Chapter 4: Status of snow cover of Subansiri basin and its impact on the
5.3 Results and Discussions
5.3.1 LULC change detection analysis for the Brahmaputra
5.3.1.1 Change detection analysis for the month of January
The areas covered by different LULC classes for the month of January from 2002 to 2012 are given in Table 5.1. Fig.5.4 shows the pie diagrams depicting the percent of total area covered by each LULC class.
Table 5.1: Area covered by different LULC classes in Brahmaputra basin for the month of January from 2002 to 2012
LULC Classes
Year wise area covered ( 104 km2)
2002 2003 2004 2005 2006 2007 2008 2009 2010 2011 2012 BS 24.71 19.47 19.61 20.06 24.40 23.81 26.31 19.46 21.03 22.42 15.74 SWB 7.10 7.47 10.31 9.03 5.35 3.85 4.36 8.94 7.35 7.87 9.96
DV 15.39 17.33 13.93 20.68 17.39 17.84 22.61 18.92 20.08 13.47 7.77 LV 17.12 13.28 16.90 10.27 16.87 16.97 11.32 8.86 12.54 17.37 20.62 SCA 3.38 10.16 6.95 7.68 3.69 5.23 3.11 11.51 6.70 6.58 13.60
It is seen that area covered by bare soil has always been the maximum except for the year 2012, where area covered by light vegetation was the maximum. The increase in light vegetation can be attributed to the fact of increasing urbanisation and agricultural land due to increase in population.
Fig. 5.4: Pie diagrams showing percent of total area covered by different LULC classes in the Brahmaputra River basin from 2002 to 2012 for the month of January
The maximum area covered by bare soil has been observed in 2008 with a value of 38.85% of the total basin area and the minimum was observed in the year 2012 with a value of 23.25%
of the total area of the Brahmaputra basin. Area covered by surface water bodies was the maximum in 2004 (15.23%) and minimum in 2007 (5.68%). Percent of total area covered by dense vegetation was the maximum in 2008 with a value of 33.40% and was the minimum in 2012 with a value of 11.48%. For light vagetaion and snow cover area the maximum were in 2012 (30.46% and 20.09% respectively) while the minimum were in 2009 (13.09%) and 2008(4.59%) respectively.
The trend analysis for each LULC class for the month of January from 2002 to 2012 are presented graphically in Fig. 5.5.
Fig. 5.5: Trends showing percent of total area covered by different LULC classes for the Brahmaputra River basin from 2002 to 2012 for the month of January
From Fig. 5.5 it is observed that for bare soil and dense vegetation, the percent of total area covered show decreasing trends from 2002 to 2012 while percent of total area covered by surface water bodies,light vegetation and snow cover area show increasing trends. The increased snow cover area and surface water bodies might have occupied the bare land leading to decrease in the area covered by bare soil. The reason behind decrease in dense vegetation and increase in light vegetation may be that deforestation occurred during this period which had been covered by agricultural lands.
The land use/land cover maps of the Brahmaputra River Basin prepared by supervised classification method in Erdas Imagine software for the Month of January from 2002 to 2012 are shown in Fig. 5.6.
Fig. 5.6:LULC maps of Brahmaputra river basin for the month of January from 2002 to 2012 The yearly changes of each LULC class from 2002 to 2012 for the month of January has also been analyzed and are shown in Table 5.2.
Table 5.2: Year wise Changes in Brahmaputra basin for different LULC classes from 2002 to 2012 for the month of January
Year LULC Classes
BS (%) SWB(%) DV(%) LV(%) SCA(%)
2002-03 -7.74 0.55 2.87 -5.66 10
2003-04 0.2 4.2 -5.02 5.34 -4.73
2004-05 0.66 -1.9 9.96 -9.79 1.07
2005-06 6.43 -5.43 -4.86 9.74 -5.88
2006-07 -0.88 -2.22 0.67 0.16 2.27
2007-08 3.68 0.75 7.05 -8.35 -3.14
2008-09 -10.1 6.78 -5.45 -3.63 12.42
2009-10 2.31 -2.35 1.71 5.43 -7.11
2010-11 2.06 0.76 -9.76 7.13 -0.19
2011-12 -9.87 3.09 -8.42 4.81 10.38
2002 2003 2004
2005 2006 2007
2008
2011 2012
2009 2010
For bare soil, maximum decrease has been observed during 2008-09 where it decreased by 10.1% and the maximum increase was during 2005-06 where it increased by 6.43%. Surface water bodies increased the most during 2008-09 (6.78%) and decreased the most during 2005-06 (5.43%). The maximum decrease in dense vegetation has been observed during 2010-11 (9.76%) and the maximum increase was observed during 2004-05 (9.96%). The maximum decrease in light vegetation and snow cover area were during 2004-05 (9.79%) and 2009-10(7.11%) respectively, while the maximum increases were during 2005-06 (9.74%) and 2011-12 (10.38%) respectively.
By taking the values of area covered by different LULC classes in the years 2002 and 2012, the overall change that has taken place in the entire decade for the month of January has been analyzed and is represented graphically in Fig. 5.7. The area covered by each LULC class along with the percent of total basin area and overall changes occurred in the entire period from 2002 to 2012 are given in Table 5.3.
Table5.3:Area and amount of change in different LULC categories in the Brahmaputra basin during 2002 to 2012 for the month of January
LULC Classes
Year
Change 2002-2012
2002 2012
Area(km2) % Area(km2) % Area(km2) %
Bare soil 247127 36.50 157436 23.25 -89691 -13.25
Surface water bodies 70983 10.48 99613 14.71 28630 4.23 Dense vegetation 153890 22.73 77715 11.48 -76175 -11.25
Light vegetation 171176 25.28 206223 30.46 35047 5.18
Snow cover area 33841 5.00 136030 20.09 102189 15.09
Fig. 5.7: LULC change in the Brahmaputra River basin during 2002 to 2012 for January While analyzing the LULC changes in the entire period from 2002 to 2012, it is seen that in case of Brahmaputra River basin for the month of January, area covered by surface water bodies, light vegetation and snow cover area increased and area covered by bare soil and dense vegetation decreased. The bare soil has decreased from 247127km2 in 2002 to 157436km2 in 2012 which accounts for 13.25%. The surface water body has increased from 70983 km2 in 2002 to 99613 km2 in 2012 which accounts for 4.23% of thetotal study area.
The dense vegetation has decreased from 153890km2 in 2002 to 77715km2 in 2012 which accounts for 10.57 %. Again, light vegetation has increased from 2002 (171176km2) to 2012 (206223km2) which accounts for 5.18%. The snow cover area has increased from 33841km2 in 2002 to 102189km2 in 2012 with percent increase of 15.09%. Theincreases in snow cover area, surface water bodies and light vegetation led to the decrease in the other classes.