Climate Change in the tropical Andes Impacts and consequences for glaciation and water resources Part III: Future recommendations A report prepared by
MATHIAS VUILLE with contributions from RAYMOND S. BRADLEY BERNARD FRANCOU GEORG KASER BRYAN G. MARK
Climate Change in the tropical Andes â€“ Impacts and consequences for glaciation and water resources Part III: Future recommendations A report for CONAM and the World Bank prepared by
MATHIAS VUILLE (University of Massachusetts)
with contributions from RAYMOND S. BRADLEY (University of Massachusetts) BERNARD FRANCOU (IRD) GEORG KASER (University of Innsbruck) BRYAN G. MARK (Ohio State University)
Amherst, Massachusetts, 29. May, 2007
TABLE OF CONTENTS SUMMARY ......................................................................................................................2 1) INTRODUCTION ...................................................................................................3 2) IMPROVE THE OBSERVATIONS .................................................................4 3) IMPROVE THE MODEL PREDICTIONS .....................................................8 4) IMPROVE COLLABORATION AND DISSEMINATION ......................12 REFERENCES ............................................................................................................13
SUMMARY This report recommends several research avenues that would allow for a better assessment of future climate change and its impact on glaciation and runoff in the tropical Andes. First and foremost the current monitoring network needs to be expanded, replaced and improved upon. A suite of high-elevation observation stations including both automated weather stations and glacier mass balance networks is needed. This would allow monitoring climate change at the elevation of the glaciers and not simply at low elevations, where the changes are likely to be much less dramatic. Such observations could be combined with new remote sensing data sets from space to obtain a spatially complete picture. Secondly the climate model applications in the region need to be improved by increased application of higher resolution (regional) climate models. It is desirable that several different models be run in ensemble mode to assess intra-model differences. The model performance over a region with such complex topography as the Andes needs to be carefully validated under modern conditions before SRES-IPCC simulations of future climate can be evaluated. These latter simulations should again be run based on several models and under different emissions scenarios, such as A2 and B2. Climate change simulations can tell us how climate might change in the Andes by the end of the 21st century, but to understand what the impacts on glaciation and runoff are they need to be coupled with a tropical glacier-climate model. When applied to selected target catchments, coupled glacier-climate model simulations can provide us with estimates of when and by how much glaciation and runoff will change. For example they may be able to tell us when and in what catchments glaciers will completely disappear, and at what fraction of their original size they may find a new equilibrium in other catchments. The ramifications of this glacier retreat (or disappearance) for runoff and water availability can equally be assessed with such models. To make these results relevant for water users, there needs to be a framework in place to disseminate the results in a way, which is scientifically correct but also socially relevant and applicable to stakeholders, decision makers and water users. Options for such a framework, which should include collaboration with national entities in Ecuador, Peru, and Bolivia and capacity building through training and education of students at host institutions involved, are discussed.
1) INTRODUCTION The previous reports have outlined the current scientific knowledge of climate change and its impacts on tropical Andean glaciers and hydrology (Part I: The scientific basis) and the ongoing research and monitoring activities by the various institutions currently active in the region (Part II: Climate and Glacier Monitoring). They provide the scientific basis that can be used in support of the decision-making process to find the best adaptation and mitigation strategies for the region and an overview of the currently installed scientific network. It is clear that some practical measures to adapt and prepare for future changes in runoff behavior need to be implemented without delay (e.g. conservation, shift to less water-intensive agriculture, creation of water reservoirs, etc., see Vergara, 2005), but at the same time significant progress needs to be made on the scientific front. This third and final report (Part III: Future Recommendations) suggests a number of research strategies that would allow answering some of the most urgent scientific questions related to Andean climate change. These strategies include: a) improvement and expansion of the current monitoring network, b) combining improved surface measurements with advanced remote sensing and GIS applications, c) improved climate modeling at higher resolution (regional climate models), with a variety of different models and based on a number of different IPCC-SRES emission scenarios, d) coupling of these regional climate models with a tropical glacier-climate model to assess the implications for glacier mass balance and water resources at a catchment-scale level, and finally e) improved collaboration and dissemination of results to local stakeholders in a fashion that is not only scientifically relevant, but also socially applicable. All these recommendations come with significant costs, but given the observed changes already under way and the dramatic changes projected for the future (see Part I) it is quite obvious that adapting to these changes will be inevitable. It is our firm belief that implementation of adequate adaptation strategies is not possible without sufficient knowledge and a high level of scientific understanding of the processes involved. For example, one of the emerging results from studies performed to date is that the hydrologic response to climate change may vary significantly from one catchment to the next, depending on the degree of glaciation, catchment hypsometry and the sensitivity of glaciers to various climate parameters. If we add to these differences in catchment response all the uncertainties surrounding future greenhouse gas emissions (which SRES scenario is most likely?), and all the discrepancies between different regional climate models, it is very clear that we still have along way to go to better understand the impacts of future climate change on Andean glaciers. Investing in climate monitoring and basic scientific research, therefore, in our opinion is money well spent.
