Spatial database Development for green house gas emission Estimation using remote sensing and GIS
c. Soil Greenhouse gases flux measurement.
Flux of carbon dioxide, nitrous oxide and methane of soil surface were measured at various land-use/land cover types in order to obtain the estimates of diurnal emissions. The emission rates indicated by changes of methane concentration per unit time (dC/dt) were developed by plotting the analyzed air samples collected using closed-chamber method at 10-minute intervals. The Flux density is calculated as follows (Khalil et. al., 1991)
f = r V (M/Noa) (dC/dt) x 6 x 10-5
f= Methane, Nitrous oxide or carbon dioxide flux (mg/m
2/hr),
r = Air density (mol/m
3),
V= Chamber volume (m
3), M= gas molecular weight (g/mole), A= Chamber basal area (m
2)
dC/dt = emission rate (ppbv/minute), obtained from consecutive measurement.
c. Combine field data measurement and GIS spatial data.
Data on aboveground carbon stock and soil surface greenhouse gases flux were combined using Look Up Table (LUT) of Arc/Info. Estimation of total above ground carbon stock were calculated by multiplying the value by total area of each land-use/land cover. The same method was applied for calculating the total emission of greenhouse gases.
Result and Discussion
Land-use/land cover changes
Figure 2a and 2b. shows land-use/land cover patterns in 1986 and 1992, while Figure 2c is the overlay result. Quantitative comparison of the changes is presented in Table 1. Proportion of primary forest decreased from 19.3% to 12.5% in 1992. Further analysis of each land-use/land cover types is presented in Figure 3. It shows that about 24% of primary forest area were converted into logged forest , shrubs (fallow lands), cash crop plantation, cultivated and settlement areas. About 30% of logged forest were converted into shrubs, cash crop plantation, a mixture of cultivated and settlements. In the case of shrubs most of them were converted into a mixture between cultivated and secondary vegetation (40.3%), cash crop plantation (7.9%), logged forest (20.2%) and secondary forest. Of about 73% of Grasslands have changed into fallow lands (48.8%), a mixture between cultivated lands and secondary vegetation (20.7%).
| Land -use/Land cover | 1986 | 1992 |
| Area(sq.km) | % of total area | Total carbon
(106ton) | Area(sq.km) | % of total area | Total carbon
(106 ton) |
| Primary forest | 165.21 | 33.91 | 416.89 | 12569.86 | 25.80 | 317.19 |
| Secondary forest | 0.00 | 0.00 | 0.00 | 1274.34 | 2.62 | 7.40 |
| Logged forest | 10022.39 | 20.57 | 155.53 | 12448.65 | 25.55 | 193.18 |
| Fallow lands | 9401.68 | 19.30 | 14.10 | 6072.66 | 12.47 | 9.11 |
| Grasslands | 535.99 | 1.10 | 0.32 | 523.19 | 1.07 | 0.31 |
| Bare lands | 3.67 | 0.01 | 0.00 | 3.67 | 0.01 | 0.00 |
| Cash crops plantation | 912.78 | 1.87 | 2.56 | 3303.17 | 6.78 | 9.25 |
| Paddy field | 1002.78 | 2.06 | 0.75 | 649.16 | 1.33 | 0.49 |
| Upland field | 0.00 | 0.00 | 0.00 | 235.84 | 0.48 | 0.18 |
| Cultivated and Secondary Vegetation | 7036.29 | 14.44 | 24.97 | 7933.39 | 16.29 | 28.16 |
| Cultivated land and Settlement | 1339.84 | 2.75 | 0.50 | 1630.68 | 3.35 | 0.61 |
| Urban areas | 0.00 | 0.00 | 0.00 | 132.17 | 0.27 | 0.00 |
| Water surface/lake | 42.41 | 0.09 | 0.00 | 42.27 | 0.09 | 0.00 |
| No data | 1896.60 | 3.89 | - | 1896.6 | 3.89 | - |
| Total | 48715.65 | 100.00 | 615.62 | 48715.65 | 100.00 | 565.88 |
Table 1. Land-use/land cover and above ground bio-mass changes between 1986 and 1992
Aboveground carbon stock changes
Aboveground carbon content estimation of each land-use/land cover were calculated by multiplying the area of each land-use/land cover with carbon stock per unit area. Table 1 above has showed the changes of above ground carbon due to land-use/lanc cover changes. Total above ground stock decrease from 6.16 x 108 ton in 1986 to 5.66 x 108 ton in 1992 or loss of about 0.50 x 108 ton within 6 years equal to 8.3 million ton per year. The loss of aboveground carbon was mainly came from primary forest conversion. IPCC have divided the loss of aboveground carbon content into on site and off-site release. These two categories were classified further into direct burning (fuel wood and slash and burn agricultural) and decomposition process release of unburned biomass (Houhton et. al., 1996). Thus the amount of carbon and greenhouse gas released to the atmosphere were depended on these processes. Estimation of the amount carbon and greenhouse gases release need yearly basis time series of spatial data and the information on commercial wood and fuelwood harvest, and burning efficiency data of each land-use/land cover type.
