87

CHAPTER 5

ANALYSIS AND RESULTS OF METEOROLOGIAL AND

AGRICULTURAL DROUGHT ASSESSMENT

5.1 GENERAL

The proposed methodology as presented in the previous chapter

was applied to the study area for the drought assessment in meteorological

and agricultural aspects. The results obtained are presented and discussed in

this chapter.

5.2 METEOROLOGICAL DROUGHT ASSESSMENT

The assessment of drought severity for crop seasonal (Samba

season) rainfall in meteorological context was carried out employing IMD

method. Meteorological drought assessment has been carried out for all the

fifteen raingauge stations and the results are presented in Table 5.1. As seen

from the Table, many stations are affected by moderate and severe drought

condition during the years 1980, 1982, 1984, 1986, 1989, 1990, 1992, 1999,

2002 and 2004. During the year 1980, 7 stations were severely affected and 7

stations were moderately affected. In 1982, 5 stations were severely affected

and 6 stations were moderately affected. It is also observed that, during the

years 1980, 1982, 1986, 1989, 1999 and 2004, major portion of the district

was affected by severe and moderate droughts.

88

Table 5.1 Meteorological drought assessment in Vellore district using IMD method

Sl.

No.Station/Year 1971 1972 1973 1974 1975 1976 1977 1978 1979 1980 1981 1982 1983 1984 1985

1 Vellore M1 M0 M2 M2 M0 M0 M0 M0 M0 M2 M0 M2 M0 M1 M1

2 Ambur M2 M0 M0 M1 M2 M0 M0 M0 M2 M3 M1 M3 M0 M3 M0

3 Gudiyatham * M1 M1 M2 M1 M0 M0 M0 M0 M3 M0 M2 M0 M2 M1

4 Tiruppathur M1 M1 M2 M1 M1 M1 M1 M0 M1 M3 M0 M3 M0 M3 M2

5 Vaniyambadi * * M2 M0 M1 M1 M0 M0 M1 M3 M0 M2 M0 M2 M0

6 Walajahpet M1 M1 M1 M2 M0 M0 M0 M0 M0 M2 M1 M2 M0 M2 M0

7 Sholinghur M0 M0 M0 M0 M1 M0 M0 M3 M2 M3 M1 M3 M1 M2 M1

8 Ranipet M1 M1 M0 M1 M0 M0 M0 M0 M0 M2 M0 M1 M0 M1 M0

9 Palar Anicut M1 M1 M0 M1 M1 M1 M0 M0 M1 M2 M0 M2 M0 M2 M0

10 Ponnai Anicut M1 M0 M1 M2 M0 M0 M0 M0 M0 M2 M1 M2 M1 M1 M1

11 Arakonam M0 M0 M0 M1 M0 M0 M0 M0 M0 M1 M0 M0 M0 M1 M0

12 Kaveripakkam M1 M0 M1 M2 M1 M0 M0 M0 M1 M2 M1 M1 M0 M1 M0

13 Panapakkam M2 M0 M0 M1 M1 M0 M0 M0 M0 M2 M1 M1 M0 M1 M0

14 Alangayam M3 M0 M2 M2 M2 M1 M0 M0 M0 M3 M0 M3 M0 M1 M0

15 Jolarpet M1 M1 M2 M0 M1 M0 M0 M1 M0 M3 M0 M3 M0 M2 M1

Contd…

89

Table 5.1 (Continued)

Sl.

No.Station/Year 1986 1987 1988 1989 1990 1991 1992 1993 1994 1995 1996 1997 1998 1999

