Results

Figures 3.8 and 3.9 display all the meteorological monsoon droughts and floods respectively which occurred between 1871 and 2005 and their tendencies. The summary of the occurrences of the meteorological monsoon floods and droughts according to their severities are displayed in Tables 3.3 and 3.4. The bold years in Tables 3.3 and 3.4 coincide with the El-Nino and La-Niña occurrences, which will be referred back in section 3.5.2 for a detailed discussion.

Figure 3.8 shows that the meteorological drought has an increasing tendency in NEIN, in which monsoon rainfall is the highest among all the study regions (see Figure 3.2).

No statistically significant trends of meteorological droughts can be seen in NWIN, WCIN, CNEIN and PENIN (Figure 3.8) with the former three having slightly increasing tendency and the PENIN region a slightly decreasing tendency. Likewise, the trend of ALLIN drought was not significant but has a slightly increasing tendency. The meteorological flooding, as shown in Figure 3.9, has slightly decreasing trends in ALLIN, CNEIN, and WCIN; whereas, the NEIN, NWIN and PENIN regions have no trend.

Since Figures 3.8 and 3.9 reveal no clear picture of the trends of different types of meteorological droughts and floods, a separate trend assessment was carried out for all types of meteorological droughts and floods. Figures 3.10 and 3.11 display trends of all

‘moderate’ events that took place in the study time interval at various regions. Figure 3.10 shows that, ‘moderate’ droughts, which have the highest probability of the occurrences every year, have increasing trends for all the regions except PENIN with the trend in NEIN being the most clear and no trend is found in CNEIN. On the other hand, as Figure 3.11 shows, a decline in ‘moderate’ flood events is found in NEIN only,

an increase is observed in PENIN and NWIN, and CNEIN, WCIN and ALLIN show no trends.

ALLIN -4

-3 -2 -1 0

1871 1881 1891 1901 1911 1921 1931 1941 1951 1961 1971 1981 1991 2001

Drought index

NWIN -4

-3 -2 -1 0

1871 1881 1891 1901 1911 1921 1931 1941 1951 1961 1971 1981 1991 2001

Drought index

(a) (b)

WCIN -4

-3 -2 -1 0

1871 1881 1891 1901 1911 1921 1931 1941 1951 1961 1971 1981 1991 2001

Drought index

CNEIN -4

-3 -2 -1 0

1871 1881 1891 1901 1911 1921 1931 1941 1951 1961 1971 1981 1991 2001

Drought index

(c) (d)

NEIN -4

-3 -2 -1 0

1871 1881 1891 1901 1911 1921 1931 1941 1951 1961 1971 1981 1991 2001

Drought index

PENIN -4

-3 -2 -1 0

1871 1881 1891 1901 1911 1921 1931 1941 1951 1961 1971 1981 1991 2001

Drought index

(e) (f)

Figure 3.8: Time series of the drought indices and their tendencies based on the rainfall data from 1871 to 2005 in various regions in India considered of (a) ALLIN, (b) NWIN, (c) WCIN, (d) CNEIN, (e) NEIN and (f) PENIN.

ALLIN

0 1 2 3 4

1871 1881 1891 1901 1911 1921 1931 1941 1951 1961 1971 1981 1991 2001

Flood index

NWIN

0 1 2 3 4

1871 1881 1891 1901 1911 1921 1931 1941 1951 1961 1971 1981 1991 2001

Flood index

(a) (b)

WCIN

0 1 2 3 4

1871 1881 1891 1901 1911 1921 1931 1941 1951 1961 1971 1981 1991 2001

Flood index

CNEIN

0 1 2 3 4

1871 1881 1891 1901 1911 1921 1931 1941 1951 1961 1971 1981 1991 2001

Flood index

(c) (d)

NEIN

0 1 2 3 4

1871 1881 1891 1901 1911 1921 1931 1941 1951 1961 1971 1981 1991 2001

Flood index

PENIN

0 1 2 3 4

1871 1881 1891 1901 1911 1921 1931 1941 1951 1961 1971 1981 1991 2001

Flood index

(e) (f)

Figure 3.9: Time series of the flood indices and their tendencies based on the rainfall data from 1871 to 2005 in various regions in India considered of (a) ALLIN, (b) NWIN, (c) WCIN, (d) CNEIN, (e) NEIN and (f) PENIN.

Since, very few statistically significant trends were found for the ‘severe’ and ‘extreme’

conditions, for the reason that the trend results could be biased by the rarity, the linear trends are not shown for these conditions. However, there are a few exceptions, which are – ‘severe’ floods for ALLIN which were found to have statistically significant decreasing trend and ‘severe’ and ‘extreme’ droughts in WCIN which were found to have statistically significant increasing trends. These increasing meteorological summer

droughts in many parts of India could be attributed to the rise in temperature in the drier summer months, reduction of the number of rainy days and increase in ENSO events, as in related work discussed later in section 3.5.2.

Table 3.3: List of meteorological drought years according to their severity indices in various regions in India.