2) IMPROVE THE OBSERVATIONS One of the most urgent tasks is to expand and improve the existing observational network of automated weather stations and glacier mass balance networks. The currently installed network is inadequate to accurately monitor the rapid changes that are taking place in the Andean climate and cryosphere. Many of the weather stations and stream gauges currently operating were installed in the middle of the 20th century (Mark and Seltzer, 2005). They are old and outdated and need to be replaced with more up-to date instrumentation (see Figure 1 for an example of an automated high-elevation weather station). It is hard to believe but true, that we are currently not in a position to accurately monitor and document the rapid changes taking place at high-elevation sites in the tropical Andes. The anticipated expansion of the installed network by eight stations (2 each in four countries), financed by the World Bank, therefore serves as a very welcome major step in the right direction.
Figure 1: Example of a high-elevation AWS design from the summit of Sajama volcano, 6550m, Cordillera occidental, Bolivia (photo credit: D.R. Hardy).
Such a network, in a first phase should focus on certain target areas, but eventually it needs to be expanded to become a connected network of sites along climatic gradients from north to south as well as across the Andes from east to west (Francou et al., 2005; Coudrain et al., 2005; Kaser et al., 2005; Casassa et al., 2007). It is of utmost importance that these stations be deployed at high elevation, near or on glaciers, where projected changes in climate are large, and not simply at low elevations, where the changes are likely to be much less dramatic (Bradley et al., 2004, 2006). The planned Global Climate Observing System (GCOS) of the World Meteorological Organization for
example, does not adequately address this problem. GCOS is a plan for long-term, high quality observations at rural locations to establish a global climate monitoring network that will provide unequivocal data to assess climate changes (Bradley et al., 2004). As shown in Figure 2 all planned GCOS stations are well below the freezing levels and only 3 stations are currently planned for elevations above 3000 m in the entire transect. It is evident from Figure 2 that the GCOS network will not adequately sample the higher elevation zones of the American Cordillera where the impact of changes in climate are likely to be greatest.
Figure 2: Mean annual change in temperature (2Ă— CO2 minus control runs) derived from 7 models, and compared to the planned GCOS network (squares). More stations at higher elevations are needed to properly assess the model projections and monitor the large changes that the models indicate will affect high montane regions. The small black triangles represent the highest elevation mountains in countries along the transect (Bradley et al., 2004).
