Browse
Recent Submissions
Item Impacts of Climate Change on Hydrological Regimes in Southern Slopes of Central Himalayas(Institute of Science & Technology, T. U., 2023-09) Budhathoki, Bhumi Raj; Dr. Tirtha Raj AdhikariEnsuring the consistent accessibility of hydrological data highlights the sgnificance of careful planning, development and management of water resource projects. Within this framework, the effectiveness of diverse hydrological models, such as the Spatial Process in Hydrology (SPHY), Hydrologiske Byrån avdeling for Vattenbalans (HBV), and Hydrologic Engineering Centre Hydrologic Modelling System (HEC HMS) models, are assessed using a range of evaluation metrics. These metrics include the Nash Sutcliffe Efficiency (NSE), Coefficient Correlation (r), Coefficient of Determination (R2), Root Mean Square Error (RMSE), RMSE-observations Standard Deviation Ratio (RSR) and Volume Difference (P-Bias). All three hydrological models were successfully calibrated and validated, demonstrating NSE values exceeding 0.62 for daily and monthly discharge data, based on observations from Busti and Rasnalu stations within the Tamakoshi river basin. Among the various statistical parameters assessed, the coefficient of determination showed a relatively close fit. Similarly, continuous hydrological records for ungauged discharge predictions at locations like Benighat, are estimated using SPHY, HEC HMS, and HBV light models by leveraging data from donor catchments. These predictions span daily, monthly, and annual time frames, sourced from upstream gauged stations. It is significant to note that the accuracy of lowflow predictions surpasses that of high flow predictions, and discrepancies in flow predictions tend to emerge primarily during peak flow periods. Nevertheless, all three hydrological models exhibit similar flow patterns in simulating ungauged streamflow, with discharge at the ungauged receiver site exceeding that of the donor site during simulations. This comparative method proves to be a preferable alternative to individual methods for estimating ungauged discharge. Among these three hydrological models, HBV light model effectively simulates streamflow components using daily input parameters in the Tamakoshi river basin. The variations in streamflow are dependent on the temporal changes in its components. In this context, it is observed that rain runoff predominantly dominates streamflow, constituting 62% of the contribution, with baseflow runoff accounting for 20%, glacier melt runoff for 13%, and snow melt runoff for 5% at the Busti gauge station during the baseline period. It is important to note that there was a positive change in storage within the water balance during the baseline period. In order to evaluate climate change impacts, this study employs four General Circulation Models (GCMs) from the Coupled Model Intercomparison Projects (CMIP 6) Assessment Report 6, along with two scenarios for projecting temperature and precipitation in the Tamakoshi river basin. The findings of this study reveal a consistent trend among all GCMs, indicating a simultaneous increase in temperature and precipitation for both scenarios. Especially, the NorESM2 MM scenario under SSP245 stands as an exception, demonstrating a noteworthy decrease in precipitation. These assessments provide valuable insights into the complex interplay between climate change and the water balance components of the hydrological cycle in the specified region. Furthermore, water balance components are evaluated using an ensemble of two GCMs from CMIP 6, coupled with two Shared Socio-economic Pathways (SSPs) scenarios (SSP245 and SSP585). The assessment covers streamflow components on an annual, monthly, and seasonal basis, focusing on baseline, Near Future (NF), Middle Future (MF), and Far Future (FF) projections. It is worth noting that streamflow predominantly leads the Far Future (FF) projections. Among the streamflow components, precipitation, discharge, actual evapotranspiration, rain runoff, and glacier melt, results showed increase, while baseflow and snow melt runoff decreases by the end of the 21st century in comparison of baseline period under both scenarios, with SSP585 having a more pronounced effect. Particularly noteworthy is the substantial increase in glacier melt runoff attributable to climate change. Moreover, precipitation, governed by monsoons, emerges as the primary determinant of river discharge during the summer season in the Tamakoshi river basin. This study contributes to projecting future climate conditions and the evolving role of streamflow components in hydrological regimes. Additionally, it provides valuable insights for future reference in generating streamflow data at ungauged sites and adderessing deficiencies in data records. This, in turn, facilitates effective planning, management, and development of water resource projects, extending from gauged stations to the outlet at Benighat within the Tamakoshi river basin. The findings also aid in the assessment of suitable models for water resource projects and water-induced disaster management, especially in the context of climate change.Item Drought Detecting and Monitoring over Terai and Mountain Region of Nepal(Institute of Science & Technology, 2023-07) Bagale, DamodarThis study was conducted using 42 years rainfall data since 1977 to 2018 of 107 meteorological stations to examine monthly to decadal rainfall variability of 107 stations over the country were used. The western region has observed low rainfall in pre-monsoons, monsoon, and post-monsoon seasons but observed heavy rainfall in winter season in comparison with the central and eastern regions. The contribution of winter rainfall to annually varied from 0.68% in the year 2006 to 7.04 % in the year 1989. Similarly, the contribution of monsoon rainfall annually varied from 76 % in the year 1992 to 86 % in 1984.The decadal wise rainfall was decreased both in monsoon and winter seasons in the recent couple of decades. There was a strong correlation between the rainfall and Southern Oscillation Index (SOI) in the monsoon season and weak in winter. Generally, large negative/positive magnitudes of SOI on the Indian and Pacific Ocean influence weakening/strengthening monsoon rainfall in Nepal. During El Niño year’s average deficit rainfall was approximately 9 % below the average monsoon rainfall. However, the