Droughts Region

Moderate Severe Extreme

ALLIN 1904,1911,1941,1951,1966,1968,1974, 1982,1985, 1986, 2004 (36%-64%)

1901,1905,1920,1965, 1979, 1987 (50-67%)

1877,1899,1918,1972, 2002 (100%) NWIN 1904,1925,1948,1968,1972,1974,1982,

1985,1986,1991,1999,2000 (34%)

1901,1905,1939,1951, 2002 (40%)

1877,1899,1911,1915 1918, 1987 (83%) WCIN 1902,1904,1965,1966,1968,1979,1995,

2004 (38%)

1905,1941,1972,1974 1987, 2002 (83%)

1877,1899,1918,1920 (75%)

CNEIN 1878,1903,1907,1918,1928,1932,1951 1959,1968,1974,1992, 2004 (25%)

1901,1965,1966,1972 (50%)

1877,1979,2002 (67%) NEIN 1900,1914,1925,1957,1958,1959,1961,

1962,1967,1975,1986,1994,1996,2001, 2005 (27%)

1884,1891,1972,1980, 1981, 1982 (50%)

1896, 1992 (50%)

PENIN 1876,1880,1884,1905,1911,1913,1930

1934,1972,1976,1987, 1999 (50%) 1891,1952

(50%) 1899,1918,2002 (100%) Note: Bold years coincide with the El-Niño occurrences. Percentages in the brackets refer to the likelihood of the droughts occurring in El-Niño years.

Table 3.4: List of meteorological flood years according to their severity indices in various regions in India.

Floods Region

Moderate Severe Extreme

ALLIN 1884,1893,1894,1910,1916,1942,1947, 1959, 1970, 1975,1983,1988,1994

(54-62%)

1878,1892,1917,1933, 1956

(80-100%)

1961 (0%) NWIN 1893,1908,1950,1956,1961,1970,

1973, 1975, 1976, 1977, 1988 (73%)

1878,1892,1894,1926 1933,1944,1945,1959

1994 (34%)

1917 (100%) WCIN 1882,1887,1894,1916,1917,1933,

1934,1938, 1942,1947,1955,1956, 1970, 1975,1990,1994 (50%)

1884,1892,1959,1983 (25%)

1961 (0%) CNEIN 1879,1893,1925,1942,1943,1953,1956

1971, 1994, 2003 (40%)

1894, 1980 (0%)

1890, 1922,1936 (0%)

NEIN 1879,1880, 1893, 1905,1956,1987 (67%) 1886,1899,1947,1988 1995

(60%)

1878,1918,1974,1993 (50%)

PENIN 1892,1916,1917,1947,1949,1959,1964, 1978, 1981,1989,1991,1998

(59%)

1889,1903,1924,1983, 1988, 1996

(60%)

1878,1897,1961,1975 (25%)

Note: Bold years coincide with the La-Niña occurrences. Percentages in the brackets refer to the likelihood of the floods occurring in La-Niña years.

ALLIN -1.6

-1.2 -0.8 -0.4 0

1871 1881 1891 1901 1911 1921 1931 1941 1951 1961 1971 1981 1991 2001

Moderate drought index

NWIN -1.6

-1.2 -0.8 -0.4 0

1871 1881 1891 1901 1911 1921 1931 1941 1951 1961 1971 1981 1991 2001

Moderate drought index

(a) (b)

WCIN -1.6

-1.2 -0.8 -0.4 0

1871 1881 1891 1901 1911 1921 1931 1941 1951 1961 1971 1981 1991 2001

Moderate drought index CNEIN

-1.6 -1.2 -0.8 -0.4 0

1871 1881 1891 1901 1911 1921 1931 1941 1951 1961 1971 1981 1991 2001

Moderate drought index

(c) (d)

NEIN -1.6

-1.2 -0.8 -0.4 0

1871 1881 1891 1901 1911 1921 1931 1941 1951 1961 1971 1981 1991 2001

Moderate drought index

PENIN -1.6

-1.2 -0.8 -0.4 0

1871 1881 1891 1901 1911 1921 1931 1941 1951 1961 1971 1981 1991 2001

Moderate drought index

(e) (f)

Figure 3.10: Time series of the moderate drought indices and their tendencies based on the rainfall data from 1871 to 2005 in various regions in India considered of (a) ALLIN, (b) NWIN, (c) WCIN, (d) CNEIN, (e) NEIN and

(f) PENIN.

All the results discussed in this section and in section 3.1 collectively show that, drought probability is the highest in North East India where the annual average rainfall is the highest and followed by WCIN. Peninsular India has an entirely different trend in all respects and no change is found in moderate drought and floods in Central North East India (CNEIN). However, increasing tendency in extreme monsoon rainfall deficit

(section 3.1) makes the region CNEIN vulnerable to monsoon water stress. Therefore, it could be concluded that the average monsoonal climate is definitely changing in all the regions in India but the changes are different, as also discussed in section 3.1.

ALLIN

0 0.4 0.8 1.2 1.6

1871 1881 1891 1901 1911 1921 1931 1941 1951 1961 1971 1981 1991 2001

Moderate flood index

NWIN

0 0.4 0.8 1.2 1.6

1871 1881 1891 1901 1911 1921 1931 1941 1951 1961 1971 1981 1991 2001

Moderate flood index

(a) (b)

WCIN

0 0.4 0.8 1.2 1.6

1871 1881 1891 1901 1911 1921 1931 1941 1951 1961 1971 1981 1991 2001

Moderate flood index

CNEIN

0 0.4 0.8 1.2 1.6

1871 1881 1891 1901 1911 1921 1931 1941 1951 1961 1971 1981 1991 2001

Moderate flood index

(c) (d)

NEIN

0 0.4 0.8 1.2 1.6

1871 1881 1891 1901 1911 1921 1931 1941 1951 1961 1971 1981 1991 2001

Moderate flood index

PENIN

0 0.4 0.8 1.2 1.6

1871 1881 1891 1901 1911 1921 1931 1941 1951 1961 1971 1981 1991 2001

Moderate flood index

(e) (f)

Figure 3.11: Time series of the moderate flood indices and their tendencies based on the rainfall data from 1871 to 2005 in various regions in India considered of (a) ALLIN, (b) NWIN, (c) WCIN, (d) CNEIN, (e) NEIN and (f)

PENIN.

In document Rainfall trends in India and their impact on soil erosion and land management (página 102-108)