Mario Rohrer

The days of plenty might soon be over in glacierized Central Asian catchments

Despite the fact that the fast-growing population of Central Asia strongly depends on glacial melt water for fresh water supply, irrigation and hydropower production, the impact of glacier shrinkage on water availability remains poorly understood. With an annual area loss of 0.36 to 0.76%, glaciers are retreating particularly fast in the northern Tien Shan, thus causing concern about future water security in the densely populated regions of Bishkek and Almaty. Here, we use exceptionally long in-situ data series to run and calibrate a distributed glacio-hydrological model, which we then force with downscaled data from phase five of the Climate Model Intercomparison Project CMIP5. We observe that even in the most glacier-friendly scenario, glaciers will lose up to two thirds (−60%) of their 1955 extent by the end of the 21st century. The range of climate scenarios translates into different changes in overall water availability, from peak water being reached in the 2020s over a gradual decrease to status quo until the end of the 21st century. The days of plenty, however, will not last much longer, as summer runoff is projected to decrease, independent of scenario uncertainty. These results highlight the need for immediate planning of mitigation measures in the agricultural and energy sectors to assure long-term water security in the densely populated forelands of the Tien Shan.

Facing unprecedented drying of the Central Andes? Precipitation variability over the period AD 1000–2100

Projected future trends in water availability are associated with large uncertainties in many regions of the globe. In mountain areas with complex topography, climate models have often limited capabilities to adequately simulate the precipitation variability on small spatial scales. Also, their validation is hampered by typically very low station density. In the Central Andes of South America, a semi-arid high-mountain region with strong seasonality, zonal wind in the upper troposphere is a good proxy for interannual precipitation variability. Here, we combine instrumental measurements, reanalysis and paleoclimate data, and a 57-member ensemble of CMIP5 model simulations to assess changes in Central Andes precipitation over the period AD 1000–2100. This new database allows us to put future projections of precipitation into a previously missing multi-centennial and pre-industrial context. Our results confirm the relationship between regional summer precipitation and 200 hPa zonal wind in the Central Andes, with stronger Westerly winds leading to decreased precipitation. The period of instrumental coverage (1965–2010) is slightly dryer compared to pre-industrial times as represented by control simulations, simulations from the past Millennium, ice core data from Quelccaya ice cap and a tree-ring based precipitation reconstruction. The model ensemble identifies a clear reduction in precipitation already in the early 21st century: the 10 year running mean model uncertainty range (ensemble 16–84% spread) is continuously above the pre-industrial mean after AD 2023 (AD 2028) until the end of the 21st century in the RCP2.6 (RCP8.5) emission scenario. Average precipitation over AD 2071–2100 is outside the range of natural pre-industrial variability in 47 of the 57 model simulations for both emission scenarios. The ensemble median fraction of dry years (defined by the 5th percentile in pre-industrial conditions) is projected to increase by a factor of 4 until 2071–2100 in the RCP8.5 scenario. Even under the strong reduction of greenhouse gas emissions projected by the RCP2.6 scenario, the Central Andes will experience a reduction in precipitation outside pre-industrial natural variability. This is of concern for the Central Andes, because society and economy are highly vulnerable to changes in the hydrological cycle and already have to face decreases in fresh water availability caused by glacier retreat.

Missing (in-situ) snow cover data hampers climate change and runoff studies in the Greater Himalayas.

The Himalayas are presently holding the largest ice masses outside the polar regions and thus (temporarily) store important freshwater resources. In contrast to the contemplation of glaciers, the role of runoff from snow cover has received comparably little attention in the past, although (i) its contribution is thought to be at least equally or even more important than that of ice melt in many Himalayan catchments and (ii) climate change is expected to have widespread and significant consequences on snowmelt runoff. Here, we show that change assessment of snowmelt runoff and its timing is not as straightforward as often postulated, mainly as larger partial pressure of H2O, CO2, CH4, and other greenhouse gases might increase net long-wave input for snowmelt quite significantly in a future atmosphere. In addition, changes in the short-wave energy balance - such as the pollution of the snow cover through black carbon - or the sensible or latent heat contribution to snowmelt are likely to alter future snowmelt and runoff characteristics as well. For the assessment of snow cover extent and depletion, but also for its monitoring over the extremely large areas of the Himalayas, remote sensing has been used in the past and is likely to become even more important in the future. However, for the calibration and validation of remotely-sensed data, and even more so in light of possible changes in snow-cover energy balance, we strongly call for more in-situ measurements across the Himalayas, in particular for daily data on new snow and snow cover water equivalent, or the respective energy balance components. Moreover, data should be made accessible to the scientific community, so that the latter can more accurately estimate climate change impacts on Himalayan snow cover and possible consequences thereof on runoff.

