Soil erodibility is an important index to evaluate the soil sensitivity to erosion. The research on soil erodibility is a crucial tache in understanding the mechanism of soil erosion. Soil erodibility can be evaluated...Soil erodibility is an important index to evaluate the soil sensitivity to erosion. The research on soil erodibility is a crucial tache in understanding the mechanism of soil erosion. Soil erodibility can be evaluated by measuring soil physiochemical properties, scouring experiment, simulated rainfall experiment, plot experiment and wind tunnel experiment. We can use soil erosion model and nomogram to calculate soil erodibility. Many soil erodibility indices and formulae have been put forward. Soil erodibility is a complex concept, it is influenced by many factors, such as soil properties and human activities. Several obstacles restrict the research of soil erodibility. Firstly, the research on soil erodibility is mainly focused on farmland; Secondly, soil erodibility in different areas cannot be compared sufficiently; and thirdly, the research on soil erodibility in water-wind erosion is very scarce. In the prospective research, we should improve method to measure and calculate soil erodibility, strengthen the research on the mechanism of soil erodibility, and conduct research on soil erodibility by both water and wind agents.展开更多
Climate extremes for agriculture-pasture transitional zone, northern China, are analyzed on the basis of daily mean temperature and precipitation observations for 31 stations in the period 1956-2001. Analysis season f...Climate extremes for agriculture-pasture transitional zone, northern China, are analyzed on the basis of daily mean temperature and precipitation observations for 31 stations in the period 1956-2001. Analysis season for precipitation is May-September, i.e., the rainy season. For temperature is the hottest three months, i.e., June through August. Heavy rain events, defined as those with daily precipitation equal to or larger than 50 mm, show no significant secular trend. A jump-like change, however, is found occurring in about 1980. For the period 1980-1993, the frequency of heavy rain events is significantly lower than the previous periods. Simultaneously, the occurring time of heavy rains expanded, commencing about one month early and ending one month later. Long dry spells are defined as those with longer than 10 days without rainfall. The frequency of long dry spells displays a significant (at the 99% confidence level) trend at the value of +8.3% /10a. That may be one of the major causes of the frequent droughts emerging over northern China during the last decades. Extremely hot and low temperature events are defined as the uppermost 10% daily temperatures and the lowest 10% daily temperatures, respectively. There is a weak and non-significant upward trend in frequency of extremely high temperatures from the 1950s to the mid-1990s. But the number of hot events increases as much as twice since 1997. That coincides well with the sudden rise in mean summer temperature for the same period. Contrary to that, the frequency of low temperature events have been decreasing steadily since the 1950s, with a significant linear trend of-15%/10a.展开更多
Modelling scenarios of land use change and their impacts in typical regions are helpful to investigate the mechanism between land use and ecological systems and process the land use allocation under the ecological sec...Modelling scenarios of land use change and their impacts in typical regions are helpful to investigate the mechanism between land use and ecological systems and process the land use allocation under the ecological security. A system dynamics (SD) model with the aim to modelling scenarios of land use change and assessing ecological impact in northern China in the next 50 years is developed here. The accuracy assessment with the historic data from 1990 to 2001 indicated the SD model is robust. After the different 'what-if' scenarios controlled by GDP, population, market, and technology advancement were built, the different scenarios of land use change in northern China from 2000 to 2050 were simulated with their ecological impact assessed. The result suggested that such factors as GDP, population, market and technology have a strong relationship with land use structural change in northern China. It also indicated that such measures as strict controlling of population increase, importing some food to keep the supply-demand balance in the region, and improving agricultural technology will be the guarantee of regional sustainable development with fast economic growth and the obvious land use structural improvement at the same time.展开更多