negative trends of annual rainfall dominated over the country. This study identified winter, summer and annual drought events using the Standard Precipitation Index (SPI). Monthly rainfall was used as an input variable to generate the SPI of 107 stations from 1977 to 2018. The SPI threshold was used to identify, categorize and monitor droughts over Nepal. For this, we investigated the frequency, duration, and severity of drought events. The SPI3, SPI4 and SPI12 month time scales were interpolated to illustrate the spatial patterns of major drought episodes and their severity. In winter large percentage of stations over the country showed a significant decreasing trend for SPI3 in comparison with the monsoon (SPI4) and annual (SPI12).The drought events in El Niño years and non-El Niño years were more strongly related between SPI and SOI than the average years. The relationship between SPI and the climate indices such as the SOI and ONI anomaly over the Niño 3.4 has suggested that one of the causes for summer droughts is El Niño. This study indicated that summer droughts occurred in both El Niño and non-El Niño years. Out of eight drought years, only four drought years were associated with El Niño episodes (1982,1992, 2009, and 2015), and the remaining four drought years (1977,1979, 2005, and 2006) were recorded in non-El Niño years. Similarly, winter and annual droughts evolved in El Niño and non-El Niño years. There is a strong correlation (0.53) between SPI4 and SOI in the monsoon season and a weak in SPI3 and SOI is - 0.31 in the winter at 95 percent confidence level. The regional analysis identified that there is strong correlation between rainfall and SOI for the western region than the central and eastern regions in the monsoon season. Similarly, the correlation coefficient between rainfall and SOI in winter is strong in the western region than in the central eastern regions. Generally, during drought years; SPI and SOI have a strong phase relation compared to average years. Droughts have been recorded more frequently in Nepal since 2000.The areas of Nepal affected by extreme, severe and moderate drought in winter were 4, 21 and 37 percent. Likewise, the areas of Nepal affected by average extreme, severe and moderate drought both in summer and annual events are 7, 9, and 18 percentages and 7, 11, and 17 percentages respectively. The drought-hazardous zones are highest in the western and northwest parts in comparison with the central and eastern regions on both SPI4 and SPI12 time scales. About 47 and 30 percent of areas of Nepal were found to be under high and very high drought hazardous zones of the total area based on SPI4 and SPI12 time scales. यो शोधकार्य नेपालका एक सय सात वटा मौसमी केन्द्रहरूको मासिक तथा वार्षीक वर्षाको परिवर्तनशीलता तथा परिणात्मक अनुसन्धान अन्वेषण गर्नका लागि गत ४२ वर्ष (सन् १९७७–२०१८) को तथ्यङ्क प्रयोग गरी गरीएको हो । पश्चिम क्षेत्रमा प्रि–मनसुन, मनसुन र मनसुन पश्चातको मौसममा कमवर्षा हुने गरेको छ । तर मध्य र पूर्वी क्षेत्रको तुलनामा त्याँहा हिउँदमा भारी वर्षा हुने गरेको पाइयो । हिउँदे वर्षा सन् २००६ मा ०.६८ प्रतिशत र सन् १९८९ मा ७.०४ प्रतिशतसम्म परेको देखियो । त्यसैगरी मनसुन वर्षाको योगदान १९९२ मा ७६ प्रतिशत र सन् १९८४ मा ८६ प्रतिशत सम्म वार्षिक भिन्नता पाइयो । पछिल्ला चार दशकहरुमा वर्षे मनसुन र जाडो मौसममा हिउदे वर्षा घटेको अनुसन्धान बाट देखिएको छ । मनसुनी वर्षा र साउदन ओसिलेसन इन्डेक्स (SOI) विचको सम्बन्ध वर्षा याममा बलियो र जाडोमा कमजोर पाइयो । सामान्यतया हिन्द र प्रशान्त महासागरमा SOI को नकारात्मक र सकारात्मक परिणामले नेपालमा मनसुन वर्षालाई कमजोर र सशक्त बनाउन प्रभाव पार्दछ । एलनिनो वर्षको समयावधीमा (कम बर्षाको अवधिमा) औसत मनसुन वर्षा भन्दा लगभग ९ प्रतिशत कम वर्षा परेको अनुसन्धानले देखायो । यद्यपि वर्षाको घढ्दो क्रम देशमा बढिरहेको छ । यस अध्ययनले जाडो, गर्मी तथा वार्षिक खडेरी घटनाहरू मानक वर्षा सूचकांक (SPI) प्रयोग गरी पहिचान गरेको छ । सन् १९७७ देखि २०१८ सम्म एक सय सात वटा मौसमी केन्द्रहरुको SPI निकाल्नको लागि मासिक वर्षालाई उपायोग गरिएको थियो । SPI थ्रेसहोल्डलाई नेपालमा खडेरी पहिचान गर्न, वर्गीकरण गर्न र निरन्तर निगरानी गर्न प्रयोग गरिएको थियो । यसका लागि खडेरीका घटनाहरुको आवृति, अवधि र गम्भीरताको अनुसन्धान गरियो । हिउँदमा (SPI3), वर्षामा (SPI4) र वार्षिक रूपमा परिमाण (SPI12), विभिन्न अवधिहरुमा, प्रमुख खडेरी एपिसोडहरु र तिनीहरुको वार्षीक मनसुनी प्रभाव को तुलनामा हिउदमा उल्लेखनीयरुपमा घट्ने प्रवृत्ति देखायो । एलनिनो वर्ष र गैर एलनिनो वर्षहरुमा खडेरीका घटनाहरु SPI र वर्षा बिचमा बढी जोडदार रूपमा सम्बन्धित बडेको पाइयो । औसत वर्ष भन्दा SPI, निनो (३.४) क्षेत्रमा SOI र ONI जस्ता जलवायु सुचकाङ्कहरु बिचको सम्बन्धले ग्रीष्म कालीन खडेरीको समयको कारण एलनिनो हो भनी कीटान गरिएको छ । यस अध्ययनले ग्रीष्मकालीन खडेरी एलनिनो (१९८२, १९९२, २००९ र २०१५) वर्षहरुमा र आठ खडेरी वर्षहरु मध्ये केवल चार खडेरी वर्षहरु एलनिनो एपिसोडहरुसंग सम्बन्धित थिए र बाकि खडेरी वर्षहरु (१९७७, १९७९, २००५ र २००६) समेत पाइएको थियो । त्यस्तै खडेरीका घटनाहरु हिउद, ग्रीष्म कालीन र वार्षिक खडेरी एलनिनो र गैर–एलनिनो वर्षहरुमा विकसित भयको पाइयो । मनसुन याममा SPI र SOI बिच बलियो सम्बन्ध र हिउँदमा केही कमजोर सम्बन्ध रहेको (९५ प्रतिशत) सार्थक स्तरमा देखियो । क्षेत्रीय विश्लेषणगर्दा मनसुन समयमा मध्य र पूर्वी क्षेत्रको तुलनामा पश्चिमी क्षेत्रको वर्षा र SOI बिच कमजोर सम्बन्ध रहेको पाइयो । त्यसैगरी, हिउँदे वर्षा र SOI बिचको सम्बन्ध गणांक मध्य पूर्वी क्षेत्रहरु भन्दा पश्चिमी क्षेत्रमा बलियो देखियो । सामान्यतया खडेरी वर्षहरुमाः SPI र SOI बिच औसत वर्षको तुलनामा बलियो चरण सम्बन्ध अध्यनले पुष्टी गरेको छ । नेपालमा सन् २००० यता खडेरी धेरै पटक रेकर्ड गरिएको छ । नेपालको हिउँदमा चरम, गम्भीर र मध्यम खडेरीबाट प्रभावित क्षेत्रहरु क्रमश ४, २१ र ३७ प्रतिशत पाइयो । त्यसैगरी ग्रीष्म र वार्षीक समयावधीमा औसत चरम, गम्भीर र मध्यम खडेरीबाट प्रभाभित क्षेत्रहरु क्रमश ७, ९ र १८ प्रतिशत र ७, ११ र १७ प्रतिशत छन् । त्यसैगरि मध्य र पूर्वी क्षेत्रहरुको तुलनामा पश्चिम र उत्तर–पश्चिमी भागहरुमा खडेरीको आँकडा उच्च र अति उच्च भएको पाइयो । दुवै क्षेत्रहरुमा वर्षाका परीमाणहरु भने सबैभन्दा बढी भएको अध्यनले देखायो । नेपालका करिब ४७ र ३० प्रतिशत क्षेत्रहरु SPI4 र SPI12 टाइम स्केलमा उच्च र अति उच्च खडेरीको जोखिमयुक्त क्षेत्रहरु अन्तर्गत रहेको पाइयो ।