Soil Water Deficit, its Variability during the Last Forty Years in Buenos Aires Province, (Argentina)

O. E. SCARPATI; ALBERTO D. CAPRIOLO; L. B. SPESCHA,

Santiago

Congreso; International Geographical Union (IGU). Regional Geographic Conference. United and Integrated with the World; 2011

International Geographical Union (IGU)

The presence of extreme hydrologic events in Buenos Aires province (Argentina) had been a constant in its social - economic development. Their impacts mainly over the agriculture have been studied with different scales and point views. In spite of that there is a lack of studies of temporal and spatial distribution. Drought is initiated by a reduction in precipitation which leads to a shortage of water relatives to a demand of water, in one or more of the useable water supplies which include ground water, soil moisture, snow coverage, reservoir storage and streamflow. The time requires for a lack of precipitation to create a significant deficit in these five supplies is quite variable and could vary from a few weeks to several years. Since the beginning of the 20th century, many authors have elaborated aridity or bioclimatic indexes through empirical approaches based on some combination of climatic variables. All these indexes have the limit to use only climatic data and they do not consider soil properties. Several kinds of information are needed to monitor drought. It is necessary to have a tool that can lead to identify the more vulnerable areas on which effective measures should be carried out. The goal of this paper is the study of the soil water deficit from 1968 to 2008 in the 16 sectors of this province according its basins (defined by the National Water Resources) and with soil water budget. The soil water balance was performed using the evapotranspitation formula of Penman - Monteith and considering the soil water constants: Field Capacity, Soil Water Moisture and Soil Wilting Point for the different types of soils of the Buenos Aires province (307,571 km2). For the statistical study, the series of soil water deficit data obtained were adjusted by means of the theoretical Normal Cubic-root probability distribution. An annual threshold value of 200 mm is considered because it is an ecological limit and upper which the drought is the consequence. The data series present values upper than 400 mm in some years. The drought has been arbitrary classified in: mild, moderate, severe and extreme according the annual values reached. Statistical significance for annual trend using Mann Kendall test is found in two sectors.