1 Vellore M2 M0 M0 M1 M1 M0 M0 M0 M0 M2 M0 M0 M0 M1

2 Ambur M1 M2 M1 M2 M2 M0 M2 M1 M1 M2 M0 M1 M2 M3

3 Gudiyatham M1 M1 M1 M3 M2 M0 M2 M0 M1 M1 M0 M0 M1 M2

4 Tiruppathur M2 M2 M1 M3 M2 M2 M3 M2 M2 M3 M0 M1 M0 M1

5 Vaniyambadi M1 M1 M1 M2 M2 M0 M1 M0 M2 M1 M0 M0 M1 M2

6 Walajahpet M2 M1 M1 M2 M1 M0 M1 M0 M0 M0 M0 M0 M0 M1

7 Sholinghur M3 M0 M0 M0 M2 M0 M1 M0 M1 M1 M0 M0 M2 M3

8 Ranipet M2 M0 M0 M2 M0 M0 M2 M0 M0 M0 M0 M1 M0 M2

9 Palar Anicut M2 M1 M1 M2 M1 M0 M0 M0 M0 M0 M0 M0 M0 M1

10 Ponnai Anicut M2 M1 M0 M1 M0 M0 M1 M0 M0 M1 M0 M1 M1 M2

11 Arakonam M2 M0 M0 M1 M0 M0 M0 M0 M1 M1 M0 M0 M0 M1

12 Kaveripakkam M2 M0 M0 M2 M2 M0 M2 M1 M1 M0 M0 M1 M0 M1

13 Panapakkam M2 M0 M0 M2 M1 M0 M0 M0 M0 M1 M0 M0 M0 M1

14 Alangayam M1 M0 M2 M2 M2 M2 M2 M2 M2 M2 M1 M2 M2 M3

15 Jolarpet M2 M2 M1 M2 M2 M0 M2 M1 M2 M3 M0 M1 M0 M3

Contd…

90

Table 5.1 (Continued)

Sl. No. Station/Year 2000 2001 2002 2003 2004 2005

1 Vellore M0 M0 M2 M0 M2 M0

2 Ambur M1 M1 M3 M2 M2 M0

3 Gudiyatham M1 M0 M1 M1 M2 M0

4 Tiruppathur M0 M0 M2 M0 M0 M0

5 Vaniyambadi M0 M0 M3 M2 M2 M0

6 Walajahpet M0 M0 M1 M1 M0 M0

7 Sholinghur M2 M0 M3 M2 M2 M0

8 Ranipet M0 M0 M2 M1 M2 M0

9 Palar Anicut M0 M0 M1 M1 M2 M0

10 Ponnai Anicut M0 M0 M2 M2 M2 M0

11 Arakonam M1 M0 M0 M1 M1 M0

12 Kaveripakkam M0 M0 M2 M0 M2 M0

13 Panapakkam M0 M0 M0 M0 M1 M0

14 Alangayam M1 M3 M2 M2 M3 M1

15 Jolarpet M1 M0 M2 M2 M3 M0

Note: M0: No drought, M1: Mild drought, M2: Moderate drought, M3: Severe drought

* For Gudiyatham and Vaniyampadi, the rainfall measurement commenced from 1972 and 1973 respectively.

91

By glancing through the results of drought assessment over a period of

time, one can’t understand the overall drought proneness of any area, as the

drought occurrences are a mixed bag of different severities of drought. Hence,

frequency analysis of drought was carried out to arrive at an indicative value

representing the overall drought proneness of an area, named as Meteorological

Drought Severity Index (MDSI). The frequencies of different severities of

meteorological drought were calculated for each raingauge station and are

presented in Table 5.2. It is observed that stations namely, Ambur, Tiruppathur,

Sholinghur, Alangayam and Jolarpet were exposed to severe drought once in 6

to 7 years. The stations namely, Vellore, Ambur, Gudiyatham, Tiruppathur,

Vaniyambadi, Sholinghur, Ranipet, Poiney, Kaveripakkam, Alangayam and

Jolarpet were exposed to moderate drought once in 2 to 5 years. Other than

Vellore, Sholinghur, Ranipet and Alangayam all the other stations will be

frequently exposed to mild droughts with return period ranging from 1 to 2

years.

5.3 METEOROLOGICAL DROUGHT SEVERITY INDEX

Meteorological Drought Severity Index (MDSI) was developed by

frequency analysis based on thirty five years of rainfall data by calculating

probability of each drought severity class. Weightages of 1, 2, 3 and 4 were

assigned and the cumulative weighted value is arrived at for MDSI. From the

IMD results presented in Table 5.1, the meteorological drought severity status of

each station was determined. The results are shown in Table 5.3. The drought

severity index ranges from 1.34 at Arakonam to 2.54 at Alangayam. Four

drought severity classes were delineated based on the range of drought severity

index as shown in Table 5.4.

