Meteorological and Agricultural Drought Monitoring Using Geospatial Techniques

Droughts occur due to scarcity of water. Meteorological drought is result of the impacts of lower than usually occurring rains and the agricultural drought is the result of impacts of non availability of sufficient water on the crops. The drought can be viewed as moisture deficit that can generate social, environmental or economic impacts. For quantifying intensity of drought a number of drought indices were developed. These indices were calculated on selected locations where the rainfall data was observed or there was some method to assess the water needs of the crops. The long term averages of rainfall played important role in computing the values of these indices. The method of deciles developed by Gibbs (Gibbs WJ, Maher JV (1967) Rainfall deciles as drought indicators. Bureau of Meteorology Bulletin No 48, Commonwealth of Australia) could define the onset, strength and cession of the drought by comparing the actual rainfall with the rainfall below deciles value. The Palmer Drought Severity Index (PDSI) was developed keeping in view the water needs of crops. Many more indices were developed using the point station data. Estimation of hydro-meteorological variables through remote sensing could help in estimating the spatial distribution of the drought indices and thus the drought intensities. The development of Normalised Difference Vegetation Index (NDVI) could help in assessing the vegetation health on large regions. Further development of a series of drought indices based on the remote sensing of other parameters combined with NDVI resulted in ability to monitor, analyse and predict droughts. The drought monitoring systems are used to get information for a country or a region or the entire globe. The objective of this chapter is meteorological and agricultural drought monitoring with emphasise on the use of remote sensing.