Drought Assessment using Z-Score for Vidarbha Region, Maharashtra

Drought is a long-period gradually creeping natural disaster, caused due to continued dry spells of rainfall with considerable lack of rainfall. Thus, it is characterized by sustained low precipitation, significant fall in groundwater and surface water levels, scarcity/non-availability of drinking water and adverse impacts on crop production. Vidarbha region of Maharashtra state is one of the most drought prone regions of India, as it frequently experiences continued dry spells. A statistical analysis has been attempted to study these dry spells over eleven districts in the Vidarbha region. The present study aims to monitor the drought occurrence on the basis of rainfall using statistical Z score in the Vidarbha region of Maharashtra. For this analysis, monthly precipitation data over 11 districts of Vidarbha have been collected from IWP during 1951-2020.  The autocorrelation function (correlogram) for these monthly precipitation data over each district of Vidarbha region, has been plotted for determining the randomness of the data set. The autocorrelation values lie outside the upper confidence level and lower confidence level, which strongly infers that the data are purely dependent. Since the data are not random so, the concept of probability distribution function fitting is not likely to be suitable for forecasting the monthly precipitation values. Different types of models, for example Markov chain model, moving average method, Box Jenikens model are more likely to be preferred for forecasting monthly precipitation.  Statistical Z score index on different time scales (3, 6, 9, 12 and 24 months) has been utilized for monitoring drought years and severity of drought conditions over the study region during 1951-2020. It has been found that higher time scales of Z score can better indicate severe drought events over individual districts of Vidarbha region.