Partición de la evapotranspiración usando isótopos estables en estudios ecohidrológicos

La ecohidrología como disciplina emergente pretende generar conocimiento para entender procesos fundamentales de los ecosistemas en función de la dinámica del ciclo hidrológico. Durante la temporada de lluvias, que coincide con las altas temperaturas en las zonas semiáridas, se desencadenan diversos procesos ecológicos relacionados con el intercambio de agua entre la superficie terrestre y la atmósfera, vía evapotranspiración (ET). A pesar de que existen diferentes metodologías para estimar ET, conocer la proporción de sus componentes, evaporación del suelo (Es) y transpiración de la vegetación (T), en escalas congruentes es todavía complicado. El presente trabajo tiene como objetivo conocer la proporción de T/ET durante un día de la temporada de lluvias en un ecosistema semiárido del noroeste de México, usando isótopos estables como trazadores de los diferentes componentes de la ET. Durante el 24 de julio de 2007 se obtuvo que la proporción T/ET fue de 59 ± 6%, pero mostró una variación importante entre la mañana y la tarde, ya que la T/ET fue de 86 ± 21% por la mañana y decayó a 46 ± 9% en la tarde. Estos resultados apuntan a que durante la mañana la vegetación se mantiene más activa, contribuyendo más a la ET vía T, en contraste con lo que se observa en la tarde. Con el uso de isótopos estables es posible separar la ET en sus componentes en nivel de ecosistema, lo cual permite el avance del conocimiento ecohidrológico

Preface paper to the Semi-Arid Land-Surface-Atmosphere (SALSA) Program special issue

The Semi-Arid Land-Surface-Atmosphere Program (SALSA) is a multi-agency, multi-national research effort that seeks to evaluate the consequences of natural and human-induced environmental change in semi-arid regions. The ultimate goal of SALSA is to advance scientific understanding of the semi-arid portion of the hydrosphere–biosphere interface in order to provide reliable information for environmental decision making. SALSA approaches this goal through a program of long-term, integrated observations, process research, modeling, assessment, and information management that is sustained by cooperation among scientists and information users. In this preface to the SALSA special issue, general program background information and the critical nature of semi-arid regions is presented. A brief description of the Upper San Pedro River Basin, the initial location for focused SALSA research follows. Several overarching research objectives under which much of the interdisciplinary research contained in the special issue was undertaken are discussed. Principal methods, primary research sites and data collection used by numerous investigators during 1997–1999 are then presented. Scientists from about 20 US, five European (four French and one Dutch), and three Mexican agencies and institutions have collaborated closely to make the research leading to this special issue a reality. The SALSA Program has served as a model of interagency cooperation by breaking new ground in the approach to large scale interdisciplinary science with relatively limited resources

Evaporation from irrigated crops : its measurement, modeling and estimation from remotely sensed data

The research described in this dissertation is predicated on the hypothesis that remotely sensed information from climatological satellites can be used to estimate the actual evapotranspiration from agricultural crops to improve irrigation scheduling and water use efficiency. The goal of the enabling research program described here was to facilitate and demonstrate the potential use of satellite data for the rapid and routine estimation of water use by irrigated crops in the Yaqui Valley irrigation scheme, an extensive irrigated area in Sonora, Mexico. The approach taken was first, to measure and model the evapotranspiration and crop factors for wheat and cotton, the most common irrigated crops in the Yaqui Valley scheme. Second, to develop and test a high-resolution (4 km x 4 km) method for determining cloud cover and solar radiation from GOES satellite data. Then third, to demonstrate the application of satellite data to calculate the actual evaporation for sample crops in the Yaqui Valley scheme by combining estimates of potential rate with relevant crop factors and information on crop management. Results show that it is feasible to provide routine estimates of evaporation for the most common crops in the Yaqui Valley irrigation scheme from satellite data. Accordingly, a system to provide such estimates has been established and the Water Users Association, the entity responsible for water distribution in Yaqui Valley, can now use them to decide whether specific fields need irrigation. A Web site (tekapucemitson. mx) is also being created which will allow individual farmers to have direct access to the evaporation estimates via the Internet.hydrology collectio

