Informations et ressources scientifiques
sur le développement des zones arides et semi-arides

Titre : Evapotranspiración y déficit híbrico en un agostadero representativo de matorral sarcocaule en La Paz, Baja California Sur

Auteur : Mercado Mancera, Gustavo

Etablissement de soutenance : Centro de Investigaciones Biológicas del Noroeste (CIBNOR)

Grade : Maestría en Ciencias en el Uso, Manejo y Preservación de los Recursos Naturales 2006

Résumé
Evapotranspiration (ETP) is defined as water transferred to the atmosphere from ground surface by evaporation and transpiration by plants, which is one of the most important processes and information for sustainable management of water to assess the physiological responses of plants to water deficit. The estimation of ETP is relevant for arid zones because in these areas ETP is commonly greater than rainfall (Pp) throughout the year (Evenari, 1985). This relationship is already known, however, there are no data in the studied zone to provide information about the magnitude of water deficit. Potential evapotranspiration and water deficit were estimated for a representative Sarcocaulescent shrub plant ecosystem in La Paz, Baja California Sur. In addition, hydrologic status and water availability of the studied zone were characterized from monthly averages of Pp and ETP for 25 years (1980 to 2005), with data from climatic stations of La Paz and Alfredo V. Bonfil. The same variables were calculated using monthly averages of Pp and ETP obtained from the climatic stations ‘Observatory’ and ‘La Paz Airport’ with data for nine years (1997 to 2005). The study zone has a dry climate ; the dominant vegetation is Sarcocaulescent shrub and the soil is sandy-loam with clear color. The analyzed data were temperature, precipitation, evaporation, wind velocity, solar radiation, humidity and atmospheric pressure. ETP values were estimated applying four methods : pan evaporation, Thornthwaite, Penmann and Penmann-Montieth. ETP and Pp were considered for the analysis of water deficit. Aridity indexes were estimated according to the methods that were proposed by Lang, De Martonne and PNUMA. Likewise, a water deficit indicator was calculated by means of a hydro-environmental availability index (IDHA), based on De Martonne’s index modified by Troyo (2004). In order to confirm numerical correspondences, analyses of multiple regressions between climatic variables and ETP, and between Pp and IDHA, were carried out. A principal component analysis was applied in order to establish the influence of each climatic variable on ETP. Results showed a greater influence of temperature and evaporation on ETP. Through the multiple regressions, the following equation reduced to its minimum expression was obtained : ETP = 78.8727 + 0.802345*Evaporation - 0.00919186*Humidity - 0.00153907*Precipitation - 0.0755447*Pressure - 0.461159*T. Maximum + 0.719289*T. Medium - 0.310138*T. Minimum. The temperature trend showed an increase in summer and a decrease in winter, with an annual average of 24.3º C. A noticeable deficit of water was observed during the year, caused by low Pp and high ETP, which is indicative of a dominance of dryness, present in the area of study. The application of a hydro-environmental availability index was useful to estimate that dryness is greater in the north of La Paz, thus impacting significantly the use and management of water as a resource. It was concluded that in the area of La Paz there is a climatic water deficit through most part of the year. The hydro-environmental availability index is a practical method for evaluating climatic dryness, applicable to similar conditions as those prevalent in La Paz, Mexico. The obtained data should be considered for planning the use and sustainable management of water resources in agricultural fields, and at the same time for planning strategies for the conservation of plant resources in the study region.

Mots Clés : Evapotranspiración ; índice de aridez ; índice de disponibilidad hidro-ambiental

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