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Thirsty World: Hydrology alone doesn’t determine water supply in Peru’s Santa River Basin

Incorporating human behavior into hydrology models is critical to predicting water availability

Over one-sixth of the world’s population lives in snow-and ice-melt-dominated watersheds. Reliant on the temporary storage provided by snowpack and glaciers, these communities currently utilize mountain run-off water for irrigation, energy, municipal water supply, industry and a host of other ecosystem services. Global and local fluctuations in climate are projected to significantly impact freshwater availability worldwide, potentially leaving hundreds of millions of people vulnerable to water stress.
 
Complex climate-glacier run-off models are currently used to analyze changes in water availability, but a 2014 study from the Journal of Hydrology argues this approach is inadequate. Without incorporating human variables, large shifts in water availability are not adequately explained by models focused only on physical and environmental forces. Using a case study approach, Canadian and U.S. researchers show human interventions in water usage, movement and storage account for a large percentage of freshwater availability fluctuations. This study teases out how social, economic, political and cultural drivers have substantially altered river flow using one of Peru’s largest rivers on the Pacific slope, the Santa River, as a case study.
 
On the arid Pacific slopes of Peru, the people of the Santa River Basin rely on waters from the highly glaciated Cordillera Blanca mountain range. Run-off from the 755 glaciers on these tropical peaks comprises 66% of stream flow in the dry season, making critical contributions to food security and community stability. These glaciers lost 36% of their coverage area since the 1930s while water demands from industrialization and urbanization only increased. 
 
Past research, using a technique called end-member tracing, showed peak water loss from the glacier already occurred. This study utilizes hydroelectric company and government records to understand current snowmelt flow patterns. River flow is still influenced by decadal climate cycles like El Niño, but generally demonstrates lower flows and bigger observable differences between seasonal high and low levels. This translates into less water during dry summer months, which can increase stress on populations and croplands.
 
Just analyzing these physical drivers of glacial retreat, however, is not enough to understand the Santa River’s past, present, and future flows. Human land use factors can have a more pronounced impact on watersheds than climate change. Instead of only analyzing hydrologic cycles, the authors develop a five-tiered framework for assessing the human dimensions of water use, including: political and economic influences to infrastructure, changes in governance, technology and engineering developments, land use changes, and grassroots localized community responses.
 
The researchers first explore political and economic influences on water usage, pointing out several key events in the last century, such as:
  • 1929: Greater economic independence resulting from the global economic crisis,
  • 1943: Construction of the Cañón del Pato hydroelectric facility,
  • Late 1900s: The national push for export-oriented agricultural development and the neoliberal privatization of dams and reservoirs.
 
Secondly, governance also affects the amount of water stored in reservoirs, released from dams, and made available for irrigation. Changes in laws and policies impact cost of water, while distribution mechanisms and disputes over policies can stall or accelerate water withdrawal.
 
Thirdly, energy conversion advancements from improved technology and engineering techniques have also changed water use. Energy innovations have increased the Cañón del Pato hydroelectric facility’s capacity from 50 MW to 250 MW since 1958. Greater efficiency translates to more available energy for development. 
 
Next, land use change, such as an increase in surface mining, makes up the fourth major factor impacting water availability. Development of the mining sector dramatically increased water usage. In 2010 there were 1,848 active mining claims in the Basin, predominantly belonging to multi-national corporations. Water-intensive extractive processing is now a major usage for Santa River water.
 
Finally, the authors argue that localized responses to water projects can impact availability. Researchers identify social forces shaping water distribution and storage practices. In one example, citizens blocked reservoir construction by Duke Energy, a large private firm with major global water resource holdings. These drivers led to dramatic changes in water governance and usage, undetectable by traditional hydrologic models.
 
The findings of this case study demonstrate human variables can impact hydrologic processes in addition to interacting with climate drivers. Analyzing temperature and glacial melt run-off rates alone would yield only a partial picture, given the complexities of water distribution in the Santa River Basin. The authors acknowledge the inherent difficulties in gauging lag time between socio-political and cultural responses to changes in water supply. However, they conclude hydro-sociological watershed models are the most accurate method for understanding water use and availability. This study is indicative of a growing need for collaborations between social scientists and hydrologists. These scientific and cultural shifts provide opportunities for widening the input parameters for hydrologic models to include social scenarios. 

 
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Original Paper: Carey M, Barear M, Mark BG, French A, Bury J, Young KR, McKenzie JM. (2013) "Toward hydro-social modeling: Merging human variables and the social sciences with climate-glacier runoff models (Santa River, Peru)." Journal of Hydrology. Pg. 1-11.
 
DOI: http://dx.doi.org/10.1016/j.jhydrol.2013.11.006
 
 
Further Reading:
Barnett TP, Adam JC, Lettenmaier DP. (2005) “Potential impacts of a warming climate on water availability in snow-dominated regions.” Nature. 438 (7066): 303-309
DOI: 10.1038/nature04141
 
Viviroli D, Archer DR, Buytaert W, Fowler HJ, Greenwood GB, Hamlet AF, Huang Y, Koboltschnig G, Litaor MI, Lopez-Moreno JI, Lorentz S, Schadler B, Schreier H, Schwaiger K, Vuille M, Woods R. (2011) “Climate change and mountain water resources: Overview and recommendations for research, management, and policy.” Hydrology & Earth System Sciences. 15: 471-504
DOI: 10.5194/hess-15-471-2011
 

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