International Archives of the Photogrammetry, Remote Sensing and Spatial Information Sciences, Vol XXXV, Part B7. Istanbul 2004 
On the contrary, hydrological drought intensity was reverse in 
the terrain while vegetation health was almost normal. During 
1995 — 1996 non-monsoon season, poor rainfall imparted stress 
on both aquifer recharge and vegetation health, particularly in 
the eastern sector. Aravalli terrain received good monsoon 
rainfall in the year 1996 except a western pocket. As a result, 
the terrain was free of hydrological drought except the western 
pocket and normal vegetation health was regained. During 1999 
— 2000, the terrain encountered two successive poor monsoons 
and an intermediate normal non-monsoon period. A good non- 
monsoon rainfall was "insufficient for aquifer recharge. 
Consequently, hydrological stress that initiated during the 
monsoon of 1999 resulted severe drought all over the terrain 
during the monsoon of 2000. Mild to moderate vegetative 
drought resulted all over the terrain during the monsoon of 
2000, as vegetation could not withstand the impact of two 
successive poor monsoons and three consecutive hydrological 
droughts. 
4. CONCLUSIONS 
The SPI maps show that meteorological drought appear in the 
Aravalli terrain frequently but in an irregular manner. They 
further reveal that meteorological drought being a function of 
precipitation is not partial to any particular sector of the Aravalli 
terrain i.e. the terrain cannot be classified into drought zones 
and no-drought zones based on SPI anomaly. Although 80% of 
the annual rainfall occurs in the monsoon season, drought visits 
the terrain in either seasons and in some years in both the 
seasons. 
The SWI algorithm and classification scheme functions 
successfully in monitoring hydrological drought in the Aravalli 
terrain. The SWI maps reveal that unlike meteorological 
drought, hydrological drought follows some patterns in the 
Aravalli terrain. They further demarcate some drought zones 
and drought prone areas. The most remarkable discovery of the 
time-series maps of SWI is the alternate shift of drought and 
drought pattern with time. 
In the Aravalli terrain, vegetative drought sets no seasonal or 
spatial pattern. The VHI maps indicate that vegetation growth is 
although dependent on water supply through rainfall and 
irrigation, it can withstand adverse meteorological and 
hydrological conditions for several seasons to maintain good 
vegetation health. In the Aravalli terrain, hydrological drought 
develops faster and recovers slower. On the contrary, vegetative 
drought is slow to begin but quicker to withdraw. 
Drought being a natural hazard refers to the adverse impacts on 
natural spheres and not to the causes for the impacts. Since 
precipitation is the primary cause for drought development, 
negative SPI anomalies do not always correspond to drought in 
reality, as it takes no account of impact. Therefore, SWI and 
VHI together presents better pictures and perceptions of 
drought, particularly in the semi-arid terrain of Aravalli. 
References from Journals: 
Agnew, C. T. 2000. Using the SPI to identify drought. Drought 
Network News, 12(1), pp. 6-12. 
Bhuiyan, C., Flügel, W. A., and Singh, R. P., 2004. Behavior of 
Ground Water Table in Response to Monsoon Rainfall in Parts 
of Aravalli Terrain, J. Hydrol. (Communicated). 
Dracup, J. A., Lee, K. S., and Paulson Jr, E. G., 1980. On the 
Definition of Droughts. Water Resources Research, 16(2), pp. 
297-302. 
Kogan, F. N., 1990. Remote sensing of weather impacts on 
vegetation in non-homogeneous areas. /nf. J. Remote Sensing, 
1 1(8), pp. 1405-1419. 
Kogan, F. N., 1995. Application of vegetation index and 
brightness temperature for drought detection. Advance in Space 
Research, 15(11), pp. 91-100. 
Kogan, F. N., 2001. Operational Space Technology for Global 
Vegetation Assessment. Bull. Amer. Meteor. Soc., 82(9), pp. 
1949-1964. 
Kogan, F. N., 2002. World Droughts in the New Millennium 
from AVHRR-based Vegetation Health Indices. Eos, 
Transactions, Amer. Geophy. Union, 83(48), pp. 562-563. 
Kogan, F. N., Gitelson, A., Edige, Z., Spivak, l., and Lebed, L., 
2003. AVHRR-Based Spectral Vegetation Index for 
Quantitative Assessment of Vegetation State and Productivity: 
Calibration and Validation. Photogrammetric Engineering & 
Remote Sensing, 69(8), pp. 899-906. 
Komuscu, A. U., 1999. Using the SPI to Analyze Spatial and 
Temporal Patterns of Drought in Turkey. Drought Network 
News, 11(1), pp. 7-13. 
Singh, R. P., Roy, S., and Kogan, F. N., 2003. Vegetation and 
temperature condition indices from NOAA-AVHRRA data for 
drought monitoring over India. /nt. J. Remote Sensing, 24(22), 
pp. 4393-4402. 
References from Books: 
Department of Science and Technology (DST), Govt. of 
Rajasthan, India, 1994. Resource Atlas of Rajasthan. 
ESRI, 1996. Using Arc View GIS. 
References from Other Literatures: 
Ground Water Department (GWD), Government of Rajasthan, 
India, 2000. Annual Report (Unpublished). 
Mc Kee, T. B., Doesken, N. J., and Kleist, J., 1995. Drought 
monitoring with multiple time scales. In: Proceedings of the 
Ninth Conference on Applied Climatology, pp. 233-236. Amer. 
Meteor. Soc., Boston. 
Acknowledgements: The author is thankful to Dr. Felix Kogan 
of NOAA for providing NOAA-AVHRR processed data, and 
for his valuable suggestions through personal communications, 
and to Prof. (Dr.) R. P. Singh, for his technical support and 
advice. Sincere thanks are due to Dr. S. M. Pandey, Ex-chief 
Geophysicist, Ground Water Department, Rajasthan, for his 
kind help and support during collection of meteorological and 
hydrological data and records. 
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