Land Use And Wind Erosion Process In Bashang Area Of Hebei Province

Wind erosion is one of nature disasters on globe. This phenomenon is widely distributed in arid and semiarid area. Most of China west region locates in that area, and agriculture product is seriously affected by wind erosion. Bashang of Hebei province locates in front transition from semiarid to semi-humid. Wind erosion studied in this area will helpful to understand develop tendency of soil erosion in east of China. This study based on summarizing previously researchers to the wind erosion. Bashang of Hebei province are investigated and researched in southeast wind erosion area of China, such as Kangbao, Zhangbei and Fengning country. Nature condition and human activity affect wind erosion are synthesis analyzed. The factors caused wind erosion is studied by way of gray time series correlation model. The key of the model is compare of geometric curve figure. The more similar geometric, the more development and changing tendency close to, and correlation of time series is big. Computations are as follows: Step 1 Original data processing Let X_ij is every index's original data, i and j are lower index, i=1,2,…m, j=1,2,…n, Data are handled initial value processing. Original time series data must average value handling. It is easy to compare and analysis. Formula for computing as follows: Where Step 2 Determine parent sequence X0 and subsequence Xi. Step 3 Compute absolute value Δ_0i(t_j) which is parent sequence minus subsequence at every time's point, that is, Step 4 Difference value which are maximal Δ_max and minimal value Δ_min are taken from table. Step 5 Compute correlation coefficient between parent sequence X₀ and subsequence X_i at every time's point, formula for computing as follows: In which, Δ_max is |X_i-X₀| the biggest value, Δ_min is |X_i-X₀| the smallest value, Δ_0i(t_j) is |X_i-X₀| value at t_j time. Step 6 Computing correlated measure, namely compute correlation coefficient's average value: Step 7 Arrangement correlation coefficient's order: Arrangement correlation coefficients as column according the big and small is called correlation order, and then clear to see "primary and secondary"and "advantage and disadvantage"relations between parent sequence and subsequence. The model refers to appendix one. According to the relationship between wind erosion and environment in this region, precipitation and temperature of nature factors are analyzed. Month and year mean precipitation and temperature are chosen as wind erosion effective factors. Human activities factors include population increase rate, per capital income, change of grassland and cultivated land area. All above factors related to wind erosion are analyzed by gray correlation model, and summarized change rule in terrain. Experiment area is chosen according to the rule. Soil erosion process and change of different land use are observed and calculated. Field investigation and experiment design are based on model research, and then do experiment in chosen area. Wind erosion is monitored by development instrument. From above study the summarized conclusion as follows: 1. Bashang of Hebei province is located in semiarid and semi-humid ecology environment north of China. The sand's soil is easy erosion in this fragility environment because of climate changing irregular and landforms conditions. By way of synthesize analyzing nature factor and human activity and then find soil erosion has followed regular pattern: winter high temperature is the direct reason to cause soil erosion. Soil's moisture evaporate is actuate when temperature is high. Soil's low moisture is intensified wind erosion process. Precipitation and human activities changing along with landforms change. Ecology environment fragility is increased from semi-humid southeast to semiarid northwest, in which precipitation is become a main factor's to affect wind erosion and environment reaction to human activity is cut down, so the human activity to wind erosion is in the second place. Precipitation is not the main reason to affect wind erosion because of nature condition is better when gradually towards semi-humid southeast. But human activity imposing on environment is reflected and become a main reason to affect wind erosion. 2. Wind is basic condition to caused wind erosion. Field observe and calculation indicate: soil erosion take place in uncovered ground when wind velocity is bigger than 5.5 m·s-1. If vegetative coverage is bigger than 17%, Wind erosion phenomenon could take place when wind velocity is bigger than 8 m·s-1. The reason of wind erosion eliminated is vegetative coverage increasing in summer. Climate factor and soil condition could not be changed by human's will, but the way of land use, which effect wind erosion, would be changed. Land vegetation coverage condition is decided by way of land use and which affect soil characteristic and wind erosion directly. Hereby we chose the study area where is affected distinctness by human activity in semiarid and semi-humid southeast area of Bashang. Different way of land using caused soil's surface layer's physic and chemical characteristic change in long-term, which effect soil latency erosion. Soil erode-ability of different land use