92

Table 5.2 Occurrence and Frequency of Meteorological drought using IMD method

Sl.

No.

Name of

Station

Occurrence and Frequency of Drought Severity Class

No Mild Moderate Severe

No. of

occurrencesFrequency

No. of

occurrencesFrequency

No. of

occurrencesFrequency

No. of

occurrencesFrequency

1 Vellore 21 0.60 6 0.17 8 0.23 0 0.00

2 Ambur 10 0.29 9 0.26 11 0.31 5 0.14

3 Gudiyatham 12 0.35 13 0.38 7 0.21 2 0.06

4 Tirupathur 10 0.29 10 0.29 9 0.26 6 0.17

5 Vaniyampadi 13 0.39 9 0.27 9 0.27 2 0.06

6 Valajapet 18 0.51 11 0.31 6 0.17 0 0.00

7 Sholingur 15 0.43 7 0.20 7 0.20 6 0.17

8 Ranipet 21 0.60 7 0.20 7 0.20 0 0.00

9 Palar Anicut 17 0.49 12 0.34 6 0.17 0 0.00

10 Poiney 15 0.43 12 0.34 8 0.23 0 0.00

11 Arakonam 24 0.69 10 0.29 1 0.03 0 0.00

12 Kaveripakkam 16 0.46 11 0.31 8 0.23 0 0.00

13 Panappakkam 22 0.63 9 0.26 4 0.11 0 0.00

14 Alangayam 8 0.23 6 0.17 15 0.43 6 0.17

15 Jollarpattai 11 0.31 9 0.26 10 0.29 5 0.14

93

Table 5.3 Meteorological Drought Severity Assessment

S.No.Name of

Station

Seasonal average

rainfall(mm)

Probability of drought severity class Drought

Severity Index

Drought

Severity ClassNo Mild Moderate Severe

1 Vellore 712.4 0.60 0.17 0.23 0.00 1.63 Mild

2 Ambur 591.2 0.29 0.26 0.31 0.14 2.31 Severe

3 Gudiyatham 632.7 0.35 0.38 0.21 0.06 1.97 Moderate

4 Tiruppathur 596.4 0.29 0.29 0.26 0.17 2.31 Severe

5 Vaniyambadi 571.0 0.39 0.27 0.27 0.06 2.00 Moderate

6 Walajahpet 736.5 0.51 0.31 0.17 0.00 1.66 Mild

7 Sholinghur 693.0 0.43 0.20 0.20 0.17 2.11 Moderate

8 Ranipet 747.9 0.60 0.20 0.20 0.00 1.60 No drought

9 Palar Anicut 836.4 0.49 0.34 0.17 0.00 1.69 Mild

10 Ponnai Anicut 714.3 0.43 0.34 0.23 0.00 1.80 Mild

11 Arakonam 863.6 0.69 0.29 0.03 0.00 1.34 No drought

12 Kaveripakkam 702.9 0.46 0.31 0.23 0.00 1.77 Mild

13 Panapakkam 841.0 0.63 0.26 0.11 0.00 1.69 Mild

14 Alangayam 523.8 0.23 0.17 0.43 0.17 2.54 Severe

15 Jolarpet 588.4 0.31 0.26 0.29 0.14 2.26 Severe

94

Table 5.4 Drought severity classification based on MDSI

Sl. No. Range Drought Severity

1 1.34 – 1.64 No drought

2 1.64 – 1.94 Mild

3 1.94 – 2.24 Moderate

4 2.24 – 2.54 Severe

The spatial interpolation of meteorological drought severity index

was carried out. It is observed that almost 50% of the districts are prone to

severe and moderate droughts. The meteorological drought severity map for

the study area is shown in Figure 5.1. In general, entire western portion of the

district is more prone to drought. Arakonam, Nemili, Kaveripakkam, Thimiri,

Arcot, Walajahpet, Sholinghur, Katpadi, Vellore and K.V.Kuppam blocks are

less prone to drought. Natrampalli, Pernumput, parts of Gudiyatham, Anaicut,

Kaniyambadi and Sholinghur blocks are under moderate drought severity

status. Southwestern blocks such as Kandili, Tiruppathur, Jolarpet,

Alangayam and Madhanur are all liable to severe drought.

