The tropical Andes are one of the regions of the globe where recent climate change is most evident, consistent with the notion that high-elevation mountain ranges that extend into the mid-troposphere will experience greater warming. As a result glaciers are receding throughout the tropical Andes, with potentially severe consequences for the availability of drinking water, and water for irrigation, mining and hydropower production. General Circulation Models (GCMs) run with a 2.CO2 scenario predict an additional warming of more than 2.5.C by the end of the century. However large uncertainties exist about these future projections, especially because the coarse resolution of GCMs is inadequate to resolve the meso- and local-scale circulation features associated with the steep Andean topography. To accurately understand and predict future climate change and its impact on tropical Andean glaciers, higher resolution models and a better simulation of variables other than temperature are required. We propose to simulate climate variability and change in the Andes under both presentday conditions (1961-90 and 1958-2001) and two different IPCC-SRES emission scenarios (2071-2100) with a regional climate model (PRECIS) to gain a better understanding of how future climate change might affect tropical Andean glaciers. Results from our regional climate model will be validated with observational data from space before they are used as input into a glacier-climate model (ITGG 2.0) to simulate how glacier mass balance will be affected by future climate change. The simulated present-day mass balance of selected glaciers will be compared with observational records from the tropical Andes to verify the accuracy of our results. To gain a better understanding of the consequences of glacier retreat, the ITGG 2.0 model will also be used to simulate changes in runoff from Andean watersheds. The anticipated results of our proposed research are: 1) The use of a high-resolution model will improve simulations of climate in this area of complex terrain and yield more accurate predictions of future climate change than are available to date from GCM.s. 2) An in-depth model validation with observational data will lead to a better assessment of model performance (for both the RCM and the ITGG 2.0). 3) We will for the first time establish robust projections of how glaciation and runoff will change in this region at the end of the 21st century. This has important implications for the anticipated future water shortage in the region and will provide much needed information to implement adaptation and mitigation strategies. 4) Finally we anticipate a significant model improvement as a result of using regional climate model data instead of course resolution reanalysis data as input into the ITGG 2.0 model. We strongly believe that our proposed research addresses a key issue related to future climate change in the tropical Andes, which is of high scientific interest but also of primary socio-economic relevance for the region. The potential for a future water crisis is evident and this water shortage is related to a projected future change in runoff, due to the observed rapid glacier retreat. The scientific merit of this proposal is therefore to gain a better understanding of both mechanisms and consequences related to the disappearance of tropical Andean glaciers. This increased knowledge on how fast and how far glaciers will recede and how much this will affect future runoff and water availability from the Andes will have a significant and broad impact on local economies and populations. Without a better and much more detailed knowledge of how future climate change will affect glaciological and hydrological systems in the Andes, no mitigation and adaptation strategies can be put in place.
