Agricultural Drought Indices - US Department of Agriculture

The analysis revealed that out of 135 years (1875–2009), SPI diagnosed five years (1877, 1899,
1918, 1972 and 2009) as All India extreme drought years when the SPI value exceeded -2.0. This
result was in agreement with the analysis of Mooley (1994), who while analyzing data from 1871 to
1996 found that in the years 1877, 1899, 1918, 1972, and 1987, Phenomenal All India droughts
affected the country. Mooley (1994) defined Phenomenal All India drought as a phenomenon
occurring when percent departure of monsoon season rainfall was ≤ -2 SD (i.e., -20%) and the
percentage area under deficient monsoon rainfall was equal to or more than mean+2 SD (i.e.,
47.7%). Therefore, Phenomenal drought years identified by Mooley (1994) have been effectively
diagnosed as extreme drought years by SPI. SPI was also able to properly diagnose the other All
India moderate/severe drought years that affected the country. Further, when SPI was used to
examine whether any trend existed in drought over the country, no trend was found (Figure 2).
However, it should be mentioned that despite the current optimism about SPI, it cannot solve all
moisture monitoring concerns. Rather, it can be considered as a tool that can be used in
coordination with other tools, such as the aridity anomaly index or remote sensing data, to detect
the development of droughts and monitor their intensity and duration. This will further improve the
timely identification of emerging drought conditions that can trigger appropriate responses by the
policy makers.
Figure 2. Temporal variation of Standardized Precipitation Index (SPI) in India, 1875-2004.
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