Using an Improved Coupling Drought Index to Predict the Persistence of Meteorological Drought over West Central India



Guha, Shreya

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The objective of this study is to investigate the role of the atmospheric boundary layer (ABL) and hence, roles of evaporation and convection in the process of intensification or persistence of meteorological droughts in west central India. The reason of choice of this region is that it is seen to be statistically significant in terms of spatial extent of droughts from 1951-2010. Although local geographic factors influence rainfall in this region, the main source of precipitation is the Southwest monsoons during the months of June, July, August and September (JJAS); which are affected by the tropical sea surface anomalies; and hence by El Nino/Southern Oscillation (ENSO), Indian Ocean Dipole (IOD) and other synoptic systems (like monsoon depressions) which are due to the dynamical instabilities of the mean circulation. These affect the slowly changing variable soil moisture; the soil moisture anomalies then affect the summer rainfall. However, most of the land-atmosphere coupling studies conducted earlier over India ignore the role of the ABL which controls the major thermodynamics and dynamical circulations. Hence, here we try to apply the concept of coupling drought index (CDI) during the periods of monsoon onset (March, April, and May [MAM]) over the entire spatial extent over the time-period of 1979-2010; when the atmosphere represents somewhat transitional coupling conditions, to identify regions of dry and wet coupling regions. Here, however, while testing the normality of the soil moisture anomaly curves, we have replaced the Kolmogorov-Smirnov Test with the Anderson-Darling test to build an improved CDI to gain more accuracy and sensitivity. Thereby, it is expected to predict whether drought will persist, intensify, or recover over the study region. The results from the developed index indicated that the drought conditions would neither intensify nor recover over the study region for the year 2011 and would continue to persist as it was for the past three decades. The observations validate this result. Keywords: Improved coupling drought index, meteorological drought, west central India, Anderson-Darling Test



Improved coupling drought index, Anderson-Darling test, Meteorological drought, West central India