The freezing level in the tropical Andes, Peru: An indicator for present and future glacier extents

Along with air temperatures, the freezing level height (FLH) has risen over the last decades. The mass balance of tropical glaciers in Peru is highly sensitive to a rise in the FLH, mainly due to a decrease in accumulation and increase of energy for ablation caused by reduced albedo. Knowledge of future changes in the FLH is thus crucial to estimating changes in glacier extents. Since in situ data are scarce at altitudes where glaciers exist (above ~4800 m above sea level (asl)), reliable FLH estimates must be derived from multiple data types. Here we assessed the FLHs and their spatiotemporal variability, as well as the related snow/rain transition in the two largest glacier-covered regions in Peru by combining data from two climate reanalysis products, Tropical Rainfall Measuring Mission (TRMM) Precipitation Radar Bright Band data, Micro Rain Radar data, and meteorological ground station measurements. The mean annual FLH lies at 4900 and 5010 m asl, for the Cordillera Blanca and Vilcanota, respectively. During the wet season, the FLH in the Cordillera Vilcanota lies ~150 m higher compared to the Cordillera Blanca, which is in line with the higher glacier terminus elevations. Coupled Model Intercomparison Project version 5 (CMIP5) climate model projections reveal that by the end of the 21st century, the FLH will rise by 230 m (±190 m) for Representative Concentration Pathway (RCP) 2.6 and 850 m (±390 m) for RCP8.5. Even under the most optimistic scenario, glaciers may continue shrinking considerably, assuming a close relation between FLH and glacier extents. Under the most pessimistic scenario, glaciers may only remain at the highest summits above approximately 5800 m asl.

Early warning systems: The “last mile” of adaptation

Recent scientific assessment studies of climate change impacts, including those from the Intergovernmental Panel on Climate Change, provide evidence of the negative effects of climate variability and change on natural and human systems. For instance, recent climate trends have caused loss in wheat and maize production, negatively affected coral reefs, and changed characteristics of some hazards in high-mountain regions. Assessment studies furthermore suggest that related risks to ecosystems, commerce, and daily life may increase over the coming decades as temperatures warm. Adaptation to climate change is required to reduce the effects of unavoidable changes, especially for the most vulnerable regions and populations.

Science in the Context of Climate Change Adaptation: Case Studies from the Peruvian Andes

Within the context of the Climate Change Adaptation Program (PACC), a number of scientific investigations on water resources, natural disasters and perceptions by local people highlight adaptation needs in the regions of Cusco and Apurimac in Peru, considering past, present-day and future climate conditions. This chapter compiles their findings and attempts a systematic evaluation with respect to their contributions to climate change adaptation. The studies consistently find aggravating water scarcity during the dry season (April to September) due to projected precipitation decreases and reduced storage capacity of shrinking glaciers. Impacts include below-capacity hydropower generation and increased crop failure risks. For natural disasters, database inconsistencies prevent a detection of trends. While the natural science studies have produced a new and more comprehensive understanding of the target regions, their implications for society have hardly been investigated anthropologically. One of the few social science studies emphasizes that climate change is only one out of many determinants of rural livelihoods in the target regions, which have not been addressed scientifically yet. We thereby find an imbalance of available scientific knowledge regarding natural vs. social sciences. Overcoming such imbalance would allow for a more comprehensive integration of scientific findings into design and implementation of adaptation measures within the local context.

On the extraordinary winter flood episode over the North Atlantic Basin in 1936

In this study, we analyze the linkage between atmosphere and ocean modes and winter flood variability over the 20th century based on long‐term flow‐discharge series, historical archives, and tree‐ring records of past floods in the North Atlantic Basin (NAB). The most extreme winter floods occurred in 1936 and had strong impacts on either side of the Atlantic. We hypothesize that the joint effects of sea surface temperatures (SSTs) over the Atlantic and Pacific Oceans and the Arctic Oscillation (AO), which is closely related to the North Atlantic Oscillation, play a significant role when describing flood variability in North America and Europe since 1900. Statistical modeling supports the assumption that the response of flood anomalies over the NAB to AO phases is subsidiary of SST phases. Besides, we shed light on the extraordinarily winter flood of 1936 that was characterized by very high SSTs over both the Atlantic and Pacific (>98th percentile) and very low, negative values of AO (<1st percentile). This outstanding winter flood episode was most likely characterized by stratospheric polar vortex anomalies, which can usually be linked to an increased probability of storms in western and southwestern Europe and increased snowfall events in eastern North America. By assessing the flood anomalies over the NAB as a coupled AO and SST function, one could further the understanding of such large‐scale events and presumably improve anticipation of future extreme flood occurrences.

Climate corridors for strategic adaptation planning

Purpose Although the importance of climate change is generally acknowledged, its impacts are often not taken into account explicitly when planning development projects. This being due to limited resources, among others, this paper aims to propose a simple and low-cost approach to assess the viability of human activities under climate change. Design/methodology/approach Many human activities are feasible only within a narrow range of climatic conditions. Comparing such “climate corridors” with future climate projections provides an intuitive yet quantitative means for assessing needs for, and the viability of, adaptation activities under climate change. Findings The approach was tested within development projects in Pakistan, Peru and Tajikistan. The approach was shown to work well for forestry and agriculture, indicating positive/negative prospects for wheat in two districts in Pakistan, temperature constraints for maize in Peru and widening elevation ranges for walnut trees in Tajikistan. Practical implications Climate corridor analyses feed into the preparation of Local Adaptation Plans of Action in Pakistan. Originality/value The simplicity and robustness of climate corridor analysis allow for efficient analysis and communication of climate change impacts. It works when data availability is limited, but it can as well accommodate a wide range of complexities. It has proven to be an effective vehicle for mainstreaming climate change into adaptation planning.