Assimilation of TRMM Precipitation into a Hydrological Model of a Southern Andes Watershed

Abstract

This paper presents results of assimilation of TRMM precipitation into a hydrological model of Los Almendros River watershed, assessed by the comparison of simulated stream flow values to observed stream flow data. Los Almendros River is a tributary to the Clarillo River, located in Reserva Nacional Rio Clarillo (National Reserve Clarillo River), Chile, South America. Los Almendros basin, covering approximately 4.9 km², is a typical Andean watershed with an average slope of 46.3. It drains an average of 18.5 L/s from a catchment area covered predominantly by grasslands (91%), while forests and savanna land cover types are less predominant (3% and 6% respectively). The hydrological model of Los Almendros watershed was developed using the Hydrological Simulation Program Fortran (HSPF). Results showed that raw TRMM precipitation time-series overestimated disaggregated precipitation values for the whole period of analysis. TRMM data required time-averaging for the monthly and annual values to be in the same range as those of disaggregated data. Time-averaging produced daily precipitation time-series consistent to disaggregated data (R²=0.85). The use of TRMM-enriched precipitation time-series for hydrological modeling of stream flow at Los Almendros watershed outlet, slightly improved a previous simulation in which only disaggregated precipitation dataset was used. When comparing simulated and observed data, the statistical fit coefficient improved from R²=0.64 (corresponding to only disaggregated precipitation data introduced into the hydrological model) to R²=0.68 (corresponding to TRMM-enriched precipitation data).