Browsing by Autor "Yoshihiro ASAOKA"

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ASSESSMENT OF AQUATIC ENVIRONMENTAL IMPACT BY A FUTURE CLIMATE CHANGE IN A RESERVOIR LOCATED IN THE BOLIVIAN ANDES
(2013) Keisuke TANI; Makoto Umeda; Tsuyoshi Kinouchi; Yoshihiro ASAOKA; Marcelo Gorritty
Glacial melt water is major water resourcess in and around La Paz, the capital of Bolivia in the center of South America. However, it is predicted that the glaciers in this area will disappearin 30 or 40 years because of climate change. In this study, water temperature around the end of the century in Tuni Reservoir, which is located at downstream of glaciers and provides domestic water to the cities nearby, were predicted with 1-dimensional hydraulic model using the outputs of a global climate model. The results indicate that surface temperature in the reservoir will basically depend on temperature rise. However, inflow rates will decrease about 60% by glacier disappearance and change more variably each year. So, it is important to consider how to take and convey water in the future.
BACKSCATTER CHARASTARISTICS OF A TROPICAL GLACIER DERIVED FROM C-BAND SAR IMAGERY
(2018) Shota Funaki; Yoshihiro ASAOKA; Hiroyuki Wakabayashi; Tuyoshi KINOUCHI; Javier Mendoza
雨季の短期・中期的な氷河融解量推定の精度向上に資するため，C-band SARを用いて2015年から2016年の熱帯氷河の後方散乱特性の解析および雪線高度の推定を行った．HuaynaPotosi West氷河を対象として，空間平均の後方散乱係数は，雨季の前半期間(11月～1月)に減少し，後半期間(2月～4月)に増加，乾季の期間は減少する傾向を示した．次に，氷河の縦断線上の後方散乱係数を抽出し，4パターンの階級値(階級幅4, 2, 1, 0.5dB)のヒストグラムを作成し，後方散乱係数の累積相対度数(0.5以上)を用いて乾季および雨季の平均的な雪線を決定する閾値を決定した．累積相対度数の階級幅を1dBおよび0.5dBとして，雨季と乾季の両時期の雪線高度を推定した．以上よりSentinel-1A, B C-band SARから得られる後方散乱係数が熱帯氷河における雪線高度の抽出に有効であることを示した．
Energy balance analysis of a tropical glacier in the Andes and identification of key meteorological variables for empirical melt estimates
(Cambridge University Press, 2025) Yoshihiro ASAOKA; Genki Saito; Takeshi Yamazaki; Edson Ramírez; Walter W. Immerzeel
Abstract This study investigated surface energy fluxes of the Huayna-Potosí Glacier in Bolivia to validate existing empirical melt estimates, including degree-day models and enhanced temperature-index models. A multilayer energy balance model of the snowpack was employed to estimate melt energy and analyze its correlation with meteorological variables. The energy balance analysis revealed that melt energy peaked in October and November, the period corresponding to the progressive development toward the core wet season. Most of the net radiation was consumed by the conductive heat flux into the snowpack or glacier ice, contributing to surface temperature increases. The remaining energy was used for melt. An analysis of diurnal variation indicated that atmospheric longwave radiation suppresses melt during the dry season while driving melt during the wet season. Variables such as specific humidity and relative humidity, which are related to atmospheric longwave radiation, emerged as primary controlling factors after solar radiation in estimating melt based on meteorological variables. This study highlights that a combination of solar radiation and specific humidity outperforms existing empirical melt models that depend exclusively on temperature or a combination of temperature and solar radiation.
ESTIMATION OF GLACIER MELT IN THE TROPICAL ZONGO WITH AN ENHANCED TEMPERATURE-INDEX MODEL
(2013) Pablo Fuchs; Yoshihiro ASAOKA; So Kazama
An enhanced temperature-index model including albedo and shortwave radiation has been applied to the tropical Zongo glacier. The model satisfactorily simulated the daily discharges and their seasonal variations with an efficiency of 0.71 (Nash-Sutcliffe). The energy balance analysis revealed that three factors mainly control melt on this glacier: incoming shortwave radiation, incoming longwave radiation and sensible heat flux. Accordingly, the model differentiates between temperature-dependent and temperature-independent components moving towards a more physically based but still simple model. Modelling was improved with respect to the traditional degree-day method in the wet season characterized by simultaneous accumulation and strong melting while capturing the low melt rates found in the dry season. However the model missed some peaks in discharge due to the underestimation of precipitation at the low elevation meteorological station.
