Sagar Bajracharya | University of New England - Australia (original) (raw)

Papers by Sagar Bajracharya

Annals of the American Association of Geographers

Journal of Hydrology: Regional Studies

Climate

Climate change (CC) is impacting the hydrology in the basins of the Himalayan region. Thus, this ... more Climate change (CC) is impacting the hydrology in the basins of the Himalayan region. Thus, this could have significant implications for people who rely on basin water for their lives and livelihoods. However, there are very few studies on the Himalayan river basins. This study aims to fill this gap by presenting a water balance for the Brahmaputra River Basin using the Soil and Water Assessment Tool (SWAT). Results show that snowmelt contributed about 6% of the total annual flow of the whole Brahmaputra, 21% of the upper Brahmaputra, and 5% of the middle Brahmaputra. The basin-wide average annual water yield (AWY) is projected to increase by 8%, with the maximum percentage increase in the pre-monsoon season. The annual snowmelt is projected to decrease by 17%, with a marked decrease during the monsoon but an increase in other seasons and the greatest percentage reduction in the upper Brahmaputra (22%). The contribution of snowmelt to AWY is projected to decrease while rain runoff w...

The objective of the GEOSS-IPCC workshop was to provide guidance on how to improve the delivery o... more The objective of the GEOSS-IPCC workshop was to provide guidance on how to improve the delivery of multidisciplinary data and data products to researchers studying climate change impacts, adaptation and vulnerability via the Global Earth Observation System of Systems (GEOSS). This objective was inspired by the recognition that the scientific literature and research that underlies the assessments of the Intergovernmental Panel on Climate Change (IPCC) could benefit enormously from improved and sustained Earth observations. Because the issues of climate change and climate impacts, adaptation and vulnerability are multidisciplinary , researchers need access to a wide array of observation data and information products in addition to published scientific literature. As GEOSS addresses nine societal benefit areas (SBAs) and their interlinkages, it has the potential to provide this research community with better access to a broad range of relevant information. To ensure that GEOSS evolves in a manner that benefits this key user group, the workshop focussed on identifying and understanding their needs. The recommendations summarized below are presented as possible guidance and incentives to the governments and organizations that contribute to GEOSS. II) Organization The workshop was organized by the IPCC and the Group on Earth Observations (GEO) with the Global Climate Observing System (GCOS), the World Climate Research Programme (WCRP) and the International Geosphere-Biosphere Programme (IGBP). IPCC Working Group II Co-Chair Christopher Field and GEO Secretariat Director José Achache served as co-chairs. Some 60 participants from the earth observation and climate research communities attended during the three days. Representing an important Earth observation user community, the IPCC advised on participants and presenters who could describe the needs of climate researchers, including quality, quantity, format and timeliness of data and information. While the IPCC itself does not conduct research, its assessment reports benefit from the high quality of published research. Its Fifth Assessment Report (AR5) will be published in 2013-2014 based primarily on the peer-reviewed literature available by cutoff dates specific to each of the three working groups in 2012 and 2013. The IPCC Plenary approved the planned IPCC-GEOSS workshop at its 31 st session in October 2009. Representing both the providers and users of Earth observations and data, GEO consists of 86 governments, the European Commission and 61 international organizations-among them the fundamentally important networks of GCOS, IGBP and WCRP. GEO identified participants and presenters who could respond to the user needs presented at the workshop by identifying opportunities for improving the collection and dissemination of relevant data and information via GEOSS. The GEO Executive Committee recognized the value of the planned workshop.

Climate Dynamics, 2014

A regional climate modelling system, the Providing REgional Climates for Impacts Studies develope... more A regional climate modelling system, the Providing REgional Climates for Impacts Studies developed by the Hadley Centre for Climate Prediction and Research, has been used to study future climate change scenarios over Indus basin for the impact assessment. In this paper we have examined the three Quantifying Uncertainty in Model Predictions simulations selected from 17-member perturbed physics ensemble generated using Hadley Centre Coupled Module. The climate projections based on IPCC SRES A1B scenario are analysed over three time slices, near future (2011-2040), middle of the twenty first century (2041-2070), and distant future (2071-2098). The baseline simulation (1961-1990) was evaluated with observed data for seasonal and spatial patterns and biases. The model was able to resolve features on finer spatial scales and depict seasonal variations reasonably well, although there were quantitative biases. The model simulations suggest a nonuniform change in precipitation overall, with an increase in precipitation over the upper Indus basin and decrease over the lower Indus basin, and little change in the border area between the upper and lower Indus basins. A decrease in winter precipitation is projected, particularly over the southern part of the basin. Projections indicate greater warming in the upper than the lower Indus, and greater warming in winter than in the other seasons. The simulations suggest an overall increase in the number of rainy days over the basin, but a decrease in the number of rainy days accompanied by an increase in rainfall intensity in the border area between the upper and lower basins, where the rainfall amount is highest.

