Possible impacts of climate change on debris-flow activity in the Swiss Alps

This study uses a long dataset of past debris flows from eight high-elevation catchments in the Swiss Alps for which triggering conditions since AD 1864 have been reconstructed. The torrents under investigation have unlimited sediment supply and the triggering of debris flows is thus mainly controlled by climatic factors. Based on point-based downscaled climate scenarios for meteorological stations located next to the catchments and for the periods 2001-2050 and 2051-2100, we study the evolution of temperature and rainfall above specific thresholds (10, 20, 30, 40 and 50mm) and durations (1, 2 or 3days). We conclude that the drier conditions in future summers and the wetting of springs, falls and early winters are likely to have significant impacts on the behavior of debris flows. Based on the current understanding of debris-flow systems and their reaction to rainfall inputs, one might expect only slight changes in the overall frequency of events by the mid-21st century, but possibly an increase in the overall magnitude of debris flows due to larger volumes of sediment delivered to the channels and an increase in extreme precipitation events. In the second half of the 21st century, the number of days with conditions favorable for the release of debris flows will likely decrease, especially in summer. The anticipated increase of rainfall during the shoulder seasons (March, April, November, December) is not expected to compensate for the decrease in future heavy summer rainfall over 2 or 3days

Possible impacts of climate change on debris-flow activity in the Swiss Alps

This study uses a long dataset of past debris flows from eight high-elevation catchments in the Swiss Alps for which triggering conditions since AD 1864 have been reconstructed. The torrents under investigation have unlimited sediment supply and the triggering of debris flows is thus mainly controlled by climatic factors. Based on point-based downscaled climate scenarios for meteorological stations located next to the catchments and for the periods 2001–2050 and 2051–2100, we study the evolution of temperature and rainfall above specific thresholds (10, 20, 30, 40 and 50 mm) and durations (1, 2 or 3 days). We conclude that the drier conditions in future summers and the wetting of springs, falls and early winters are likely to have significant impacts on the behavior of debris flows. Based on the current understanding of debris-flow systems and their reaction to rainfall inputs, one might expect only slight changes in the overall frequency of events by the mid-21st century, but possibly an increase in the overall magnitude of debris flows due to larger volumes of sediment delivered to the channels and an increase in extreme precipitation events. In the second half of the 21st century, the number of days with conditions favorable for the release of debris flows will likely decrease, especially in summer. The anticipated increase of rainfall during the shoulder seasons (March, April, November, December) is not expected to compensate for the decrease in future heavy summer rainfall over 2 or 3 days

Assessing Climate Impacts on Hydropower Production: The Case of the Toce River Basin

The aim of the presented study is to assess the impacts of climate change on hydropower production of the Toce Alpine river basin in Italy. For the meteorological forcing of future scenarios, time series were generated by applying a quantile-based error-correction approach to downscale simulations from two regional climate models to point scale. Beside a general temperature increase, climate models simulate an increase of mean annual precipitation distributed over spring, autumn and winter, and a significant decrease in summer. A model of the hydropower system was driven by discharge time series for future scenarios, simulated with a spatially distributed hydrological model, with the simulation goal of defining the reservoirs management rule that maximizes the economic value of the hydropower production. The assessment of hydropower production for future climate till 2050 respect to current climate (2001–2010) showed an increase of production in autumn, winter and spring, and a reduction in June and July. Significant change in the reservoir management policy is expected due to anticipation of the date when the maximum volume of stored water has to be reached and an increase of the reservoir drawdown during August and September to prepare storage capacity for autumn inflows

