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172 JOURNAL OF HYDROMETEOROLOGY VOLUME 16 Physically Based Mountain Hydrological Modeling Using Reanalysis Data in Patagonia SEBASTIAN A. KROGH Department of Civil Engineering, Universidad de Chile, Santiago, Chile JOHN W. POMEROY Centre for Hydrology, University of Saskatchewan, Saskatoon, Saskatchewan, Canada JAMES MCPHEE Department of Civil Engineering, and Advanced Mining Technology Center, Universidad de Chile, Santiago, Chile (Manuscript received 30 October 2013, in final form 15 August 2014) ABSTRACT A physically based hydrological model for the upper Baker River basin (UBRB) in Patagonia was de- veloped using the modular Cold Regions Hydrological Model (CRHM) in order to better understand the processes that drive the hydrological response of one of the largest rivers in this region. The model includes a full suite of blowing snow, intercepted snow, and energy balance snowmelt modules that can be used to describe the hydrology of this cold region. Within this watershed, snowfall, wind speed, and radiation are not measured; there are no high-elevation weather stations; and existing weather stations are sparsely distributed. The impact of atmospheric data from ECMWF interim reanalysis (ERA-Interim) and Climate Forecast System Reanalysis (CFSR) on improving model performance by enhancing the representation of forcing variables was evaluated. CRHM parameters were assigned for local physiographic and vegetation characteristics based on satellite land cover classification, a digital elevation model, and parameter transfer from cold region environ- ments in western Canada. It was found that observed precipitation has almost no predictive power [Nash– Sutcliffe coefficient (NS) , 0.3] when used to force the hydrologic model, whereas model performance using any of the reanalysis products—after bias correction—was acceptable with very little calibration (NS . 0.7). The modeled water balance shows that snowfall amounts to about 28% of the total precipitation and that 26% of total river flow stems from snowmelt. Evapotranspiration losses account for 7.2% of total precipitation, whereas sublimation and canopy interception losses represent about 1%. The soil component is the dominant modulator of runoff, with infiltration contributing as much as 73.7% to total basin outflow. 1. Introduction comprehensive hydrometric network, the processes re- sponsible for the hydrology of Patagonia are poorly Chilean Patagonia contains some of the largest water understood, and so the reliability of historical information reserves in the southern cone of South America. Tied for streamflow prediction cannot be evaluated. In light of with economic growth, increasing energy demands have ongoing environmental change, hydrological investiga- turned public attention to the region’s rivers (the largest tions are crucial to achieve a better understanding of en- in Chile) and their yet untapped hydropower potential. vironmental systems dynamics and their possible response Although the statistical properties of flow for the major to human interference across spatial and temporal scales. rivers in the area are known because of a reasonably A particular concern is climate change, which has recently resulted in substantial glacier retreat in the region (Rivera et al. 2007) with unknown impacts on river flow. Corresponding author address: James McPhee, Department of Civil Engineering, Universidad de Chile, Av. Blanco Encalada In spite of these concerns, very few studies of the hy- 2002, Santiago 8370449, Chile. drology and climatology of the region have been con- E-mail: [email protected] ducted. Aravena (2007) developed a 400-yr precipitation DOI: 10.1175/JHM-D-13-0178.1 Ó 2015 American Meteorological Society Unauthenticated | Downloaded 10/02/21 11:37 PM UTC FEBRUARY 2015 K R O G H E T A L . 173 reconstruction using tree ring data and glacier fluctua- infiltration through frozen soils, and cold water bodies tions in the Austral Chilean Andes, finding important control the hydrograph timing. CRHM has a limited decadal variations for the northwest and central Patago- need for calibration (Pomeroy et al. 2007), and most nia and also a strong biannual oscillation for the south- (but not all) of its parameters can be inferred from in- ernmost region. Garreaud et al. (2009) described the tensive field or modeling studies. This, together with its mean annual and decadal patterns of precipitation in modular nature and open structure, makes it particularly South America and how they are influenced both by cli- suitable for testing hydrological hypothesis in poorly matic indexes (Pacific decadal oscillation, Antarctic gauged or ungauged basins. Gonthier (2011) developed Oscillation, and El Niño–Southern Oscillation) and oro- the first hydrological