Glacier melt is known to provide an important source of water to streamflow in glacierized tropical regions, especially during the dry season. Groundwater also contributes a significant amount to streamflow. However, the linkage between the two is often unclear: How much groundwater originates from glacier melt? More broadly, how will groundwater and surface water contributions to streamflow change as glaciers retreat and climate changes? We developed a glacio-hydrological model in the Cold Region Hydrological Modelling platform to explore the complex interactions among the cryosphere, surface water, and groundwater in Peru's Cordillera Blanca, specifically in the Quilcayhuanca valley. The model uses meteorological observations from the valley and is parameterized using numerous data sources and process-based studies in the valley. Our findings reveal that during the dry season, 24 % of streamflow is routed through the groundwater reservoir, increasing to 40 % during the lowest flows. In a simulation without glaciers, streamflow discharge decreases by 34 % during the wet season and by 54 % during the dry season, with the groundwater contribution to streamflow decreasing by 55 % and 52 % for the wet and dry seasons, respectively. This simplified approach suggests that approximately half of the annual groundwater contribution to the stream originates from glacier wastage. We conducted sensitivity scenarios to evaluate the basin's resilience to the range of possible changes in precipitation, temperature and glacier cover expected by 2100. In a nearly deglaciated basin, the sensitivity to the range of tested temperature (+0 to 5 °C) produced a streamflow ranging from -60 to -49 % of current conditions in the dry season, and the range of tested precipitation (-20 % to +20 %) produced a streamflow ranging between -78 to -35 % of current conditions, indicating a larger sensitivity to potential changes in precipitation. Expected ratio changes were smaller during the wet season but followed a similar pattern. In the most likely scenarios by 2100, under RCP 8.5, wet season streamflow is predicted to decrease by 17 to 27 %, and dry season streamflow by 28 to 52 %. Despite a substantial decline in snow and ice contributions under climate change and deglaciation, the groundwater zone's contribution to streamflow shows relatively minor changes, demonstrating the low sensitivity of the groundwater system to climate shifts and glacier variations.

While mountain water faces threats posed by climate change, particularly in snow-dominated and glacierized systems, the role of groundwater (GW) in sustaining streamflow in these systems remains elusive. Changing mountain headwaters, marked by reduced snowpacks, retreating glaciers, shifting precipitation patterns, and rising temperatures, pose a crucial question: what is the resilience of streamflow in these mountains, and what role does GW play in this resilience? This is particularly uncertain in tropical high mountains where the seasonality of precipitation and glacier melt govern streamflow generation. A glacio-hydrological model was created using the Cold Regions Hydrological Modelling platform to investigate cryosphere-surface water-GW interactions in the Quilcayhuanca Basin, in Peru's Cordillera Blanca. The model was forced by in-situ meteorological observations and parameterized using numerous data sources and process-based studies in the basin. Model results show that during the dry season, 37% of streamflow is generated from GW discharge, increasing to 56% during the lowest flows. Evapotranspiration is the largest mass flux from the basin at the peak of the dry season. Precipitation, temperature, and glacier change scenarios were used to assess the sensitivity of basin hydrology to climate change and glacier retreat. In a warmer, wetter, and nearly deglaciated future, Quilcayhuanca basin streamflow is expected to decrease by 4%-19% annually, with a larger volumetric change in overland and vadose zone flow than in GW flow. The range in values is more closely linked to uncertainty in precipitation change than temperature change. Despite a strong reduction in snow and ice contribution to streamflow with warming and deglaciation, the concomitant increase in precipitation can limit the changes in streamflow and GW flow, showcasing the resilience of the system to shifts in climate and glacier cover.

Runoff from glacierised Andean river basins is essential for sustaining the livelihoods of millions of people. By running a high-resolution climate model over the two most glacierised regions of Peru we unravel past climatic trends in precipitation and temperature. Future changes are determined from an ensemble of statistically downscaled global climate models. Projections under the high emissions scenario suggest substantial increases in temperature of 3.6 °C and 4.1 °C in the two regions, accompanied by a 12% precipitation increase by the late 21st century. Crucially, significant increases in precipitation extremes (around 75% for total precipitation on very wet days) occur together with an intensification of meteorological droughts caused by increased evapotranspiration. Despite higher precipitation, glacier mass losses are enhanced under both the highest emission and stabilization emission scenarios. Our modelling provides a new projection of combined and contrasting risks, in a region already experiencing rapid environmental change.