Item Comparison of spatial interpolation methods for estimating the rainfall in Lumbini Province, Nepal(Department of Hydrology and Meteorology, 2023) Bastakoti, YojanaFor strategic management and long-term use, it is important to have a better understanding of the spatial distribution of rainfall data. The current study assesses the geographic distribution of rainfall over Nepal’s Lumbini Province, 39 data sites were used for the study. The spatial distribution of rainfall was obtained by interpolating the observed data using the various geostatistical interpolation algorithms offered by ArcGIS. The Ordinary Kriging (OK), Simple Kriging (SK), Inverse Distance Weighting (IDW), and Radial Basis Function (RBF), spatial interpolation methods were investigated. Based on the cross-validation results and the statistical parameters Correlation (R) and Root Mean Square Error (RMSE), the performances of different interpolation algorithms were assessed with R and RMSE values of 0.61 and 26.35 respectively. The Ordinary Kriging seems to have performed well for the region. The Ordinary Kriging interpolation method was used to map the spatial distribution of rainfall over the low and high lands of Lumbini Province. The results showed that the average annual rainfall during 22 years period ranged between (1058 to 2555 mm). At the Meantime, province’s southwest region has lower rainfall of 1058 to 1431 mm, whilst high rainfall in the range of 2046 to 2555 mm occurs in the province’s northeast region and appears to be gradually decreasing towards the lower altitude. Additionally, seasonal precipitation range of pre-monsoon, monsoon, winter monsoon and post monsoon are observed. Furthermore, pre-monsoon, monsoon and winter monsoon follow the highly similar pattern of overall precipitation pattern throughout the years. However, distribution of post monsoon rainfall pattern is discreate over the territory.Item Remote sensing and ground based analysis of drought in Karnali River Basin (KRB), Nepal(Department of Hydrology and Meteorology, 2023) Acharya, PrabinDrought, a frequent and impactful climatic extreme, has significant impact on the context of topographically varied Karnali River Basin (KRB) in Nepal. This study executed a comprehensive assessment of drought dynamics by employing two key indices based on Vegetation Condition Index (VCI) derived from Moderate Resolution Imaging Spectroradiometer (MODIS) data, and single parameter based Standard Precipitation Index (SPI) from ground based station data, with a focus on spatial and temporal variations. Remote sensing and Ground based indices were utilized across all seasons within a year, while also establishing correlations between vegetation dynamics and climatic parameter (precipitation). MK-Trend test have been performed to analysis SPI trend inside the basin. Drought indices derived by climatic data were correlated with Southern Oscillation Index (SOI) to evaluate relationship with indices and seasons. This analysis revealed that drought has occurred more than half of the study period, underscoring its recurrent nature inside the KRB spatially. In particular, the winter and monsoon SPI drought patterns exhibited an alarming increasing rate, which can be surmounted by concerning decrease in precipitation by 4 mm per year. Concurrently, the VCI time series demonstrated an upward trajectory of drought occurrences during the pre-monsoon and winter seasons inside the basin emphasizing increasing winter drought in the lower altitude and summer monsoon drought in the whole basin accessing 50% area experienced vegetation failure temporally. Further investigation revealed that the manifestation of drought is intricately linked not only to local conditions but also to larger climatic oscillations, notably the SOI. Negative value examined between drought events and SOI index in the monsoon season, with enhancing El-Nino phase. The correlation between VCI and precipitation, particularly when precipitation leads VCI by one month, proved to be a robust and noteworthy observation, emphasizing the predictive utility of this relationship. Notably, during the pre-monsoon season, the correlation nearly doubled when a one-month lag in VCI-precipitation is considered. Lower elevations face heightened pre-monsoon and winter drought, while higher altitudes encountered intensified monsoon-related droughts. This results from shifting atmospheric circulation patterns, uneven convection, and increased temperatures, leading to excessive evaporation and soil moisture loss within the year. These findings hold crucial implications for water resource man-agement, agriculture, and overall resilience strategies in the face of changing climatic conditions inside the KRB. Keywords: Drought, SPI, VCI, SOI, Nepal, KRB.Item Investigation of Meteorological condition during air dynasty Helicopter crash using WRF model(Department of Hydrology and Meteorology, 2022) Pudasainee, SarojMountain flight remains a considerable challenge in Nepal because of rugged terrain. Since 1979 A.D, there have been 36 helicopter accidents over different parts of the country that have claimed 85 lives. Most of the accidents are reported to have unfavorable weather conditions as the main cause. However, the detailed meteorological analysis for most of the accidents has not been done yet. A detailed understanding of the meteorological condition and reliable forecast that may developed over the complex terrain of the mid-hills of Eastern Nepal Himalaya is yet to be achieved. This study assesses the weather conditions possibly associated with the most recent fatal crash at Pathivara Peak on 27 February 2019 using Advanced Research version of the Weather Research and Forecasting (WRF-ARW) model. Prevailing weather condition during accident time such as; low ceiling with cloud base, light to moderate snowfall, poor visibility, below freezing temperature, high amount of water droplets suggests possible icing on rotor. Icing could be major factor responsible for the fatal crash. WRF-ARW was reasonably able to simulate the weather condition. This research recommended that aviation stakeholders and pilots should fly only after a clear route forecast over the complex geographical condition for the safety of flights. Keywords: Aviation, Forecast, Icing, Visibility, WRF-ARWItem Analysis of Heat Wave over Nepal(Department of Hydrology and Meteorology, 2022) Bhattarai, Hira PrasadClimate change imposed negative impact on socio-economic sectors of the mountainous region like Nepal. The 21 st century has brought many records breaking warm year. Such warm periods brought many health-related problems, heat wave is one among them. Daily maximum temperature data of 46 stations of DHM is used to calculate the heat wave (HW)patterns over the country. To better understand the