Glacial lakes as sentinels of climate change in Central Himalaya, Nepal

Transcription

1 Glacial lakes as sentinels of climate change in Central Himalaya, Nepal Sudeep Thakuri 1,2,3, Franco Salerno 1,3, Claudio Smiraglia 2,3, Carlo D Agata 2,3, Gaetano Viviano 1,3, Emanuela C. Manfredi 1,3, Gianni Tartari 1,3 1 Water Research Institute, National Research Council (IRSA-CNR), Brugherio; 2 Graduate School of Earth, Environment and Biodiversity, University of Milan, Milan; 3 Ev-K2-CNR Committee, Bergamo Italy Corresponding thakuri@irsa.cnr.it

2 Presentation synopsis Introduction Ongoing activities Focus of this presentation: objective Data and method Results and discussion Conclusion

3 Introduction Mount Everest region = debris-covered glaciers and glacial lakes Scientific knowledge gaps Num. of papers Himalayan glacier and ice caps - sources of water resources and contributes to major rivers system (Indus, Brahmaputra, Ganges, Yangtse, Yellow river) Himalaya- the water tower of Asia Water resources billion 20% population, even though the contribution to Ganges is not much (Immerzeel et al. 2010)

4 Ongoing activities Coupling climate forcing with glacial and periglacial environment response in the Mount Everest region to understand the hydrologic process and future water resources scenario Temperature and precipitation reconstruction: using instrumentation records (the Climate Observatory- Pyramid stations), downscaling of reanalysis and global model data [NCEP/NCAR, GHCN/CAMS (NOAA), ERA40, GPCC, Aphrodite] and tree ring proxy Spatio-temporal analysis (1950s-2008) of glaciers Mapping & changes (terminus, surface changesaccumulation and ablation, SLA using multi-temporal maps, optical and laser satellite imagery, DEMs and coupling with climate variables

5 Lakes variations analysis (1950s to 2008) Mapping, variation, coupling with climatic variables Analysis of river discharge series of DHM hydrometric station from 1950 to 2010 in order to identify the main variations of river flow components (in time and frequency domain) though non-stationary models (e.g. Wavelet Analysis). Application of stochastic non-stationary models (e.g. Wavelet Analysis) in order to analyze the changing in time of relevant crossing frequencies.

6 Focus of this presentation: Objective Mapping of both (glaciers and lakes) - water resources conducted with the aim at understanding climate change impacts in Mount Everest region Conditions of formation of lakes - evidence of climate change impact at high altitudes characterized by debris covered glaciers. Nepal (Himalaya) Capability of EO product in monitoring the earth s resources

7 Data and Methods Satellite imagery: ALOS/ AVNIR-2 onboard ALOS, received from a Japanese Earth Observation satellite launched in January 2006 Acquisition: 24 October 2008 Resolution: medium-high resolution (10 m) Image data were orthorectified and corrected for the atmospheric effects using the 6S code (Vermote et al, 1999, Giardino et al, 2010 ) onscreen digitization- visual interpretation Temperature and precipitation AWS at Pyramid Laboratory (alt m)

8 a ALOS- AVNIR-2 Image Acquisition 24 Oct 2008; Cloud cover: 0-2% 10m res.

9 Results and discussion Mapping of glaciers and lakes: The ALOS imagery properly characterize 64% of lakes (with error <15%) in terms of surface and allows correctly characterizing the whole glaciers (error 2%) (±2%) (±18%)

10 a b c a. ALOS- AVNIR-2 b. Lake types c. Uncertainty of measurement associated with to different image resolution

11 a b a. Sagarmatha National Park with delineated glaciers and lakes b. Mapping of glaciers and lakes: a highlight of Ngojumba glacier basin

12 a a. Frequency distribution of glaciers and lakes relative to their elevation b b. Frequency distribution of lakes relative to their area and typology

13 a) Relationship among lake sizes, basin surface and glacial coverage. The error bar represents the AEi. The linear model is computed considering the inverse of the AEi for each lake. b) Normal q-q plot of residuals of the regression model basin surface/lake sizes.

14 Elevation profile of five glaciers in Mt Everest region

15 Multiple regression for supraglacial lake distribution a) Correlation matrix b) Scatterplot of final regression model (confidence levels - 95%) c) Normal q-q plot of residuals of final regression model d) Relative importance each predictor for final regression model e) Comparison between predicted and measured supraglacial lake surfaces for each glacier.

16 Temperature (AWS ) - Increasing trend of temperature - Winter temperature- Nov. and Dec- significance

17 Precipitation (AWS ) - Decreasing trend of precipitation - Significance for Dec., Jun., Aug. months

18 Unconnected glacier lakes: Surfaces of unconnected-glacial lakes are correlated with the dimension of their drainage basin, No correlation found with the glacier cover in the basin Considering the evaporation/precipitation ratio at these altitudes is around 0.34 the evolution of these lakes appears to be a helpful sign for detecting the precipitation trend.

19 Glacier-fed lakes(directly unconnected lakes), indicator of precipitation changes

20 Supraglacial lakes: Low velocity and high ablation rates at the glacier terminus are main responsible factor for their formation. The slope of glacier where lakes are located, mainly influences the velocity, providing boundary condition favorable for lake formation. The slope of the glacier upstream influences both velocity and ablation. The multiple regression model considering the slopes of the two glacier areas is able to predict 90% of the supraglacial lake surfaces.

21 Progracial lakes: The formation of proglacial lakes is closely connected with the supraglacial lakes. They can be considered a precursor of terminus disintegration

22 Conclusion Glaciers lakes show better, visible, and quick response to climate making it possible to map the long term impact of climate change on water resources; Defined the condition of formation of supraglacial lakes and therefore of proglacial ones; Further, we conclude with underlining the importance of unconnected glacier lakes study for detecting precipitation trend in local scale.

23 Further reading: The results of the current presentation has recently been published in International Journal of Global and Planetary Change

24 THANK YOU