Recent research and IPCC reports extensively document the varied effects of climate change on basins worldwide. This study evaluates the impact of climate change and land use change on the Seti-Gandaki watershed's hydrological regime of Nepal. Using a calibrated hydrological SWAT model, forced with climate scenarios (SSP245 and SSP585), the study projects increased precipitation (2-129% and 3-139%) and a warming trend in temperature. Streamflow at the watershed’s outlet is expected to rise (up to 49% in monsoon, 96% in winter in SSP245; up to 61% in monsoon, 89% in winter in SSP585), with increased flow extremes, potentially leading to floods and landslides. The combined impacts project a 52-125% increase in streamflow in SSP245 and a 100-136% increase in SSP585, attributed to the shift from rural to urban settlements. These findings provide crucial insights for water resource planners and managers to develop location-specific strategies for sustainable water resource use in the Seti-Gandaki Watershed.

Hydrology is vital for understanding water on earth, its properties, distribution, and interactions with the environment amid changing factors like urbanization, industrialization, deforestation, and climate change. Continuous hydrological modeling using HEC-HMS was applied in the Narayani Watershed to simulate stream flows at four major hydrological stations. Calibration (1998-2006) was performed for Bimalnagar, Kotagaun, Devghat, and Kalikhola, evaluating model performance with metrics showing good results at Kalikhola and Devghat with NSE 0.76 and 0.86 respectively and satisfactory results at Bimalnagar and Kotagaun with NSE 0.69 and 0.65 respectively. After validation (2007-2010) the NSE obtained for Bimalnagar, Kotagaun, Devghat, and Kalikhola were 0.84, 0.76, 0.81 and 0.91.This stream flow simulation aids in flood investigations and studying climate and land use impact on future stream flow.

Wheat is a staple crop contributing to food security in Nepal.To ensure adequate crop yield in the context of changing drivers such as climate change, water management, soil quality, and fertilizer.There is a need to know how these drivers will impact crop phenology and, ultimately, its production.Study used the AquaCrop 7.0 model in a farmer-managed irrigation system in order to evaluate predicted changes in crop water requirements and wheat crop yield in Chitwan in the context of climate change. The future climate was projected by using couple model intercomparison project phase 6 (CMIP6).An ensemble of five Global Climate Models (GCMs) was used with two scenarios (SSP245 and SSP585) for the near (2025-2050), mid-2051-2075, and far future (2076-2099). Crop yield was simulated for three scenarios (rainfed, partially-irrigated, and fully irrigated). Baseline period was taken from 1985 to 2015. Results showed, in general, there is increase in crop water requirement, and mixed results for crop yield depending upon context. Wheat yield is projected to increase by 13-29% for rainfed and 10-17% for irrigated conditions in SSP245 scenarios. And the net irrigation requirement is projected to decrease slightly from baseline period of 130 mm in the climate change context.

Study region: The study region is 23 different watersheds across Nepal. Study focus: This study aims at assessing the strengths and weaknesses of widely used regional-ization methods for simulating daily hydrograph and flow duration curve in a comparatively large sample of 23 medium to small-sized watersheds across Nepal. We employed a deductive approach based on extractable watershed properties to test the performance of four regionalization methods: principal component regression (PCR), random forests (RF) under regression-based methods, spatial proximity (SP), and physical similarity (PS) under donor-based methods in a leave-one-out cross-validation (LOOCV) setting. New hydrological insights for the region: The GR4J rainfall-runoff model coupled with Cemaneige snow module (GR4J-CN) could provide good simulation for majority of the watersheds with median NSE of 0.76 and 0.74 for calibration and validation periods respectively. Model simulation using parameter values predicted from different regionalization methods showed satisfactory results in majority of the watersheds for daily hydrograph simulation. While there wasn't a single method that performed well in all of the watersheds, the physical similarity methods was found to be the most robust. Visual comparison of errors in flow duration curve (FDC) also indicated physical similarity method as a better approach in ungauged watersheds of Nepal. Further experiment using multiple donors using the output averaging option was found to increase the performance of donor-based methods while the parameter averaging option resulted in a drop in performance. The study provides a comprehensive assessment of regionalization methods and advocates the use of hydrological model regionalization as a promising tool for streamflow prediction in ungauged Himalayan watersheds.

Runoff prediction in ungauged basins is a vital task in hydrologic sciences. This study implements a GR4J rainfall-runoff model to simulate runoff in two nested basins of western Nepal. The calibrated model parameters are then interchanged in a proxy-basin framework in order to assess spatially transferability of model parameters for runoff simulation in ungauged basin. The calibrated model showed good performance for both the downstream Chamelia basin and upstream Naugragad basin with a NSE of 0.86 and 0.83 during calibration and 0.84 and 0.64 during validation respectively. Spatial transfer of calibrated model parameters from upstream to downstream basin and vice-versa closely match the hydrograph obtained from calibrated model. The results show spatial transfer of model parameters as a feasible option for streamflow prediction in ungauged basins of Nepal.