Vulnerability to Water Scarcity and Glacier Fed Water Availability, Peru

Runoff from glaciers in the Cordillera Blanca dominates water availability in the Callejn de Huaylas, Peru, during the pronounced dry season (May - August) as well as during the transitional periods after and before the wet season (November - March). Different user groups have adapted to these conditions, including respective seasonal and year to year variability, through long traditions in water management techniques. E.g. channel systems and water distribution rules date as far back as pre-Inca epochs. Both aspects, the glacier runoff and the societal structures in the region, have been subject of intensive studies since several decades. Both rural society and climate driven glacier runoff are now undergoing substantial changes which increasingly lead to water related conflicts. The implementation of adaptation and mitigation measures lack from insufficient knowledge and understanding of drivers and processes that interact in a complex way in a system of socio-political structures and environmental conditions. With this joint project study we propose a three way analytical approach in which MODULE 1 analyses vulnerabilities of rural households and relevant power relations in a study area east of the regional capital city of Huarz and MODULE 2 identifies processes and consequently models glacier runoff from the water shed of the study area. In MODULE 3 the major challenge will be to jointly identify the time scales and magnitudes of glacier runoff variability and the respective relevance for rural families` vulnerabilities in order to identify temporal and spatial interferences of the natural and the societal processes. MODULE 1 covers the full spectrum of socio- political varieties from pastoral use of the highest valley floors to densely populated and cultivated areas in the lowest portions, typical for the entire region. MODULE 2 investigates glacier dominated runoff from the Shallap basin which is subject of ongoing glaciological studies of our research group since 1999 (3 FWF projects) by combining detailed glacier mass balance modelling with the tracing of runoff characteristics in different conceptual steps downriver. Observed and analyzed present day conditions will be the basis for scenarios under potential future climate change. These two modules use each their classical and proved methods whereas in MODULE 3 the questions that need to be answered from both perspectives shall be approached in an incessant iterative and active inter-disciplinary way. We aim for providing enhanced knowledge and understanding on a complex problem which shall become beneficial to a wide spectrum of science fields, stakeholder groups, and policy makers (at different levels from local to national up to the global international) and NGO organizations.

Within this project we worked on water availability and water demand questions in Quebrada Shallap, an area with a glacierfed river and small peasant settlements. Within a first step we applied an advanced model approach to calculate glacier mass gain and loss (=melt water production) at hourly time steps. Before we could use model results we had to compare them against measured changes of the glacier surface height caused by mass gain (snow fall) and mass loss (mainly melt). We found that the previously tested model approach yielded results markedly differently than the measurements in some periods or at some points. The reason for the lower model skill at our study site compared to other regions was found to be the very frequent change in surface conditions between snow free (relatively dark glacier ice exposed) and snow covered (relatively bright surface conditions) on our glacier. Combined with the high amounts of solar radiation throughout the year (due to the location close to the equator) these frequent changes control glacier melt. We could improve the model to better deal with these conditions and we have published the magnitudes of the detected model uncertainty to give clear hints to other scientists working with similar methods. Building upon these improvements we could estimate glacier mass gain and loses as well as glacier surface energy fluxes (mainly radiation fluxes and turbulent heat exchange) for a two year period with high temporal resolution. From our results we found that despite the typically low variations of temperature in the Tropics, slight differences in temperature between the two years have markedly impacted the amount of liquid and solid precipitation, and consequently the glacier mass balance (sum of mass losses and gains). For Tropical glaciers this temperature effect has not been detected before. Coming back to water demand and water availability, from our interrogations we meanwhile found that surprisingly, only few famers had access to riverfed irrigations systems and thus, mainly depended on rainfed farming. However, peasants stated that rainfed farming has become more challenging in the last decades due to changing precipitation characteristics (e.g. later onset of the wet season or more irregular precipitation during the wet season including heavy precipitation events harming plants). Motivated by these statements we have analyzed daily precipitation records available in the region for the last 20-40 years in detail but couldnt find clear evidence for the human perceptions on changed precipitation patterns. As only few precipitation data were available and human memories are also unprecise it is not fully clear yet which information source is more reliable. In any case there were many other environmental and social changes (deforestation, soil erosion, changes in crop types, decrease in product prices, loss of man power,) besides climate change in the region that could have negatively impacted water availability/demand or generally small scale farming. It would be interesting to further investigate the whole range of changes and their impacts on peasant communities.