A 2.4-m-long core was extracted from Diaojiao Lake (41?8′N, 112?1′E) at the foot of the northern part of Daqingshan Mts. High-resolution pollen analysis results of two sites showed 10 arboreal genera, including Pinu...A 2.4-m-long core was extracted from Diaojiao Lake (41?8′N, 112?1′E) at the foot of the northern part of Daqingshan Mts. High-resolution pollen analysis results of two sites showed 10 arboreal genera, including Pinus, Betula, Picea, Abies, Carpinus, Quercus, Ulmus and more than 20 non-arboreal genera, mainly of Artemisia, Labiatae, Nitraria, Polygonaceae, Ranunculus, Thalictrum, Umbelliferae, Caryophyllaceae and Cyperaceae dominating the record. Fern spores, aquatic pollen and algae were also observed in some sections of the cores. The sequence was divided stratigraphically into six pollen assemblage zones by a stratigraphically-constrained cluster analysis using an incremental sum of squares method. The vegetation underwent the following stage changes: steppe with sparse trees, steppe, forest, and steppe. During the middle Holocene, a mixed forest of Pinus, Betula and Quercus occurred on the mountainous areas, and Pinus forest dominated the frontal plains. Six climatic stages were inferred from total pollen flux and pollen percentage from the two sites using a transfer function: humid-cool (10000—7800 aBP), arid-cold (9200—7800 aBP), arid-warm (7800—7100 aBP), humid-warm (7100—4400 aBP), arid-warm (4400—3000 aBP), arid-cold (3000—2100 aBP) phases were identified.展开更多
The relationship between the Arctic Oscillation (AO) and daily temperature variance of 150 Chinese stations are investigated in the present study for wintertime (1 No-vember through 31 March) in the period of 1954-200...The relationship between the Arctic Oscillation (AO) and daily temperature variance of 150 Chinese stations are investigated in the present study for wintertime (1 No-vember through 31 March) in the period of 1954-2001. Re-sults show that the temperature variance significantly de-creases during the high AO years, and increases in low AO cases. A key factor connecting them is the Siberian High, particularly the high-frequency fluctuations of the High. Within the seasonal time scale, the frequency of low-temperature extremes (daily temperature anomaly below 2σ,σ is the standard deviation of daily temperature for a given winter and a given station) displays an odd relation to the variance: a larger (smaller) variance is found to be asso-ciated with smaller (greater) frequency o low-temperature events. That is due to the non-normal distribution of the temperatures, and also influenced by the hhases of AO. Dur-ing the last 50 years or so, AO experiences a significant increasing trend, meanwhile the variance of daily sea level pressure (SLP) in the central region of Siberian High has decreased at a rate of 10.7%/10 a. These result in a signifi-cant weakening of the daily temperature variance in China with a trend of 4.1%/10 a, and a significant increaswe in the intra-seasonal low-temperature extremes at a rate of 0.16d/10 a.展开更多
文摘Soil erodibility is an important index to evaluate the soil sensitivity to erosion. The research on soil erodibility is a crucial tache in understanding the mechanism of soil erosion. Soil erodibility can be evaluated by measuring soil physiochemical properties, scouring experiment, simulated rainfall experiment, plot experiment and wind tunnel experiment. We can use soil erosion model and nomogram to calculate soil erodibility. Many soil erodibility indices and formulae have been put forward. Soil erodibility is a complex concept, it is influenced by many factors, such as soil properties and human activities. Several obstacles restrict the research of soil erodibility. Firstly, the research on soil erodibility is mainly focused on farmland; Secondly, soil erodibility in different areas cannot be compared sufficiently; and thirdly, the research on soil erodibility in water-wind erosion is very scarce. In the prospective research, we should improve method to measure and calculate soil erodibility, strengthen the research on the mechanism of soil erodibility, and conduct research on soil erodibility by both water and wind agents.
文摘Climate extremes for agriculture-pasture transitional zone, northern China, are analyzed on the basis of daily mean temperature and precipitation observations for 31 stations in the period 1956-2001. Analysis season for precipitation is May-September, i.e., the rainy season. For temperature is the hottest three months, i.e., June through August. Heavy rain events, defined as those with daily precipitation equal to or larger than 50 mm, show no significant secular trend. A jump-like change, however, is found occurring in about 1980. For the period 1980-1993, the frequency of heavy rain events is significantly lower than the previous periods. Simultaneously, the occurring time of heavy rains expanded, commencing about one month early and ending one month later. Long dry spells are defined as those with longer than 10 days without rainfall. The frequency of long dry spells displays a significant (at the 99% confidence level) trend at the value of +8.3% /10a. That may be one of the major causes of the frequent droughts emerging over northern China during the last decades. Extremely hot and low temperature events are defined as the uppermost 10% daily temperatures and the lowest 10% daily temperatures, respectively. There is a weak and non-significant upward trend in frequency of extremely high temperatures from the 1950s to the mid-1990s. But the number of hot events increases as much as twice since 1997. That coincides well with the sudden rise in mean summer temperature for the same period. Contrary to that, the frequency of low temperature events have been decreasing steadily since the 1950s, with a significant linear trend of-15%/10a.