Climate projections for glacier change modelling over the Himalayas

Glaciers are of key importance to freshwater supplies in the Himalayan region. Their growth or decline is among other factors determined by an interaction of 2‐meter air temperature (TAS) and precipitation rate (PR) and thereof derived positive degree days (PDD) and snow and ice accumulation (SAC). To investigate determining factors in climate projections, we use a model ensemble consisting of 36 CMIP5 General Circulation Models (GCMs) and 13 Regional Climate Models (RCMs) of two Asian CORDEX domains for two different representative concentration pathways (RCP4.5 and RCP8.5). First, we downsize the ensemble in respect to the models' ability to correctly reproduce dominant circulation patterns (i.e. the Indian summer monsoon (ISM) and Western Disturbances (WDs)) as well as elevation dependent trend signals in winter. Within this evaluation, a newly produced dataset for the Indus, Ganges and Brahmaputra catchments is used as observational data. The reanalyses WFDEI, ERA‐Interim, NCEP/NCAR and JRA‐55 are used to further account for observational uncertainty. In a next step, remaining TAS and PR data are bias corrected applying a new bias adjustment method, Scale Distribution Mapping and subsequently PDD and SAC computed. Finally, we identify and quantify projected climate change effects. Until the end of the century, the ensemble indicates a rise of PDD, especially during summer and for lower altitudes. Also TAS is rising, though the highest increases are shown for higher altitudes and between December and April (DJFMA). PRs connected to the ISM are projected to robustly increase, while signals for PR changes during DJFMA show a higher level of uncertainty and spatial heterogeneity. However, a robust decline in solid precipitation is projected over our research domain, with the exception of a small area in the high mountain Indus catchment where no clear signal emerges. This article is protected by copyright. All rights reserved

Investigation of Climate Change Impact on Water Resources for an Alpine Basin in Northern Italy: Implications for Evapotranspiration Modeling Complexity

<div><p>Assessing the future effects of climate change on water availability requires an understanding of how precipitation and evapotranspiration rates will respond to changes in atmospheric forcing. Use of simplified hydrological models is required beacause of lack of meteorological forcings with the high space and time resolutions required to model hydrological processes in mountains river basins, and the necessity of reducing the computational costs. The main objective of this study was to quantify the differences between a simplified hydrological model, which uses only precipitation and temperature to compute the hydrological balance when simulating the impact of climate change, and an enhanced version of the model, which solves the energy balance to compute the actual evapotranspiration. For the meteorological forcing of future scenario, at-site bias-corrected time series based on two regional climate models were used. A quantile-based error-correction approach was used to downscale the regional climate model simulations to a point scale and to reduce its error characteristics. The study shows that a simple temperature-based approach for computing the evapotranspiration is sufficiently accurate for performing hydrological impact investigations of climate change for the Alpine river basin which was studied.</p></div

Mean monthly discharge for the period 2041–2050 as simulated by the FEST-WB and FEST-EWB hydrological models driven by the REMO or RegCM3 regional climate models versus the control period (2001–2010): a) FEST-EWB driven by REMO, b) FEST-WB driven by REMO, c) FEST-EWB driven by RegCM3, and d) FEST WB driven by RegCM3.

<p>Mean monthly discharge for the period 2041–2050 as simulated by the FEST-WB and FEST-EWB hydrological models driven by the REMO or RegCM3 regional climate models versus the control period (2001–2010): a) FEST-EWB driven by REMO, b) FEST-WB driven by REMO, c) FEST-EWB driven by RegCM3, and d) FEST WB driven by RegCM3.</p

Daily mean (<i>T</i>), maximum (<i>T_max</i>) and minimum (<i>T_max</i>) temperature and mean annual precipitation (<i>P</i>) observed and simulated by error corrected REMO and RegCM3 climate models for control period (2001–2010).

<p>Daily mean (<i>T</i>), maximum (<i>T_max</i>) and minimum (<i>T_max</i>) temperature and mean annual precipitation (<i>P</i>) observed and simulated by error corrected REMO and RegCM3 climate models for control period (2001–2010).</p

Mean monthly and cumulated actual evapotranspiration as computed for 2001–2010 by the FEST-EWB (left) and FEST-WB (right) hydrological models driven by the REMO and RegCM3 regional climate models and the weather observations during the control period (2001–2010).

<p>Mean monthly and cumulated actual evapotranspiration as computed for 2001–2010 by the FEST-EWB (left) and FEST-WB (right) hydrological models driven by the REMO and RegCM3 regional climate models and the weather observations during the control period (2001–2010).</p