<p>In the Santa River catchment (Cordillera Blanca) in Peru, water availability is threatened by climate change and socio-economic factors, but little is known about relations and interactions of multiple climatic and non-climatic stressors.</p><p>We developed a conceptual integrated water balance model that combines hydro-climatic and socio-economic scenarios, in order to analyze variability of water resources and water availability in the Santa River basin until 2050. The model is based on a lumped HBV model including a glacier - snow model (GSM) to simulate the hydro-climatic processes. In addition, the model was extended by feedback loops for agricultural and domestic water use. The model was calibrated and validated using the Peruvian Interpolated Data of SENAMHI&#8217;s Climatological and Hydrological Observations (PISCO) temperature and precipitation data. To assess future water balance challenges we used monthly CORDEX scenarios for 2020-2050 for simulations of future changes in hydro-climatology. These climate scenarios are combined with possible socio-economic scenarios, which were based on stakeholder interviews, workshops and analysis of available data and information concerning water demand. The scenarios that describe changes in the future socio-economic conditions were developed by means of Cross-Impact Balance Analysis (CIB), a semi-formalized method from systems analysis which allows the construction of socio-economic scenarios based on an impact network of different (socio-economic) drivers.</p><p>The uncertainty in the climate projections is accounted for by using different global circulation model-regional climate model (GCM-RCM) combinations from CORDEX data. The uncertainty in the socio-economic scenarios was addressed by using possible ranges for future developments in water demand depending on the tendencies provided by the CIB analysis (e.g. increasing, constant or decreasing water demand). The climate and socio-economic scenarios are randomly combined in multiple model runs, which result in an ensemble of possible future discharges of the Santa River for each scenario combination.</p><p>Results suggest that the mean annual discharge is projected to increase by 10% (&#177;12%) driven by an increase in annual precipitation amounts of about 14% (RCP2.6) and 18% (RCP8.5), respectively. In contrast, mean dry-season discharge is projected to decrease by 33% and 36% (&#177;24%) by 2050, for RCP2.6 and RCP8.5, respectively, mainly driven by diminishing glacier melt discharge. We found that the projected socio-economic changes compared to climatic changes are less pronounced mainly due to higher variations in the trends of the global climate models. Nonetheless, the socio-economic drivers have a major effect on dry-season water availability. The increase of wet season and the decrease of dry season discharge call for different adaptation measures including improvements in water use efficiency, infrastructure and storage capacities.</p><p>&#160;</p>
<p>High mountain regions, like the Andes, face various risks due to climate change. In the Santa River catchment in Peru which includes the glaciated Cordillera Blanca, water availability is threatened by many climatic and non-climatic impacts. The water resources in the catchment heavily rely on seasonal precipitation and during the dry season glacier melt water plays an important role. However, both, precipitation patterns and glacier extent are affected by climate change impacts. Additionally, socio-economic changes put further pressure on water resources and hence on water availability.</p> <p>Within the AguaFuturo Project we established a conceptual integrated water balance model based on a semi-distributed HBV model for the data scarce Santa River catchment. The hydrological model processes are extended by feedback loops for agricultural and domestic water use. The model runs on daily time scale and includes two hydrological response units. One includes the irrigated agricultural areas which are predominately located in the valley of the catchment; the other includes non-irrigated areas and domestic water use.</p> <p>To assess future water balance challenges we downscaled and disaggregated monthly CORDEX scenarios for 2020-2050 using information from the new Peruvian precipitation dataset PISCO (Peruvian Interpolated data of the SENAMHI&#8217;s Climatological and hydrological Observations) for simulations of future changes in hydro-climatology. In the model, these climate scenarios are combined with possible socio-economic scenarios which are translated into time series for domestic and agricultural water demand. The socio-economic scenarios are developed by using the Cross-Impact-Balance-Analysis (CIB), a method used for analyzing impact networks. Using CIB, the interrelations between 15 social, economic and policy descriptors were analyzed and as a result a total of 29 possible consistent scenarios were determined. For further analysis and validation of these scenarios a participatory process was included, involving local experts and stakeholders of the study region.</p> <p>The climate and socio-economic scenarios are independent and can be combined randomly. The uncertainties of the climatic and socio-economic scenarios are quantified by Monte Carlo simulations.</p> <p>The output of the model runs is an ensemble of possible future discharges of the Santa River, which can be further analyzed statistically to assess the range of the possible discharges. This evaluation provides an estimate of the probability of water shortages, especially with regard to conflict potential with hydropower production and the large scale irrigated agriculture areas in the adjacent coastal desert which also rely on water from the Santa River.</p>
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