Environmental Sensitivity Evaluation of Aba Tibetan and Qiang Autonomous Prefecture Based on GIS and RS

. This study takes Aba Tibetan and Qiang Autonomous Prefecture in China as the research object, and establishes an ecological sensitivity evaluation index system based on the current ecological environment of the state using land use data, combined with field surveys and socio-economic and other data. And the ecological sensitivity evaluation was carried out based on Geographic Information System (GIS) and Remote Sensing (RS) using a hierarchical analysis method. The results of the study showed that the overall ecological sensitivity of Aba Tibetan and Qiang Autonomous Prefecture showed spatial variability with low in the northwest and high in the southeast; among them, the extremely sensitive area accounted for only 3.53% of the total area, the moderately sensitive area accounted for 30.10% of the total area, and the slightly sensitive area and insensitive area accounted for 47.82% of the total area. The study provides a theoretical basis for the ecological economy and sustainable development of the state.


Introduction
The contradiction and conflict between the ecological environment and socio-economic development is a common challenge facing the whole world nowadays, protecting and improving the ecological environment have become major issue of increasing importance to all countries and regions in the world today. Conducting ecological sensitivity analysis, formulating ecological and environmental protection plans, and guiding the sustainable development of the regional economy are strategies commonly used around the world nowadays 1 .
Ecological sensitivity refers to the ability of ecological factors to adapt to external pressures or changes without loss or degradation of environmental quality 2,3 . In-depth analysis and evaluation of regional ecological sensitivity can provide a scientific basis for the prevention and management of the ecological environment, as well as the formulation of relevant regional policies. At present, most studies on ecological sensitivity in China are focused on the ecological construction of cities and towns, ecological protection of watersheds, protection, and construction of nature reserves or tourist scenic areas, and evaluation of land use and soil erosion. International studies on ecological sensitivity cover a wide range of areas, such as the ecological sensitivity of continental shelf 4 , ecological sensitivity of agriculture in India 5 , locust control in ecologically sensitive areas 6 , and seagrass ecosystems in ecologically sensitive areas of wetlands 7 .
The Aba Tibetan and Qiang Autonomous Prefecture (Aba Prefecture) is the upstream region of the Yangtze and Yellow rivers. It bears important ecosystem functions such as soil conservation, water connotation and carbon sequestration [8][9][10] , so it is necessary to carry out ecological sensitivity evaluation in Aba Prefecture to establish ecological protection mechanisms and sustainable use of resources.

Study area
Aba Prefecture is located in northwestern Sichuan Province, southeast of the Qinghai-Tibet Plateau( Figure  1). It has a total area of 84,242 km 2 between 100°0′~104°7 ′E and 30°5′~34°9′N. Aba Prefecture is dominated by plateaus and high mountain valleys, with a complex topography and diverse climate, and the temperature decreases from southeast to northwest and decreases with the increase in altitude. It is an important water source for the upper reaches of the Yangtze and Yellow Rivers. At the end of 2020, the total resident population of Aba was 822,600 11 , and grassland animal husbandry is the pillar and characteristic industry of the state 12 .

Data sources
In this study, the datas on soil texture, topographic relief, vegetation type, and vegetation cover (2020) were obtained from Data Centre Resource and Environmental Science Data, Chinese Academy of Science (http: //www.resdc.cn). Other datasets(2020)were provided by National Tibetan Plateau Data Center (http://data.tpdc.ac.cn) and China Meteorological Data Network (http://data.cma.cn/). All spatial resolution was 1 km.

Selection of evaluation indicators
Selecting rainfall erosivity, soil texture, relief intensity, vegetation coverage, sand-laden wind days, drying index, and soil salinity as the evaluation factors according to the unique ecological environment of the study area. The comprehensive ecological sensitivity was evaluated from land erosion, soil desertification, and soil salinization. Reference to relevant studies on the sensitivity of the Tibetan Plateau，The sensitivity of each ecological factor is divided into five levels (Table 1.).

Determination of weights
Using hierarchical analysis (AHP) calculates the weights of each factor. 8 experts were invited to evaluate the relative importance of any 2 factors in the 3 criterion layer ecological factors and the sub-criterion layer factors under them. Constructing a judgment matrix and using YAAHP to calculate the weight values of each evaluation factor, and it was determined by consistency test so that they could be used as the weights for evaluation (Table 2.).

Data analysis
Using the spatial analysis function of GIS to conduct a weighted superposition analysis of each ecological sensitivity factor and calculate the ecological sensitivity of a single factor of the criterion level as well as the integrated ecological sensitivity. The mathematical model equation is as follows.
In the equation： is the number of evaluation unit； k is the number of evaluation factors ； n is the total number of evaluation factors； is the composite value of the i-th evaluation unit； is the weight value of the k-th evaluation factor； is the sensitivity evaluation index of the i-th evaluation factor of the first evaluation unit.

