Application of GIS in researching and mapping land degradation map of Lang Son in 2015


Posted at: 11:07:58 05/07/2016 - Read: 153
Từ khóa Key words: Land degradation, degradation, GIS

Land is a precious natural resources, provide the material and energy resources in the process of socioeconomic development of human society and the biological world. In the begining of 21st century, the human civilization entered a period of scientific development and high technology, but human awareness are increase and people recognize that land is an esential natural resource and can not be replaced, it is the special asset, labor subject of all nationalities. However, the increases of land degradation and desertification becoming one of the major problems of the current global environment. Land degradation reduce the food and crops production, leading to migration, food insecurity, destroys basic resources, disrupt ecosystems, loss of biological diversity,...

Land degradation is related to the decline in soil quality, caused by the misuse and improper use of man. Land degradation is related to a reduction in production capacity of the soil through the changes for the worse of the nutrients, organic matter in soil, soil structure morphology, concentration of ions in the soil and the chemical hazardous substances in the soil, the process of land degradation including erosion, solid ground, acidification, tightly, organic degradation, depletion of soil fertility, biological degradation and pollution.

Lang Son province has diverse land resources, the crop structure has changed strongly, the demand of land for infrasture construction, urbans construction and development, agriculture and forestry are increasing. Beside, more and more specific reasons of land degradation appearing such as erosion, drought, laterization,  fertility depletion, salinization. Therefore, the identification and evaluation of land degradation in Lang Son province is very importance to building statistical indicator system "degraded land area"  according to the degradation types and degradation soil types from the national statistical indicators system in Lang Son province. In other way, we can evatuate the reasons of land degradation and proposing solutions to minimize land degradation of Lang Son.

Approaching the assessment methods of land degradation in Vietnam and the world, from the research programs and project of land degradation show that: we need to evaluate and investigate land degradation from general to detail, from macro to micro. From these approachs , the geoinformatics research center of Thai Nguyen university of agriculture and forestry using GIS technology combine with practical investigation for mapping land degradation map of Lang Son province in the scale 1: 100.000 for evaluating the land degradaion of the project “ Investigating land degradation in Lang Son province”. The land degradation map in Lang Son province was builded as following:

Figure 1: The process of building land degradation map in Lang Son province

Firstly, we need to build the input dada from 4 data layers which are the result of mapping 4 types of land degradation. After that, using GIS algorithm in ArcGIS to overlay this 4 data layers (declining fertility, erosion, drought, laterised) to become a new data layer with *.shp format. The new data layer contain the attribute data of 4 old data layers. Thus, the result of overlay map giving the land zone investigation which have attribute data of all degradation layers.

Using export tool in ArcGIS to convert the data from *.dbf format to become *.xls format. In the next steps, using this *.xls file to decentralize the degradation value S and intergrate the data to the map. The land degradation map of Lang Son province in 2015 was build by overlay these maps: Soil erosion map, soil laterization map, the drought map and the land declining fertility map. All the database of these maps are constructed, managed in GIS system. Classifying the degradation levels by MCE (Multi Criteria Evaluation) method according to the levels: no degradation, low level degradation, medium level degradation, high level degradation.  

 (1), Building the comparison matrix and identifying the weight number
Classifying the degradation levels by MCE (Multi Criteria Evaluation) method according to the levels: no degradation, low level degradation, medium level degradation, high level degradation. The land degradation map of Lang Son province in 2015 was build by overlay these maps: Soil erosion map, soil laterization map, the drought map and the land declining fertility map. All the database of these maps are constructed, managed in GIS system.Using export tool in ArcGIS to convert the data from *.dbf format to become *.xls format. In the next steps, using this *.xls file to decentralize the degradation value S and intergrate the data to the map.Firstly, we need to build the input dada from 4 data layers which are the result of mapping 4 types of land degradation. After that, using GIS algorithm in ArcGIS to overlay this 4 data layers (declining fertility, erosion, drought, laterised) to become a new data layer with *.shp format. The new data layer contain the attribute data of 4 old data layers. Thus, the result of overlay map giving the land zone investigation which have attribute data of all degradation layers.

Figure 1: The process of building land degradation map in Lang Son province.

Lang Son has hilly terrain so the priority of the degradation type is: Soil erosion, laterited, drought, and declining fertility, after building the comparition matrix, we can identify the weight number of each Criteria as follow:

Table 1: The weight number of indicators

Criteria (i)

Weight number (Wi)

Erosion

0,565

Laterited

0,262

Drought

0,118

Declining fertility

0,055

(2), Calculating the degradation value (Si)

The degradation value (Si) is calculated arccording to the fomular: Si = Xi x Wi. Calculating the Xi value base on the principle providing that the total score of Xi of a creteria is 100% ( the total Si of a creteria equal the weight number of that creteria) and identify  according to the ascending levels of importance to clarify the difference of the Si value in the next steps.

Table 2:  The Xi and Si value of criteria

 

Criteria

Xi

Si

Erosion

No erosion

5%

0,0283

Low level erosion

15%

0,0848

medium erosion

25%

0,1413

High level erosion

55%

0,3108

laterited

No laterite

5%

0,0131

Low level laterite

10%

0,0393

medium laterite

25%

0,0656

High level laterite

60%

0,1442

drought

No drought

5%

0,0059

Low level drought

10%

0,0118

Medium level drought

25%

0,0294

High level drought

60%

0,0705

Declining

fertility

No decline fertility

5%

0,0028

Low level declining fertility

15%

0,0055

Medium level declining fertility

25%

0,0138

high level declining fertility

55%

0,0332

(3), Decentralization of the land degradation value S.

- Assigning the degeneration values Si to each land zoning according to the norm and calculating the total degradation value S as following formular: S= . The result of decentralize the total degradation value S:

Table 3: Decentralization of total degeneration value S in Lang Son province

Number

Degradation levels

symbol

Decentralization

1

No degradation

TN

< 0,14

2

Degradation low level

T1

≥ 0,14; ≤ 0,2

3

Degradation medium level

T2

> 0,2; < 0,28

4

Degradation high level

T3

≥ 0,28

Finally, using the intergration algorism in GIS to convert the result of land degradation according to MCE method. Using symbology tool in ArcGIS software to mapping the Land digradation map of Lang Son.

Figure 2: The land degradation map of Lang Son 2015

Posted by: GIRC

GeoInformatics Center - Thai Nguyen University of Agriculture and Forestry

Address: Quyet Thang commune, Thai Nguyen city, Vietnam | Tel: +84904.031.103

Email: girc.tuaf@gmail.com | Website: www.girc.tuaf.edu.vn