The Mt. Everest region was declared as "Sagarmatha National Park" in 1976 with a missio... more The Mt. Everest region was declared as "Sagarmatha National Park" in 1976 with a mission to conserve and maintain the biological and cultural values, and scenic beauty of its landscape for the benefit of the present and future generations primarily as sources of inspiration, recreation, education and prestige; and to support livelihoods of the local people in a manner that will not harm its integrity. It has also been inscribed as a World Heritage Site by UNESCO in 1979 for its aesthetic and scientific values. The extreme relief and younger geology with high seismic activities make the Himalaya an extremely hazardous region. Earthquakes, landslides, rock falls, avalanches and flash floods are the common types of natural hazards in these mountains. Due to limited lands suitable for inhabitation and farming in the mountains, the land resources are heavily exploited and people are forced to live in danger zones. Pressures due to increased population and tourism activities hav...

Journal of Flood Risk Management, 2011

In Nepal, as the spatial distribution of rain gauges is not sufficient to provide detailed perspe... more In Nepal, as the spatial distribution of rain gauges is not sufficient to provide detailed perspective on the highly varied spatial nature of rainfall, satellite-based rainfall estimates provides the opportunity for timely estimation. This paper presents the flood prediction of Narayani Basin at the Devghat hydrometric station (32 000 km 2) using bias-adjusted satellite rainfall estimates and the Geospatial Stream Flow Model (GeoSFM), a spatially distributed, physically based hydrologic model. The GeoSFM with gridded gauge observed rainfall inputs using kriging interpolation from 2003 was used for calibration and 2004 for validation to simulate stream flow with both having a Nash Sutcliff Efficiency of above 0.7. With the National Oceanic and Atmospheric Administration Climate Prediction Centre's rainfall estimates (CPC_RFE2.0), using the same calibrated parameters, for 2003 the model performance deteriorated but improved after recalibration with CPC_RFE2.0 indicating the need to recalibrate the model with satellite-based rainfall estimates. Adjusting the CPC_RFE2.0 by a seasonal, monthly and 7-day moving average ratio, improvement in model performance was achieved. Furthermore, a new gauge-satellite merged rainfall estimates obtained from ingestion of local rain gauge data resulted in significant improvement in flood predictability. The results indicate the applicability of satellite-based rainfall estimates in flood prediction with appropriate bias correction.

ABSTRACT Snow and ice constitute an important component of the hydrologic regime of many large mo... more ABSTRACT Snow and ice constitute an important component of the hydrologic regime of many large mountain ranges and regions, including the Himalayas. However, the hydrologic regime of Himalayan catchment basins, and the role of glaciers in the hydrologic regime of this mountain range (particularly their contribution to base flow) are not well understood. There are concerns about the impact of climate change on cryosphere as well as population growth, changing economic activity, land use change, rapid urbanization and inefficient water use on water resources. The HIMALA project, funded by the NASA's Applied Sciences Program and the United States Agency for International Development (USAID), in collaboration with the Integrated Center for Integrated Mountain Development (ICIMOD), Nepal, addresses the urgent need for integrated snow and ice hydrology in the Himalaya. Specific objectives are to: (i) introduce the use of NASA Earth Science products and models to ICIMOD and its member countries through collaboration with USAID and USGS and (ii) enhance the decision making capacity of ICIMOD and its member countries for management of water resources (floods, agricultural water) in the short (snow, rainfall) and the long-term (glaciers). Here we present methodology and preliminary results for a sub-basin hydrological model for Langtang watershed in Nepal, that includes modeling both snow and glacier-melt water contributions to streamflow. Snow- and glacier-melt and outflow is estimated using a spatially distributed version of the Utah Energy Balance (UEB) snow accumulation and ablation model, driven by remotely sensed data (TRMM) downscaled model data (MERRA) and meteorological data. Glacier outlines and glacier characterization parameters (albedo and volume) are derived from Landsat (1980s to present) and ASTER data (2000 to present) and used as input to the UEB model. Snow cover and albedo are acquired from MODIS data. We estimate the relative contribution by snow and glacier melt to total melt, which is validated using discharge at various gauge stations in the watersheds. We use the Geospatial Stream Flow Model (GeoSFM) hydrologic model to simulate dynamics of runoff processes. Static input data are SRTM DEM, land cover, and soil information. The model is forced by daily estimates of precipitation and evaportranspiration to predict daily streamflow at ground rain gauge stations. We are developing new user interfaces so that models will be easy to learn and can be used to monitor streamflow in other basins in the region. ICIMOD will implement the prototype model in three large basins of the Himalaya (Koshi, Manas and Jhelum) ranging from east to west. This will provide a better understanding of the contribution of snow and ice to hydrology in the region with relation to the Asian monsoon.

