The dynamics of cultivation and floods in arable lands of central Argentina

EF VIGLIZZO; EG JOBBÁGY; LV CARREÑO; FC FRANK; RM ARAGON; L DE ORO; VS SALVADOR

HYDROLOGY AND EARTH SYSTEM SCIENCES

Copernicus International

Lugar: Bruselas; Año: 2009 vol. 13 p. 491 - 502

1027-5606

Although floods in watersheds have been associatedwith land-use change since ancient times, the dynamicsof flooding is still incompletely understood. In this paperwe explored the relations between rainfall, groundwaterlevel, and cultivation to explain the dynamics of floods in theextremely flat and valuable arable lands of the Quinto riverwatershed, in central Argentina. The analysis involved anarea of 12.4 million hectare during a 26-year period (1978–2003), which comprised two extensive flooding episodes in1983–1988 and 1996–2003. Supported by information fromsurveys as well as field and remote sensing measurements,we explored the correlation among precipitation, groundwaterlevels, flooded area and land use. Flood extension wasassociated to the dynamics of groundwater level. While nocorrelation with rainfall was recorded in lowlands, a significantcorrelation (P<0.01) between groundwater and rainfallin highlands was found when estimations comprise a timelag of one year. Correlations between groundwater level andflood extension were positive in all cases, but while highlysignificant relations (P<0.01) were found in highlands, nonsignificant relations (P>0.05) predominate in lowlands. Ouranalysis supports the existence of a cyclic mechanism drivenby the reciprocal influence between cultivation and groundwaterin highlands. This cycle would involve the followingstages: (a) cultivation boosts the elevation of groundwaterlevels through decreased evapotranspiration; (b) as groundwaterlevel rises, floods spread causing a decline of landcultivation; (c) flooding propitiates higher evapotranspirationfavouring its own retraction; (d) cultivation expands againfollowing the retreat of floods. Thus, cultivation would triggera destabilizing feedback self affecting future cultivationin the highlands. It is unlikely that such sequence can work inlowlands. The results suggest that rather than responding directlyand solely to the same mechanism, floods in lowlandsmay be the combined result of various factors like local rainfall,groundwater level fluctuations, surface and subsurfacelateral flow, and water-body interlinking. Although the hypotheticalmechanisms proposed here require additional understandingefforts, they suggest a promising avenue of environmentalmanagement in which cultivation could be steeredin the region to smooth the undesirable impacts of floods