Finally these stations would provide valuable information not only for climate change detection and attribution, but also for validation of model studies. Currently it is very difficult to asses how realistic climate models simulate climate at such high elevations sites, simply because of the lack of in-situ climate observations. Interpreting model projections of future climate change however, fist requires an accurate model validation of the present-day control runs. An additional benefit of installing such a network on glaciers would be that they could be equipped to record much needed information on glacier energy balance. So far only a handful of stations with these capabilities have been installed on tropical Andean glaciers (see Part II: Climate and Glacier Monitoring). The network installed and maintained by the IRD seems a logical starting point from where to expand. However, it is important that the glacier monitoring network, in a next step be extended to include larger glaciers as well. We desperately need more data on the behavior of large glaciers, which may show less sensitivity to climate change and therefore offer the best hope to retain some catchments water retention capacity in a warmer world. Despite the logistic
difficulties, these large glaciers must also be monitored in the future, albeit probably based on new techniques, such as repeated laser scanning. Installing new AWS is urgent, but it is equally important that a commitment for maintaining these stations for a number of years (preferable a decade or longer) is made. The value of theses stations increases with the length of their climate record retrieved, and installing new stations is rather pointless if their maintenance and proper functioning can not be guaranteed for at least the next 5-10 years. Servicing and repairing stations is costly and labor-intensive, but without such a maintenance data quality will rapidly deteriorate and the stations will eventually be lost. AWS located on glaciers for example need to be constantly raised or lowered in order to prevent them from being buried by snow or melting out and tipping over (depending whether they are installed on the ablation or accumulation zone). Frequent exchange of instruments is necessary in order to recalibrate sensors or replace damaged instruments. In summary, the financial costs involved in maintaining such a network for several years are high and go well beyond the initial costs of station deployment. It involves costs for spare parts and instruments, costs for training local personnel and finally a commitment for financial support of the persons in charge of maintaining these stations over a period of several years. To effectively discern the changing climatic impact on glaciers and hydrology that affects human society, glacier mass balance and climate monitoring need to be combined with instrumentation throughout the watershed, culminating in stream discharge. Stream discharge measurements are a critical component of the network because they are an effective net yield of the hydrological cycle for the watershed. Combined with good precipitation gauges, these provide first order mass flux terms to determine the relative role of glacier melt water where people utilize the water resource. Finally, while networks of glacier, climate and runoff measurements sites are important and needed, they are also costly, labor-intensive and by their very nature limited in space. They should therefore be complemented by increased use and application of available remote sensing techniques and data sets from space. New advances in combining digital elevation models, SRTM data, GPS and satellite data such as Landsat, ASTER and SPOT, offer the opportunity to give a more detailed large-scale picture of changes in both the atmosphere and the cryosphere. While they are no substitute for on-site measurements, they can provide a much needed complementary picture. The Peruvian Andes, for example have been selected as a priority site to monitor glaciers with ASTER data under the Global Land Ice Measurements from Space (GLIMS) umbrella (Mark and Seltzer, 2005). Initial studies of glacier monitoring from space have shown very encouraging results (e.g. Georges, 2004; Jordan et al., 2005; Silverio and Jaquet, 2005; Raup et al., 2006, Racoviteanu et al., 2007). New initiatives, such as the Japanese Space Agency Advanced Land Observing Satellite (ALOS) will provide additional, high-resolution remote sensing capabilities to monitor glacier change in the tropical Andes (W. Vergara, pers. comm., 2007).
3) IMPROVE THE MODEL PREDICTIONS Apart from the needed improvements in on-site and remote monitoring, it has also become increasingly clear that we need better and more detailed scenarios of future climate change in this region of steep and complex topography. Output from GCMâ€™s can at best provide us with a broad-brush perspective. High-resolution regional climate models, which allow for a better simulation of climate in mountain regions, coupled with tropical glacier-mass balance models, such as the one used by Juen et al. (2007) could provide the necessary scientific breakthrough to better understand and predict future climate changes and their impacts on tropical Andean glaciers and associated runoff. Vuille (2006) recently proposed such a modeling strategy, which should allow us to establish robust projections of how glaciation and runoff will change in this region at the end of the 21st century. Figure 3 shows how such a research strategy, involving a multidisciplinary team, could provide much needed information for policy- and decisionmakers, with potentially far reaching implications.
Figure 3: Flow chart of proposed modeling and validation studies, and participation of members during the stages of the project (Vuille, 2006).
Step 1 â€“ Regional Climate Modeling. Regional climate models (RCMs) can be used to simulate both current and future climate in the tropical Andes. They can provide much more realistic simulations of present and future climate change in the Andes than 7
would be possible based on GCMs. There are however, significant differences between models, which makes it imperative to compare results from more than just one model (Roads et al., 2003). Results can also differ depending on model resolution (Rojas, 2006), domain choice (Rauscher et al., 2006), or whether the driving model is based on reanalysis data or data from a GCM (Seth and Rojas, 2003; Rojas and Seth, 2003; Seth et al., 2004, 2006). To date no comprehensive assessment exists regarding regional climate model performance for the Andes. Clearly the Andes provide a particularly difficult challenge, given the complex topography with steep climatic gradients ranging from tropical rainforest in the east to absolute desert on the Pacific coast. On the other hand, however, the Andes are also a region where regional climate models could yield the most significant improvement, as the coarse GCMs are not capable of resolving the geographic complexity of regional climate. For the central Andes (~300 km wide) for example, at least 6 (12) grid-points are placed over the mountain range and its slopes for a 50 (25) km resolution; in contrast the Andes are represented by only 2 or 3 grid points in a coarser GCM of 2.5° resolution. Figure 4 illustrates the improved spatial resolution of a regional model, by showing the remarkably detailed total cloud cover fields along the Andes. These fields show significantly more spatial detail and structure, especially along the Andes, than similar diagnostics in a GCM or in reanalysis data.