Acta Meteorologica Sinica, 2011

Measuring rainfall from space appears to be the only cost effective and viable means in estimatin... more Measuring rainfall from space appears to be the only cost effective and viable means in estimating regional precipitation over the Tibet, and the satellite rainfall products are essential to hydrological and agricultural modeling. A long-standing problem in the meteorological and hydrological studies is that there is only a sparse raingauge network representing the spatial distribution of precipitation and its quantity on small scales over the Tibet. Therefore, satellite derived quantitative precipitation estimates are extremely useful for obtaining rainfall patterns that can be used by hydrological models to produce forecasts of river discharge and to delineate the flood hazard area. In this paper, validation of the US National Oceanic and Atmospheric Administration (NOAA) Climate Prediction Center (CPC) RFE (rainfall estimate) 2.0 data was made by using daily rainfall observations at 11 weather stations over different climate zones from southeast to northwest of the Tibet during the rainy season from 1 June to 30 September 2005 and 2006. Analysis on the time series of daily rainfall of RFE-CPC and observed data in different climate zones reveals that the mean correlation coefficients between satellite estimated and observed rainfall is 0.74. Only at Pali and Nielamu stations located in the southern brink of the Tibet along the Himalayan Mountains, are the correlation coefficients less than 0.62. In addition, continuous validations show that the RFE performed well in different climate zones, with considerably low mean error (ME) and root mean square error (RMSE) scores except at Nielamu station along the Himalayan range. Likewise, for the dichotomous validation, at most stations over the Tibet, the probability of detection (POD) values is above 73% while the false alarm rate (FAR) is between 1% and 12%. Overall, NOAA CPC RFE 2.0 products performed well in the estimation and monitoring of rainfall over the Tibet and can be used to analyze the precipitation pattern, produce discharge forecast, and delineate the flood hazard area.

Mountain Research and Development, 2010

Journal of Flood Risk Management, 2008

In this study, we have described a hydrologic modelling system that uses satellitebased rainfall ... more In this study, we have described a hydrologic modelling system that uses satellitebased rainfall estimates and weather forecast data for the Bagmati River Basin of Nepal. The hydrologic model described is the US Geological Survey (USGS) Geospatial Stream Flow Model (GeoSFM). The GeoSFM is a spatially semidistributed, physically based hydrologic model. We have used the GeoSFM to estimate the streamflow of the Bagmati Basin at Pandhera Dovan hydrometric station. To determine the hydrologic connectivity, we have used the USGS Hydro1k DEM dataset. The model was forced by daily estimates of rainfall and evapotranspiration derived from weather model data. The rainfall estimates used for the modelling are those produced by the National Oceanic and Atmospheric Administration Climate Prediction Centre and observed at ground rain gauge stations. The model parameters were estimated from globally available soil and land cover datasetsthe Digital Soil Map of the World by FAO and the USGS Global Land Cover dataset. The model predicted the daily streamflow at Pandhera Dovan gauging station. The comparison of the simulated and observed flows at Pandhera Dovan showed that the GeoSFM model performed well in simulating the flows of the Bagmati Basin.

Sustainability, 2021

Nepal is highly vulnerable to flood-related disasters which cause considerable loss of lives and ... more Nepal is highly vulnerable to flood-related disasters which cause considerable loss of lives and property. The vulnerability of communities to flood-related hazards can be reduced by proper planning, preparedness, and responses using various structural and nonstructural measures. The community-based flood early warning system is one such tool that enables local communities to enhance their resilience to flooding risks. This paper highlights the efficacy of the community assessment of flood risks and early warning systems. Using qualitative and quantitative methods, this paper evaluates the progress of a community-based flood early warning system implemented in the Ratu River—a small tributary of the Koshi River. The establishment of a community network in 2015 was instrumental in the dissemination of flood early warning information and in building local capacities to understand the risks and take timely action. The flood early warning resulted in awareness-raising, strengthened upst...