基金Young TeacherFoundation ofBeijing N orm alU niversity,N o.10770001
文摘Modelling scenarios of land use change and their impacts in typical regions are helpful to investigate the mechanism between land use and ecological systems and process the land use allocation under the ecological security. A system dynamics (SD) model with the aim to modelling scenarios of land use change and assessing ecological impact in northern China in the next 50 years is developed here. The accuracy assessment with the historic data from 1990 to 2001 indicated the SD model is robust. After the different 'what-if' scenarios controlled by GDP, population, market, and technology advancement were built, the different scenarios of land use change in northern China from 2000 to 2050 were simulated with their ecological impact assessed. The result suggested that such factors as GDP, population, market and technology have a strong relationship with land use structural change in northern China. It also indicated that such measures as strict controlling of population increase, importing some food to keep the supply-demand balance in the region, and improving agricultural technology will be the guarantee of regional sustainable development with fast economic growth and the obvious land use structural improvement at the same time.
基金supported by the National Key Basic Research Support Foundation Project(Grant No.G2000018604).
文摘A 2.4-m-long core was extracted from Diaojiao Lake (41?8′N, 112?1′E) at the foot of the northern part of Daqingshan Mts. High-resolution pollen analysis results of two sites showed 10 arboreal genera, including Pinus, Betula, Picea, Abies, Carpinus, Quercus, Ulmus and more than 20 non-arboreal genera, mainly of Artemisia, Labiatae, Nitraria, Polygonaceae, Ranunculus, Thalictrum, Umbelliferae, Caryophyllaceae and Cyperaceae dominating the record. Fern spores, aquatic pollen and algae were also observed in some sections of the cores. The sequence was divided stratigraphically into six pollen assemblage zones by a stratigraphically-constrained cluster analysis using an incremental sum of squares method. The vegetation underwent the following stage changes: steppe with sparse trees, steppe, forest, and steppe. During the middle Holocene, a mixed forest of Pinus, Betula and Quercus occurred on the mountainous areas, and Pinus forest dominated the frontal plains. Six climatic stages were inferred from total pollen flux and pollen percentage from the two sites using a transfer function: humid-cool (10000—7800 aBP), arid-cold (9200—7800 aBP), arid-warm (7800—7100 aBP), humid-warm (7100—4400 aBP), arid-warm (4400—3000 aBP), arid-cold (3000—2100 aBP) phases were identified.
文摘The relationship between the Arctic Oscillation (AO) and daily temperature variance of 150 Chinese stations are investigated in the present study for wintertime (1 No-vember through 31 March) in the period of 1954-2001. Re-sults show that the temperature variance significantly de-creases during the high AO years, and increases in low AO cases. A key factor connecting them is the Siberian High, particularly the high-frequency fluctuations of the High. Within the seasonal time scale, the frequency of low-temperature extremes (daily temperature anomaly below 2σ,σ is the standard deviation of daily temperature for a given winter and a given station) displays an odd relation to the variance: a larger (smaller) variance is found to be asso-ciated with smaller (greater) frequency o low-temperature events. That is due to the non-normal distribution of the temperatures, and also influenced by the hhases of AO. Dur-ing the last 50 years or so, AO experiences a significant increasing trend, meanwhile the variance of daily sea level pressure (SLP) in the central region of Siberian High has decreased at a rate of 10.7%/10 a. These result in a signifi-cant weakening of the daily temperature variance in China with a trend of 4.1%/10 a, and a significant increaswe in the intra-seasonal low-temperature extremes at a rate of 0.16d/10 a.