regional pattern of HW all the stations are further classified into 6 different regions: East Terai, Central Terai, Western Terai, Eastern Mountain, Central Mountain and Western Mountain based on the 3 large river basins (Koshi, Gandaki and Karnali). The percentile-based method is used for the calculation of the HW. The 90 th percentile values are used as the threshold and HW is declared after the daily maximum temperature on exceeding the threshold and the normal temperature of the station by 4° C for at least 3 consecutive days. Based on the criteria, HW’s different characteristics like the total number of events, total days of HW, longest event, average days in HW, Maximum deviation of temperature in HW, the onset date of HW and the withdrawal date of HW are calculated using MATLAB and MS-Excel. The western region records the highest frequency and total heat wave days. The central and western mountain region shows the highest maximum temperature deviation than the Terai regions. Although the HW events are more severe in the mountain region but terai region shows consistent severe HW in these regions. The average days of heat wave event throughout the country is 2.6 days. Also, the monsoon event controls the heat wave events. The ElNino phenomena shows no significant relation with the heat wave but the peak of the heat wave is found at ElNino+1 year. The criteria used in this study is very easy to calculate and can be used for the national decision-making process.Item Impacts of climate change on river hydrology and energy economics in Budhigandaki river basin(Faculty of Hydrology and Metrology, 2022) Marahatta, SureshWater management has become a challenging task due to the increasing population, rapid urbanization and industrialization. Availability of observed hydro-meteorological data plays a crucial role in water budgeting for the country like Nepal that relies heavily on hydroelectricity for its energy needs. Quantification of available water at the local scale and examining how it is impacted by climate change (CC) is extremely important from the water management perspective at the river basin level. Budhigandaki River Basin (BRB) of Nepal, was chosen for this study in assessing climate change impact on river hydrology utilizing well calibrated and validated Soil Water Assessment Tool (SWAT), consequent impact on hydroelectric energy generation. Extending this aspect further, the micro-economic assessment of the Budhigandaki hydroelectric project was also made in this study. This study assessed the interannual variability of hydroclimatic condition of the BRB using daily hydrological and meteorological data for the period from 1983 to 2012. To evaluate the impact of climate change on hydrological phenomenon in the study basin, future climate data under two Representative Concentration Pathways (RCP 4.5 and RCP 8.5) with four climatic conditions (cold-wet, warm-wet, warm-dry and cold-dry) for each RCP were considered. Digital elevation model (DEM) data, land use and land cover, and soil data of the basin are the spatial data required in the hydrological simulation that were utilized. The climate change impact on flow, hydroelectric energy generation and energy economics were evaluated by comparing these variables with the baseline. Historical data shows that there is a very high variability in daily, monthly, seasonal and interannual flow in the study basin. Future annual precipitation in BRB varies significantly and is projected from -9% to 23% for RCP 4.5 and -11% to 21% for RCP 8.5 scenarios compared to the baseline value (1530 mm). The mean annual temperature increases 1.7 o C for RCP 4.5 and 3.9 o C for RCP 8.5 by the end of this century. SWAT model was calibrated and validated at Arughat gauging station considering 30 years daily flow data. Model evaluation using four statistical parameters (NSE, PBIAS, RSR and KGE) showed that the developed model performed very well to simulate river flow. Additional validation of the model done at three supplementary points; two in the upstream and one in the downstream of calibration point (Arughat) also showed that vi the developed SWAT model for BRB is well calibrated. To compare the performance of flow simulation methods in the basin level, a new evaluation statistical index, the Global Performance Index (GPI), was introduced in this study. SWAT hydrological model preformed the best among the different methods considered for flow estimation as evaluated by GPI in BRB. Annual mean flows are projected to increase in the future scenarios; 10 to 31% in RCP 4.5 and 5 to 57% in RCP 8.5 scenarios with respect to the baseline flow of 240 m /s. The analysis of future extreme flow shows an increasing trend in case of annual maximum one-day flow and a decreasing trend in low flow case. These results indicate a need to alter the design of hydraulic structures and selection of storage project over runoff-river project for climate resilience. Future annual energy of the Budhigandaki Hydroelectric Project is expected to increase by 9 to 13% compared to the baseline value (3385 GWh) that is equivalent to annual revenue of 20 to 28 million USD. Results of this study show that storage hydroelectric projects with the provision of flexible operating rules are desirable. Financial policies related to hydroelectricity need to be revised with the changes in the future climatic conditions. The findings of this study are expected to be useful for hydrologists, economists and decision-makers to plan the use of available water judiciously in the future. Keywords: Climate change, river hydrology, hydroelectricity, energy economics, GPI, SWAT, BudhigandakiItem Flood Inundation Mapping of Kankai River Basin, Nepal(Department of Hydrology and Meteorology, 2020) Dhakal, Binod BabuFlood is growing as major water related hazard in the world. The degree of impairment that it causes to each and every component goes on increasing with the time. The main objective of this research is to analyze the flood frequency, prepare inundation map of Kankai river basin corresponding to different return period, and to identify the hazardous region along the Kankai river basin. Kankai river basin of 1284 km² area is selected for the study. Frequency analysis is done with Gumbel calculation method and HEC-HMS. Flood hazard mapping is the one of the procedure to find the inundation level. Flood hazard map was