iscomputed according to soil's latency erosion calculation formula, and prediction wind erosion quantity of different land use. In this region the value from big to small is abandon cultivated-field, cultivated-field, artificial forestation and grassland. The biggest of latency erosion is abandon cultivated-field and the value is 63.8545%, the smallest of latency erosion is grassland and its value is 50.7872%. Cultivated-field and artificial forestation's value locates in the second and the third place. The value is 53.0202% and 54.2122% respectively. Soil latency erosion is closely related to soil physical and chemistry characteristic. Once land use had been changed, soil surface characteristic and latency erosion would be changed too. 3. Soil sample of Bashang is used in wind erosion simulation experiments. The relationship between soil surface characteristic (vegetation coverage and soil moisture) and wind erosion is analyzed and find it has inverse proportion between them. This experiment is used in field to research of wind erosion after summarizing simulation process. It has better result that affected by soil humidity and vegetation coverage when soil surface shape changing measure instrument applied to measure wind erosion. Erosion depth is 1.7mm when no vegetation coverage. With the increasing of coverage the wind erosion quantity is decreased. Erosion depth is 0.13mm when vegetation coverage is 50%.Soil surface shape is simulated by software Surfer and then discovered: erosion process caused surface shape change when vegetation coverage is increased. This is action result between wind velocity and vegetation coverage. The increasing of vegetation coverage disturbed air current and caused erosion shape change. Effect of soil humidity to wind erosion is decided by soil surface humidity, not all sections. Measured wind erosion depth is only 0.139 cm when soil surface humidity is 12.84%. Erosion depth is reach 1.383 cm when humidity is only 3.09%. This process explained the importance of soil surface humidity to reduce wind erosion quantity. 4. Invariableness wind velocity is used in experiment to measure soil erosion of different land use and then discovered: Wind erosion quantity is closely related to the type of land use. Vegetation coverage, soil surface moisture and soil characteristic are decided by the type of land use. Land use accelerates the soil characteristic change and brings different anti-wind-erosion ability. Soil surface shape has been changed after wind eroded which is reflected the soil erosion change process. Soil construction is changed when it disturbed by human activity and easy erosion. Wind erosion is measured in field in July 6, 2002 and discovered: Grassland average erosion depth is only1.51mm, artificial forestation is 1.61mm. But the cultivated field is as big as 13.82mm, it is known from the result: soil erosion depth is most related to soil's disturbing degree by land use. Cultivated field is affected by every year's till. Its erosion depth is the biggest. But artificial forestation soil is less affected by human activity and its erosion depth is small. There is little effect to grassland soil and its erosion depth is the smallest. 5. Erosion substance would be moved along soil surface when wind erosion takes place. Near ground, the wind erosion particles collection instrument is used to research sand movement and distribution regularly in space. It is discovered by collecting erosion substance near ground 0²m: with the increasing of height erosion substance quantity and size becoming little and small, the organic obviously reduced. 6. Increasing of grazing intensity has more affected to grassland that is related to livestock'stypes and number. The relationship between grazing intensity and grassland degradation is studied by math in which grassland carrying capacity must be based on regional environment condition and then to avoid degradation caused wind erosion. Vehicle is one of the reasons to cause road wind erosion. The difference between road and around land is measured and calculated in field. To compare road with around land and discovered: vehicle accelerates wind erosion on road and every year erosion depth is 2.9-3.8 cm. The changing of road shape makes air current changed which affect erosion way to road. 7. Phenomenon of wind and water double erosion is widespread in the research area. Double erosion is not plus wind and water erosion together simply. But its action between them accelerated or decelerated on erosion process, in which what degree that they reached still need further study. Its action rules express as follows: formula F(t)=f(t)+â–³f, in which F(t) and f(t) are erosion intensity (g·cm-2·min-1)changing along with time, t represents time, â–³f is changing intensity from wind and water erosion action. â–³f is probably positive, it is also probably negative. Two new types of instruments applied in this research. Namely "Soil surface shape changing measure instrument"and "near ground wind erosion particles collection instrument". It is easy to do experiment in field when measure method is improved. This method is very helpful to measure wind erosion quantity and erosion substance movement rules. It is significant to wind erosion research.