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This study examines the seasonal and diurnal variations of carbon dioxide and energy fluxes over three land cover types of Nepal by using the eddy covariance method from March to November 2016. The surface energy balance closures were moderate with the values of about 56%, 61%, and 64% closure at Kirtipur, Simara, and Tarahara sites respectively. The monthly average values of net radiation flux and latent heat flux peaked in August at Kirtipur and Tarahara sites whereas in June at the Simara site respectively. The maximum monthly average measured sensible heat flux was 37 W m−2, 43.6 W m−2, and 36.3 W m−2 in April for all the sites whereas soil heat flux was 5.1 W m−2 and 2.9 W m−2 in April for Kirtipur and Simara sites and 6.2 W m−2 in June for the Tarahara site. The magnitude of diurnal peak of net ecosystem CO2 exchange (NEE) reached up to 11.04 μmol m−2 s−1 at Kirtipur, 15.04 μmol m−2 s−1 at Simara, and 10.44 μmol m−2 s−1 at Tarahara sites respectively. Among the three study sites, the ecosystem at the Kirtipur site was a good carbon source; the ecosystems at Simara and Tarahara sites were low and good carbon sink in the growing season. In addition, all three different land cover ecosystem were carbon source when accounted for the measurement period. [ABSTRACT FROM AUTHOR]

The southeastern part of Nepal is traditionally known as the entrance of the South Asian summer monsoon system (SASM) and plays a vital role in the development of the national agro-economy. This research examined the diurnal and seasonal variation in the heat and mass fluxes. The study area lies in the agricultural fields that maintain crop cycles. Half-hourly data for a period of 54 months starting in October 2012 were obtained from the Tarahara surface flux observation system (SFOS), and the analyzed data included fast response eddy covariance measurements. The results show that all radiation components changed diurnally and seasonally, except for downward longwave radiation, which revealed weak diurnal variation during winter months. The winter surface albedo of the agricultural field was higher than the summer surface albedo and varied from 0.13 to 0.19. Latent heat release was found to be strongest during the summer season and was associated with atmospheric moisture content and precipitation. Sensible heat becomes weaker during summer and exhibits significant variation during winter months. The sensible heat flux increased rapidly with the increasing radiation flux during the pre-monsoon, which is a major energy source for driving atmospheric systems. The partitioning of energy into turbulent fluxes was also analyzed and it was found that the released latent heat consumed 67% of the net radiation; furthermore, 21% was consumed by the released sensible heat. The response of the land surface heat fluxes to the large-scale circulation system was clearly identified on the basis of the highest peak values observed in 2015 and 2016. [ABSTRACT FROM AUTHOR]

In recent days there have been discussions regarding the impact of climate change and its vagaries of the weather, particularly concerning extreme events. Nepal, being a mountainous country, is more susceptible to precipitation extreme events and related hazards, which hinder the socioeconomic development of the nation. In this regard, this study aimed to address this phenomenon for one of the most naturally and socioeconomically important regions of Nepal, namely, Eastern Nepal. The data were collected for the period of 1997 to 2016. The interdecadal comparison for two periods (1997–2006 and 2007–2016) was maintained for the calculation of extreme precipitation indices as per recommended by Expert Team on Climate Change Detection and Indices. Linear trends were calculated by using Mann‐Kendall and Sen's Slope estimator. The average annual precipitation was found to be decreasing at an alarming rate of −20 mm/year in the last two decades' tenure. In case of extreme precipitation events, consecutive dry days, one of the frequency indices, showed a solo increase in its trend (mostly significant). Meanwhile, all the intensity indices of extreme precipitation showed decreasing trends (mostly insignificant). Thus, it can be concluded that Eastern Nepal has witnessed some significant drier days in the last two decades, as the events of heavy, very heavy, extremely heavy precipitation events, and annual wet day precipitation (PRCPTOT) were found to be decreasing. The same phenomena were also seen in the Tropical Rainfall Measuring Mission 3B42 V7 satellite precipitation product for whole Nepal. Key Points: Extreme precipitation indices were subjected to their spatial and temporal analysis for the period of 1997 to 2016Average annual precipitation was found to be decreasing at an alarming rate of −20 mm/yearDecreasing precipitation in the Eastern Nepal can also be seen in the satellite precipitation product (TRMM 3B42 V7) [ABSTRACT FROM AUTHOR]

