statistically significant trend (at 95% confidence level) for
JJAS season and annual timescale for 1951–2016 (Fig. 6.1
d–f). The period 1951–2016 also witnessed 1.2%, 1.2% and
1.3% increase in dry area per decade for SW, NE monsoon
seasons and annual timescale, respectively. It is interesting
to note that the drying trends are slightly higher for annual
scale droughts. The analysis thus shows that the period
1951–2016 witnessed an increase in frequency and areal
extent of droughts. Consistent with this, previous studies
also reported an increase in frequency, duration as well as
the intensity of the monsoon droughts for the post-1960
period compared to the pre-1960 period (Mallya et al. 2016;
Mishra et al. 2016). Further, a relative enhancement of
moderate to severe drought frequency has occurred during
the recent epoch of 1977–2010 compared to 1945–1977
(Niranjan Kumar et al. 2013). Interestingly, an increase in
the episodes of two consecutive years with deficient monsoon has also occurred during the post-1960 period
(Fig. 6.1a; Niranjan Kumar et al. 2013). Studies highlight an
increasing trend in dry areas (Niranjan Kumar et al. 2013;
Mallya et al. 2016). The similar conclusions reached by
different studies using different datasets and approaches
provides a “high confidence” finding that frequency, as well
as percentage area under drought, have increased over the
Indian subcontinent during the second half of the twentieth
century when compared to the first half of the century.
Significant drying trend (negative values in SPEI), during
the SW monsoon season, was observed over the humid
regions of Central India, and over some regions of north-east
as well as west coast of India during 1951–2016 (Fig. 6.2a).
A wetting trend is noticed over north-west and few parts of
southern peninsular India (Fig. 6.2a). This indicates that the
humid regions exhibit a tendency towards drying and more
intense droughts during 1951–2016. This drying tendency is
seen prominently during recent decades (Yang et al. 2019).
Long-term (1901–2002) multiple data sources and methods
also revealed that droughts are becoming much more
regional in recent decades and depict a general migration
from west to east and over the Indo-Gangetic plain (Mallya
et al. 2016). This study also identified an increase in the
duration, severity and spatial extent of droughts during the
recent decades, highlighting the Indo-Gangetic plain, parts
of coastal south India and central Maharashtra as regions that
are becoming increasingly vulnerable to droughts. Strong
drying over the central and the north Indian regions
(Fig. 6.2a) has also been revealed from other observational
studies using rainfall observations (Krishnan et al. 2013;
Preethi et al. 2017a) and various drought indices (Pai et al.
2011; Niranjan Kumar et al. 2013; Damberg and AghaKouchak 2014; Yang et al. 2019). It is to be noted that these
regions are also accompanied by an increase in aridity
(Ramarao et al. 2019; Yang et al. 2019). As a result, the
conclusion regarding, the drying and potential for increasing
drought propensity over central and northern India, is a high
confidence finding.
During the NE monsoon season, the spatial trends in
SPEI depict an increase in drought intensity over the
majority of region (Fig. 6.2b). A similar pattern as that of
SPEI-SW is seen for the entire year (Fig. 6.2c) probably due
to the dominance of rainfall contribution from SW monsoon
compared to that of NE monsoon. It is worth noting that the
regions which witnessed significant drying trend, e.g. Central India, Kerala, some regions of the south peninsula, and
north-eastern parts of India, also experience higher annual
frequency of droughts, with more than two droughts per
decade on average for the 1951–2016 period (Fig. 6.2d),
thus confirming that these regions are becoming more vulnerable to droughts during recent decades (high confidence).
The frequent and intense droughts will likely pose significant challenges for food and water security in India by
depleting soil moisture and groundwater storages (Asoka
et al. 2017). Soil moisture droughts hamper crop production
in India, where the majority of the population depends on
agriculture and leads to famines over the region (Mishra
et al. 2019). Past studies have reported that the frequency
and areal extent of soil moisture-based droughts have
increased substantially during 1980–2008 (Mishra et al.
2014), and hence, efforts are being made to provide forecasts
of standardized soil moisture index over India (Mishra et al.
2018;
https://sites.google.com/iitgn.ac.in/expforecastland
surfaceproducts/erf-forecasted-sri-and-ssi).
Apart from the aforementioned observational studies, a
limited number of investigations using climate models are
available that provide additional insight into the drought
occurrence and variability. Among the various climate models participated in the Coupled Model Intercomparison Project 5 (CMIP5), very few could capture the observed
monsoon rainfall variability, particularly the frequent occurrence of droughts and spatial variability of rainfall during
drought years in the recent historical period (Preethi et al.
2019). Further, a marked increase in the propensity of monsoon droughts similar to the observations during the
post-1950s is reasonably well simulated by the high resolution (horizontal grid size *35 km) Laboratoire de
Météorologie Dynamique (LMDZ4) global model with telescopic zooming over the South Asia region (Krishnan et al.
