Further, in this study, Standardized Precipitation Index (SPI) popularly known for drought monitoring using rainfall data coupled with Tennant method widely used for describing the environmental flow (EF) condition of a river in terms of percentage of average annual flow (%AAF) using the flow data during low and high flow season. For the conservation of natural and healthy ecosystem, minimum amount of good quality water, also known as environmental flow (EF), has to be preserved in rivers for their survival. For low flow season, the rainfall-runoff data of three catchments of Mahanadi basin (viz. Ghatora, Kurubhata and Salebhata); two catchments of Brahmani-Baitarini basin (Anandpur and Jaraikela); two catchments of the Godavari basin (Hivra and Nandgaon), and four catchments of Narmada basin (viz. Mohegaon, Manot, Hridaynagar and Sher) has been used. For high flow season, the rainfall-runoff data of five catchments of Mahanadi (viz., Salebhata, Ghatora, Kurubhata, Rampur and Simga), nine catchments of Godavari (viz., Hivra, Jagdalpur, Kumhari, Nandgaon, Nowrangpur, Penganga, Ramakona, Sardaput, Satrapur), one catchment of Brahmani-Baitarini basin (i.e. Anandpur), and one catchment of Tapi basin (i.e. iii Burhanpur) were used. The analysis reveals the existence of strong relationship between the two enabled EF prediction for even ungauged watersheds using SPI (rather than %AAF) derivable from more easily available rainfall data only. The suggested approach can be used to describe the environmental flow conditions during high and low flow season using easily available rainfall data only, useful for ungauged catchments.