About climate variabilitiy leading the hydric condition of the soil in the rainfed region of Argentina.

PANTANO VC, PENALBA OC

Cancun

Congreso; AGU Meeting of the Americas; 2013

Extreme events of temperature and rainfall have a socio‐economic impact in the rainfed agricultureproduction region in Argentina. The magnitude of the impact can be analyzed through the water balancewhich integrates the characteristics of the soil and climate conditions. Changes observed in climate variablesduring the last decades affected the components of the water balance. As a result, a displacement of theagriculture border towards the west was produced, improving the agricultural production of the region. Theobjective of this work is to analyze how the variability of rainfall and temperature leads the hydric conditionof the soil, with special focus on extreme events.The hydric conditions of the soil (HC= Excess‐ Deficit) were estimated from the monthly water balance(Thornthwaite and Mather´s method, 1957), using monthly potential evapotranspiration (PET) and monthlyaccumulated rainfall (R) for 33 stations located in the region of rainfed agriculture production in Argentina(period 1970‐2006). Information of temperature and rainfall was provided by National Weather Service andthe effective capacity of soil water was considered from Forte Lay and Spescha (2001). An agriculturalextreme condition occurs when soil moisture and rainfall are inadequate or excessive for the developmentof the crops. In this study, we define an extreme event when the variable is less (greater) than its 20% and10% (80% and 90%) percentile.In order to evaluate how sensitive is the HC to water and heat stress in the region, different conditionalprobabilities were evaluated. There is a weaker response of HC to extreme low PET while extreme low Rleads high values of HC. However, this behavior is not always observed, especially in the western region.This marginal zone shows a limitation for agriculture production: extreme high and low PET show a strongerinfluence over the HC.Finally, to analyze the temporal variability of extreme PET and R, leading hydric condition of the soil, thenumber of stations presenting extreme conditions was computed for each month. As an example,interesting results were observed for April. During this month, the water recharge of the soil is crucial to letthe winter crops manage with the scarce rainfalls occurring in the following months. In 1970, 1974, 1977,1978 and 1997 more than 50% of the stations were under extreme high PET; while 1970, 1974, 1978 and1988 presented more than 40% under extreme low R. Thus, the 70´s was the more threatened decade of theperiod. Since the 80`s (except for 1997), extreme dry events due to one variable or the other are mostlypresented separately, and over smaller areas. The response of the spatial distribution of HC is stronger whenboth variables present extreme conditions. In particular, during 1997 the region presents extreme lowvalues of HC as a consequence of extreme low R and high PET.Communities dependent on agriculture are highly sensitive to climate variability and its extremes. In thestudied region, it was showed that scarce water and heat stress contribute to the resulting hydric condition,producing strong impact over different productive activities. Extreme temperature seems to have a strongerinfluence over extreme unfavorable hydric conditions.