Abstract
Near surface air temperature (Ta) is one of the key input parameters in land surface models and hydrological models as it affects most biogeophysical and biogeochemical processes of the earth surface system. For distributed hydrological modeling over glacierized basins, obtaining high resolution Ta forcing is one of the major challenges. In this study, we proposed a new high resolution daily Ta estimation scheme under both clear and cloudy sky conditions through integrating the moderate-resolution imaging spectroradiometer (MODIS) land surface temperature (LST) and China Meteorological Administration (CMA) land data assimilation system (CLDAS) reanalyzed daily Ta. Spatio-temporal continuous MODIS LST was reconstructed through the data interpolating empirical orthogonal functions (DINEOF) method. Multi-variable regression models were developed at CLDAS scale and then used to estimate Ta at MODIS scale. The new Ta estimation scheme was tested over the Langtang Valley, Nepal as a demonstrating case study. Observations from two automatic weather stations at Kyanging and Yala located in the Langtang Valley from 2012 to 2014 were used to validate the accuracy of Ta estimation. The RMSEs are 2.05, 1.88, and 3.63 K, and the biases are 0.42, −0.68 and −2.86 K for daily maximum, mean and minimum Ta, respectively, at the Kyanging station. At the Yala station, the RMSE values are 4.53, 2.68 and 2.36 K, and biases are 4.03, 1.96 and −0.35 K for the estimated daily maximum, mean and minimum Ta, respectively. Moreover, the proposed scheme can produce reasonable spatial distribution pattern of Ta at the Langtang Valley. Our results show the proposed Ta estimation scheme is promising for integration with distributed hydrological model for glacier melting simulation over glacierized basins.
Highlights
Near surface air temperature (Ta), usually referring to the sheltered thermometer temperature at 2 m above ground, is one of the key input parameters in land surface models and hydrological models [1,2] and has been widely used in various fields, such as glacier melting modeling, crop growth simulation, evapotranspiration estimation, drought monitoring, urban heat island and global climate change [3,4,5,6,7,8,9]
People use the temperature lapse rate to obtain at glacierized basins
The first one is that this method assumes the lapse rate is a constant over rate is a constant over the whole watershed, and only considers the influence of elevation on Ta and the whole watershed, and only considers the influence of elevation on Ta and ignores the impacts from ignores the impacts from other factors, such as the land cover and terrain aspect, which limits the other factors, such as the land cover and terrain aspect, which limits the application of this method application of this method over very heterogeneous surface
Summary
Near surface air temperature (Ta), usually referring to the sheltered thermometer temperature at 2 m above ground, is one of the key input parameters in land surface models and hydrological models [1,2] and has been widely used in various fields, such as glacier melting modeling, crop growth simulation, evapotranspiration estimation, drought monitoring, urban heat island and global climate change [3,4,5,6,7,8,9]. Station observation is the most direct and accurate method and is always used as the ground truth to validate the Ta estimated from other approaches. Observations are recorded four times per day (00:00, 06:00, 12:00 and 18:00 in UTC time) while the observation frequency at automatic weather stations can be up to one minute. The situation is even worse at glacierized basins due to their harsh natural condition
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