Fig. 4: Total fractional cloud cover simulated in PRECIS for DJF 1979/80 (left) and JJA 1980 (right).
In the research strategy proposed in Figure 3 two regional climate models are used: PRECIS, which is a new version of the Hadley Center Regional Climate Modeling System, and RegCM3. Both models are available at the Climate System Research Center and could therefore be run at the University of Massachusetts, Amherst. PRECIS can be run under Linux on a high-end PC at either 50 × 50 km or 25 × 25 km resolution. RegCM3 is commonly run at 50 × 50 km or 80 × 80 km resolution. Potentially, if
available, a third model, such the Earth Simulator from the Meteorological Research Institute, Japan could supplement this suggested modeling strategy. Step 2 – Model validation. All climate models intended for use in future climate change scenarios need to be validated under present day conditions first, to assess their capabilities of accurately simulating current climate. A model which can not reproduce today’s observed climate with reasonable accuracy will likely not provide adequate projections of future climate change either. In addition, if certain biases in the regional climate model (e.g. excess precipitation in the tropical Andes) are known, these can be taken into account when interpreting results from future climate change scenarios. Validation of regional climate models with observational data (both in-situ and from space) is therefore an important step toward a realistic prediction of regional climate change. Finally it is important to keep in mind that a higher resolution does not automatically imply a better model performance. If the GCM produces an erroneous climate over South America, so will the RCM. Any errors in the GCM predictions will be carried through to the RCM simulation. Step 3 – Glacier climate Modeling. Once the models have been validated and their biases are known, the modeled climate data can serve as input into a glacier-climate model to evaluate how glaciers and glacial runoff respond to climate. The best currently available model is the ITGG 2.0-R, developed by the Innsbruck Tropical Glaciology Group. It has the advantage of being specifically designed to meet the particular climatic conditions of glaciers in the tropics (Kaser et al., 2005). The ITGG 2.0-R model simulates tropical glacier mass balance with reasonable accuracy and it has been successfully applied to simulate the seasonal cycle of mass balance (Kaser, 2001), as well as seasonal and interannual variations of glacial runoff (Juen, 2006; Juen et al., 2007) in the Cordillera Blanca in Peru. The glacier-climate model is applied to selected catchments, which will have to be selected based on certain requirements and priorities. Obviously catchments where downstream water use is heavily dependent on glacial runoff are of highest priority, but validation of the glacier-climate model requires that mass balance and runoff records of sufficient quality are available from the catchments (see step 4). The main challenge which up to now has precluded the more wide-spread use of this and other glacier-climate models in the tropics is the need to feed them with climatic input data of high enough quality so that accurate predictions of glacier advance or retreat are possible. Unfortunately the necessary input variables, such as accumulation, albedo, atmospheric emissivity, incoming solar radiation and air temperature are not routinely measured in the tropical Andes. Hence very little is known how these parameters have changed in recent decades, let alone how they might be affected by increased greenhouse gas concentrations. This is where regional climate models can provide a significant scientific advance as they offer the opportunity to improve the simulation of these parameters, but also to assess how they might change under various greenhouse gas scenarios. Step 4 – Model –Data Comparison. Similar to the RCM, the ITGG 2.0-R model also needs to be calibrated and validated before it can be used for future glacier-climate scenarios. This validation is done by comparing the simulated mass balance and runoff
(when fed with data from the regional model) with observational records. This necessary validation procedure explains why the application of the model is restricted to catchments where mass balance or runoff records are available. Juen et al. (2007) for example successfully simulated the observed runoff in the Llanganucco catchment in the Cordillera Blanca with this model (Fig. 5). The comparison of mass balance and runoff simulations fed with data from the regional climate model with observational records allows assessing the uncertainty and accuracy of the present-day simulations. This is an important step to quantify the error bars in the climate change simulations (Step 5).
