Analysis of regional droughts intensity and frequency over north Gujarat

Drought is one of the most frequently happening national disasters in India. Droughts are the costliest natural disaster of the world and affect more people than any other natural disaster (Wilhite, 2000). First Scarcity Manual was Droughts are generally considered as periods with insufficient precipitation, soil moisture and water resources for sustaining and supporting the socio-economic activities of a region. Indian agriculture continues to be a gamble of the vagaries of monsoon, rainfall being most critical because nearly 70 % of the net sown area is still rain dependent (Narain et al,. 2006). Greogory and Parthasrathy (1986) studied large-scale droughts over India. In north Gujarat monsoon-rainfall is the only possible mean for ground water recharge. The monsoon activity commences from middle of June and retreats by mid September in the region. A continuous spell of poor rainfall during successive years in combination with high temperature affects ground water recharge and imparts stress on ground water resources leading to severe drought in many parts of this region. The rainfall distribution is extremely uneven and irregular as the state is located at the peripheral boundary of the main current of SouthWest monsoon. The average annual rainfall over different parts of north Gujarat varies widely from 250 mm in the Western half of Kutchh to 1000 mm in the eastern parts. Generally, the number of rainy days increases towards the eastern and the southern parts of the state.

Drought is one of the most frequently happening national disasters in India. Droughts are the costliest natural disaster of the world and affect more people than any other natural disaster (Wilhite, 2000). First Scarcity Manual was Droughts are generally considered as periods with insufficient precipitation, soil moisture and water resources for sustaining and supporting the socio-economic activities of a region. Indian agriculture continues to be a gamble of the vagaries of monsoon, rainfall being most critical because nearly 70 % of the net sown area is still rain dependent (Narain et al,. 2006). Greogory and Parthasrathy (1986) studied large-scale droughts over India. In north Gujarat monsoon-rainfall is the only possible mean for ground water recharge. The monsoon activity commences from middle of June and retreats by mid September in the region. A continuous spell of poor rainfall during successive years in combination with high temperature affects ground water recharge and imparts stress on ground water resources leading to severe drought in many parts of this region. The rainfall distribution is extremely uneven and irregular as the state is located at the peripheral boundary of the main current of South-West monsoon. The average annual rainfall over different parts of north Gujarat varies widely from 250 mm in the Western half of Kutchh to 1000 mm in the eastern parts. Generally, the number of rainy days increases towards the eastern and the southern parts of the state. were selected for study where long period (>30 yeras) rainfall data were available. The drought intensity as per the India Meteorological Department classification (annual rainfall deficit from normal) as given below was calculated.

Criterion for drought intensity
Departure of rainfall from normal (%) Drought intensity 0-25% Mild 26-50% Moderate >50% Severe Bhuj experienced 7 mild, 6 moderate and 11 severe droughts during the past 42 years. Drought of different intensities at Bhuj is demonstrated in Table 1. Annual rainfall of Bhuj varied from 13.6 mm in 1987 to 917.0 mm in 1989 with a normal of 384.2 mm with standard deviation (SD) of 247.9 mm and coefficient variance (CV) 64.5%. During the last 42 years, 22 years (15%) rainfall were below normal. The severe droughts were occurred once in 4 years, while moderate droughts occurred once in 7 years and mild droughts occurred in every 4 years ( Table 1).
Drought of different intensities at Kandla showed that the severe drought occurred once in 5 years moderate droughts occurred once in 6 years and mild droughts occurred in every 5 years (Table 1).
The frequency of drought conditions were more common at Sardarkrushinagar followed by Deesa, Ider, and Ahmedabad.
Sixty two percent (19 years) of the years received rainfall less than normal at Sardarkrushinagar. Drought of different intensities at Sardarkrushinagar (Table 1) showed severe drought years. The severe drought was occurred once in 7 years while moderate droughts occurred once in 9 years and mild droughts occurred once in 6 years (Table  1). Nine years received more than 20% rainfall than normal rainfall during the period of 31 years (1981 -2010).

Received : December 2011 ; Accepted : May 2012
years received more than 20% rainfall than mean rainfall during the period of 42 years (1969 -2010).
The maximum rainfall deficiency occurred during at region Ider, which was characterized as severe drought years. The severe drought was occurred once in 11 years, while moderate droughts occurred once in 11 years and mild droughts occurred in every 4 years (Table 1). Ten years received more than 20% rainfall than normal during the period of 40years (1969-74 and 1977-2010. Fifty seven percent (23 years) of the years received rainfall less than normal at Ider.