Soil respiration in Mexico: Advances and future directions

Soil respiration (RS) is a CO2 efflux from the soil to the atmosphere defined as the sum of autotrophic (respiration by roots and mycorrhizae), and heterotrophic (respiration of microorganisms that decompose fractions of organic matter and of soil fauna) respiration. Globally, RS is considered to be the second largest flux of C to the atmosphere. From published literature it is clear that its main controls are soil temperature, soil moisture, photosynthesis, organic matter inputs and soil biota composition. Despite its relevance in C cycle science, there have been only twenty eight studies in Mexico in the last decade where direct measurement of gas exchange was conducted in the field. These studies were held mostly in agricultural and forest ecosystems, in Central and Southern Mexico where mild subtropical conditions prevail. However, arid, semi-arid, tropical and wetland ecosystems may have an important role in Mexico’s CO2 emissions because of their extent and extensive land use changes. From the twenty eight studies, only two provided continuous measurements of RS with high temporal resolution, highlighting the need for long-term studies to evaluate the complex biophysical controls of this flux and associated processes over different ecological succession stages. We conclude that Mexico represents an important opportunity to understand its complex dynamics, in national and global context, as ecosystems in the country cover a wide range of climatic conditions. This is particularly important because deforestation and degradation of Mexican ecosystems is rapidly increasing along with expected changes in climate

Initial response of phenology and yield components of wheat (Triticum durum L., CIRNO C2008) under experimental warming field conditions in the Yaqui Valley

"This work evaluates the experimental warming effects on phenology and grain yield components of wheat in the Yaqui Valley, Sonora, México, using CIRNO C2008 variety from Triticum durum L., as a model during the cropping cycle of 2016–2017 (December to April). Infrared radiators were deployed to induce experimental warming by 2 °C above ambient crop canopy temperature, in a temperature free-air controlled enhancement system. Temperature was controlled by infrared temperature sensors placed in eight plots which covered a circle of r = 1.5 m starting five days after germination until harvest. The warming treatment caused a reduction of phenophases occurrence starting at the stem extension phenophase. Such phenological responses generated a significant biological cycle reduction of 14 days. Despite this delay, CIRNO C2008 completed its biological cycle adequately. However, plant height under the warming treatment was reduced significantly and differences were particularly observed at the final phenophases of the vegetative cycle. Plant height correlated negatively with spikes length, spikes mass, and number of filled grains. Warming also reduced grain yield in 33%. The warming treatment caused a stress intensity (SI = 1-yield warming/yield control) of 39.4% and 33.2% in biomass and grain yield, respectively. The differences in stress intensities between biomass and grain yield were based on plant height reduction. Grain mass was not affected, demonstrating the crop capability for remobilization and adequate distribution of elaborated substances for the spikes under warming conditions.

Determination of crop evapotranspiration of table grapes in a semi-arid region of Northwest Mexico using multi-spectral vegetation index

The main goal of this research is to develop and to evaluate a relationship established between Normalized Difference Vegetation Index (NDVI) and crop coefficient (K-c) for estimating crop evapotranspiration (ETc) of table grapes vineyards (Vitis vinifera L., cvs. Perlette and Superior) in the semi-arid region of Northwest Mexico. Two consecutive growing seasons (2005 and 2006) of continuous measurements of ETc with the eddy covariance system were used to test the performance of the K-c-NDVI relationship. An exponential relation relating K-c to NDVI (R-2 = 0.63) is proposed and tested here as the basis for calculating ETc. The obtained results indicate that the K-c-NDVI approach estimates ETc reasonably well over two growing seasons. The root mean square error (RMSE) between measured and derived ETc from NDVI during 2005 and 2006 were respectively about 0.45 and 0.76 mm day(-1). Some discrepancies between measured and simulated ETc occurred when NDVI saturates at high values, causing the under-estimation of evapotranspiration