Effect of Climate change on various Rainfall events and

Weather and Climate Services over Mountainous Regions

1Indian Meteorological Society-Shillong Chapter North Eastern Space Applications Centre

Effect of Climate change on various Rainfall events and itsglobal Teleconnections over South Peninsular India during

Northeast Monsoon

Dr. Murali Nageswara Rao,

UCAR Visiting Scientist,

NOAA Center for Weather and Climate Prediction. Email: [email protected], [email protected] , [email protected]

M.M.Nageswararao1, 2*, M.C. Sannan3 and U. C. Mohanty3

1University Corporation for Atmospheric Research, Boulder, Colorado, USA 2NOAA Center for Weather and Climate Prediction, CPC International Desks, College Park, USA

3School of Earth, Ocean and Climate Sciences, IIT Bhubaneswar, Argul, Jatni, Odisha

Author(s)

Presented by:

mailto:[email protected]



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Introduction

In recent decades, a significant increase in global temperature has beenobserved and some of the findings indicate that the last three decadeshave been successively warmer on the Earth’s surface than anypreceding decade since 1850 (IPCC 2014).

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Introduction

The changes in temperature primarily affect the rate of evaporationfrom the oceans and leading to an increase in the water vapor contentin the atmosphere all over the globe (Trenberth 2011), Hence leadingto a huge change in the rainfall distribution and its variability.

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Introduction

Impacts of climate change are felt not only at a global levelbut also at a regional and local scale, Some effects compriseof fluctuating droughts and excess rains, changes in cycloneintensity, sea level rise, heat waves etc.

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Introduction

• Parts of India experience rainfalls through two monsoon seasons,the Southwest monsoon(SWM) and Northeast monsoon(NEM).

• About 80% of the annual rainfall in India is contributed by SWM ,however a large portion of Southern part of India that falls underthe rain shadow region, receive most of its rainfall in the NEMseason (Doraiswamy, 1946).

Northeast Monsoon Southwest Monsoon

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Introduction

• NEM season lasts from October to December and it is of a hugesocietal importance as it supports the main cultivation season (Rabi)over South Peninsular India (Krishna Rao and Jagannadhan, 1953;Kumar et al. 2007).

• The variability of NEM rainfall (28%) is more compared to SWMrainfall (10%)(Nageswararao, 1999).

Source : Kumar et al., 2007

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Introduction

• A few studies have pointed out that the NEM rainfall have strongrelationship with ocean-atmosphere phenomena such as El Niño/Southern Oscillation (ENSO) and Indian Ocean Dipole (IOD) (Deand Mukhopadhyay 1999; Bhanu Kumar et al. 2004; Kripalani andKumar 2004; Kripalani and Kumar (2004) and Rajeevan et al.(2012))

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Motivation & Objective

• Any irregular alteration of rainfall due to changes in regional climate

may cause a severe threat to the sustainability of life.

• Hence, a detailed study of the rainfall characteristics and its events

over this region is vital for provision of information to risk

management sectors for development of sustainable resources for

the region in the present global warming era.

• The Aim of this study is to analyze the long–term climatology,

variability and trends in the daily rainfall events over SPI at a sub-

divisional level during NEM and it’s changes in the recent period

under the influence of climate change.

• A necessary investigation of the variability of these rainfall events

and the associated rainfall with climate indices such as South

Oscillation Index (SOI), Niño3.4 SST, IOD mode index (IODMI),

ISMR is also conducted for the same.

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Study Domain

• SPI consists of the six meteorological

subdivisions, Coastal Andhra Pradesh

(CAP), Rayalaseema (RS), South

Interior Karnataka (SIK), Coastal

Karnataka (CK), Kerala (KL), and Tamil

Nadu (TN) as shown in the Figure .

• During the NEM season, India receives

about 11% of its annual rainfall, while

subdivisions of SPI receive 17–49% of

their annual rainfall and particularly TNreceives more (40–60%)

CAP- Coastal Andhra Pradesh

RS- Rayalaseema

SIK- South Interior Karnataka

CK- Coastal Karnataka

KL- Kerala

TN- Tamil Nadu

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Data and Methodology

• The high-resolution gridded daily rainfall analysis dataset (0.25°×

0.25°) from 1901 to 2016 by the India Meteorological Department

(IMD) is used to extensively analyze the rainfall.

• The rainfall events were classified into seven categories as per IMD

criteria as shown in the table below.