5.3.1 Advantages of Meteorological Drought Severity Index

The results of the drought assessment methods using the IMD and

the proposed Meteorological Drought Severity Index using frequency analysis

were studied. It is observed that the stations such as Ambur, Tiruppathur,

Alangayam and Jolarpet are prone to moderate drought based on IMD

method. These stations are drought prone areas over the years.

95

Figure 5.1 Meteorological Drought Severity map of the study area

96

This is very well observed from the frequency based Meteorological Drought

Severity Index developed in this study. According to this proposed

methodology, the above stations were assessed to be as severe drought prone

areas.

The methodology developed for meteorological drought assessment

in the present study which is based on frequency analysis identifies drought

prone areas more precisely than IMD method. Both the above methods have

the same origin and basis and the proposed methodology is an improvement

on the IMD method.

5.4 AGRICULTURAL DROUGHT ASSESSMENT

5.4.1 Classification of Land use map

Land use map of Vellore district was collected from IRS, Anna

University which was prepared from IRS-1C LISS III image of October 2000.

The collected land use map was digitized using Arc Map GIS software for

different thematic layers. The digitized land use map is shown in Figure 5.2.

Land use classification in terms of area and its percentage is presented in

Table 5.5. Out of the total geographical area of 5, 92, 071 ha, 55.5% is under

agriculture land, 8.4% is under waste land, 27.3% is under forest, 3.6% is

under built-up and 5.2% is under water bodies.

5.4.2 NDVI based ADSI

Remotely sensed dataset during November 2001 and November

2002 of Samba season were used for agricultural drought assessment.

Agricultural Drought Severity Index (ADSI) developed in this study,

involving area under crop land and fallow land, delineated from remote

sensing data based on the NDVI response during the crop season.

97

Figure 5.2 Landuse map of the study area

98

Table 5.5 Land use classification of Vellore district

Sl.No. Class Area (ha) Percentage

1. Agriculture Land

i) Crop land

ii) Plantations

iii) Aquaculture

iv) Fallow land

230815

68793

3

29069

39.0

11.6

0.0

4.9

Sub-total 328680 55.5

2. Waste Land

i) Barren / Rocky

outcrop

ii) Land with scrub

iii) Land without scrub

iv) Mining / Industrial

v) Salt affected land

1383

32887

13480

349

1820

0.2

5.5

2.3

0.1

0.3

Sub-total 49919 8.4

3. Forest Land 161379 27.3

4. Built-up land 21516 3.6

5. Water Bodies

i) Tanks, Canals and River 30580 5.2

Overall total 592074 100.0

99

The total crop area mask under agricultural vegetation has been prepared for

the NDVI images by eliminating the area under forest, barren lands and land

put to non agricultural usage. In eliminating these areas, different GIS layers

have been used from the digitized landuse map of the study area. All the

NDVI values falling between 0.10 and 0.60 were grouped to obtain the spatial

extent of crop land area and remaining NDVI values that are below 0.1 and

near zero were grouped to obtain the spatial extent of fallow land area.

Figures 5.3 and 5.4 show the spatial extent of area under crop land

and area under fallow land in Samba season for the years 2001 and 2002

respectively. It is observed from the Figures that, crop area in the year 2001

was 3,34,158 ha and the same in 2002 was 1,28,797 ha. The crop land and

fallow land derived from the images were dissolved blockwise in Arc GIS.

Using this, Agricultural Drought Severity Index (ADSI) was formulated and

used to calculate the extent of agricultural drought severity. The ADSI value

ranges from 0 to 1, which is divided into 4 drought severity classes with an

equal interval of 0.25 and is given in Table 5.6.