The Science of the total environment, Jan 4, 2018

The Hindu Kush-Himalayan region is an important global freshwater resource. The hydrological regi... more The Hindu Kush-Himalayan region is an important global freshwater resource. The hydrological regime of the region is vulnerable to climatic variations, especially precipitation and temperature. In our study, we modelled the impact of climate change on the water balance and hydrological regime of the snow dominated Kaligandaki Basin. The Soil and Water Assessment Tool (SWAT) was used for a future projection of changes in the hydrological regime of the Kaligandaki basin based on Representative Concentration Pathways Scenarios (RCP 4.5 and RCP 8.5) of ensemble downscaled Coupled Model Intercomparison Project's (CMIP5) General Circulation Model (GCM) outputs. It is predicted to be a rise in the average annual temperature of over 4°C, and an increase in the average annual precipitation of over 26% by the end of the 21st century under RCP 8.5 scenario. Modeling results show these will lead to significant changes in the basin's water balance and hydrological regime. In particular, ...

Proceedings of the International Association of Hydrological Sciences

According to Liu et al. (2014), borrowing, substituting and generating (BSG) are the main methods... more According to Liu et al. (2014), borrowing, substituting and generating (BSG) are the main methods people used to acquire the discharge at ungauged stations. Two of the substitution (modelling and disaggregation) methods in combination with the borrowing idea are compared for simulating discharge for the Upper Salween and Mekong River Basin (USMRB). It is seen that with a simple borrowing/ disaggregating method, the Nash-Sutcliffe Efficiency (NSE) can reach 0.82. The similarity in the seasonal variation pattern is a more important requirement to identify if the two stations are to be considered as having hydrological similarity. From the experience obtained for the USMRB, an upstream station with shorter geographical distance may be more in hydrological similarity than a station in the far downstream. The NSE is quite low when borrowing occurs within the low altitude downstream region. The efficiency will be decreased when we borrow information from several stations which may be not in hydrological similarity.

Journal of Flood Risk Management

ABSTRACT The use of appropriate hydrological models with real time satellite rainfall estimates c... more ABSTRACT The use of appropriate hydrological models with real time satellite rainfall estimates can help mitigate flood damage, provide support to contingency planning, and provide warning to people threatened by floods. In this study, the simulated streamflow from the Geospatial Stream Flow Model (GeoSFM) using NOAA Climate Prediction Centre Rainfall Estimates Version 2.0 (RFE) data was compared with observed streamflow in the Bagmati basin. The model showed poor performance when forced with 2002 monsoon RFE. However, the simulated streamflow showed a significant improvement when using improved RFE by incorporating local rain gauge data into the rainfall estimate. Simulated streamflow was much closer to the observed discharge, with a Nash-Sutcliffe Efficiency Coefficient of 0.91, flow ratio 1.1, and coefficient of determination 0.92. Thus improved RFE can be considered for use in flood prediction. A flood hazard map prepared using the extreme rainfall event, showed an inundation area of 315 km2, 8.4 per cent of the basin.

International Journal of Climatology, 2017

River System Analysis and Management, 2016

International Journal of Climatology, 2016

The Koshi river basin is a sub-basin of the Ganges shared among China, Nepal, and India. The rive... more The Koshi river basin is a sub-basin of the Ganges shared among China, Nepal, and India. The river system has a high potential for investment in hydropower development and for irrigation in downstream areas. The upper part of the basin contains a substantial reserve of freshwater in the form of snow and glaciers. Climate variability, climate change, and climate extremes might impact on these reserves, and in turn impact on systems that support livelihoods, such as agriculture, biodiversity and related ecosystem services. Climatological variability and trends over the Koshi river basin were studied using RClimDex. Daily temperature data (20 stations) and precipitation data (50 stations) from 1975 to 2010 were used in the analysis. The results show that the frequency and intensity of weather extremes are increasing. The daily maximum temperature (TXx) increased by 0.1 ∘ C decade −1 on average between 1975 and 2010 and the minimum (TNn) by 0.3 ∘ C decade −1. The number of warm nights increased at all stations. Most of the extreme temperature indices showed a consistently different pattern in the mountains than in the Indo-Gangetic plains, although not all results were statistically significant. The warm days (TX90p), warm nights (TN90p), warm spell duration (WSDI), and diurnal temperature range (DTR) increased at most of the mountain stations; whereas monthly maximum and minimum values of daily maximum temperature, TX90p, cool nights (TN10p), WSDI, cold spell duration indicator (CSDI), DTR decreased at the stations in the Indo-Gangetic plains, while the number of cold days increased. There was an increase in total annual rainfall and rainfall intensity, although no clear long-term linear trend, whereas the number of consecutive dry days increased at almost all stations. The results indicate that the risk of extreme climate events over the basin is increasing, which will increase people's vulnerability and has strong policy implications.

Springer Remote Sensing/Photogrammetry, 2016