**Abstract**

In arid region, shelterbelt is the ecological barrier for oasis. Understanding its ecological effects can provide theoretical supports for its long-term management and sustainable development. Two standard meteorological stations were used to monitor climatic factors continuously for 7 years, and two 50 m dust monitoring towers were used to continuously monitor sandstorm for 10 times, which were located inside and outside oasis shelterbelts in the northeastern edge of Ulan Buh Desert. The microclimate differences were analyzed, as well as the ecological effects of oasis shelterbelts was clarified inside and outside oasis. In the present study, under the influence of a large-scale shelterbelts, air temperature, land ground temperature and evaporation respectively decreased 5.13% ~ 24.74%, 2.38% ~ 20.09% and 7.06% ~ 17.68%, whereas the relative humidity and precipitation respectively increased 6.93% ~ 25.53% and 4.30% ~ 50.15%. During the occurrence of sandstorms, the wind speed inside and outside shelterbelt showed an increasing trend with the increase in height. The relationship between wind speed and height was expressed as a power function. The wind direction was mainly W, WNW and NE, but the proportion of each direction was different inside and outside shelterbelt. When the sandstorm passed through oasis shelterbelts, the wind speed was significantly weakened, with an average reduction of 30.68%. The horizontal aeolian sediment flux decreased 414.44 g·m−2 and the aeolian deposition flux decreased 0.81 g·m−2. The results revealed that the microclimate was improved by oasis shelterbelts, especially in the growing season. Therefore, oasis shelterbelts help to maintain the sustainable development of oasis.

**Keywords:** meteorological factor, sandstorm, oasis shelterbelts, Ulan Buh Desert

#### **1. Introduction**

Oasis is a unique geographical landscape in arid and semi-arid regions, which plays an extremely role in the development of human society [1, 2]. In arid region, oasis is irreplaceable in landscape, environment and function. Climate change is an important driving factor affecting ecosystem services. Rising temperature, precipitation change, and extreme climate events will have a great impact on the ecosystem [3]. Climate resources are the most important renewable resources for the development of oasis. Meanwhile, oasis will have a significant impact on climate change [4]. Sandstorm will cause long-term climate effects [5]. Wind is an indispensable dynamic condition for the occurrence of sandstorm, and it is also the main indicator for determining sandstorm intensity [6]. Dust monitoring is a necessary means to provide early warning of sandstorm, to study prevention and control measures, and to reduce the damage caused by sand-dust disasters [7]. The near-surface layer (0 ~ 50 m) not only provides the source of dust, but also the main space for people's life, industrial and agricultural production. Therefore, strengthening the monitoring of near-surface dust and making early warning has important practical significance in disaster prevention.

Ulan Buh Desert is one of important sand sources in China, which has serious wind and sand disasters. It is located at 106°09′–106°57′ E and 39°16′–40°57′ N, the arid region of northwest China, covering nearly 11,000 km<sup>2</sup> [8]. The desert lies at an elevation from 1028 to 1054 m [9], where the southwest area is topographically higher than the northeast [10]. Geomorphologically, the types of sand dunes in the area include moving, fixed, and semi-fixed dunes, the proportions of which are almost equal [11]. The desert is expanding to east and south, which affect the normal functions of the transportation network and water conservancy facilities in its territory, threaten the ecological security of the oasis, the development of agriculture and animal husbandry, and the health of residents [12, 13]. As an important part of the "Three-North Shelter Forest Program", Oasis in Ulan Buh Desert plays an important role in promoting the economic development of the Hetao region and reducing wind and sand disasters. Many studies have been carried out in windbreak structure and configuration of shelterbelts, even effectiveness of shelterbelt [14, 15], dust reduction mechanism and effect of sand reduction [16–18]. In recent years, the impact of meteorological elements (wind speed, precipitation and temperature, etc.) and underlying surface elements (vegetation coverage, soil moisture, degree of surface consolidation or looseness and sediment size) on sandstorms were studied worldwide, including Mojave Desert, Junggar Basin, North and Northwest China [19–22]. However, there were relatively few systematic studies on the ecological effects of oasis shelterbelt systems [23].

In arid region, oasis is a necessary condition for economic development, while the climatic factors play a vital role in maintaining the sustainable development of oasis [24]. Therefore, it is particularly important to explore the ecological effects of oasis shelterbelt system in the Ulan Buh Desert. Therefore, the annual dynamic of climate was studied by meteorological data from 2012 to 2018, which came from two meteorological stations inside and outside oasis shelterbelts in Ulan Buh Desert. Meanwhile, sandstorm was analyzed by the wind speed, wind direction and dust flux data from 10 sandstorms of 50 m dust monitoring tower. Therefore, the differences and causes of microclimates are discussed inside and outside the oasis shelterbelts. And effectiveness of shelterbelts is explained. The results can help to predict the trend of microclimate changes precisely in the future, reveal the characteristics of low-altitude sandstorm on the northeastern edge of Ulan Buh Desert, and give theoretical foundation for the management and sustainable development of the oasis shelterbelts.