prepared by using the HEC-RAS 5.0.7 with integration of ArcGIS 10.1 and its extension HEC-GeoRAS. ASTER DEM of 20*20 spatial resolution was used for the research. The discharge data we have used is validated with the discharge data we have measured in the study area. The discharge value was seen to be simultaneously increasing with the return period of 2, 10, 50, 100, 200, 500, 1000 years. The magnitude of flood depth increased with the increasing return period. The number of household inundated corresponding to the return period is also calculated. The maximum depth of inundation we obtained was 6.46m, which was of 1000 year return period and along the chure range where the cross-section is shorter and depth is greater and going downward the depth of inundation decreases. The depth is categorized as high risk, medium risk and low risk based on DHM reference for Kankai river. Inundation of area of settelements indicates that in future human lives are more prone to flood disaster. Thus, the study may help in future planning and management for future probable disaster.Item Impact of Climate Change on Flow Regime in Himalayan Basins, Nepal(Faculty of Hydrology and Meteorology, 2014) Adhikari, Tirtha RajThis research studied the hydrological regime of three glacierized river basins in Khumbu, Langtang and Annapurna regions of Nepal using the Hydraologiska Byrans Vattenbalansavde (HBV), HVB-light 3.0 model. Future scenario of discharge is also studied using downscaled climate data derived from statistical downscaling method. General Circulation Models (GCMs) successfully simulate future climate variability and climate change on a global scale; however, poor spatial resolution constrains their application for impact studies at a regional or a local level. The dynamically downscaled precipitation and temperature data from Coupled Global Circulation Model 3 (CGCM3) was used for the climate projection, under A2 and A1B SRES scenarios. In addition, the observed historical temperature, precipitation and discharge data were collected from 14 different hydro-metrological locations for the implementation of this studies, which include watershed and hydro-meteorological characteristics, trends analysis and water balance computation. The simulated precipitation and temperature were corrected for bias before implementing in the HVB-light 3.0 conceptual rainfall-runoff model to predict the flow regime, in which Groups Algorithms Programming (GAP) optimization approach and then calibration were used to obtain several parameter sets which were finally reproduced as observed stream flow. Except in summer, the analysis showed that the increasing trends in annual as well as seasonal precipitations during the period 2001 - 2060 for both A2 and A1B scenarios over three basins under investigation. In these river basins, the model projected warmer days in every seasons of entire period from 2001 to 2060 for both A1B and A2 scenarios. These warming trends are higher in maximum than in minimum temperatures throughout the year, indicating increasing trend of daily temperature range due to recent global warming phenomenon. Furthermore, there are decreasing trends in summer discharge in Langtang Khola (Langtang region) which is increasing in Modi Khola (Annapurna region) as well as Dudh Koshi (Khumbu region) river basin. The flow regime is more pronounced during later parts of the future decades than during earlier parts in all basins. The annual water surplus of 1419 mm, 177 mm and 49 mm are observed in Annapurna, Langtang and Khumbu region, respectively.Item Hydro-Meteorological Study of Dudhkoshi Basin with Frequency Analysis and Flood Forecasting using HEC-HMS Model(Department of Hydrology and Meteorology, 2015) Adhikari, Dhruba LochanMany rivers in Nepal are either ungauged or poorly gauged due to complex terrains, extreme monsoon climate and lack of technical and financial capabilities. In this context, the role of hydrological models are extremely useful. A model, once calibrated and verified on catchments, provides a multi-purpose tool for further analysis. Hydrological simulation methods are relatively simple and reasonably accurate in practical applications. The study was carried out in DudhKoshi River basin, Nepal. Long term hydrology, Flood frequency analysis using statistical approach and Regional Climate Model (RCM) were used to determine the characteristics of high flow events in the basin. High flow events are a key component in river engineering, for the design and risk assessment of various projects. In case of ungauged basin where no historical data are available, regional flood frequency analysis is considered as a viable means to approximate at-site flood characteristics by exploiting the information available at neighboring sites. This research investigates the potential changes on discharge and flood events in future in DudhKoshi Basin. For this study, a lumped hydrological model developed in HEC-HMS 4.0 is implemented over the study area (3849 km 2 ), calibrated and validated at a daily time step, fed by ground observations and using the future decadal climate data obtained from the RCM named Providing Regional Climates for Impact Studies (PRECIS). The result shows that HEC-HMS has the best fit among the methods used. The simulation depicts a univocal increasing trend of discharge for middle centuries (2030-2060) indicating the possibility of increased frequency and intensity of floods. It is suggested that the calibrated model then can be used as a decision support tool in the operation and management of DudhKoshi Dam Reservoir. Hence, Hydrological modeling is a powerful technique in the planning and development of integrated approach for management of water resources.Item Analysis of Drought Events and its Comparison with Cereal Crops Yield at Karnali Basin(Department of Hydrology and Meteorology, 2015) Karki, BickkyNepal’s fragile geology and steep topography makes it one of the most disaster pronecountries in world. Floods, landslides, earthquakes, GLOFs (glacial lake outburst floods) and droughts are the most common natural hazards. In recent years, due to the climate relateddisasters like drought has resulted in higher food insecurity in the most vulnerable communities, particularly in Western Nepal.Karnali is one of the most affected drought region of Nepal and also the study of drought is limited in Nepal