Estimation of Glacier Melt Water Contribution for Human Consumption in the Royal Andes Considering Temperature Measurement Errors
(Scientific Research Publishing, 2014) V. Moya Quiroga; A. Mano; Yoshihiro ASAOKA; Keiko Udo; Shuichi KURE; J. Mendoza
Glaciers from the West side of the Royal Andes are an important source of fresh water for some of the most important Bolivian cities like El Alto. Temperature is an important datum for hydrological modelling and for glacier melt estimation. All temperature measurement devices have some degree of uncertainty due to systematic errors; thus, any temperature measurement has some errors. It is important to estimate the influence of such errors on the results from hydrological models and the estimation of melt water. The present study estimates the melt water contribution from the glaciers Tuni and Huayna West as a source of water supply for human consumption of El Alto considering the errors from temperature measurements. The hydrologic response of the basins was simulated with a hydrologic model. The glacier melt contribution was estimated as the difference between the discharge from the current scenario (with glaciers) and the discharge from a scenario without glaciers. Several volumes of melt water were estimated considering the temperature measurement and its possible errors. The uncertainty of such melt water volume was addressed by performing a Monte Carlo analysis of the possible melt water. The melt water contribution from glacier Tuni and Huayna West during the hydrologic year 2011-2012 was between 1.37 × 106 m3 and 1.72 × 106 m3. Such water volume is enough to meet the yearly water demand of between 6.81% and 8.55% of El Alto.
HEAT BALANCE ANALYSIS ON THE GLACIER WITH SUMMERPRECPITATON SEASONALITY AND EFFECT OF SNOW -A CASE STUDY OF ANDEAN TROPICAL GLACIER-
(2013) Yoshihiro ASAOKA; Takeshi Yamazaki; Shunsuke Miyata; So Kazama; Edson Ramírez
The tropical glacier in Andes Mountain has summer precipitation seasonality. A multi-layer snow model was applied to Zongo glacier, Bolivia to evaluate the heat balance on the glacier and the effect of snow on glacier melt. Model simulation at observation point successfully accounted for variations in surface temperature on the glacier in both dry and wet season. Main components of melt heat were shortwave radiation in the dry season and long wave radiation in wet season. Melt flux in mid-wet season was lower than in early-wet season due to continuous snow cover and its high albedo. Moreover, simulation results showed that snow cover on the glacier decline the melt rate in the wet season. This result suggests that mass balance is affected by summer precipitation seasonality and vulnerable to temperature rise.
Modeling glacier melt and runoff in a high-altitude headwater catchment in the Cordillera Real, Andes
(2013) Tsuyoshi Kinouchi; T. Liu; J. Mendoza; Yoshihiro ASAOKA
Abstract. Runoff from catchments with partial glacier cover is an integrated process of glacier melt, snowmelt, and surface and subsurface runoff of meltwater and rain from glacierized and non-glacierized areas. Additionally, inherent characteristics of the tropical Andes such as large meteorological variability, high elevation and steep slopes, hydrological effects of wetlands and lakes, and rapid glacier retreat make it difficult to model glacio-hydrological responses under changing climate. In this study, we developed a semi-distributed conceptual model applicable to partially glacierized catchments in the tropical Andes that considers all of these aspects, and we applied the model to the Huayna Potosi West headwater catchment in the Cordillera Real, Bolivia. Based on the latest 2 yr dataset of meteorological and hydrological monitoring, we showed the spatial and temporal variability of air temperature and precipitation in the region, and the dataset was used to calibrate model parameters and validate the performance of the daily runoff simulation. Variations in the simulated streamflow agreed well with the observed seasonal and temporal variations, and the result also showed that uncertainty pertaining to the spatial and temporal variations in air temperature and precipitation as well as the retarding effect of a wetland and lake strongly affected the runoff hydrograph. The simulated runoff components indicated that runoff from glacier melt occurs mainly in the initial period of the wet season, from October to early December, and in the late period of the wet season, March and April, although the runoff is relatively small in the latter period. Between these two periods in the wet season, major runoff components were estimated to be subsurface runoff in the non-glacierized area and surface runoff due to snowmelt. Given the future meteorological conditions based on the observational data and a predictive general circulation model output, the model quantified the long-term changes in runoff, glacierized area, and cumulative glacier and snow mass balance. The glacier retreat is estimated to continue to 2050, with the magnitude of area decrease and negative cumulative mass balance depending on the increasing temperature trend used. For higher temperature trends, in particular, greater seasonal variation in runoff and larger contributions from subsurface runoff and surface runoff by rainfall were simulated to occur in the wet season, but the change in annual total runoff between the present and 2050 was not significant. These results suggest that it is important to consider how to best adapt to greater seasonal runoff variations in terms of water availability in the downstream region.