## **2. Materials and methods**

#### **2.1 Study area**

The study area is located in the northeast edge of Ulan Buh Desert. It belongs to Dengkou County, Inner Mongolia. The region has a temperate continental monsoonal climate, which are affected by the southeast monsoon in summer and autumn, and are controlled by the Siberian-Mongolian cold anticyclone in winter and spring. The mean annual air temperature was 7.8°C [9], with highest air

*Ecological Effects of Oasis Shelterbelts in Ulan Buh Desert DOI: http://dx.doi.org/10.5772/intechopen.98679*

temperature of 25.6°C in July and lowest air temperature of −11.5°C in January. The mean annual precipitation was 140.0 mm, primarily distributed in the summer. However, mean annual potential evaporation was 2372 mm. The mean annual wind speed was 3.7 m/s with the mean annual windy days of 10–32 d. The frost free days were 168d. The annual sunshine time was 3229.9 h [25]. The soil types are mainly eolian soil and sandy loam soil. The natural vegetation is dominated by *Nitraria tangutorum*, *Artemisia ordosica*, *Calligonum alaschanicum* and *Haloxylon ammodendron* [26]. The dominant tree of shelterbelt is *Populus alba var. pyramidalis* in oasis. The distance between two observation sites is 2.85 km. There are fixed and semi-fixed dunes outside shelterbelt, which dominated by *Nitraria tangutorum* with the height of 1.2 ~ 3.6 m. The area of the shelterbelt system is 1487.3 ha. The width of a belt is 32 m, which is composed of 8 rows of trees, with the auxiliary forest belt spacing of 98 m, and the miniature forest belt spacing of 398 m. The characteristics and locations of vegetation inside and outside shelterbelt are shown in **Figure 1**.

### **2.2 Data sources and research methods**

### *2.2.1 Meteorological factors*

The parallel comparative experimental observation of meteorological elements inside and outside oasis shelterbelt were conducted by Windsonic two-dimensional ultrasonic wind speed and direction sensors (1590-PK-020, Campbell, USA) and temperature and humidity sensors (1590- PK-020, Campbell, USA). The data was collected from January 1, 2012 to December 31, 2018. The start wind speed of wind speed and direction sensor is 0.01 m·s−1, with the accuracy of ±2% and wind direction of ±3°, which range from 0 ~ 60 m·s−1 and 0 ~ 359°, with the resolution of 0.01 m·s−1 and 1°, respectively. The precipitation and evaporation were collected in accordance with the relevant regulations of the "Ground Meteorological Observation Regulations" issued by the China Meteorological Administration [27]. The observation time was 8:00, 14:00, and 20:00 (Beijing time) every day. The data at Site 1 and Site 2 were observed simultaneously and recorded instantly inside and outside shelterbelt, respectively. Refer to the definition of high temperature defined by the China Meteorological Administration, the temperature ≥ 35°C is a high temperature weather, and the number of high temperature days is the number

**Figure 1.** *The location map of the observation plot.*

#### *Deserts and Desertification*

of days with the highest temperature ≥ 35°C. The high temperature data was the daily maximum temperature from 2012 to 2018, and the statistical period was 08:00–08:00 (Beijing time).

Temperature and relative humidity were obtained at a height of 1 m. Wind speed and direction was obtained at a height of 12 m. And precipitation and water surface evaporation were obtained at a height of 10 m. The quality of data was controlled by the simultaneous calibration of two observation points, the logical extreme value check, and the non-conformance time consistency check. According to the dividing method of four seasons in Chinese meteorology [28], spring was defined from March to May, summer was defined from June to August, autumn was defined from September to November, and winter was defined from December to February. The average value of each season's environmental factors was analyzed by Excel 2016. The variation trend graph of each meteorological factor was drawn by Origin 2017.

### *2.2.2 Dust collection device*

The height of dust monitoring tower is 50 m, with horizontal eolian dust samplers and dust deposition traps respectively mounted at 18 heights of 0.50, 1.0, 2.0, 4.0, 6.0, 8.0, 10.0, 12.0, 16.0, 20.0, 24.0, 28.0, 32.0, 36.0, 40.0, 44.0, 48.0 and 50.0 m above the ground (**Figure 2**). The horizontal eolian dust sampler and dust deposition traps were developed by the Key Laboratory of Desert and Desertification, Chinese Academy of Sciences [29]. The horizontal eolian dust sampler was used to track the variation of wind direction and collect sand and dust from a dust inlet with the size of 20 mm × 50 mm. A dust deposition trap was designed to collect eolian sediment at different heights. This trap is a transparent glass container with an Inner diameter of 15 cm and a depth of 30 cm. There are a wind speed and direction sensor mounted at each height of 1.0, 2.0, 4.0, 8.0, 12.0, 16.0, 24.0, 36.0 and 48.0 m above the ground.

The monitor of eolian sediment flux was completed within 1 day after the end of the sandstorm. In order to ensure that the collected samples are natural air-drying, precipitation should be avoided during the sampling process. The collected samples were weighed by an electronic balance with the accuracy of 0.001 g. The 10 times sandstorms were monitored from January 2017 to June 2020. The wind speed and direction were automatically recorded during this period, and the data collection frequency was 10 min.

#### **Figure 2.**

*The 50 m dust monitoring towers inside and outside shelterbelt, the 18 horizontal eolian dust samplers and 18 dust deposition traps.*

### *2.2.3 Data calculation method*

The horizontal aeolian sediment was calculated by formulas (1):

$$\mathbf{M}\_H = \mathbf{W}\_H \mid ab \tag{1}$$

Where *M*H is the horizontal aeolian sediment flux (g·m−2); *W*H is the net weight of dust collected in the horizontal aeolian sediment samplers (g); *a* is the width of the horizontal aeolian sediment samplers opening (mm); *b* is the height of the horizontal aeolian sediment samplers opening (mm).

The aeolian deposition flux was calculated by formulas (2):

$$\mathbf{M}\_{\rm V} = \mathbf{W}\_{\rm V} \wedge \pi r^2 \tag{2}$$

Where *MV* is the amount of aeolian deposition fluxes (g·m−2); *WV* is the net weight of dust received in the aeolian deposition traps (g); *r* is the radius of the aeolian deposition traps opening (cm).
