SR-8 : Hydrological aspects of drought in 1985-86 (an interim report)

Abstract

National Institute of Hydrology established a Drought Studies Division in February 1986 with the major objective to study the hydrological aspects of drought and develop both short and long term drought management strategies. In view of the gravity of the drought situation during 1985-86, the Institute sent-out scientific and tech- nical teams to the States of Andhra Pradesh, Gujarat, Karnataka, Madhya Pradesh,Maharashtra and Rajasthan to acquaint with the drought situation and to collect necessary data and information for drought studies with emphasis on hydrological aspects. Due to limited time, only selected drought prone districts could be covered. Efforts were made to collect the required data for last 8 to 10 years including the latest ones for 1985-86. However, data in respect of the year 1985-86 could not become available for all the places. Therefore, the data of few selected sites have been used to demonstrate the hydrological aspects of drought and to emphasize their significance in analysing the drought situation of a particular area. On the basis of limited available data and preliminary analysis some interim conclusions have been made which perhaps may not be generalised for all the areas. The rainfall patterns of 1984 and 1985 over drought affected

meteorological sub-divisions indicate that Saurashtra region had

maximum rainfall deficit during the monsoon of 1985 which was of the

order of 55% as against 12% in 1984. Maharashtra had monsoon deficit

of the order of 30% to 40%. In Karnataka both South-West and North-

East monsoons failed during 1985 resulting in severe drought situ-

ation. Telangana and Rayalseema region of Andhra Pradesh continue to have rainfall deficits of about 30%. The categorisation of districts

on the basis of this year's and last year's rainfall deficits

indicates that in a number of districts there was Persistent effect

of deficit.Mahboobnagar in Andhra Pradesh appears to be having deficit for the last 3 years in succession, Prakasam and Cuddapah for the

last 2 years in succession In Gujarat except the Kutch, most of

the areas had a deficit of about 40% to 50% in 1985. Due to non-avail-

ability of rainfall data in Karnataka for the past few years, no

comparative study could be made. In Madhya Pradesh Dhar, Jhapua.,Betul

Shandol recorded a rainfall deficit of about 30% to 40% in 1985

whereas Khargon is having rainfall deficit for the second year in

succession. In Maharashtra 11 districts-Nasik,Ahmednagar, 5Ddapur,

Sangli, Aurangabad, Jalna,Parbhani,Beed,Nanded,Osmanabad and Latur are having persistent c.ainfall deficits for the last 2 years in succession. In Rajasthan, Tonk, Jodhpur and Barmer also recorded rainfall deficits for the second year in succession. In Andhra Pradesh, data of two reservoirs,Pedderu and Bahuda in Chittoor district indicate relatively lower reservoir levels during end of 1985 and beginning of 1986 as compared to their corresponding levels of past few years. However, the rainfall deficit in Chittoor appears to be less than 20%. In Gujarat, the data of surface water storages for Saurashtra region indicate significant reductions during 1985 causing irrigation and drinking water problems. Surface water storages in Rajkot, Jamnagar and Amreli were so poor that no area was irrigated. Rainfall deficit during monsoon was of the order of 25-50% in these areas except Amreli where it was less than 20%.

In Karnataka, mdiaprabhareservoir was affected in 1985 drought whereas Ghataprabha reservoir appears to have sufficient water. The flow data of Bhima and Sina (tributaries of Krishna) in Maharashtra indicatt significantly low flows during 1985 as compared to previous years. The available water in the major and medium irrigation tanks in Maharashtra confirms the severe drought situation. The deficit in reservoir storage (available water as percentage of designed live storage capacity) of the order of 70% to 80% has been observed in some of the districts in Maharashtra which by and large had rainfall deficit also for the second year in succession. Similar trends were observed in Madhya Pradesh and Rajasthan. The tanks located at Dungarpur, Banswara and Jodhpur in Rajasthan had significantly more deficit during 1985. Based on various observations it can be deduced that the deficit in reservoir storages is caused not only due to failure of monsoon in current year but also due to lack of the carryover-storage from the previous years. The groundwater levels in Prakasam district of Andhra Pradesh show decreasing trends in accordance with the decreasing rainfall trends. However, well-hydrographs in few blocks of Anantpur, Chittoor rnd Cuddapah districts do not show significant decreasing trends. It .s inferred that this might be due to the increased absifaction of froundwater as a result of which the system is tending to adjust to new equilibrium. Groundwater in western Madhya Pradesh is also obs- Tved to be affected. The premonsoon levels in the wells located n districts Dhar and Jhabua show drying of wells. The post-monsoon evels are observed to go down progressively with each year indicat- ng insufficient recharge. In Maharashtra, the lowering of groundwater ables and the problem of wells going dry during 1985 is evident from

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the data of seed and Ahmednagar which are facing rainfall deficits for the second consecutive year. Data for other districts could not be obtained. No conclusion can be drawn about Gujarat and Rajasthan as data were not readily available. Soil moisture data of sufficient magnitude and duration were not available to draw pertinent conclusions. In general there was acute shortage of drinking water and fodder in drought prone areas. No definite conclusions can be made for want of data. Crop production in general was affected during the Kharlf and Rabi 1985-86. This is observed from the crop yields estimates of different States. The report also concludes that it is not sufficient to go by the variability in total amount of rainfall alone but also to analyse and understand the time and space variability in the surface runoff streamflow, soil moisture conditions and ground water levels as well as the demand patterns to appreciate the very nature of impact that a drought situation causes. It is also suggested to have proper data base, regular hydrological monitoring viz-a-viz drought monitoring and soil moisture mcnitoring on regular basis.