Future hydrological regimes and glacier cover in the Everest region: The case study of the upper Dudh Koshi basin

Assessment of future water resources under climate change is required in the Himalayas, where hydrological cycle is poorly studied and little understood. This study focuses on the upper Dudh Koshi river of Nepal (151 km2, 4200–8848 m a.s.l.) at the toe of Mt. Everest, nesting the debris covered Khumbu, and Khangri Nup glaciers (62 km2). New data gathered during three years of field campaigns (2012–2014) were used to set up a glacio-hydrological model describing stream flows, snow and ice melt, ice cover thickness and glaciers' flow dynamics. The model was validated, and used to assess changes of the hydrological cycle until 2100. Climate projections are used from three Global Climate Models used in the recent IPCC AR5 under RCP2.6, RCP4.5 and RCP8.5. Flow statistics are estimated for two reference decades 2045–2054, and 2090–2099, and compared against control run CR, 2012–2014. During CR we found a contribution of ice melt to stream flows of 55% yearly, with snow melt contributing for 19%. Future flows are predicted to increase in monsoon season, but to decrease yearly (− 4% vs CR on average) at 2045–2054. At the end of century large reduction would occur in all seasons, i.e. − 26% vs CR on average at 2090–2099. At half century yearly contribution of ice melt would be on average 45%, and snow melt 28%. At the end of century ice melt would be 31%, and snow contribution 39%. Glaciers in the area are projected to thin largely up to 6500 m a.s.l. until 2100, reducing their volume by − 50% or more, and their ice covered area by − 30% or more. According to our results, in the future water resources in the upper Dudh Koshi would decrease, and depend largely upon snow melt and rainfall, so that adaptation measures to modified water availability will be required

Assessment of the hydrological components in the glacierized Dudh Koshi river catchment (Nepal)

International audienceThe Himalayan water resources, vital for 800 million people, come mainly from the monsoon and from the melting of the cryosphere. The impact of climate change on these resources, especially on the cryosphere, is a major issue in the Himalayan range. In this context, assessment of the rainfall, snowmelt and ice-melt components of the water balance is crucial. Consequently, a distributed conceptual hydrological model (HDSM) was developed to estimate the contribution of each component to the Dudh Koshi river flow from 2001 to 2005. The Dudh Koshi river basin (3700 km2), with 14% of glacierized area and Mount Everest as the highest peak, is located in eastern Nepal. The snow-cover area, calibrated with satellite data (MOD10A2), and the daily runoff are correctly simulated by the model. Nevertheless, to obtain these results the ice degree-day factor is overestimated (~36 mm °C–1 d–1), leading to an ice-melt contribution around 60% of annual discharge, against 5% in the literature. This overestimation offsets underestimation around 80% of precipitation, especially solid precipitation. After correction of the precipitation, the contributions of rainfall, snowmelt and ice melt represent, respectively, 63%, 9% and 29% of the Dudh Koshi annual discharge from 2001 to 2005. These results highlight large uncertainties in the hydro-climatic data of the Dudh Koshi river basin, which limit understanding of the hydrological and cryospheric processes. They also underline the limited influence of the glacier melting in the context of climate change on the annual Dudh Koshi river’s water resources, since the monsoon rainfall is the main component of the flow

Conceptual rainfall-runoff model with a two-parameter, infinite characteristic time transfer function

International audienceA two-parameter transfer function with an infinite characteristic time is proposed for conceptual rainfall-runoff models. The large time behaviour of the unit response is an inverse power function of time. The infinite characteristic time allows long term memory effects to be accounted for. Such effects are observed in mountainous and karst catchments. The governing equation of the model is a fractional differential equation in the limit of long times. Although linear, the proposed transfer function yields discharge signals that can usually be obtained only using non-linear models. The model is applied successfully to two catchments, the Dud Koshi mountainous catchment in the Himalayas and the Durzon karst catchment in France. It compares favourably to the linear, non-linear single reservoir models and to the GR4J model. With a single reservoir and a single transfer function, the model is capable of reproducing hysteretic behaviours identied as typical of long term memory effects. Computational efficiency is enhanced by approximating the infinite characteristic time transfer function with a sum of simpler, exponential transfer functions. This amounts to partitioning the reservoir into several linear subreservoirs, the output discharges of which are easy to compute. An efficient partitioning strategy is presented to facilitate the practical implementation of the model

