Climatic and atmospheric properties vary significantly within a small area for a topographically diverse region like Nepal.Remote sensing can be used for large-scale monitoring of atmospheric parameters in such divers...Climatic and atmospheric properties vary significantly within a small area for a topographically diverse region like Nepal.Remote sensing can be used for large-scale monitoring of atmospheric parameters in such diverse terrains.This work evaluates the Landsat-based METRIC(Mapping Evapotranspiration at High Resolution with Internalized Calibration)model for estimating Evapotranspiration(ET)in Nepal.The slope and aspect of terrain are accounted for in our implementation,making the model suitable for regions with topographical variations.The estimations obtained from the model were compared with ground-based measurements.The root-meansquare error for hourly ET(daily ET)was 0.06 mm h-1(1.24 mm d-1),while the mean bias error was0.03 mm h-1(0.29 mm d-1).These results are comparable with results from other studies in the literature that have used the METRIC model for different regions of the world.Thus,this work validates the applicability of the METRIC model for ET estimation in a mountainous area like Nepal.Further,this implementation provides ET estimation at a very high resolution of 30 m compared to the best available resolution of 5 km in earlier works,without compromising on the accuracy.ET estimation with high resolution over a large region in Nepal has applications in agricultural planning and monitoring,among others.展开更多
A coupled numerical model of the global atmosphere with a qualified biosphere (GOALS/LASG) has been used to assess the nature of the physical mechanisms for land-atmosphere interactions, and the impacts of the Asian/N...A coupled numerical model of the global atmosphere with a qualified biosphere (GOALS/LASG) has been used to assess the nature of the physical mechanisms for land-atmosphere interactions, and the impacts of the Asian/North American land-surface evapotranspiration on the regional and global climate. This sensitivity study suggests that the simulated climate would be relatively sensitive to land surface evapotranspiration, especially over the Asian regions. The removal of evapotranspiration in Asia would create a warmer and drier climate to a certain degree. Furthermore, the surface evapotranspiration anomalies would make a substantial contribution to the formation and variation of subtropical anticyclones through the changes in monsoon precipitation and the β -effect, but also make a large contribution to the variations of the atmospheric circulation in the Northern Hemisphere and even the globe. Therefore, besides the traditional perception that we have generally emphasized on the influence of subtropical anticyclones activities on the boreal summer precipitation over the regions of eastern China, the surface evapotranspiration anomalies, however, also have substantial impacts on the subtropical anticyclones through the changes in monsoon precipitation. For this reason, the variation in the internal heating sources of the atmosphere caused by the land surface evapotranspiration and the vapor phase change during the boreal summer is an important external factor forcing the weather and climate.展开更多
On the basis of eight atmospheric reanalyses, we analyzed the spatial-temporal characteristics of global evaporation and also briefly evaluated the eight reanalyses. The results indicate that the long-term mean annual...On the basis of eight atmospheric reanalyses, we analyzed the spatial-temporal characteristics of global evaporation and also briefly evaluated the eight reanalyses. The results indicate that the long-term mean annual evaporation obtained from different reanalyses are consistent over most regions, with significant maritime-continental contrasts, as well as differences in meridional directions, and the land evaporation generally decreases with the increase of altitude. In addition, the temporal evolution of global evaporation varies significantly among the datasets, MERRA, ERA-Interim, NCEP-NCRA, and NCEP-DOE are very similar, whereas CFSR agrees best with ERA-40. Comparison of the inter-annual to inter-decadal variability of land evaporation reveals large differences among the reanalyses, whereas MERRA, CFSR, and NCEP-DOE are exactly similar. The temporal variation of evaporation over the oceans showed a relatively high consistency, which indicates that the quality of the reconstructed evaporation values over the oceans is higher, and even greater uncertainties lie in the estimates of evaporation over the land. In general, MERRA and NCEP-DOE may appropriately reflect the spatial-temporal characteristics of global evaporation, showing strong representativeness. The CFSR and ERA-40 are capable of revealing the characteristics of land evaporation, whereas ERA-Interim, NCEP-NCAR, OAFlux, and HOAPS are relatively applicable for research focused on the evaporation over the oceans. According to ERA-40, NCEP-NCAR, and OAFlux, global evaporation significantly decreased for the period of 1958–1978. In contrast, most of the eight reanalyses show a significant linear increase for the period of 1979–2011, and evaporation over the oceans was even more pronounced. Furthermore, the results are presented for the mean annual cycle of global evaporation, the changes at the low latitudes in the Northern Hemisphere are most distinct, and the monthly variation amplitude of the land evaporation was higher than that of the evaporation over the oceans.展开更多
基金funded by the Second Tibetan Plateau Scientific Expedition and Research Program grant number2019QZKK0103the Strategic Priority Research Program of the Chinese Academy of Sciences grant number XDA20060101the National Natural Science Foundation of China grant numbers 41830650,91737205,and 91837208。
文摘Climatic and atmospheric properties vary significantly within a small area for a topographically diverse region like Nepal.Remote sensing can be used for large-scale monitoring of atmospheric parameters in such diverse terrains.This work evaluates the Landsat-based METRIC(Mapping Evapotranspiration at High Resolution with Internalized Calibration)model for estimating Evapotranspiration(ET)in Nepal.The slope and aspect of terrain are accounted for in our implementation,making the model suitable for regions with topographical variations.The estimations obtained from the model were compared with ground-based measurements.The root-meansquare error for hourly ET(daily ET)was 0.06 mm h-1(1.24 mm d-1),while the mean bias error was0.03 mm h-1(0.29 mm d-1).These results are comparable with results from other studies in the literature that have used the METRIC model for different regions of the world.Thus,this work validates the applicability of the METRIC model for ET estimation in a mountainous area like Nepal.Further,this implementation provides ET estimation at a very high resolution of 30 m compared to the best available resolution of 5 km in earlier works,without compromising on the accuracy.ET estimation with high resolution over a large region in Nepal has applications in agricultural planning and monitoring,among others.
