Surendra Poonia and A.S.Rao (Division of Natural Resources and Environment, Central Arid Zone Research Institute, Jodhpur-342 003, India)
ABSTRACT
Meteorological drought, which results due to failure of rainfall, is a common phenomena in arid Rajasthan. The rainfall below a critical level that is required for established economy leads to failure of crops and scarcity for drinking water. There are several indices viz., Palmer Drought Severity Index, Standardized Precipitation Index, Aridity Anomaly Index etc., for quantification of meteorological drought. Globally, the Standardized Precipitation Index (SPI) has gained wider acceptance for quantification of meteorological drought and its spatial extent. The main advantage of the SPI, in comparison with other indices, is that the SPI enables both determination of drought conditions at different time scales and monitoring of different drought types. This index captures the accumulated deficit (SPI < 0) or surplus (SPI > 0) of precipitation over a specified period, and provides a normalized measure (i.e. spatially invariant Z score) of relative precipitation anomalies at multiple time scales.
A detailed analysis of temporal and spatial extent of meteorological drought showed that the SPI classification limits originally proposed and developed for Colorado by McKee et al. (1993) is not indicating historical drought years 1987 and 2002 into neither severe or extreme drought category and therefore the classification limits of SPI are modified to suit SPI as a good meteorological drought indicator for the Indian arid region. The analysis showed that the decade 2000-2009 experienced highest number of moderate and severe droughts during 1960-2009 period. This is the period that the arid Rajasthan noticed decreasing rainfall trend and higher air temperatures compared to that in other decades in the region. The district-wise meteorological drought classification shows that the eastern parts have a lower frequency of drought occurrence (25-29 out of 50 years) compared to western parts of arid Rajasthan (28-32 out of 50 years) and details for each district were presented. Monthly SPI also calculated to know drought characteristics of onset, severity and spatial extent on a year to year basis. To validate the SPI as a drought indicator a multiple-linear regression analysis between SPI of June, July, August and September as independent variables and pearl millet grain yield as dependent variable was made. The regression model for prediction of pearl millet yield with SPI explained 71% of millet grain yield and thus SPI is found useful as a good indicator for monitoring drought in the arid Rajasthan.
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