2016). It is reported that the SPEI index at 12-month and
24-month timescales in historical simulation (with both natural and anthropogenic forcings) exhibits an increase in the
frequency and intensity of droughts during 1951–2005, which
is possibly attributed to the influence of anthropogenic forcing on the weakening monsoon circulation and rainfall over
the India subcontinent (Krishnan et al. 2016). It is important
to note that the climate models have a large bias in simulating
monsoon rainfall and its variability on different timescales
(Turner and Annamalai 2012; Chaturvedi et al. 2012;
122
M. Mujumdar et al.
JJAS season and annual timescale for 1951–2016 (Fig. 6.1
d–f). The period 1951–2016 also witnessed 1.2%, 1.2% and
1.3% increase in dry area per decade for SW, NE monsoon
seasons and annual timescale, respectively. It is interesting
to note that the drying trends are slightly higher for annual
scale droughts. The analysis thus shows that the period
1951–2016 witnessed an increase in frequency and areal
extent of droughts. Consistent with this, previous studies
also reported an increase in frequency, duration as well as
the intensity of the monsoon droughts for the post-1960
period compared to the pre-1960 period (Mallya et al. 2016;
Mishra et al. 2016). Further, a relative enhancement of
moderate to severe drought frequency has occurred during
the recent epoch of 1977–2010 compared to 1945–1977
(Niranjan Kumar et al. 2013). Interestingly, an increase in
the episodes of two consecutive years with deficient monsoon has also occurred during the post-1960 period
(Fig. 6.1a; Niranjan Kumar et al. 2013). Studies highlight an
increasing trend in dry areas (Niranjan Kumar et al. 2013;
Mallya et al. 2016). The similar conclusions reached by
different studies using different datasets and approaches
provides a “high confidence” finding that frequency, as well
as percentage area under drought, have increased over the
Indian subcontinent during the second half of the twentieth
century when compared to the first half of the century.
Significant drying trend (negative values in SPEI), during
the SW monsoon season, was observed over the humid
regions of Central India, and over some regions of north-east
as well as west coast of India during 1951–2016 (Fig. 6.2a).
A wetting trend is noticed over north-west and few parts of
southern peninsular India (Fig. 6.2a). This indicates that the
humid regions exhibit a tendency towards drying and more
intense droughts during 1951–2016. This drying tendency is
seen prominently during recent decades (Yang et al. 2019).
Long-term (1901–2002) multiple data sources and methods
also revealed that droughts are becoming much more
regional in recent decades and depict a general migration
from west to east and over the Indo-Gangetic plain (Mallya
et al. 2016). This study also identified an increase in the
duration, severity and spatial extent of droughts during the
recent decades, highlighting the Indo-Gangetic plain, parts
of coastal south India and central Maharashtra as regions that
are becoming increasingly vulnerable to droughts. Strong
drying over the central and the north Indian regions
(Fig. 6.2a) has also been revealed from other observational
studies using rainfall observations (Krishnan et al. 2013;
Preethi et al. 2017a) and various drought indices (Pai et al.
2011; Niranjan Kumar et al. 2013; Damberg and AghaKouchak 2014; Yang et al. 2019). It is to be noted that these
regions are also accompanied by an increase in aridity
(Ramarao et al. 2019; Yang et al. 2019). As a result, the
conclusion regarding, the drying and potential for increasing
drought propensity over central and northern India, is a high
confidence finding.
During the NE monsoon season, the spatial trends in
SPEI depict an increase in drought intensity over the
majority of region (Fig. 6.2b). A similar pattern as that of
SPEI-SW is seen for the entire year (Fig. 6.2c) probably due
to the dominance of rainfall contribution from SW monsoon
compared to that of NE monsoon. It is worth noting that the
regions which witnessed significant drying trend, e.g. Central India, Kerala, some regions of the south peninsula, and
north-eastern parts of India, also experience higher annual
frequency of droughts, with more than two droughts per
decade on average for the 1951–2016 period (Fig. 6.2d),
thus confirming that these regions are becoming more vulnerable to droughts during recent decades (high confidence).
The frequent and intense droughts will likely pose significant challenges for food and water security in India by
depleting soil moisture and groundwater storages (Asoka
et al. 2017). Soil moisture droughts hamper crop production
in India, where the majority of the population depends on
agriculture and leads to famines over the region (Mishra
et al. 2019). Past studies have reported that the frequency
and areal extent of soil moisture-based droughts have
increased substantially during 1980–2008 (Mishra et al.
2014), and hence, efforts are being made to provide forecasts
of standardized soil moisture index over India (Mishra et al.
2018;
https://sites.google.com/iitgn.ac.in/expforecastland
surfaceproducts/erf-forecasted-sri-and-ssi).
Apart from the aforementioned observational studies, a
limited number of investigations using climate models are
available that provide additional insight into the drought
occurrence and variability. Among the various climate models participated in the Coupled Model Intercomparison Project 5 (CMIP5), very few could capture the observed
monsoon rainfall variability, particularly the frequent occurrence of droughts and spatial variability of rainfall during
drought years in the recent historical period (Preethi et al.
2019). Further, a marked increase in the propensity of monsoon droughts similar to the observations during the
post-1950s is reasonably well simulated by the high resolution (horizontal grid size *35 km) Laboratoire de
Météorologie Dynamique (LMDZ4) global model with telescopic zooming over the South Asia region (Krishnan et al.
2016). It is reported that the SPEI index at 12-month and
24-month timescales in historical simulation (with both natural and anthropogenic forcings) exhibits an increase in the
frequency and intensity of droughts during 1951–2005, which
is possibly attributed to the influence of anthropogenic forcing on the weakening monsoon circulation and rainfall over
the India subcontinent (Krishnan et al. 2016). It is important
to note that the climate models have a large bias in simulating
monsoon rainfall and its variability on different timescales
(Turner and Annamalai 2012; Chaturvedi et al. 2012;
122
M. Mujumdar et al.