This article presents a comprehensive hydrometeorological dataset collected over the past two decades throughout the Cordillera Blanca, Peru. The data-recording sites, located in the upper portion of the Rio Santa valley, also known as the Callejon de Huaylas, span an elevation range of 3738–4750 m a.s.l. As many historical hydrological stations measuring daily discharge across the region became defunct after their installation in the 1950s, there was a need for new stations to be installed and an opportunity to increase the temporal resolution of the streamflow observations. Through inter-institutional collaboration, the hydrometeorological network described in this paper was deployed with the goal of evaluating how progressive glacier mass loss was impacting stream hydrology, and understanding better the local manifestation of climate change over diurnal to seasonal and interannual time scales. The four automatic weather stations supply detailed meteorological observations and are situated in a variety of mountain landscapes, with one on a high-mountain pass, another next to a glacial lake, and two in glacially carved valleys. Four additional temperature and relative humidity loggers complement the weather stations within the Llanganuco valley by providing these data across an elevation gradient. The six streamflow gauges are located in tributaries to the Rio Santa and collect high-temporal-resolution runoff data. The datasets presented here are available freely from https://doi.org/10.4211/hs.35a670e6c5824ff89b3b74fe45ca90e0 (Mateo et al., 2021). Combined, the hydrological and meteorological data collected throughout the Cordillera Blanca enable detailed research of atmospheric and hydrological processes in tropical high-mountain terrain.

Precipitation, snow and ice melt from Andean river basins provide a crucial water source to mountain and downstream communities equally. Precipitation and temperature changes due to global climate change are likely to affect agriculture, hydropower generation and hazard risks, but are poorly constrained, especially in future projections. Here we focus on two heavily glacierised regions of the Peruvian Andes, the Cordillera Blanca, and the Cordillera Vilcanota-Urubamba, to assess projected changes in extreme meteorological events and droughts. Previous work suggests increasing temperatures in both regions in the 21st century, with contrasting projections of precipitation trends. There has been little focus, however, on how extremes in precipitation and temperature might vary in the future. Having created a bias-corrected regional climate model from 1980-2018, we use empirical quantile mapping to statistically downscale 30 CMIP5 models. This ensemble is analysed to determine future changes in climate extremes. Both minimum and maximum daily temperatures are projected to increase in the from 2018 to 2100. This leads to a large reduction in the number of frost days in both regions, and suggests that under a high-emissions scenario, almost every day in the late 21st century will be in the 90th percentile of temperatures experienced during 1980-2018. The number of wet and dry days is not projected to change, but precipitation falling on very wet days (in the 95th percentile of the 1980-2018 period) is projected to increase significantly. Lastly, we consider changes in future meteorological droughts using the standardised precipitation evapotranspiration index (SPEI) which considers potential evapotranspiration, as well as precipitation. We estimate potential evapotranspiration from temperature projections, using the Hargreaves method. Despite projected precipitation increases, temperature increases leading to an increase in evaporation may be large enough to increase meteorological droughts in the future, with the total number of drought months projected to almost double under high emission scenarios by the end of the 21st century. In a region that already experiences water stress and hazards, these changes to both extreme rainfall and drought could have a significant impact for communities in the Peruvian Andes, and for the downstream urban areas and industry that rely on mountain river flow.

The Peruvian Andes contain the vast majority of the world’s tropical glaciers. Warming temperatures due to climate change have caused a dramatic shrinking of these glaciers, posing a threat to water supplies. Two of the most heavily glacierised areas of Peru are the Cordillera Blanca, which includes the Rio Santa River Basin to the north of Peru, and the Cordilleras Urubamba, Vilcabamba, and Vilcanota towards the south. Due to the topographic and climatic complexity of the regions, spatial variations in precipitation and temperature are high, and spatially distributed high-resolution climate data can offer a crucial tool to understand those variations, in a way which is not possible from limited, individual ground stations. Here we present a new high-resolution climate dataset over both regions, created by bias-correcting Weather Research and Forecasting (WRF) model output at 4 km spatial resolution against observations. The spatial variation in precipitation differs over the two river basins. In the region of the Cordillera Blanca, precipitation mostly increases with elevation and distance upstream. Around the southern cordilleras, there are regions of greater precipitation near the mountains and glaciers which lie further downstream, but the high elevations of the cordillera Vilcanota, further upstream, are much drier. Analysis of the precipitation and temperature trends from 1980 to 2018 demonstrates a clear warming trend in both regions. The precipitation trends are less uniform, with the Rio Santa showing a general trend for increasing precipitation, but with a less clear trend over the higher, glacierised regions of the valley. Around the Cordilleras Urubamba, Vilcabamba and Vilcanota, there is no clear trend in precipitation over recent decades. Using a range of CMIP5 models, the high-resolution precipitation and temperature datasets are statistically projected into the future, using quantile mapping. Future trends in precipitation and temperature are analysed over both regions, and the inter-model variability in the CMIP5 models is examined.

