Variability and changes of daily climate extremes over northeastern Argentina

ERNESTO H. BERBERY; MIGUEL A. LOVINO; MÜLLER, OMAR V.; GABRIELA V. MÜLLER

Vienna

Congreso; EGU General Assembly; 2019

Climate in northeastern Argentina poses great challenges to the population that needs to cope with extreme events.Climate variability and changes are leading to an increased vulnerability which in turn can produce unprecedenteddisasters. This study investigates the long-term changes and interannual variability of daily temperature andprecipitation extremes, discusses their impacts on agriculture and human settlements, and assesses to what extentglobal reanalyses reproduce the observed variability. Climate extremes are characterized in space and time byrelevant indices, like those proposed by the Expert Team on Climate Change Detection and Indices. The leadingmodes of variability were detected with spectral analysis, and their spatial distribution was assessed throughnonparametric trends.The results confirm that temperature extremes are changing towards warmer conditions. Since 1990 thenumber of warm days has been increasing, while the number of cold days has been decreasing. Likewise, warmand cold nights show a significant signal of warming, although the trend seems to be stabilizing in recent decades.The duration of heat spells increased while cold spells decreased in recent decades. At present, heat spellsalmost double the frequency and duration of cold spells. Longer heat spells are associated with longer dry spellsimpacting a region where intense agricultural activity is rainfed. Changes in temperature regimes are importantfor agriculture when the spells agree with the crops? critical periods. The growth periods of maize and sunflowerare sensitive to the increase of warm days, leading to a reduction of their yields. On the other hand, the decreasein cold nights shortens crops? critical growth periods reducing wheat and barley yields. Likewise, the decreaseof cold days may reduce the flowering and yield of winter wheat. More relevant for health, the longer durationof heat waves may increase the population mortality risk by heat strokes and produce more frequent collapses ofenergy systems.Intense precipitation events in most of the region increased steadily since 1970. The intensity and frequencyof annual maximum 1-day and 5-day precipitation events increased from the 1970s to the 2000s, stabilizing inrecent years. The increased intensity of heavy precipitation events constitutes a growing risk for urban settlementswhere heavy rainfall may exceed the capacity of drainage systems, causing significant infrastructure losses and, inthe most extreme cases, deaths. Intense precipitation events in the predominantly flat agricultural plains lead toextensive waterlogging with significant economic impacts due to loss of crops and decreased livestock productivity.A similar analysis based on reanalysis data (ERA-Interim and NCEP2 reanalysis) reveals mixed results.ERA-Interim can recognize temperature extremes in time and space, while the older NCEP2 presents systematicbiases. Both reanalyses reproduce dry spells and the annual maximum 5-day precipitation with large biases, whichare particularly noticeable at each observation station. Although reanalyses would be expected to add informationfor climate extremes in areas of scarce observations, they still need to be used with great caution and only as acomplement to observations.