Rainfall elasticity of the main river discharges in La Plata basin

CARLA GULIZIA; INÉS CAMILLONI

Ciudad del Cabo

Congreso; Joint IAPSO-IAMAS-IAGA Assembly; 2017

IAPSO-IAMAS-IAGA

The main objective of the present study is to comprehend the amplification of the hydrological response in La Plata basin (LPB) in South America, and thus evaluate to what extent precipitation is able to explain runoff changes and variability. For this purpose, six sub-basins corresponding to the main rivers of LPB are selected within 1931-2010 period. Monthly runoff data was gathered from hydrological stations at six closing points and areal-averaged precipitation was derived from the Global Precipitation Climatology Centre gridded dataset. Comparing sub periods 1931-1970 and 1971-2010, precipitation exhibit an increase in the latter period (4% to 6% in all sub-basins, except 11% in Uruguay River basin), while runoff positive changes are amplified, ranging between 27% and 37%. Given the non-linear relationship between precipitation and runoff, a non-parametric runoff elasticity index is calculated over each of the six sub-basins considering separately the period 1931-2010 and the two 40-yrs sub-periods, as well as for El Niño, La Niña and Neutral events? years, respectively. The elasticity index associates the percent change in runoff given a unit percent change in climate (i.e. represented by precipitation). The more recent period, after 1970, exhibits smaller elasticity indices than the previous one for almost all river basins. These results could be partially explained by the possible influence of land-use change activities in LPB streamflows. Two additional parameters (coefficient of variation (CV) and amplification) at different timescales (annual, decadal and centennial) are analyzed. The CV is calculated as the ratio between the standard deviation and the long-term mean for each hydrological variable. The ratio between runoff and precipitation CVs is considered as an indicator of the streamflow?s variability amplification relative to that of precipitation. Runoff CVs are considerably higher than precipitation CVs for all basins, which consequently exhibits runoff amplification, especially for El Niño years. However, CV corresponding to 1931-2010 period is explained to a greater extent considering only the ENSO neutral years. Furthermore, traditional Budyko Framework equations are also applied to infer observed runoff variability amplification, with consistent results particularly at the annual and decadal timescales.