study in Chile using CRHM. He graphic effects using a large-scale paleoclimatic approach. analyzed three high mountain basins in the Chilean Lopez et al. (2008) studied variability in snow-covered semiarid Andes (328S), calibrating parameters regarding areas (SCAs) of the Northern Patagonian Ice Field soil moisture and routing processes against streamflow (NPIF) during 2000–06 and correlated SCA to precip- records. All results showed Nash–Sutcliffe coefficient itation and air temperature, obtaining the highest corre- (NS) values below 0.6 and overestimation of snow ac- lations for temperature (r2 5 0.75). Rivera et al. (2007) cumulation up to 400% with respect to local snow pillow quantified decreases in the NPIF of up to 4.0 6 data. Poor modeling results were attributed in part to 2 0.97 m yr 1 for ice thickness and up to 3.2% 6 1.5% or the very low density of meteorological measurements 140 6 61 km2 for area over 1975–2001, based on remote within the basin and thus great uncertainty in meteo- sensing and in situ data. rological driving variables. Fang and Pomeroy (2007) Although the above studies represent improvements developed a CRHM with the aim of understanding the on their respective fields, there remains a major gap in dynamical processes that govern drought phenomena in published comprehensive hydrological investigations in the Canadian prairies. A sensitivity analysis to meteo- the region. Dussaillant et al. (2012) present the first rological input data was carried out, showing that even description of the main hydrological patterns (pre- under moderate drought scenarios of 15% reduction in cipitation, temperature, and streamflow) of the Baker winter precipitation and 2.58C increase in winter mean River basin using observed data. They also discuss the air temperature, spring runoff may disappear com- difficulties associated with undertaking this task given pletely. Ellis et al. (2010) developed a CRHM to assess the sparse distribution of gauging stations, together with the differences in snowmelt and snow accumulation in the significant topographical and climatological gradi- forest and clearing sites, achieving an NS model effi- ents existing in the region. Barría (2010) developed ciency value of 0.51 for snow water equivalent (SWE), a statistical approach for obtaining monthly streamflow with slightly better representation on clearing sites; forecasts for the Baker and Pascua river basins. How- these results show the CRHM predictive potential when ever, because this research was entirely data driven, it no calibration is undertaken. Another study was de- does not increase knowledge of the physical processes veloped by Fang and Pomeroy (2009), who character- governing water movements in the basin. Given the ized blowing snow redistribution in prairie wetlands, combination of climate change and increased pressure obtaining good results either with an aggregated or to use the water resources in the region, it becomes a fully distributed spatial representation. Pomeroy et al. paramount for the scientific and decision-making (2012) developed a CRHM in a forested mountainous community to increase their knowledge on the hy- basin with minimal calibration in order to simulate the drological functioning of this relatively pristine envi- impacts of forest disturbance in the basin hydrology. ronmental system. Results show different streamflow volume responses Physically based models offer the opportunity of for each scenario, ranging from 2% for small forest comprehending physical interactions between processes reduction impacts to 8% for a complete forest-burning and variables within the hydrological cycle, an advan- event. A recent study developed a CRHM for an alpine tage that cannot be achieved with other types of models to subalpine Canadian Rockies catchment and evalu- (empirical, conceptual, or statistical, for example). The ated uncalibrated model performance against snow Cold Regions Hydrological Model (CRHM; Pomeroy accumulation, soil moisture, groundwater, and sub- et al. 2007) is a physically based model developed at the basin and basin streamflow over several years (Fang Centre for Hydrology, University of Saskatchewan, with et al. 2013) with acceptable predictive performance for the aim of improving the understanding of hydrological all variables except groundwater. Tests of CRHM in processes in cold environments, which are particular in alpine and steppe environments of the Qinghai Tibetan the sense that a host of specific phenomena such as snow Plateau show good performance for snowpack, runoff, and ice accumulation, interception, transport and melt, and streamflow simulation when blowing snow, energy Unauthenticated | Downloaded 10/02/21 11:37 PM UTC 174 JOURNAL OF HYDROMETEOROLOGY VOLUME 16 balance snowmelt, and frozen soil infiltration