High-elevation climate

The “High Elevation Climate” session showcased a geographically and thematically diverse range of cutting-edge mountain climate science.

In the first talk of the session, Kenichi Ueno enlightened the session on the complexity of climate processes in the Japanese Alps and on-going research initiatives to better characterise them. Particularly interesting was the description of the broad-ranging topics – ecosystem changes, carbon cycle, climate change, water and material cycles – addressed by the recent JALPS programme (2010-2014). This spanned research strands from paleo-climate reconstructions to high-resolution dynamical climate model downscaling and associated projected implications for ecosystems. Kenichi also spoke enthusiastically about current proposals for a “Future Earth”-relevant project on land surface processes in mountains to better characterise land-atmosphere interactions.

In the second talk, Emma Bryder derscribed her PhD work on carbon fluxes in the Glenfeshie Moine Mhor in the headwaters of the Spey River. Emma delivered an engaging talk describing the context of her project in the Cairngorms National Park with a focus on peatland degradation/restoration processes its implications for water quality and climate change mitigation. Emma also gave a detailed account of her data collection and analytical methodology along with initial findings highlighting identification of a clear relationship between stream stage (discharge) and dissolved organic carbon indicating the physical processes driving carbon fluxes in the Moine Mhor. Emma also explained how differing approaches to wildlife management amongst Cairngorms estates complicates strategies to encourage peatland regeneration.

In the third talk, Nick Pepin presented results of his on-going work to compare high-elevation Moderate Resolution Imaging Spectrometer (MODIS) remotely sensed land surface temperatures (LST) to near surface air temperature (NSAT) through a dense transect of local observations he has established on Mount Kilimanjaro. Nick explained how Kilimanjaro, as the highest freestanding mountain in Africa, presents nearly unique setting to investigate research questions related to elevation dependent warming (EDW) in the tropics. Nick described the diversity of land cover – ranging from cultivated lowland zones through rainforest, giant heather and alpine heath to the arid summit zone – sampled by the over 4000m elevation gain of his transect. Nick described his on-going work to derive MODIS LST prediction of NSAT based on the transect observations. His key findings to date include the diurnal asymmetry of LST relationships to NSAT and the strong influence of relative humidity (RH) in modulating LST skill as an NSAT predictor.

In the fourth talk, Geoff Klein described his PhD research to derive a new method for assessment of snowmelt dates in the Swiss Alps. Geoff first described how the background climate context of large decreases in areal snow cover and fraction of precipitation falling as snow in in winter and spring in Switzerland and the northern hemisphere as a whole set the stage for his work. Geoff then detailed the network of 120 sub-daily (half-hourly) snowdepth monitoring sites covering an elevation range from 1600m to 3000m along with his methods for data clearing/corrections. He concluded by highlighting his key findings on the relative influences of snowpack depth and springtime temperatures on snowmelt data variability as well as previewing his next analytical phase on assessment of post-snowmelt vegetation growth.

As session convener, I delivered the fifth talk describing on-going work to use historical imagery from the Advanced Very High Resolution Radiometer (AVHRR) derive MODIS-equivalent spatial climate data products for the High Mountain Asia (HMA) region comprising the Hindu Kush, Karakoram and Himalaya mountain ranges along with the Tibetan Plateau. I began my talk explaining the potential historical record span of AVHRR-derived data products and the scientific imperative – driven by EDW science questions and the broader need for detailed HMA spatial climatologies – for its development. I then detailed the key spatial climate variables – cloud cover fraction, snow covered area and LST – that can be derived from AVHRR along with their relevance to high elevation mountain contexts. I then explained potential approaches (and their limitations) for the critical step in HMA-specific data product derivation of differentiating snow cover from cloud in acquired imagery. I concluded with examples of “spectral obstacles” peculiar to HMA cloud-snow discrimination that on-going research is seeking to overcome.

In the sixth talk, Silvia Terzago gave a comprehensive assessment of the simulation of historical and future precipitation in the Himalaya region by the CMIP5 ensemble of global climate models (GCMs). Silvia described the gridded observational data sets and methodology her team had used to asses GCM ensemble member skill at precipitation over two sub-regions defined by atmospheric circulation sources: (monsoonal) Himalaya and (winter westerly disturbance) Hindu Kush Himalaya (HKH). Silvia further described work by her team to assess GCM skill at snow depth simulation using global meteorological reanalyses as proxies for observations. Silvia concluded her talk showing findings of CMIP5 ensemble projections of EDW and elevation-influence on precipitation. In both cases larger elevation-dependency was found for the HKK sub-region than the monsoonal central and eastern Himalaya.

Our session concluded with Mengben Wang’s presentation of his global analysis of warming amplification at high elevation sites in recent decades. Having defined a threshold of 500m to differentiate high and low elevation zones, Mengben described his three-phase methodology for analysing a data set with nearly 3000 available records: a) paired regional site analysis, b) elevation-band “binning” of stations to calculate mean trends, and c) step-wise multiple regression using both elevation and latitude as predictor variables. Mengben’s stand-out findings include clear evidence for EDW, evidence of EDW ‘acceralation’ in the last 25 years compared with the last 50 and substantial contributions of both elevation and latitude to warming amplification. Mengben concluded that he see’s the unifying element as the ‘Stefan-Boltzmann’ effect of longwave radiation-driven greater warming at lower absolute temperatures, i.e. colder sites/contexts will warm faster than those that are already warm. This has very important implications for mountains in particular.

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