Analyse cinématique optimale d'un corps solide à l'aide d'un recalage multiple par consensus médian

International audience

Geostatistical Estimation of Daily Monsoon Precipitation at Fine Spatial Scale: Koshi River Basin

International audienceThe use of appropriate space and time scales is fundamental to model the water budget in mountainous regions and to give appropriate replies to the initial requests. However, at a daily scale, the determination of precipitation behavior is not an easy task due to its high variability in mountainous areas. Seven years (2001–2008) of accurate precipitation maps (1 km ground resolution) have been produced for the monsoon season over the Koshi River basin (Nepal) to be used for hydrological modeling. Due to field and topographical constraints, the geostatistical method of ordinary cokriging interpolation (OCK) was used to compute precipitation grids over a 57,800  km2 basin with a rain gauge network made of 47 stations. Using elevation as a covariable, regionalization models were run to produce 976 daily precipitation grids. They describe temporal and spatial variability close to observed data. Comparisons of the OCK results to an Aphrodite’s reference grid (resolution of 25 km) show that the OCK grids are characterized by a higher spatial variability. Both OCK and Aphrodite data sets underestimate observations, with OCK grids showing the best fit to observed data. However, the OCK method, with an eventual adaptation of the cokriging model, appears consistent for situations where the resolution of the precipitation’s spatial distribution is insufficient and an alternate explaining variable such as elevation is available

Extraction and evaluation of anatomical patient surface and associated respiratory motion with a time-of-flight (ToF) camera

International audienceObjectives: A ToF camera is a new technology which provides a real-time depth map of a scene with a sufficiently high frequency to monitor respiratory motion. As such this technology makes a good alternative to systems currently used clinically since it provides a mark-less real-time monitoring of the complete patient's surface. The objective of this work was to evaluate the accuracy measuring displacements in real-time throughout the recorded patient surface. Methods: The surface provided by the camera was modeled using B-splines, including a correction methodology associated with accurately measuring recorded surface motion information irrespective of the angle between the camera and the patient. An anatomical torso phantom moved by a linear actuator was used in the evaluation. Measurements were made under static and moving conditions (triangular motion of 10 mm in amplitude and 4 seconds as period) on the B-splines control points with or without Gaussian filtering. Accuracy of the surface motion measurements was investigated with the camera placed at different distances (from 0.6m to 1.4m) and angles (α=0° to 45°) from the surface. The repeatability of accurately measuring surface displacement information was assessed on 100 repeated measurements for each experiment. Results: At 80cm between the camera and the phantom, considering all of the surface B-spline control points, motion estimation accuracy was 1.0±0.3mm and 1.3±0.5mm for an angle α = 0° and 45° respectively. Using a 3x3 Gaussian filtering, the motion estimation accuracy improved to 0.7±0.1mm and 1.1±0.3mm for α=0° and 45° respectively. The repeatability of motion estimation throughout the model's surface ranged from 0.7±0.1mm to 1.1±0.1mm for a distance between the camera and the phantom between 60cm and 1.4m. Conclusions: A millimetric accuracy for the monitoring of a patient surface can be obtained using a ToF camera. This technology can be therefore considered for monitoring respiratory motion displacements in real-tim

Location of the ulno-humeral joint axis based on anatomical landmarks

Proper placement of orthosis is of the greatest importance in order to ensure its life expextency. Promising results have been found applying quadric fitting on the humeral joint surface in order to locate the ulno-humeral joint axis. Unfortunately, joint surfaces are not necessarily intact preventig this fitting method to be applied. Our goals were to provide an estimated joint axis location based on anatomical landmarks thanks to a model designed using scanned humeri and to compare different rotation axes with a joint coherence index