hence the study is made onthis topic at Karnali basin. For the study, simple and flexible tool was used named SPI on the basis of precipitation as the only input parameter around the basin. The study mainly focuses the meteorological and agricultural drought so the drought analysis was done with the time scale of 3 months (June,July and August) or SPI-3 for a period of 34 years (1980 to 2013). There were total thirteen stations made final after eliminating other stations due to data unavailability for the study atthe basin. Based on the study, all the stations were recorded by normal drought (extremely, very,moderately wet and near normal are merged as normal) event and then moderate type werefound in most of the stations for same or different years. And lastly severe and extreme were recorded after the previous two types. Similarly the result also shows that the number of drought events is highest in the month of June during the 7 years of time interval i.e. from1987-2013 with 22 droughts in total. And finally the drought events were compared with different cereal crops yield such as paddy, maize and millet from 1999 to 2011. The resultshows that all the crops yield were not in decreasing phase, it was in increasing trend rather apart from two or three years throughout the period of eleven years used for comparison. It was quite unknowing that theyields were not affected more by drought in this part of area from 1999 to 2011,the reason may be the use of more chemical fertilizers for quick production by the farmers and also the development of canals for irrigation purpose that made the crops good enough for the increment of yield.Item Hydro-Meterological Study of Budhigandaki Storage Hydroelectric Project(Department of Hydrology and Meteorology, 2013) Sigdel, RajeshBudhigandaki storage hydroelectric project was first detected in 1974 A.D. by SMEC, following the study of the Gandaki River basin; Budhigandaki is one of the most favored due to its high potential and its location in Central Nepal near the main load center. Budhigandaki is a tributary of the Narayani originated from Lark Himal and Ladak Himal in Tibet. The total river length is about 188 km and the total basin area is about 5007 km 2 . Annual rainfall in the Arughat is 2614 mm. Statistical Analysis showed that the 24 hour maximum rainfall for 50 year and 100 year return periods are 160 mm and 173 mm respectively. There are three major flood disaster occurred in Budhigandaki River on 05 Mar 1968, 17 Jun 1968 and 02 Aug 1968. This was caused by LLOF at Lapubensi upstream of hydrological station no 445. The highest flood was 5210 m 3 /s recorded at hydrological station 445. A one-dimensional hydraulic model in HEC-RAS was developed and executed which enabled the analysis of flooding under different scenarios. Hydraulic models coupled with Geographic Information System are powerful tools for quantitative and qualitative monitoring of spatial and temporal variation of flows in the river. For purpose of Elevation-Area-Volume curve it shows the area of 32.87 km 2 .Item The Impact of Climate Change on Runoff Generation in Langtang Basin Nepal(Department of Hydrology and Meteorology, 2014) Adhikari, GopiClimate change has potential impacts on economy, ecology, and environment of Himalayas.Climate change studies in Himalayan regions have focused mainly on glacier melting and retreating, Glacial Lake Outburst Flood (GLOF) etc. Changing temperature has direct impacts on glaciers and snow that affects the snow melt and river discharge.Hence, this research has been carried out to understand the impact of climate change on runoff generation of Langtang basin.This runoff is important for planners and designers in the aspect of irrigation, hydropower,and drinking water supply and so on.So, the runoff estimation study is essential.This study is carried out using monthly Thornthwaite water balance model.Thornthwaite monthly water balance model is one of the popular model developed by USGS for the runoff estimation and can be applied to estimate the runoff of snow and glacier bound catchment. This study also focuses on the runoff estimation of past, present and future scenario at Langtang region of Nepal by using the Thornthwaite model.The outputs of the analysis on temperature trend revealed a fasterwarming trend in Langtang area (i.e. 0.084 ºC/year).The mean annual soil moisture storage is increasing pattern (i.e.0.71mm/year).The precipitation and runoff are also observed increasing (i.e.10.59mm/year and0.8mm/year).The coefficient of determination of calibration and validation are 0.926and 0.996 that implies that the model is well validated and calibrated as well.The increase/decrease in temperature and runoff has proportional relationship and increase/decrease in rainfall and runoff has also proportional relationship.The projected runoff by the model is slightly decreasing from 2001 to 2060 this result shows that the chances offlood in summer and possible droughtin winter may further enhanced in the future.The main outputs of this study help to implement appropriate strategy for water resources management and hydropower development and provide a strong message on the scenario of the Global impact of warming in the Himalayan region.Item Verification of the Observed Discharge Data by Using Tank Model and Flood Forecasting by Gumbel’s Method in Kathmandu Valley of Bagmati Basin at Khokana(Department of Hydrology and Meteorology, 2013) Shrestha, SurajFlow estimation at a point in a river is vital for a number of hydrologic applications including flood forecasts. This paper presents the results of a basin scale rainfall-runoff and hydraulic modeling in Bagmati river basin in Nepal. A distributed lumped conceptual flood forecasting model, namely Tank Model was calibrated in this study for the Bagmati River Basin of Kathmandu valley at Khokana. Ten years rainfall, evaporation and discharge data were collected from DHM and compiled as an input toTank Model. The simulation was done for a period of ten years data, eight years during calibration and two years during validation. Statistical method and objective functions were applied to evaluate the verification capability of the Tank Model. Eight years of flood data were used to calibrate the Tank Model and the performance of the model was verified by using 2007 and 2008 data. A set of tank coefficients that suit tank