Descriptive Term used for event Rainfall amount in mm

Dry 0

Wet > 0

Very light Rain (VLR) 0.1- 2.4

Light Rain (LR) 2.5 – 7.5

Moderate Rain (MR) 7.5 – 35.5

Rather Heavy Rain(RHR) 35.5 – 64.4

Heavy Rain (HR) 64.4 – 124.4

Very Heavy Rain (VHR) 124.4 – 244.4

Extremely Heavy Rain (EHR) >244.4

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• The entire study is conducted in 2 time slices within the study

period (1901 to 2016),the pre-warming (1901–1958) period [P1]

and recent warming period (1959–2016) [P2].

• The daily grid point rainfall events aggregated over each

subdivision were used to inspect the various long-term statistical

features such as Climatology, inter-annual variability (IAV), and

linear trends of the daily rainfall events over six subdivisions and

SPI as a whole.

• Simple linear regression methods are used for computing the

trends. And the Student’s t-test has been applied to discern the

statistical significance of the trends and differences between the

two periods.

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• The secular variations in the relationship of various NEM rainfall

events with SOI, Niño 3.4 region SST, DMI, and summer monsoon

rainfall over SPI have been obtained by finding the sliding

correlations for a 31-years moving window for the period 1901–

2016.

• The data for climate indices (SOI, Niño 3.4 region SST and DMI) are

obtained from the Earth System Research Laboratory (ESRL) data

repository by National Oceanic and Atmospheric Administration

(NOAA) (https://www.esrl.noaa.gov) while the time series of

summer monsoon rainfall over SPI is prepared using the IMD high-

resolution (0.25° × 0.25°) daily gridded rainfall dataset.

https://www.esrl.noaa.gov/

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Results and Discussion

The spatial distribution of

NEM (OND) rainfall in mm

over SPI for the study period

(1901–2016).

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Fig. 5: Same as Fig. 5, but for frequency of various NEM rainfall (Wet, VLR, LR, MR,

RHR, HR, VHR and EHR) events.

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Results and DiscussionNormalized time series of accumulated rainfall & frequency of various

NEM rainfall events over South Peninsular India

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Results and DiscussionNormalized time series of accumulated rainfall & frequency of various

NEM rainfall events over South Peninsular India

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Results and DiscussionPercentage of various categorical rainfall events in NEM wet days and

their percentage contribution of rainfall over SPI

29.4 days

339 mm

SPI CAP RS

23.5 days

315 mm

22.2 days

226 mm

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22.2 days

203 mm

26.4 days

253 mm

42.3 days

494 mm

38.4 days

465 mm

SIK CK KL TN

Percentage of various categorical rainfall events in NEM wet days and

their percentage contribution of rainfall over SPI

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Results and DiscussionSub-division wise Climatology and IAV of NEM rainfall over SPI

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Results and DiscussionSub-division wise Climatology and IAV of NEM rainfall events over SPI

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Results and DiscussionContribution (in %) of various rainfall events to increase/decrease in the NEM

seasonal rainfall of the recent period (P2) with respect to earlier period (P1).

The line plot indicates the rainfall difference (P2-P1).

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Results and DiscussionSecular variations of simultaneous relationships of various NEM rainfall

events and associated seasonal rainfall with various climate Indices.

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Summary and Conclusion

• In the recent warming period, the seasonal NEM rainfall increased remarkably over TNand RS, while a widely spread decrease is noticed over KL, SIK, and CK. However, theIAV is found to have increased in all the subdivisions and particularly more in TN andKL.

• It was found that the contribution of MR events to the seasonal total rainfall over SPI ismore compared to rest of the rainfall events. Although, in the recent period, MR eventscontributions to the NEM rainfall have remarkably decreased while the contributionsfrom high-intensity rainfall events (RHR, HR, VHR and EHR) have increased. The hugedecrease in MR events leads to decrease the Seasonal NEM rainfall.

• The various NEM rainfall events and associated NEM rainfall have a promisingrelationship with SOI, Niño–3.4 regions SST, DMI, and ISMR. However, theserelationships vary from the period–to–period in a wave manner throughout the century.The relationship of NEM rainfall with ENSO is found to have increased in the recentyears after 1995. But the relationship of the same with IODM remain comparativelylower.

• This study is very useful in determining the effects on various sectors due to thevariability of heavy rainfall events over SPI during this season and assists the riskmanagement sectors in adapting advanced technologies for a sustainable future in thepresent global warming era.

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Acknowledgements

Thank You for

AttentionPresenting Author contact details

Dr. Malasala Murali Nageswara Rao, UCAR Visiting Scientist,

NOAA Center for Weather and Climate Prediction, college park, MD, USA

Email: [email protected], [email protected] , [email protected]

A heartfelt gratitude for India Meteorological Department (IMD) for

providing observed gridded rainfall datasets and other data taken

from the Web sites.




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Effect of Climate change on various Rainfall events and