Modelling melt, runoff, and mass balance of a tropical glacier in the Bolivian Andes using an enhanced temperature-index model
(2016) Pablo Fuchs; Yoshihiro ASAOKA; So Kazama
This paper evaluates the feasibility of applying a coupled melt, runoff, and mass balance model to the tropical Zongo glacier (Cordillera Real, Bolivia) during two hydrological years. Melt rate was estimated using the standard degree-day method (DDM) and an enhanced temperature-index model (ETI). The latter was run with values of parameters obtained for Haut Glacier d’Arolla and a recalibrated parameter set for Zongo glacier. Glacier mass balance was calculated using snowfall inputs and modelled melt and sublimation. Estimated monthly mass balance and discharge were compared with observations from a stake network in the ablation zone and data from a hydrometric station. We concluded that ETI model agrees very well with the reference runoff and mass balance. Net mass balance over the whole glacier was predicted accurately in the ablation zone, but the model overestimated mass balance in the accumulation zone owing to the absence of observations at higher elevations; the equilibrium line altitude and accumulation area ratio were predicted within reasonable limits. The results demonstrate that ETI model is applicable in tropical conditions, provided that the parameters are recalibrated for the climatic settings of this region.
Probabilistic estimation of glacier volume and glacier bed topography: the Andean glacier Huayna West
(2013) V. Moya Quiroga; A. Mano; Yoshihiro ASAOKA; Keiko Udo; Shuichi KURE; J. Mendoza
Abstract. Glacier retreat will increase sea level and decrease fresh water availability. Glacier retreat will also induce morphologic and hydrologic changes due to the formation of glacial lakes. Hence, it is important not only to estimate glacier volume, but also to understand the spatial distribution of ice thickness. There are several approaches for estimating glacier volume and glacier thickness. However, it is not possible to select an optimal approach that works for all locations. It is important to analyse the relation between the different glacier volume estimations and to provide confidence intervals of a given solution. The present study presents a probabilistic approach for estimating glacier volume and its confidence interval. Glacier volume of the Andean glacier Huayna West was estimated according to different scaling relations. Besides, glacier volume and glacier thickness were estimated assuming plastic behaviour. The present study also analysed the influence of considering a variable glacier density due to ice firn densification. It was found that the different estimations are described by a lognormal probability distribution. Considering a confidence level of 90%, the estimated glacier volume is 0.0275 km3 ± 0.0052 km3. Considering a confidence level of 90%, the estimated glacier thickness is 24.98 m with a confidence of ±4.67 m. The mean basal shear stress considering plastic behaviour is 82.5 kPa. The reconstruction of glacier bed topography showed the future formation of a glacier lake with a maximum depth of 32 m.
Water security in high mountain cities of the Andes under a growing population and climate change: A case study of La Paz and El Alto, Bolivia
(Elsevier BV, 2019) Tsuyoshi Kinouchi; Takashi Y. Nakajima; Javier Mendoza; Pablo Fuchs; Yoshihiro ASAOKA