The intensity of recent droughts and the uncertainty of moisture variability in the context of increasing temperatures and decreasing precipitation have affected the Mongolian grassland. Mongolia typifies the steppe t...The intensity of recent droughts and the uncertainty of moisture variability in the context of increasing temperatures and decreasing precipitation have affected the Mongolian grassland. Mongolia typifies the steppe terrain and semiarid to arid continental climate that extends across much of Central Asia. In semi-arid areas like Mongolian steppe, vegetation type and distribution are directly relate to the amount of water that plants can extract from the soil. An index for assessment of moisture availability (ma: defined as the ratio of actual to reference evapotranspiration) was developed, namely NTDI [1] 08D0C9EA79F9BACE118C8200AA004BA90B02000000080000000E0000005F005200650066003400300031003800340037003500380031000000 . NTDI (Normalized Day-Night Surface Temperature Difference Index) is defined as the ratio of the difference between the maximum daytime surface temperature and the minimum nighttime surface temperature, to the difference between the maximum and minimum surface temperatures estimated from meteorological data by applying energy balance equations. A verification study conducted at Liudaogou River Basin of the Loess Plateau, China, indicated the capability of NTDI to estimate ma accurately, (R2=0.97,p<0.001) [1] 08D0C9EA79F9BACE118C8200AA004BA90B02000000080000000E0000005F005200650066003400300031003800340037003500380031000000 . In Bayan Unjuul, Mongolia, application of NTDI during the growing season showed a significant inverse exponential correlation with ma (R2=0.86,p<0.001). This result indicates that the NTDI is potent to be used as a surrogate of moisture availability in steppe terrain of Central Asia.展开更多
The differences between the oasis region and the regions of the Nile delta and Nile valley in Egypt are due mainly to the regions’ access to water. The oasis region depends on underground water, while the other regio...The differences between the oasis region and the regions of the Nile delta and Nile valley in Egypt are due mainly to the regions’ access to water. The oasis region depends on underground water, while the other regions rely on the Nile River. Numerous studies on cultivation in the Nile delta have been accumulated. However, few studies have addressed cultivation in the oasis region. This study examines cultivation throughout the government and local well districts using meteorological and satellite data from 2001 to 2010, and the interview in Rashda Village, Dakhla Oasis. Since the reference evapotranspiration (ET0) is lower in winter than in summer, cultivation in winter makes sense from the viewpoint of saving irrigation water. Evapotranspiration is highest in the order of date palm, rice paddy, winter wheat, and clover hay under sufficient wet conditions in Rashda Village. Cultivation features and water requirements were examined using the Normalized Difference Vegetation Index (NDVI) and Normalized Difference Water Index (NDWI). Results indicated a distinct difference in cultivation systems between the summer and winter seasons in the government well district. Water requirements for date palm in the local well district were 2.6 times those for winter plants in the government well district, using the accumulated NDWI value.展开更多
This study presents experimental results of the change in threshold friction velocity and dust emission strength as a function of soil moisture content. The dust and soil moisture data were obtained from irrigated plo...This study presents experimental results of the change in threshold friction velocity and dust emission strength as a function of soil moisture content. The dust and soil moisture data were obtained from irrigated plots of a bare, sandy soil （no vegetation） situated in the Mongolian steppe. Dust flux was measured using the PI-SWERL^（R） device, while soil moisture was measured using gravimetric methods. Our results demonstrate the strong controlling effects of soil moisture on both the threshold friction velocity and dust emission strengths. Threshold friction velocity increased from 0.44 m/s for dry soil （0.002 g/g） to 0.67 m/s for wet soil （0.06 g/g）, confirming the importance of soil moisture for controlling dust events. Dust emission strength was significantly depressed for wet soils, starting at a soil moisture value of 0.02 g/g. From these results, we developed a simple dust diagram that may be useful as part of a warning system to identify initial sensitivity to threshold conditions as well as conditions that could lead to potentially significant dust emissions. Overall, the research findings in this study could be used to provide foreknowledge of conditions that would be conducive to high dust emissions for this area of Mongolia.展开更多
文摘The intensity of recent droughts and the uncertainty of moisture variability in the context of increasing temperatures and decreasing precipitation have affected the Mongolian grassland. Mongolia typifies the steppe terrain and semiarid to arid continental climate that extends across much of Central Asia. In semi-arid areas like Mongolian steppe, vegetation type and distribution are directly relate to the amount of water that plants can extract from the soil. An index for assessment of moisture availability (ma: defined as the ratio of actual to reference evapotranspiration) was developed, namely NTDI [1] 08D0C9EA79F9BACE118C8200AA004BA90B02000000080000000E0000005F005200650066003400300031003800340037003500380031000000 . NTDI (Normalized Day-Night Surface Temperature Difference Index) is defined as the ratio of the difference between the maximum daytime surface temperature and the minimum nighttime surface temperature, to the difference between the maximum and minimum surface temperatures estimated from meteorological data by applying energy balance equations. A verification study conducted at Liudaogou River Basin of the Loess Plateau, China, indicated the capability of NTDI to estimate ma accurately, (R2=0.97,p<0.001) [1] 08D0C9EA79F9BACE118C8200AA004BA90B02000000080000000E0000005F005200650066003400300031003800340037003500380031000000 . In Bayan Unjuul, Mongolia, application of NTDI during the growing season showed a significant inverse exponential correlation with ma (R2=0.86,p<0.001). This result indicates that the NTDI is potent to be used as a surrogate of moisture availability in steppe terrain of Central Asia.
文摘The differences between the oasis region and the regions of the Nile delta and Nile valley in Egypt are due mainly to the regions’ access to water. The oasis region depends on underground water, while the other regions rely on the Nile River. Numerous studies on cultivation in the Nile delta have been accumulated. However, few studies have addressed cultivation in the oasis region. This study examines cultivation throughout the government and local well districts using meteorological and satellite data from 2001 to 2010, and the interview in Rashda Village, Dakhla Oasis. Since the reference evapotranspiration (ET0) is lower in winter than in summer, cultivation in winter makes sense from the viewpoint of saving irrigation water. Evapotranspiration is highest in the order of date palm, rice paddy, winter wheat, and clover hay under sufficient wet conditions in Rashda Village. Cultivation features and water requirements were examined using the Normalized Difference Vegetation Index (NDVI) and Normalized Difference Water Index (NDWI). Results indicated a distinct difference in cultivation systems between the summer and winter seasons in the government well district. Water requirements for date palm in the local well district were 2.6 times those for winter plants in the government well district, using the accumulated NDWI value.
文摘This study presents experimental results of the change in threshold friction velocity and dust emission strength as a function of soil moisture content. The dust and soil moisture data were obtained from irrigated plots of a bare, sandy soil （no vegetation） situated in the Mongolian steppe. Dust flux was measured using the PI-SWERL^（R） device, while soil moisture was measured using gravimetric methods. Our results demonstrate the strong controlling effects of soil moisture on both the threshold friction velocity and dust emission strengths. Threshold friction velocity increased from 0.44 m/s for dry soil （0.002 g/g） to 0.67 m/s for wet soil （0.06 g/g）, confirming the importance of soil moisture for controlling dust events. Dust emission strength was significantly depressed for wet soils, starting at a soil moisture value of 0.02 g/g. From these results, we developed a simple dust diagram that may be useful as part of a warning system to identify initial sensitivity to threshold conditions as well as conditions that could lead to potentially significant dust emissions. Overall, the research findings in this study could be used to provide foreknowledge of conditions that would be conducive to high dust emissions for this area of Mongolia.