Statistical downscaling model (SDSM) was applied in downscaling precipitation in the three climatic regions of Nepal. The study includes the calibration of the SDSM model by using large-scale atmospheric variables encompassing National Centers for Environmental Prediction (NCEP) reanalysis data, the validation of the model, and the outputs of downscaled scenarios A2 and B2 of the HadCM3 model for the future. The average R value during validation period was 0.84, indicating the good applicability of SDSM for simulating precipitation. Under both scenarios A2 and B2, during the prediction period of 2010-2099, the change of annual mean precipitation in the three climatic regions would present a tendency of surplus of precipitation as compared to the mean values of the base period. On the average for all three climatic regions of Nepal, the annual mean precipitation would increase by about 13.75 % under scenario A2 and increase near about 11.68 % under scenario B2 in the 2050s. The model showed better performance over humid region; moreover, simulated results for the peak monsoon months seem to be overestimated over subhumid and arid regions. [ABSTRACT FROM AUTHOR]

To better understand the basic characteristics of the land surface energy budget, nearly 7 years of continuous measurements at the Qomolangma Station for Atmospheric and Environmental Observation and Research, Chinese Academy of Sciences (QOMS/CAS) (28.21°N, 86.56°E, 4276 m a.s.l.) have been analyzed systematically. Seasonal and annual variations of micrometeorological measurements and land surface energy balance were analyzed. The general nature of the diurnal variation of the surface winds on the north of Mt. Everest is represented by a maximum in the afternoon and a constant wind speed in the early morning, which is controlled not only by the significant glacier wind but also by the local mountain-valley circulation and upper-level wind. Surface albedo decreases with increasing soil moisture content, showing the typical exponential relation between surface albedo and soil moisture. The data set disclosed that the high soil moisture in summer is coordinated with low albedo. The ratio between sensible heat and net radiation (H/Rn) can be as high as 0.49 when the soil is dry. The ratio (H/Rn) decreases to 0.14 with the increasing of soil moisture. On the contrary, the ratio between latent heat flux and net radiation (LE/Rn) is increased when soil moisture is rising. The highest ratio (LE/ Rn) can be as high as 0.5 when soil moisture changes between 15% and 20%. After defining the effects of different soil moisture level on partitioning of surface available energy into sensible and latent heat fluxes, we can qualify how much the sensible heating is decreasing and the latent heating is increasing in this region under current plateau environment changes of warming and moistening. [ABSTRACT FROM AUTHOR]

The land-atmosphere interaction processes are unique at Mt. Everest as a result of high elevation. Based on turbulent data collected from April 2005 to March 2006 with the eddy covariance method at Quzong in the Rongbu Valley on the northern slope of Mt. Everest, land-atmosphere energy budget before and after the southwest monsoon onset and surface layer turbulent characteristics are studied for the first time. It is found that energy budget components (net radiation flux, sensible heat flux, latent heat flux, and soil heat flux) and surface heating field have strong diurnal and seasonal variations. In particular, under the influence of the southwest monsoon, the characteristics of surface parameters can be clearly identified. From pre-monsoon to monsoon season, the sensible heat flux decreases whereas the latent heat flux increases. The latent heat flux and Evaporative Fraction at Quzong are relatively high most of the year. Furthermore, the intensity of heating source in the wet season (from June to August) is much greater than that in the dry season (from October to December). The relationship between normalized standard deviation of wind speed and atmospheric stability, variations of normalized standard deviation of temperature, and humidity with atmospheric stability are analyzed using the Monin-Obukhov similarity theory. The result reveals that the normalized standard deviation of velocity components of the three-dimensional wind speed follows similarity relationships in the convective and near-neutral surface layer, but does not seem to be valid in stable surface layer. However, the normalized standard deviation of temperature and humidity does not obey Monin-Obukhov similarity theory in the entire interval of atmospheric stratifications. [ABSTRACT FROM AUTHOR]

• PhenoRice based rice area show good agreement with statistical record of Nepal. • Rice cultivation occurs earlier in western Nepal than eastern Nepal. • Rice cultivation area in Nepal decreased significantly in the recent decade. Monitoring paddy rice cultivation is essential for ensuring food security and for land resource management in agrarian countries of South Asia. In this study, we investigated the spatial and temporal variation of rice cultivated area and phenological metrics in Nepal between 2003 and 2018 using the time series MODIS data and PhenoRice algorithm. Comparisons of PhenoRice outputs with ancillary data show that implementation of PhenoRice with the MODIS data can be used for long-term change analysis of rice cultivation. Results on spatial distribution illustrate: rice cultivation is concentrated in the low elevation belt in the south; the cultivation begins earlier in the western region compared to the eastern region and begins earlier in the hilly region compared to the plains. The inter-annual trend analysis found a statistically significant decrease of rice cultivated area at the rate of 19.13 thousand hectares per year during the recent decade; the loss of rice fields was more prominent in the eastern plains while rice farming expanded in the mid-hills in the western region. Our study provides insights regarding timely and cost-efficient monitoring of rice farming at a large scale in the mountainous region. [Display omitted] [ABSTRACT FROM AUTHOR]