Water flux from soil under extreme temperature and precipitation, in the region of major agricultural production in Argentina

PENALBA O.C., PÁNTANO V,

Santiago de Chile

Conferencia; 11th International Conference on Southern Hemisphere; 2015

Extreme events of temperature and rainfall have a socio-economic impact in the rainfed agricultureproduction region in Argentina. These extreme conditions may produce different responses of soil. The flux ofwater returning to the atmosphere is limited by water and energy availability, depending on precipitationand temperature, among other factors (runoff, wind, etc). The aim of this study is to analyze the flux of waterfrom soil under extreme events, through evapotranspiration in global circulation models. Becauseevapotranspiration also depends on vegetation and soil parameterizations, seven independent models ofWCRP/CMIP5 were used. The study was focused on the region of major agricultural production in Argentina:region of rainfed production, for the period 1970-2005, for monthly mean temperature, precipitation andevapotranspiration, during January and July. Initially, mean monthly precipitation and temperature werevalidated in comparison with reanalysis data from GPCC, ERA-Interim and University of Delaware reachingless than 125 mm and 5 °C mean square error and correlation of 0.4 to 0.9 and larger than 0.95, respectively.In order to identify the threshold that defines an extreme event representative for water balance studies,three categories were considered for low (less than 20th, 10th, and 5th percentiles) and high (more than80th, 90th and 95th percentile) values. Different conditional probabilities were evaluated: percentage ofevapotranspiration below/above extreme thresholds, under extreme conditions of precipitation ortemperature. There is a weaker response of evapotranspiration to extreme temperature than extremeprecipitation conditions. In general, when using more extreme thresholds, conditional probabilities decrease.This means that under more extreme weather conditions, the soil response is not necessarily as extreme,because the memory of it may diminish the impact. During July, conditional probabilities of extremeevapotranspiration reach 50% under extreme precipitation and below 17% under extreme temperature, forCanESM2. ACCESS1.0 and MIROC5 also present strong difference between both variables: most above 30%under extreme precipitation and most below 10% under extreme temperature. For CESM1-CAM5 and EC-EARTH, conditional probabilities are barely higher for extreme precipitation (between 12 and 40%) thanextreme temperature (between 10 and 30%). Finally, for IPSL-CM5A-MR and MPI-ESM-MR, difference ismarkedly different using the most extreme threshold: below 6% under extreme temperature and between 12and 20% under extreme precipitation. Conditional probabilities under extreme precipitation are higherduring January, except for CanESM2, while values are lower under extreme temperature. This means that, ingeneral, extreme temperature conditions do not lead to extreme evapotranspiration while extreme high andlow precipitations lead to extreme evapotranspiration (between 20 and 60% of the times). Finally, for bothmonths, when analyzing the more extreme threshold, high values cause stronger impact than low valueswhile the opposite is identified when using 20th and 80th percentile. This study will let us evaluate theregions of greater soil response to extreme precipitation under different climate scenarios. The impact ofthese extreme events depends on the vegetation and soil parametrization and the time of the year. However,water limitation and supply have a stronger influence on water flux from soil to the atmosphere.