| In this study, we utilized climate data, land use data, vegetation type and socioeconomic data and adopted remote sensing and mathematical statistics to analyze climate change trend, land use pattern and vegetation succession trend, and their co-evolution.From the aspect of climate change study, multi-year climate data were analyzed to explore the processes and trend of climate change. For the study on ecological processes, vegetation classification system was established according to physical circumstances of Shiyang River Basin. Then based on the system, remotely sensed images were used as the data source and maps of vegetation type were plotted through "3S" technology for analyzing the distribution pattern of different vegetation types in different period. According to vegetation type maps, various vegetation and land use landscape indexes were calculated for quantitative description of landscape patterns in different period in the Shiyang River Basin. In addition, this study adopted landscape transfer matrix to dynamically depict the transfer processes of different vegetation types.Combined with socioeconomic data, this study revealed different influences of climate change and human activities on vegetation cover, vegetation type and ecological health of the ecosystem in the Shiyang River Basin. Meanwhile, this study also explored coevolution of climate change and ecological processes and control mechanism. The main results are listed as below:1.There is an increasing trend in multi-year precipitation in the Shiyang River Basin, however, this indreasing trend has significantly abrupt spatical-temporal change. The statistical test results of variation rang of multi-year precipitation showed that the rainfall variability in summer and early fall was higher than in other seasons. Among the weather stations, the precipitation records in Minqin county demonstrated significantly abrupt change in February of1986-1990, December of1996-2000and2001-2005,and the Cramer’s test value were3.08,-1.88and1.93,respectively.2.In the past5decades, air temperature increased gradually in the Shiyang River Basin, and the incidence of abrupt change in air temperature increased, especially for the rise of temperature in winter. The Mann-Kendall test results of air temperature showed an increasing trend in average air temperature according to all the records of weather stations except for the one in Wushaoling. Therein the average air temperature in March showed a slightly descending trend and the value was-0.22.The statistical test results of changes in magnitude showed that the increasing rate of air temperature in winter was higher than other seasons, especially in February in Wuwei station and Gulang station, the value of statistical test of changes in magnitude was nearly0.08, which is obviously higher than in other months.From the Cramer’s test results, we could realize that the rate of abrupt change in air temperature was relatively high, and significant changes happened mainly in summer and winter.3.The changes in monthly average relative humidity and monthly average evaporation showed complex special-temporal variability. Generally, this change showed a trend towards warming-drying climate. The monthly average relative humidity showed a descending trend, the value of Mann-Kendall test of certain weather stations was-2.For evaporation, there was a slightly descending trend in monthly average evaporation in the upper reaches of the Shiyang River Basin, however, the evaporation in other places were increased in various degrees, and the values of Mann-Kendall test were basically above1.The change rate of evaporation increased fast in summer and late spring, especially in Yongchang station, the values of change in magnitude were obviously higher in July, August, and September than in other stations.From the two aspects mentioned above, the climate in the basin showed a trend towards drying.4.The area with vegetation cover has been gradually shrinking in the Shiyang River Basin, however, artificial vegetation has shown an increasing trend since the last decade.From1990to2000, vegetation coverage was decreased very quickly. By the year of2009, vegetation cover percentage had been less than40%. The area of desert was the largest and accounted for more than50%of the total area of the entire basin. The area covered with snow all the year round was the smallest and only accounted for less than1%of the entire basin. In addition, vegetation change was affected by dual fuction of climate change and human activities. Among various vegetation types, artificial vegetation coverage was the largest. From1990to2009, the vegetation cover were slightly decreased and then dramatically increased, and the percentage of vegetation cover accounted for about10%of the total watershed. The areas of Sandy land and saline land-shrub zone had a trend similar to artificial vegetation change and accounted for5%of the entire basin area. By vegetation transfer matrix, the vegetation types changed towards desert vegetation. Based on socioeconomic data and field investigation, this change was mainly induced by the clear cutting of coniferous, broad leaved forests and sandy-shrub vegetation, saline-shrub vegetation.Thus, human activities had significant influences on these two types of vegetation. 5.The results of landscape pattern analysis showed that landscapes in the entire basin were changing to desertification. The number of patches of bare land, sandy land and saline-shrub zone were relatively large and the average number for each type was more than40,000. The maximum and minimum patch area was in desert and water body, respectively. The maximum density of patches was in bare land, desert and saline-shrub zone, and the average density for each type was over0.9. The landscape dominance of desert was supreme and that of water body was minimal. Among different vegetation types, the landscape dominance of artificial vegetation was supreme and that of mountainous sparse vegetation was minimal, and the value was0.07,0.03,respectively. For the whole landscape pattern in the watershed, fragmentation index were decreased first and then increased. In the four stages, the fragmentation index was7.1%,6.6%,5.1%,and5.5%, respectively. Landscape diversity index was decreased yearly from1990to2009, which means landscape diversity has been decreasing yearly.6. For the entire basin, ecological carrying capacity was gradually decreasing and ecological footprint was gradually increasing. The per capita ecological carrying capacity decreased year by year from0.914hm2/person in2000to0.899hm2/person in2010. Therefore we could see that the ecological environment in the region was gradually deteriorating, and the natural resources provided to local people were decreasing. From the results of the per capita ecological footprint, ecological footprint per capita value was gradually increased, and the value was0.760hm2/person,0.766hm2/person and0.789hm2/person, respectively. Thus, local people relied more heavily on natural resources and more lands were needed for disposal of wastes from production and daily life.In summary, there is a complex and coulpled relationship between climate change and earth surface processes in the Shiyang River Basin. The interaction between climate change and earth surface processes is very complicated. By the effects of short-term economic development, ecological processes showed a trend in deterioration generally but with regional amelioration, causing increased change frenquency and level of microclimate. While global climate change has a long-term effect on reginal ecological processes, thus the cumulative effects of ecological processes and social economic development will lead to the deterioration of ecosystem health.This study can provide certain scientific bases for environmental protection and restoration. Also, this study helps to use as a scientific reference for the sustainable development of local people’s production in the Shiyang River Basin. |
PDF Full Text Request