Peruvian glaciers are important contributors to dry season runoff for agriculture and hydropower, but they are at risk of disappearing due to climate warming. Their energy balance and ablation characteristics have previously been studied only for individual glaciers, with no comparisons between regions. We applied the physically-based, energy balance melt component of the model Tethys-Chloris at five on-glacier meteorological stations: three in the Cordillera Blanca near Huaraz (with glaciers above ~4300 m a.s.l.), and two in the Cordillera Vilcanota east of Cusco (with glaciers above ~ 4800 m). The climate of these regions is strongly seasonal, with an austral summer wet season and winter dry season. Our results revealed that at most sites the energy available for melt is greatest in the wet season. This is a consequence of the dry season energy losses from the latent heat flux and net longwave radiation which counter-balance the high dry season net shortwave radiation, which otherwise dominates the energy balance. The sensible heat flux is a relatively small contributor to melt energy in both seasons. Comparison of the five sites suggests that there is more energy available for melt at a given elevation in the Cordillera Vilcanota compared to the Cordillera Blanca. At three of the sites the wet season snowpack was discontinuous, forming and melting within a daily to weekly timescale. Albedo and melt are thus highly variable in the wet season and closely related to the precipitation dynamics. At the highest site, in the accumulation zone of the Quelccaya Ice Cap, 81% of ablation was from sublimation. Sublimation was less important at the lower sites, but it reduces dry season melt. Correlation of the NOAA Oceanic El Niño Index (ONI) to the outputs of the two sites with the longest records revealed that the warmer wet season temperatures characteristic of a positive ONI were associated with a decreased albedo, greater net shortwave radiation, a more positive sensible heat flux and increased melt rates. Air temperature and precipitation inputs were also perturbed at all five sites to understand their sensitivity to climate change. Enhanced mass loss was predicted with a static increase of 2°C or more, even with a +30% precipitation increase, with the lower elevation Cordillera Blanca sites at risk of the greatest mass loss due to warming.

Peruvian glaciers are important contributors to dry season runoff for agriculture and hydropower, but they are at risk of disappearing due to climate change. We applied a physically based, energy balance melt model at five on‐glacier sites within the Peruvian Cordilleras Blanca and Vilcanota. Net shortwave radiation dominates the energy balance, and despite this flux being higher in the dry season, melt rates are lower due to losses from net longwave radiation and the latent heat flux. The sensible heat flux is a relatively small contributor to melt energy. At three of the sites the wet season snowpack was discontinuous, forming and melting within a daily to weekly timescale, and resulting in highly variable melt rates closely related to precipitation dynamics. Cold air temperatures due to a strong La Niña year at Shallap Glacier (Cordillera Blanca) resulted in a continuous wet season snowpack, significantly reducing wet season ablation. Sublimation was most important at the highest site in the accumulation zone of the Quelccaya Ice Cap (Cordillera Vilcanota), accounting for 81% of ablation, compared to 2%–4% for the other sites. Air temperature and precipitation inputs were perturbed to investigate the climate sensitivity of the five glaciers. At the lower sites warmer air temperatures resulted in a switch from snowfall to rain, so that ablation was increased via the decrease in albedo and increase in net shortwave radiation. At the top of Quelccaya Ice Cap warming caused melting to replace sublimation so that ablation increased nonlinearly with air temperature.

Peru is facing imminent water resource issues as glaciers retreat and demand for water increases, yet limited observations and model resolution hamper understanding of hydrometerological processes on local to regional scales. Much of current global and regional climate studies neglect the meteorological forcing of lapse rates (LRs) and valley and slope wind dynamics on critical components of the Peruvian Andes' water cycle, and herein we emphasize the wet season. In 2004 and 2005 we installed an autonomous sensor network (ASN) within the glacierized Llanganuco Valley, Cordillera Blanca (9° S), consisting of discrete, cost-effective, automatic temperature loggers located along the valley axis and anchored by two automatic weather stations. Comparisons of these embedded hydrometeorological measurements from the ASN and climate modeling by dynamical downscaling using the Weather Research and Forecasting model elucidate distinct diurnal and seasonal characteristics of the mountain wind regime and LRs. Wind, temperature, humidity, and cloud simulations suggest that thermally driven up-valley and slope winds converging with easterly flow aloft enhance late afternoon and evening cloud development, which helps explain nocturnal wet season precipitation maxima measured by the ASN. Furthermore, the extreme diurnal variability of along-valley-axis LR and valley wind detected from ground observations and confirmed by dynamical downscaling demonstrate the importance of realistic scale parameterizations of the atmospheric boundary layer to improve regional climate model projections in mountainous regions.

Spatially distributed surface temperature is an important, yet difficult to observe, variable for physical glacier melt models. We utilize ground‐based thermal infrared imagery to obtain spatially distributed surface temperature data for alpine glaciers. The infrared images are used to investigate thermal microscale processes at the glacier surface, such as the effect of surface cover type and the temperature gradient at the glacier margins on the glacier's temperature dynamics. Infrared images were collected at Cuchillacocha Glacier, Cordillera Blanca, Peru, on 23–25 June 2014. The infrared images were corrected based on ground truth points and local meteorological data. For the control points, the Pearson's correlation coefficient between infrared and station temperatures was 0.95. The ground‐based infrared camera has the potential for greatly improving glacier energy budget studies, and our research shows that it is critical to properly correct the thermal images to produce robust, quantifiable data.