Design and application of a simple rainfall‐runoff statistical model in La Plata Basin

GULIZIA, CARLA; HANNART, ALEXIS; CAMILLONI, INÉS

Santiago de Chile

Conferencia; 11th Meeting of the International Conference on Southern Hemisphere Meteorology and Oceanography; 2015

American Meteorological Society

La Plata basin (LPB) is the fifth largest basin in the world and thesecond in South America. Much of its economy comes from agriculture andhydroelectric power generation which are both highly vulnerable toprecipitation variability and change. Given its socio-economic importance, itis essential to generate information that is relevant to hydrologists and waterresources managers. However, one challenge to achieve this goal is that theperformance of the classical hydrological distributed models is highlyconstrained by the complexity of the hydrological system and the limited availabilityof data to describe it accurately. This constraint is particularly important inlarge river basins such as LPB where observations are limited. On the contrary,a simple statistical model in which calculations can be undertaken with littlecomputational resources and minimal information on the basin?s state, may beuseful to understand more clearly specific aspects of a river basin?s responseat a large scale. For instance, an approach using such a low complexityrainfall-runoff statistical model (RRM) may allow to assess the extent to whichthe climate forcing variability explains runoff variability. The main objectiveof this study is to apply this approach to properly understand the long-termrelationship between three hydroclimatic variables: precipitation,evapotranspiration, and streamflow. For this purpose, a RRM is developed withinthe unit hydrograph framework under a linear regression setting and using theTurc-Pike empirical estimation to represent evapotranspiration. The model isevaluated over three main rivers of LPB: Paraguay, Parana and Uruguay,considering the period 1931-2010. Overall, river discharges derived by our RRMcaptured well observed streamflows variability, though significant deficiencieswere found in Paraguay River in representing extreme fluctuations. Uruguaysub-basin had shown both the variability and magnitude fairly well represented.The skill of the RRM to represent observed river discharges at the monthly andannual scale is quantified for each sub-basin based on mean square error. Particularlyin Parana and Paraguay rivers, RRM captured very accurately some aspects of theannual cycle (at monthly basis, 66% and 47% of the total variance wasexplained, respectively). Uruguay River simulations were able to explain morethan 60% of the total observed variance of monthly runoff and 90% at the annualscale. In addition, RRM performance in Uruguay River basin is compared with theone derived by the state-of-the-art VIC hydrological model. The RRM is found tooutperform the VIC model on periods where limited data was available to run thelatter, and to perform only slightly worse otherwise, thus highlighting thepotential of the RRM for studies of the hydroclimatic variability on largeriver basins that are poorly observed, and for the generation of futurehydrological scenarios under climate change.