configuration selected for Bagmati River Basin were determined by trial and error calibrations. The predicted peak discharge was close to the observed value and the smaller discharges followed the observed trend. A mean of 15m 3 /s, 11m 3 /s was calculated for the observed discharge while the mean of the simulated discharge was 16m 3 /s, 12m 3 /s, during the validation period of 2007 and 2008 respectively.The standard deviation was 25m /s for the observed discharge and 17m 3 /s, 10m 3 /s for the simulated discharge during the validation period of 2007 and 2008 respectively. The overall correlation coefficient between observed and simulated discharge was 0.84, 0.90, 0.85, 0.91, 0.91, 0.91, 0.83,and 0.79 during calibration period.The maximum instantaneous flow of 942m /s was recorded while the lowest flood flow of 103 m 3 /s was recorded during observation. The17-year mean instantaneous flood flow is 420.76m 3 /s with a skewness of 0.98 and Confidence Level (95%) of 126.31.The maximum instantaneous flow of 820.41 m /s was recorded while the lowest flood flow of 59.25m 3 /s was recorded during simulation. The10-year mean instantaneous flood flow is 221.26m 3 /s with a skewness of 2.64 and Confidence Level (95%) of 158.08. Measured and predicted flood flows show no significant differences hence, a goodness of fit of the Gumbel distribution. 3 /s, 13m 3 3 3Item Impact of Climate Change on Snow melt in Marshyangdi River Basin of Nepal(Department of Meteorology, 2015-11) Tuitui, AnitaThe climate change in general is the change in precipitation and temperature pattern which has potential impacts on economy, ecology and environment of Himalayas. Most of the studies of glacier melting and retreating are the main focus in Himalayas. Most of the study of glacier of Nepal shows that the glacier is undergoing rapid deglaciation. Snow and glacier melt contribution in Marshyangdi River have not been studied. Hence this study implemented the process-oriented distributed hydrological model J2000 model to investigate the contribution of snow and glacier melt in snow fed stream. The J2000 model able to distinguish between different runoff components including snow and glacier melt contribution. Hydrological modelling plays an important role in understanding hydrological process of a basin. The dynamically downscaled precipitation and temperature data were used for the future climate scenarios prediction for period of 2020-2050s, under the Representative Concentration Pathway’s scenarios RCP4.5 and RCP8.5 scenarios. The downscaled RCPs data was used to run the distributed hydrological J2000 to study the climate change impacts on snowmelt of Marshyangdi River basin. Increase temperature in future scenarios results the increase snowmelt contribution. The result of the model show there was total 20% contribution of snow melt to stream flow which will increase by 29% and 38% in RCP4.5 and RCP8.5 scenarios respectively which shows the shifting of snowline to higher altitude in future due to the increase temperature. The study shows that 5.4% increase of rain precipitation increases 14% of discharge in RCP4.5 scenario and 3.9% increase of rain precipitation increases 13% of discharge in RCP8.5 scenario. High snowmelt contribution in future scenarios increases the river discharge of study basin. The analysis shows the contribution of base flow will decrease whereas the overland flow will increase by 30% and 23% in RCP4.5 and RCP8.5 respectively. Actual evapotranspiration is highly affected by the climate change. The non-parametric Mann Kendall and Sen’s slope estimator for the trend analysis shows warming of the basin. And precipitation trend at northern part of basin is decreasing whereas the lower part of basin show increasing trend. With respect to the result of various runoff components, the overland flow RD1 will increase in future scenarios which conclude there will be increase of flood event in future.Item Simulation of Severe Thunderstorm Event on 29 th April 2019 in Pokhara Using Advance Research Weather Research and Forecasting Model (WRF-ARW)(Department of Hydrology and Meteorology, 2021) Prajapati, Krishna RamDuring the pre-monsoon (March, April and May) in Nepal, severe thunderstorms and hailstorms cause significant property and agricultural damage, in addition to loss of life from lightening. In the present study, Severe thunderstorm event occurred at Pokhara, 800 asl, in Central Nepal on 29 th April, 2019, during early afternoon is performed. The event was lasted half hour and produced the golf ball-sized hailstones that destroyed vehicles windshields, damaged the crops worth millions of rupees and more. The Advanced Research-Weather Research and Forecasting (WRF-ARW) model was used to simulate the features associated with a severe thunderstorm and examined its sensitivity to six different micro-physical (MP) schemes (Thompson, Morrison, Goddard, Lin, WSM6 and Ferrier). The three nested domains with the innermost domain of 1km horizontal resolution and integrated for 36hr with the spin-up time of 24 hr. Numerical study of thunderstorms have been discussed with its antecedent thermodynamic stability indices that include K Index, Total totals index (TTI), Convective Available Potential Energy (CAPE), Convective Inhibition Energy (CINE), and Precipitable Water (PW) used for the short range prediction of thunderstorms. For validating simulated features of the thunderstorm, Automatic Weather Station data of Lumle station and observed data of Pokhara synoptic station were used with statistic error analysis using Root Mean Square Error (RMSE), Mean Absolute Error (MAE) and Correlation Coefficient (CC). All the microphysics scheme well predicts the instability indices required for the thunderstorm occurrence. Overall Morrison and Thompson scheme performed well with same correlation coefficient of 0.80, whereas WSM6 has least results with mean correlation coefficient of 0.46 compared to the observed. Keywords: WRF-ARW, Microphysics, Thunderstorm, Instability Indices.Item Sensitivity of Microphysics and Planetary Boundary Layer Configurations for Extreme Rain Forecast over the Western Nepal using WRF-ARW Model.