Table 5.6 Classification of drought severity

Sl. No. Classification Drought severity

1 1 to 0.75 No drought

2 0.75 to 0.5 Mild

3 0.5 to 0.25 Moderate

4 0.25 to 0 Severe

100

Figure 5.3 Area under Crop land and Fallow land in 2001(Samba season)

101

Figure 5.4 Area under Crop land and Fallow land in 2002 (Samba season)

102

5.4.3 Development of ADSI map

Table 5.7 shows the block wise agricultural drought severity

assessment in the study area. Figure 5.5 shows the agricultural drought

severity map for Samba season in the year 2001. Out of 20 blocks, 17 were

under no drought, 2 under mild drought and 1 under moderate drought

condition. 85% of the blocks in the district were falling under no drought

condition in the year 2001. The IMD method of rainfall analysis shows that,

out of 15 raingauge stations in the district, 13 raingauge stations are falling

under no drought classification. Figure 5.6 shows the agricultural drought

severity map for Samba season in the year 2002. Out of 20 blocks, 6 blocks

were under mild drought, 5 under moderate drought and 9 under severe

drought condition. 70% of the blocks in the district were affected by moderate

and severe droughts.

The IMD method of rainfall analysis shows that, out of 15

raingauge stations in the district, 10 raingauge stations are falling under

moderate and severe drought classification.

5.5 SUMMARY

The above analyses of meteorological drought using rainfall data

and agricultural drought using remote sensing data indicate that a good

correlation exists between rainfall and crop area in the study area. So, the

extent of crop land and fallow land may be taken as the true indictors of the

monsoon variations. But, there are so many other factors causing drought and

the development of Integrated Drought Assessment is explained in the

Chapter 6.

103

Table 5.7 Agricultural drought severity assessment

S.No. Block

2001(Samba season) 2002 (Samba season)

Crop

land

(ha)

Fallow

land (ha)

Drought

Severity

Index

Drought

Severity Class

Crop

land (ha)

Fallow

land (ha)

Drought

Severity

Index

Drought

Severity

Class

1 Alangayam 21567.81 840.69 0.92 No drought 13023.26 9199.23 0.17 Mild

2 Anaicut 19983.25 746.61 0.93 No drought 11954.98 9072.09 0.14 Mild

3 Arakonam 9532.71 6876.71 0.16 Mild 915.45 14639.47 -0.88 Severe

4 Arcot 16723.96 1868.89 0.80 No drought 3257.74 15369.42 -0.65 Severe

5 Gudiyatham 18912.94 974.95 0.90 No drought 10996.77 8937.69 0.10 Mild

6 Jolarpet 18781.00 677.34 0.93 No drought 7853.66 11784.08 -0.20 Moderate

7 K.V.Kuppam 17339.04 399.36 0.95 No drought 10404.88 7269.69 0.18 Mild

8 Kandili 20809.99 2287.91 0.80 No drought 5093.68 17973.64 -0.56 Severe

9 Kaniyambadi 10542.61 178.61 0.97 No drought 7968.98 2807.63 0.48 Mild

10 Katpadi 12343.55 775.03 0.88 No drought 4545.68 8755.29 -0.32 Moderate

11 Kaveripakkam 21090.09 11219.77 0.31 Mild 1056.89 30925.59 -0.93 Severe

12 Madhanur 13993.60 771.17 0.90 No drought 7321.63 7585.61 -0.02 Moderate

13 Natrampalli 13739.78 1576.56 0.79 No drought 3209.77 12112.29 -0.58 Severe

14 Nemili 9762.65 17081.85 -0.27 Moderate 305.22 25637.15 -0.98 Severe

15 Pernamput 20091.90 1868.65 0.83 No drought 9746.27 12485.22 -0.12 Moderate

16 Sholinghur 22326.73 2835.15 0.77 No drought 5005.59 20222.78 -0.60 Severe

17 Thimiri 27008.32 3837.85 0.75 No drought 6593.07 24390.74 -0.57 Severe

18 Tiruppathur 17265.80 139.11 0.98 No drought 12881.23 4633.85 0.47 Mild

19 Vellore 7599.31 733.63 0.82 No drought 4043.56 4332.69 -0.03 Moderate

20 Walajahpet 14743.11 3232.27 0.64 No drought 2619.16 15866.09 -0.72 Severe

104

Figure 5.5 Agricultural Drought Severity map of 2001 (Samba season)

105

Figure 5.6 Agricultural Drought Severity map of 2002 (Samba season)