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
5.3.1.2 Change detection analysis for the month of April
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.
Table 5.4: Area covered by different LULC classes in Brahmaputra basin for the month of April from 2002 to 2012
LULC Classes
Year wise area covered ( 104km2)
2002 2003 2004 2005 2006 2007 2008 2009 2010 2011 2012 BS 17.04 18.63 21.18 22.12 19.87 23.56 18.08 21.21 12.70 17.39 14.95 SWB 9.02 8.15 11.33 9.44 8.12 3.55 12.00 9.31 6.99 11.18 9.93 DV 16.60 16.14 13.52 15.89 11.95 17.05 14.85 14.17 17.68 16.27 13.95 LV 13.91 15.06 15.87 12.23 19.43 14.54 13.18 13.62 23.26 15.13 19.63 SCA 11.13 9.72 5.81 8.03 8.34 9.01 9.60 9.40 7.08 7.74 9.24
The Table 5.4 shows that during this decade, area covered by bare soil, surface water bodies, dense vegetation, light vegetation and snow cover area were the maximum in 2007, 2008, 2010, 2010 and 2002 respectively. The minimum areas of these classes have been found in 2010, 2007, 2006, 2005 and 2004 respectively.
Fig. 5.8: 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 April
It is observed that the maximum per cent of total area covered by bare soil during the time period was in the year 2007 with a value of 34.79% of the total basin area, while the minimum was in the year 2010 with a value of 18.76% of the total area. Area covered by surface water bodies was the maximum in 2008 (17.72%) and the minimum was observed in 2007 (5.24%). Percent of total area covered by dense vegetation was the maximum in 2010 with a value of 26.11% and was the minimum in 2006 with a value of 17.65%. For light vagetaion and snow cover area, the maximum were observed in 2010 (34.35%) and 2002 (16.43%) respectively while the minimum were observed in 2005 (18.07%) and 2004 (8.58%) respectively.
Fig. 5.9 gives the trend analysis of percent of total area of the Brahmaputra basin covered by each LULC class from 2002 to 2012 for the month of April.
Fig. 5.9: Trends showing percent of total area covered by different LULC classes for the Brahmaputra River basin from 2002 to 2012 for the month of April
It is clear from the figure that except for light vegettaion and surface water bodies where increasing trends are observed, all other LULC classes show decreasing trends from 2002 to 2012. Deforestation and development of agricultural land due to the increase in population
might have led to the increase in light vegetation and decrease in bare land and dense vegetation. In other words, the decreased bare soil, dense vegetation and snow cover area had been covered with light vegetation and surface water bodies.
The LULC maps for the month of April from 2002 to 2012 are given in Fig. 5.10.
Fig. 5.10: LULC maps of the Brahmaputra River basin for the month of April from 2002 to 2012
The yearly changes taken place in the Brahmaputra basin for each LULC class from 2002 to 2012 for the month of April are shown in Table 5.5.
Table 5.5: Year wise Changes in Brahmaputra basin for different LULC classes from 2002 to 2012 for the month of April
Year LULC Classes
BS (%) SWB (%) DV (%) LV (%) SCA (%)
2002-2003 2.35 -1.28 -0.68 1.70 -2.08
2003-2004 3.76 4.69 -3.88 1.20 -5.77
2004-2005 1.39 -2.79 3.51 -5.38 3.28
2005-2006 -3.33 -1.95 -5.82 10.63 0.46
2002 2003 2004
2005 2006 2007
2008 2
2009 2010
2011 2012
2006-2007 5.45 -6.75 7.53 -7.22 0.99
2007-2008 -8.10 12.48 -3.25 -2.01 0.87
2008-2009 4.63 -3.97 -1.00 0.64 -0.30
2009-2010 -12.57 -3.43 5.18 14.24 -3.42
2010-2011 6.92 6.19 -2.08 -12.00 0.97
2011-2012 -3.61 -1.84 -3.42 6.55 2.22
The maximum increase in bare soil, surface water bodies, dense vegetation, light vegetation and snow cover area have been observed during 2010-11, 2007-08, 2006-07, 2009-10 and 2004-05 with percent increase values of 6.92%, 12.48%, 7.53%, 14.24% and 3.28%
respectively. The maximum decrease for these classes have been observed in 2009-10, 2006- 07, 2003-04, 2010-11 and 2003-04 where the areas decreased by 12.57%, 6.75%, 3.88%, 12% and 5.77% respectively.
The overall changes that have taken place in the decade (from 2002 to 2012) for the month of April were analyzed and are represented in Fig. 5.11. The changes are tabulated in Table 5.6.
Table 5.6: Area and amount of change in different LULC categories in the Brahmaputra basin during 2002 to 2012 for the month of April
LULC categories
Year
Change 2002-2012
2002 2012
Area(km2) % Area(km2) % Area(km2) %
Bare soil 170432 25.17 149473 22.08 -20959 -3.09
Surface water bodies 90196 13.32 99342 14.67 9145 1.35 Dense vegetation 165978 24.52 139502 20.61 -26476 -3.91
Light vegetation 139148 20.55 196314 28.90 57166 8.35 Snow cover area 111262 16.43 92386 13.65 -18875 -2.79
Fig. 5.11: LULC change in the Brahmaputra River basin during 2002 to 2012 for April For the entire period from 2002 to 2012, it is seen that for the month of April, area covered by light vegetation and surface water bodies had increased and area covered by other classes had decreased. The bare soil decreased from 170432km2 in 2002 to 149473km2 in 2012 which accounts for 3.09%. The surface water body increased from 90196 km2 in 2002 to 99342 km2 in 2012 which accounts for 1.35% of thetotal study area. The dense vegetation decreased from 165978km2 in 2002 to 139502km2 in 2012 which accounts for 3.91 %. Again, light vegetation increased from 2002 (139148km2) to 2012 (196314km2) which accounts for 8.35%. The snow cover area has decreased from 111262km2 in 2002 to 92386km2 in 2012 which accounts for 2.79% of the total area of the basin. The increased light vegetation depicts the increase in population in the basin as more land had been used for agricultural purpose.