Figure 5: Modeled (qmod) and measured (qmeas) monthly mean runoff depths for the validation period 1975 to 1985 in the Llanganucco catchment, Cordillera Blanca, Peru (Juen et al., 2007).
Step 5 – Climate Change Assessment and Impacts on Glaciation and Runoff. Once the ITGG 2.0-R model simulates streamflow that is comparable to observations (Figure 5), the entire cascade of the flow chart in Figure 3 is rerun, but this time based on IPCC- SRES scenarios. These final analyses will yield estimates of how glacier mass balance at selected target sites in the Andes will change under different greenhouse gas emission scenarios (for example for the years 2070-2100) and how it might affect streamflow and water resources in these previously glaciated watersheds. Vuille (2006) suggested focusing on the A2 and B2 simulations, as these are high and low emissions scenarios, which can bracket the most likely climate change, but theoretically these simulations can be run with any emission scenario. While the IPCC SRES-A2 scenario is based on a medium-high emission and high population-growth scenario (15 billion people by 2100), greenhouse gas emissions and population growth are much lower in the B2 scenario (10.4 billion by 2100). Although there is no ‘most likely’ scenario, the SRES-A2 simulation is expected to give a clear signal of climate change against the noise of natural variability, thereby providing robust patterns of change. The B2 scenario on the other hand will provide a lower-end projection of climate change. When combined and run as ensembles based on different RCMs , the two scenarios span a broad range of future changes in emissions and population growth and will yield an estimate of the upper and lower bounds of the expected change in climate, glaciation and runoff.
4) IMPROVE COLLABORATION AND DISSEMINATION A number of recent workshops have tried to establish a collaborative research network in the Andes to improve collaboration and integration, and to facilitate information and data-sharing between agencies and institutions (Francou and Coudrain, 2005, Diaz et al., 2006, Casassa et al., 2007). The research frame work proposed in the previous sections could equally be used to initiate a closer collaboration and jump-start this process, once adequate funding is in place. It is a research strategy which combines the scientific strengths of the various institutions involved, such as climate dynamics and climate modeling (UMass-Amherst), on-site climate- and glacier- monitoring (IRD), glacier-climate modeling (ITGG Innsbruck), and glacier-runoff hydrology (Ohio State). It is only by having such a multi-disciplinary team, where every partner involved brings his or her scientific expertise to the table, that scientific breakthroughs and significant advances will be made. Given the challenges that nations such as Peru or Bolivia face, such an effort will yield a high return compared to the costs required. Much of the proposed work could be done in collaboration with local partner agencies in Ecuador, Peru and Bolivia. Such collaboration should include exchange of scientific expertise, education and capacity building. This could be achieved, for example, through summer schools (one is already planned by IRD for September 2007 in Lima), fellowships, and through training and education of South American students at the involved partner universities in the U.S., Austria or France. A successful training course in mass balance measurements for example, was organized in La Paz in 2005 by IRD, the International Commission on Snow and Ice (ICSI) and UNESCO (Francou and Ramirez, 2005). To be truly relevant and successful, scientific results need to be disseminated to the public, especially to local populations affected by climate change, but also to stakeholders and decision makers at various levels. After all the glacier-climate research in the tropical Andes is relevant not only from a purely scientific stand point but has very direct and immediate applications in the region. In addition the problems surrounding a future water shortage in Andean countries are not only climatic in nature but also a result of the economic and social developments in the region. One of the challenges to scientists is therefore to provide scientific information which is not only scientifically relevant but also socially applicable (Mark, 2007). One starting point for such an exchange would be to organize a meeting of all partners involved (scientists, decision makers, users), with visits to selected catchments where the most significant impacts on glacier hydrology are expected. This could be a meeting under the umbrella of the Mountain Research Initiative (MRI), or organized by the World Bank, CONAM or the IRD. This would ascertain that both climatic and socio-economic factors be taken into consideration when discussing adaptation and mitigation strategies. Such a discourse between scientists, policy- and decision makers and water users might also help closing the disjuncture, often observed between scientific and technical studies examining hydrologic resources, the national institutions involved in water management and the demands and needs of the local population (Young and Lipton, 2006). It is our hope that the three reports provided here will in some way contribute to this goal.
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Published on Jul 23, 2012
Climate Change in the tropical Andes – Impacts and consequences for glaciation and water resources - Part III: Future recommendations A repo...