Periodic Reporting for period 1 - EPIC (EPIC - ExPloring the ecohydrological Impacts of a changing Cryosphere in the Peruvian Andes)
Okres sprawozdawczy: 2024-01-01 do 2025-12-31
The runoff from the glaciers of the Peruvian Andes is vital to the population, economy and ecosystems downstream. Glaciers act as crucial buffers to variations in water supply, with their importance to downstream users growing in the dry season and during droughts. Water security and ecosystem health are threatened by glacier recession. Runoff from the Rio Santa catchment is in decline in response to glacier recession with predicted warming likely to be dramatic. Furthermore, deglaciation has led to the exposure of barren land and vegetation colonisation. Idealised modelling suggests that the additional evapotranspiration associated with vegetation succession would act to further reduce runoff in catchments where glacier runoff has already peaked.
However, previous modelling schemes have yet to provide a full picture of the past and future changes in glaciers and the resulting impact on water supplies. Work incorporating vegetation change also assumed a direct relationship between vegetation biomass and evapotranspiration, neglecting the fundamental control of energy and water availability on evapotranspiration rates. It is thus vital to move to holistic models that can capture the changing glaciers and snow conditions in realistic ways, and also include the hydrological impact of vegetation in the assessment of future catchment runoff. These new assessments have the potential to change our understanding of how high mountain catchments will respond to warming.
Our aim is to provide a new understanding of the possible futures of the hydrology of the Cordillera Blanca, combining changes in climate, glaciers and ecosystems, and disentangling their interactions. We will elucidate the controls on past glacier and ecosystem change, focusing on these research questions:
What are the main drivers of the changes in glacier energy and mass balance?
What is the overall impact of vegetation on the present catchment water balance?
Then we will look to the future, to determine the controls on projected runoff, to answer:
Are glaciers close to a tipping point of more rapid change, and what processes control this?
Will future vegetation changes exacerbate or mitigate the runoff reduction caused by glacier recession?
However, previous modelling schemes have yet to provide a full picture of the past and future changes in glaciers and the resulting impact on water supplies. Work incorporating vegetation change also assumed a direct relationship between vegetation biomass and evapotranspiration, neglecting the fundamental control of energy and water availability on evapotranspiration rates. It is thus vital to move to holistic models that can capture the changing glaciers and snow conditions in realistic ways, and also include the hydrological impact of vegetation in the assessment of future catchment runoff. These new assessments have the potential to change our understanding of how high mountain catchments will respond to warming.
Our aim is to provide a new understanding of the possible futures of the hydrology of the Cordillera Blanca, combining changes in climate, glaciers and ecosystems, and disentangling their interactions. We will elucidate the controls on past glacier and ecosystem change, focusing on these research questions:
What are the main drivers of the changes in glacier energy and mass balance?
What is the overall impact of vegetation on the present catchment water balance?
Then we will look to the future, to determine the controls on projected runoff, to answer:
Are glaciers close to a tipping point of more rapid change, and what processes control this?
Will future vegetation changes exacerbate or mitigate the runoff reduction caused by glacier recession?
The glacier-hydrological model TOPKAPI-ETH was set-up for the Rio Santa catchment at a 100 m resolution for a present period (2008-2018), this allowed the validation of model outputs against a range of data, including field and remotely-sensed glacier mass balance, river runoff, surface albedo and MODIS snow line elevations. The model results were then analysed to investigate the importance of snow and ice melt for runoff both spatially and seasonally. The results revealed the ephemeral nature of the snow cover below 5000 m a.s.l. which results in a highly variable wet season snowpack. The results of this work were published in Nature Communications Earth and Environment.
The TOPKAPI-ETH model was then run for the past period (1987-2018), with the outputs successfully validated against three datasets of historical glacier outlines. The outputs of the past runs were analysed to investigate the spatial and temporal variation in glacier mass balance. This allowed the drivers of glacier mass balance and runoff change to be determined, with a particular focus on the role of El Niño on influencing catchment processes. The model was then run into the future, from 2018-2100. These runs were forced by 12 CMIP5 projections under an RCP 4.5 emissions scenario which had been statistically downscaled to match the WRF climatology. These results were analysed alongside the past run to investigate the ‘peak water’ paradigm within the Rio Santa catchment. To do this the long-term variation in ice and snowmelt contributions to runoff were analysed, not only at the scale of the entire Rio Santa basin, but also at the sub-catchment level, revealing contrasting responses depending upon the sub-catchment glacier cover.