基金the Key Project of National Basic Research (G1998040911,G1998040900), the National Natural Science Foundation of China (Grant Nos. 49823002, 49805003, 49835010, 49635170), and Chinese Academy of Meteorological Sciences Foundation for doctorate scholars
文摘A coupled numerical model of the global atmosphere with a qualified biosphere (GOALS/LASG) has been used to assess the nature of the physical mechanisms for land-atmosphere interactions, and the impacts of the Asian/North American land-surface evapotranspiration on the regional and global climate. This sensitivity study suggests that the simulated climate would be relatively sensitive to land surface evapotranspiration, especially over the Asian regions. The removal of evapotranspiration in Asia would create a warmer and drier climate to a certain degree. Furthermore, the surface evapotranspiration anomalies would make a substantial contribution to the formation and variation of subtropical anticyclones through the changes in monsoon precipitation and the β -effect, but also make a large contribution to the variations of the atmospheric circulation in the Northern Hemisphere and even the globe. Therefore, besides the traditional perception that we have generally emphasized on the influence of subtropical anticyclones activities on the boreal summer precipitation over the regions of eastern China, the surface evapotranspiration anomalies, however, also have substantial impacts on the subtropical anticyclones through the changes in monsoon precipitation. For this reason, the variation in the internal heating sources of the atmosphere caused by the land surface evapotranspiration and the vapor phase change during the boreal summer is an important external factor forcing the weather and climate.
基金supported by the National Basic Research Program of China(Grant Nos.2013CB430204,2012CB955900)the National Natural Science Foundation of China(Grant Nos.41375078,41175084)the Special Scientific Research Fund of Meteorological Public Welfare Profession of China(Grant No.GYHY201106016)
文摘On the basis of eight atmospheric reanalyses, we analyzed the spatial-temporal characteristics of global evaporation and also briefly evaluated the eight reanalyses. The results indicate that the long-term mean annual evaporation obtained from different reanalyses are consistent over most regions, with significant maritime-continental contrasts, as well as differences in meridional directions, and the land evaporation generally decreases with the increase of altitude. In addition, the temporal evolution of global evaporation varies significantly among the datasets, MERRA, ERA-Interim, NCEP-NCRA, and NCEP-DOE are very similar, whereas CFSR agrees best with ERA-40. Comparison of the inter-annual to inter-decadal variability of land evaporation reveals large differences among the reanalyses, whereas MERRA, CFSR, and NCEP-DOE are exactly similar. The temporal variation of evaporation over the oceans showed a relatively high consistency, which indicates that the quality of the reconstructed evaporation values over the oceans is higher, and even greater uncertainties lie in the estimates of evaporation over the land. In general, MERRA and NCEP-DOE may appropriately reflect the spatial-temporal characteristics of global evaporation, showing strong representativeness. The CFSR and ERA-40 are capable of revealing the characteristics of land evaporation, whereas ERA-Interim, NCEP-NCAR, OAFlux, and HOAPS are relatively applicable for research focused on the evaporation over the oceans. According to ERA-40, NCEP-NCAR, and OAFlux, global evaporation significantly decreased for the period of 1958–1978. In contrast, most of the eight reanalyses show a significant linear increase for the period of 1979–2011, and evaporation over the oceans was even more pronounced. Furthermore, the results are presented for the mean annual cycle of global evaporation, the changes at the low latitudes in the Northern Hemisphere are most distinct, and the monthly variation amplitude of the land evaporation was higher than that of the evaporation over the oceans.