(Department of Hydrology and Meteorology, 2021) Rana, KumarThe occurrence of a value of a weather or climate variable above (or below) a threshold value near the upper (or lower) ends of the range of observed values of the variable is known as extreme, in many cases, a weather or climate event with high impact is also known as extreme. Even though extreme events do not occur often, they can be harmful, can cause great devastation to infrastructures, can affect our economy, and can even cause the loss of life. Monsoon season is a one of the crucial seasons for the precipitating extreme rainfall. Every monsoon affects the environment as well as life style of all living things, causing landslide, floods and affect socioeconomic sector. If the monsoon event could be predicted ahead of event days, we can minimize the loss of property or life. Study of past rainy days shows that all the extreme event were on monsoon season (data taken from 2010 to 2018). In this study WRF (v4.0.3) was used to simulate extreme events to test the sensitivity of the combination of planetary boundary layer physics and microphysics scheme, using initial and boundary condition data from NCEP FNL with 1 0 x1 0 spatial resolution and 6 hourly temporal resolutions. From this study no single scheme combination performs best for all rainfall category. In this study two methods were depicted to overcome a conclusion. Continuous verification shows Thompson-Mynn is best, with result value of RMSE value 68.86. From categorical verification, Skill score test statistics ‘Probability of Detection’ showed Thompson-Mrf, Wdm6-Mynn, and Lin-Mynn best for low, moderate and heavy rainfall category with value 0.671, 0.436, 0.419. ‘Proportion Correct’ showed Morrision-Mynn, Thompson-Mrf and Wdm6-Mynnwas best for low, moderate and heavy rainfall category with the score value 0.336, 0.255, 0.264. ‘False Alarm Ratio’ showed Morrision-Mynn, Morrision-Mrfand Wdm6-Mynn best for low, moderate and heavy rainfall category with value 0.566, 0.559, 0.433. It comes to the point that there must be a different physical combination for different rain category.Item Estimation of Surface Runoff Available by Thron Model for Major Crops of Kaski District, Nepal(Department of Hydrology and Meteorology, 2018) Nagarkoti, GangaNot AvailableItem Observed Trends and Spatial Distribution in Daily Precipitation Indices of Extremes over the Narayani Basin, Nepal(Department of Hydrology and Meteorology, 2020) Lamichhane, DipendraClimate change is one of the biggest environmental challenge that plays out through changing intensity, duration, and frequency of extreme events. To fulfill the research gap in understanding and quantifying the recent changes in precipitation extremes over the Narayani river basin of central Nepal, the long-term daily precipitation data from 1980 to 2018 were run in ClimPACT2 an R software package to calculate ET-SCI extreme precipitation indices. In this study physically relevant 14indices obtained from 23 stations were examined for their spatial and temporal variation. Before the calculation of indices data quality and homogeneity test was performed. The results suggest that the variations of extreme indices throughout the study area are quite different from that of seasonal and annual patterns to some extent. The monsoonal precipitation was mostly concentrated in the central part of the basin within the Middle Mountain region (Lumle and its surroundings). Especially the lowlands (Terai and Siwaliks) and including some parts of middle mountains the precipitation intensity-based indices like as, percentile indices (R95p) and absolute indices (RX1day, RX3day, RX5day) were in the increasing trends, but the frequency of precipitation like threshold indices (R1mm, R10mm, R20mm) along with the duration of precipitation seemed to be decreasing. This implies that the lowlands regions bringing about rainfall related hazards like floods and soil degradation with inundation and may cause possible impact on agriculture and livelihood due to intense rainfall and prolongation of dry spells with the weakening of rainfall duration (days/year). However, the light to moderate precipitation and associated days over the high altitude and that could be the possible cause of landslides. This study also highlights the suggestion that there may be a possible impact on agriculture facilities, food security, and water scarcity in the eastern part of the basin due to the significant decreasing trend of annual total wet days precipitation (PRCPTOT)Item A Study on Spatial and Temporal Distribution of Rainfall in Province Number 3, Nepal(Department of Hydrology and Meteorology, 2019) Kuinkel, Hridaya RajDaily observed precipitation data of 23 stations for the period of 1980-2015 is used in the study of spatial and temporal distribution of rainfall in Province 3 of Nepal. The study is basically focused on the study of space time variation and principal component analysis of rainfall. About 80.6% of annual rainfall is covered by monsoon rainfall so both spatial and temporal distribution of annual rainfall is proportionate with monsoon rainfall (JJAS). Highest rainfall pocket area is observed in northeastern part of Province in the periphery of Gumthang, Sindhupalchok with rainfall of 3828 mm while lowest rainfall is observed in Tamachit, Rasuwa with 720 mm. Temporally rainfall is high in 1999 with rain 2399.4 mm and low in 1992 with rain 1508 mm. July is highest rain month and November is lowest. Seasonally, increasing trend of rainfall is seen in Pre monsoon while decreasing trend is seen in Monsoon, Post monsoon and winter. On decadal rainfall analysis it is obtained highest rainfall in third decade (2000-2009) and lowest in last decade (2010-2015). Analysis of rainfall shows average annual rainfall in lowland is 1883.8 mm and highland is 1959.6 mm. The correlation coefficient between rainfall in highland and lowland is 0.79. In most of the La Nina year there is increased rainfall and El Nino year the rainfall is decreased. So, we can conclude that there is some influence of large scale atmospheric phenomena like ENSO. First component (PCA1) of Principal component analysis which covers largest information of space time variation of rainfall shows that pre monsoon precipitation pattern is highly concentrated in central part of the Province while monsoon is concentrated in southern part of the Province. Similarly, Post monsoon precipitation pattern is concentrated in central part of the Province while winter precipitation pattern is concentrated over both the central as well as southwestern part of the Province.