Then the work shifted in scale to the Shallap sub-catchment, where the Tethys-Chloris model was applied. A suite of field data were collected within the Shallap catchment over two field seasons in June 2024 and July 2025, designed to provide input, calibration and validation data for the modelling work.The field work included the installation of soil temperature and moisture sensors, trail cameras for snow monitoring, vegetation data collected within the proglacial forefield, glaciological data of ablation and debris-thickness and drone imagery across the catchment.
The Tethys-Chloris model includes a full energy and mass balance approach to modelling catchment processes allowing a more in-depth assessment of the impact of succession vegetation on catchment runoff. The multi-point set-up of the model was run to allow calibration and initial assessment of the model results. Then, the fully distributed model was run at a 50 m resolution (2015-2019) to give results on the importance of glacier, snow and vegetation processes on the water and energy balance of the catchment. These results allow insights into the relative importance of the cryosphere compared to ecological processes, and provide the basis for an assessment of how these will shift under future conditions.
The TOPKAPI-ETH model was then run for the past period (1987-2018), with the outputs successfully validated against three datasets of historical glacier outlines. The outputs of the past runs were analysed to investigate the spatial and temporal variation in glacier mass balance. This allowed the drivers of glacier mass balance and runoff change to be determined, with a particular focus on the role of El Niño on influencing catchment processes. The model was then run into the future, from 2018-2100. These runs were forced by 12 CMIP5 projections under an RCP 4.5 emissions scenario which had been statistically downscaled to match the WRF climatology. These results were analysed alongside the past run to investigate the ‘peak water’ paradigm within the Rio Santa catchment. To do this the long-term variation in ice and snowmelt contributions to runoff were analysed, not only at the scale of the entire Rio Santa basin, but also at the sub-catchment level, revealing contrasting responses depending upon the sub-catchment glacier cover.
Then the work shifted in scale to the Shallap sub-catchment, where the Tethys-Chloris model was applied. A suite of field data were collected within the Shallap catchment over two field seasons in June 2024 and July 2025, designed to provide input, calibration and validation data for the modelling work.The field work included the installation of soil temperature and moisture sensors, trail cameras for snow monitoring, vegetation data collected within the proglacial forefield, glaciological data of ablation and debris-thickness and drone imagery across the catchment.
The Tethys-Chloris model includes a full energy and mass balance approach to modelling catchment processes allowing a more in-depth assessment of the impact of succession vegetation on catchment runoff. The multi-point set-up of the model was run to allow calibration and initial assessment of the model results. Then, the fully distributed model was run at a 50 m resolution (2015-2019) to give results on the importance of glacier, snow and vegetation processes on the water and energy balance of the catchment. These results allow insights into the relative importance of the cryosphere compared to ecological processes, and provide the basis for an assessment of how these will shift under future conditions.
The research conducted significantly increased the understanding of the functioning of high-Andean catchments and especially the role of the cryosphere. We determined the spatial and temporal importance of snow and ice melt for runoff in the Rio Santa basin, Peruvian Andes, with snow melt being more important than previously realised. Snow dynamics here are also dominated by short-lived snow events which are likely to be indicative of conditions across the Peruvian Andes. The work shed new light on the past variability of glacier mass balance in the region, with warmer air temperatures linked to El Niño events leading to more negative mass balance years, although precipitation rates are also crucial drivers. Looking to the future, further glacier recession is expected in the Rio Santa catchment, but importantly the degree of change is specific to the sub-catchment, with higher elevation and steeper glaciers being more resilient to increasing air temperatures. The response of glaciers to change then impacts on the long-term runoff patterns. The project also revealed the role of vegetation in the water balance of the Shallap catchment (within the Rio Santa basin), suggesting that although succession vegetation contributes to catchment losses through evapotranspiration, this is smaller than the role of evapotranspiration lost from mature shrubs and lakes. Future work will build on this understanding to reveal how the energy and water balance will shift as glaciers recede and vegetation colonisation continues.