| This thesis will use the erosive precipitation and the monthly temperature data from the 177 stations including hydrologic stations and weather stations in Northeast China from 1980 to 2009, and will also use 30d maximum synthesis of vegetation index MOD 13A3 data products provided by NASA to analyze temporal and spatial distribution of periodic the environment of rainfall erosion in Northeast China in recent 30 years. And on this basis, this thesis will analyze the temporal variation of rainfall erosion and establish the basic model of the temporal variation of rainfall erosion. The main conclusions are as follows:1. Temporal and spatial evolution of the environment of rainfall erosion in Northeast China in recent 30 years(1) The average annual rainfall of 1980-2009 in Northeast China is 420.22mm. For 30 years, the average annual rainfall in Northeast China is zonal distribution, and gradually decreased from southeast to northwest. The seasonal rainfall resembles the annual rainfall in space distribution. They are both zonal distribution, descending from the southeast to the northwest. And the summer rainfall in the southeast area is the most. Moreover, in southeast, the precipitation reaches more than 600mm.(2)In Northeast China, the average temperature is 4.69℃, and its spatial distribution is characterized by low temperature in the north, high in the south. The average temperature changes in the range of 14℃. The difference of the temperature is obvious. The region with the highest temperature in the four seasons is mainly distributed in most areas of Liaoning Province. And the lowest temperature is mainly in the northern part of Da Hinggan Mountains. This distribution is mainly affected by latitude.(3)The coverage of vegetation in the northeast China shows a rising trend, and the slope of the trend line is 0.0029. It denotes that the coverage of vegetation is improved obviously. From 2000 to 2009 Northeast China’s vegetation coverage overall improvement area is larger than the degenerated area. And the area been improved is 107.46 km2, accounting for 86.28%; the area basically unchanged is 7.99 km2, accounting for about 6.47%; the degradation area is 8.07 km2, accounting for about 6.53%. The rainfall area in Northeast China which is positively related to the NDVI is 86.49km, accounting for 60.19%; and the area of negative correlation is 57.21 km2, accounted for 39.81%. Among them the positive correlation area accounts for 8.23 km2, occupying 6.45%, and the negative correlation area accounts for 3.19km, occupying 2.98%; in Xiao Hinggan Ling and north of the Northeast Plain, the rainfall and NDVI show negative correlation extremely and their coefficient of correlation is large. It shows a trend when rainfall reduces the coverage of vegetation increases, indicating that human activities on Vegetation in the region have a positive role.2. The temporal and spatial evolution of rainfall erosion and the establishment of a simple model based on annual rainfall in the Northeast of China during the last 30 years(1) In Northeast China from 1980 to 2009 to 30 years, with an average rainfall erosion for 2158.81 MJ·mm/hm2·h·a, the maximum value for the 3822.08 MJ-mm/hm2·h·a, minimum 1520.06 MJ-mm/hm2-h-a,and the standard deviation of rainfall erosion for 499.71, and the coefficient of variation (CV) is 0.23. So the erosion of annual changes is not significant. In the month, rainfall erosion in July is the largest reaching to 504.15 MJ-mm/hm2-h-a, accounting for 35.17% annually, followed by August, accounting for 29.11%. Rainfall erosion distribution is extremely uneven, the annual 79.42% concentrated in summer, but rainfall erosion in winter is only 0.60%.Rainfall erosion from July to September accounts for 87.40%. In general, the range of rainfall erosion has little change, but the time distribution is concentrated.(2) According to the analysis of the rainfall and annual rainfall erosion in the Northeast China in last 30 years, the coefficient of correlation is 0.935. The significant level is enhanced. Then by analyzing the annual rainfall and rainfall erosion force values, we can ensure that the coefficient R2 was 0.913, and we can work out the regression fitting equation between annual rainfall and annual rainfall erosion. By estimating the average erosion force and the reference value of linear regression, R2 of 0.996. The Calculation of annual rainfall erosion is with certain accuracy and in algorithm is simpler than that based on daily rainfall algorithm and is not subjected to unlimited self recording rainfall data, so it can be used as simple algorithm of the annual rainfall erosion in Northeast China. |
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