Runoff Generation at Sub-basin Scale in Peru (Pacific and Titicaca Basins)

The hydrological model GR2M (Global Rainfall-runoff two Parameter Model) developed by CEMAGREF (Center for Agricultural Research and Environmental Engineering of France) was proposed for the reconstruction of runoff, using precipitation and potential evapotranspiration, it was possible to generate runoff from 1981 to 2015 within the sub-basins in the Pacific and the Titicaca watershed.

In the present research, an adaptation of the GR2M model was used from a sub-basin approach (with aggregation in cascades, for which the sub-basin aggregation topology was performed) for the generation of runoff in a semi-distributed approach. Two parameters are considered in the model: the maximum storage capacity of production X1 (mm), the maximum storage capacity of the transit tank X2 (mm). For the disaggregation of the model, the basin was discretized in sub-basins of aggregation up to the outlet of the integral watershed.

The selected basins were 26 in the Pacific and 4 in the Titicaca watershed. Precipitation and Potential Evapotranspiration data used correspond to the PISCO product (peruvian interpolation of the SENAMHI`s climatological and hydrological data observed) elaborated by the National Service of Meteorology and Hydrology of Peru (SENAMHI) of 5 km of spatial resolution from 1981 to 2015. The X1 Parameter was estimated on the soil water holding capacity map developed by the IRD (Institut de recherche pour le développement), which was obtained together with parameter X2 through global optimization having as function the Nash-Sutcliffe efficiency objective, it was later possible to regionalize the parameters of the model through an analysis of similarity between the neighboring basins without data.

With the calibrated model, we proceeded to reconstruct the runoff for the period 1981-2015 in the integral basins of the Pacific and Titicaca watershed, besides to the sub-basins, the model has responded satisfactorily for the generation of monthly runoff with a semi- distributed approach, it represents an important tool for the watershed management within the Pacific and Titicaca basins.