Soil erosion sensitivity evaluation
The three factors that mainly affect the sensitivity of soil erosion in Aba are rainfall erosivity, soil texture and relief intensity. The overall sensitivity is mainly influenced by the topographic relief and soil texture, showing a phenomenon of high in the southeast and low in the northwest. It can be seen that the southeastern Aba has high topographic relief, fragmented terrain, and poor ecological resistance. At the same time, there are differences in soil texture in Aba, with sandy loam soil, silty clay and loam clay concentrated in the southeast. The area of extremely sensitive areas accounted for 6.67% of the state, highly sensitive areas accounted for 23.43%; moderately sensitive areas accounted for 33.36%; and slightly sensitive and insensitive areas accounted for 28.87% (Figure 2).

Soil desertification sensitivity evaluation
Soil desertification is one of the more serious ecological problems in Aba, influenced by vegetation coverage, soil texture and the sand-laden wind days. From the perspective of soil desertification, Ruoergai County and Jiuzhaigou County in northern Aba are better, mostly insensitive and slightly sensitive types, with vegetation cover greater than 70%. Central area like Aba County, Hongyuan County, and Songpan County are dominated by slightly sensitive soil desertification types, with moderately sensitive types scattered pointwise in the central part and concentrated linearly in southern Aba. On the whole, the extremely sensitive and highly sensitive areas are distributed in the south of Aba, accounting for 11.38%, with vegetation coverage of less than 30% and mostly loamy and sandy soil; the slightly sensitive areas account for the highest percentage, 43.27%, with vegetation coverage ranging from 50% to 70% (Figure 2.).

Soil salinization sensitivity evaluation
The degree of soil salinization is mainly influenced by the drying index and soil salinity. The sum of insensitive areas and slightly sensitive areas is 76.04% of the total area. They were distributed in blocks in Aba County, Songpan County, Hongyuan County and various places to the south, with the drying index less than 3000 and soil salinity less than 0.14. The highly and extremely sensitive areas accounted for 10.31% and were concentrated in the middle-elevation plains, basins, and low-elevation plains and tablelands in Ruoergai County, with the drying index is greater than 6000 and soil salinity is higher than 0.16 ( Figure 2).

Comprehensive ecological sensitivity evaluation
With the support of ArcGIS10.8, the sensitivity level raster data of 3 factors were superimposed by using a weighted summation model to obtain the comprehensive ecological sensitivity level of Aba, and it was classified into five levels ( Figure 2). The characteristics of ecological sensitivity distribution can be seen in the figure. Areas of Extremely sensitive and highly sensitive are 22.08% of the total. Moderately sensitive areas mainly in the southeastern Aba, and local areas in the western and northeastern Aba. The sum of insensitive areas and slightly sensitive areas is 47.82%, they are mainly located in the northwestern Aba, where the topographic relief and slope is small and the terrain is gentle.

Extremely and highly sensitive areas
The sum of extremely sensitive areas and highly sensitive areas is 22.08%. These two sensitive types of areas are mainly located in the southeastern Aba, as well as local areas in the western and northeastern Aba. The area has large topographic relief, slope, and low vegetation cover, especially the southeast is dominated by high mountain valleys, with many vertical changes in climate, harsh conditions, extreme weather time, hard to resist external disturbances; at the same time, there is high risk of soil erosion and soil desertification in the area, so it has highly sensitivity.

Moderately sensitive areas
The area of moderately sensitive areas is 30.10%, covering most of the southwest and northeast of Aba. Among them, the southwestern area have a higher elevation, a low risk of soil salinization, with arable land and grassland distribution, people can carry out appropriate farming activities there. In the northeast, the drying index and soil salinity are higher, the number of sand-laden wimd days is higher than 15 days, so the risk of soil salinization is high, but due to the high vegetation coverage and good water conditions, the overall vulnerability is mostly at a medium level.

Slightly sensitive and insensitive areas.
47.82% of the land belongs to lightly sensitive and non sensitive areas, mainly located in the northwestern Ruoergai County, Aba County, Hongyuan County, and the western Songpan County, where the population density is relatively small and human activities are infrequent. The northwestern Aba has high elevation, small topographic relief and slope, wide and flat ground in the area of Ruoergai County and Hongyuan County, and gentle side slopes. The Yellow River and the Yangtze River flow through the area, which is the distribution area of water system.

Conclusion and Discussion
From the spatial distribution pattern of comprehensive sensitivity, the overall trend in Aba Prefecture is low in the northwest and high in the southeast. In Ruoergai County, Aba County, Hongyuan County, and the western Songpan County, the sensitivity is low. In these areas, the population density is smaller, and they have relatively poor economic development, so the local economy should be developed according to local conditions based on protecting the local ecological environment, such as the "Jiuzhaigou path", making full use of ecological advantages, based on the whole-area tourism, to develop High-quality economic. With high relief intensity and low vegetation coverage, the local sensitivity of southeastern, western, and northeastern Aba is high, especially the population density of Xiaojin County, Wenchuan County, and Mao County in the southeastern Aba is high, human activities are frequent, and has higher ecological security requirements. This study provides a theoretical basis for ecological protection and ecological economy construction in Aba Prefecture; it is of practical significance for implementing the strategy of sustainable development in Aba; at the same time, it has a theoretical value for constructing a "human-nature life community" in ethnic areas of China. "It has certain theoretical value.