Modeling for Global Land Degradation
using Remote Sensing and GIS
2.2 Physical and bio process model
Besides the climatic model, the physical processes of land degradation such as water and wind erosion can also be modelled by using the remote sensing data in combination to such processes, the remotely sensed data, particularly, NOAAGVI data, can be specially useful for such studies.
i.
Water erosion
Water erosion is a function of land use/cover, rainfall, topography and soil characteristics. However, due to the scale factor, it is necessary to make some generalizations in case of global study. For example, to relate the topography for land degradation, instead of calculating the slope in absolute values, some topographic roughness factor may be more appropriate. Fig 2 illustrates the procedure for analysis of water erosion.
Figure 2 Flow chart of methodology for analysis of water erosion.
ii.
Wind erosion
Wind erosion is function of speed and direction of wind, land use/cover and the soil properties. Some inference about wind conditions can also be made from the duration of dry period based on the rainfall data.
iii.
Net primary productivity.
Since vegetation degradation is one form of desertification, the net primary productivity can also be taken as an indicator of the land degration. It has been shown by various authors (such as Box and Bai 1993) that NOAA GVI data have good correlationship with the primary productivity.
3. Preliminary Results and Discussion
So far, preliminary results from the climatic modeling have been produced. The results of Aridity zoning and the moisture index have been represented in Tables 1 and 2 respectively..
the results of the aridity zoning indicate the forest area of about 42% based on the climatic data. But the actual amount of forest is less than this, approximately 33% of the total area, as found by some authors (Murai and Honda 1991) by using remote sensing for mapping actual vegetation. This can be considered as an indication of deforestation from the natural forest cover for the given climatic conditions to other land use type.
Table 2 Areas under different Aridity zones
| SR No |
Aridity Zone |
AI |
Percent area |
| 1 |
Desert |
<=5 |
7.34 |
| 2 |
Semi-desert |
5-10 |
5.94 |
| 3 |
Grass land |
10-30 |
31.47 |
| 4 |
Forest |
>30 |
41.96 |
| 5 |
Cold |
- |
13.29 |
Table 3 Areas under different zones based on Moisture Index
| SR No |
Zone |
MI |
Percent area |
| 1 |
Hyperarid |
<0.05 |
2.45 |
| 2 |
Arid |
0.05-0.20 |
8.39 |
| 3 |
Semi-arid |
0.20-0.50 |
14.69 |
| 4 |
Dry subhumid |
0.05-0.65 |
6.99 |
| 5 |
Humid |
>0.65 |
54.90 |
| 6 |
Cold |
- |
12.59 |
The moisture index (Table 2) values show the smaller area of hyperaird and arid zones and larger area of humid zones compared to the results of the desertification atlas(UNEP 1992). The reason may be related to the different method used for calculating the potential evapo6ranshpiration. The PET used here is taken from the global PET dataset produced by Ahn and Tateishi at 0.5 resolution.
Figure 3 Aridity zoning based on Martonne's Arigty Index
4. Conclusions and Further Research
The research based on climatic model so far has demonstrated the usefulness of GIS for classifying the globe into different aridity and moisture index zones, which are important indicators of desertification. More work is underway to demonstrate the applicability of remote sensing and GIS for land degradation Studies at the Global level. Further research is being continued i9n the following way:
-
Developing models for physical processes of land degradation such as water and wind erosion.
- Linking the climatic model with the physical process model.
- Linking local, regional and global level studies of land degradation.
References
- Box, E.O. and X. Bai (1993): "A Satellite Based World Map of Current Terrestrical
Net Primary Productivity" in Seisan-Kenkyu (monthly journal of IIS, Univ. of Tokyo), Vol. 45, No. 9.
- Murai, S and Y. Honda (1991): "World Vegetation Map from NOAA GVI Data" in S. Murai (Ed), Applications of Remote Sensing in Asia and Oceania, AARS.
- United Nations Environment Program (1992) : World Atlas of Desertification
