Distributed hydrologic modeling in northwest mexico reveals the links between runoff mechanisms and evapotranspiration

Adistributed hydrologicmodel is used to evaluate howrunoffmechanisms-including infiltration excess (R I), saturation excess (R S), and groundwater exfiltration (R G)-influence the generation of streamflow and evapotranspiration (ET) in amountainous region under the influence of theNorthAmericanmonsoon (NAM). The study site, the upper SonoraRiver basin (~9350 km 2) inMexico, is characterized by a wide range of terrain, soil, and ecosystem conditions obtained from best available data sources. Three meteorological scenarios are compared to explore the impact of spatial and temporal variations of meteorological characteristics on land surface processes and to identify the value of North American Land Data Assimilation System (NLDAS) forcing products in the NAM region. The following scenarios are considered for a 1-yr period: 1) a sparse network of ground-based stations, 2) raw forcing products from NLDAS, and 3) NLDAS products adjusted using available station data. These scenarios are discussed in light of spatial distributions of precipitation, streamflow, and runoffmechanisms during annual, seasonal, and monthly periods. This study identified that the mode of runoff generation impacts seasonal relations between ET and soilmoisture in the water-limited region. In addition, ET rates at annual and seasonal scales were related to the runoff mechanism proportions, with an increase in ET when R S was dominant and a decrease in ET when R I was more important. The partitioning of runoffmechanisms also helps explain themonthly progression of runoff ratios in these seasonallywet hydrologic systems. Understanding the complex interplay between seasonal responses of runoff mechanisms and evapotranspiration can yield information that is of interest to hydrologists and water managers. © 2012 American Meteorological Society

Soil Respiration Is Influenced by Seasonality, Forest Succession and Contrasting Biophysical Controls in a Tropical Dry Forest in Northwestern Mexico

Soil respiration (RS) is an important component of the C cycle because it contributes significant CO2 emissions to the atmosphere that result from metabolism and respiration of its autotrophic and heterotrophic components. However, the relative importance of different biophysical controls that drive the variability of this flux and their influence along forest succession pathways is still unknown. We incorporate multiyear RS, ecosystem flux and meteorological measurements in old-growth (OG), mid-secondary (MS) and early-secondary (ES) tropical dry forests (TDFs) with the goal of assessing the temporal variation of RS and identifying the biophysical controls at each site by applying structural equation models (SEM). Along forest succession, RS followed the pattern of precipitation events; we identified by the end of the wet season that RS was sustained by a longer period at OG, while in MS and ES, RS decreased according to the soil moisture availability. According to SEM, soil moisture and soil temperature exert an effect on the variability of RS in all sites. However, we found that RS was also controlled by the vapor pressure deficit at MS and gross primary production at OG and ES. Our results suggest that seasonality has a different impact on RS along forest succession in TDFs found in northwestern Mexico and highlights the relevance of considering additional biophysical controls of RS for a better understanding this critical process of the C cycle

Soil Respiration Is Influenced by Seasonality, Forest Succession and Contrasting Biophysical Controls in a Tropical Dry Forest in Northwestern Mexico

Soil respiration (RS) is an important component of the C cycle because it contributes significant CO2 emissions to the atmosphere that result from metabolism and respiration of its autotrophic and heterotrophic components. However, the relative importance of different biophysical controls that drive the variability of this flux and their influence along forest succession pathways is still unknown. We incorporate multiyear RS, ecosystem flux and meteorological measurements in old-growth (OG), mid-secondary (MS) and early-secondary (ES) tropical dry forests (TDFs) with the goal of assessing the temporal variation of RS and identifying the biophysical controls at each site by applying structural equation models (SEM). Along forest succession, RS followed the pattern of precipitation events; we identified by the end of the wet season that RS was sustained by a longer period at OG, while in MS and ES, RS decreased according to the soil moisture availability. According to SEM, soil moisture and soil temperature exert an effect on the variability of RS in all sites. However, we found that RS was also controlled by the vapor pressure deficit at MS and gross primary production at OG and ES. Our results suggest that seasonality has a different impact on RS along forest succession in TDFs found in northwestern Mexico and highlights the relevance of considering additional biophysical controls of RS for a better understanding this critical process of the C cycle

Calibración in situ del sensor cosmos para determinar humedad del suelo en escalas intermedias (~1 km)

La heterogeneidad del suelo influye ampliamente en el contenido de humedad, dificultando la precisa determinación de este parámetro en estudios con fines hidrológicos y ecológicos que requieren de mediciones continuas y representativas para escalas intermedias (~1 km). En este contexto un sensor de neutrón de rayo cósmico The COsmic-ray Soil Moisture Observing System (COSMOS) permite cuantificar humedad del suelo de manera continua y a escalas espaciales de cientos de metros. El objetivo de este estudio fue evaluar un esquema de calibración para un sensor COSMOS CRS-1000. El estudio se realizó en una sabana de zacate buffel (Pennisetum ciliare) en Rayón Sonora, México. En este sitio se instaló el COSMOS CRS-1000 y para su calibración se realizaron muestreos de suelo en dos etapas. A estas muestras se les determinó el contenido de humedad y su densidad aparente por técnicas gravimétricas. Con el contenido de humedad de estas muestras, expresado en términos volumétricos, se obtuvo por aproximación el parámetro de calibración para el COSMOS CRS-1000. El valor obtenido para este parámetro fue de 4121 conteos por hora (tasa de conteo del neutrón sobre suelo). Con este valor se realizó la corrección a los valores estimados originalmente por el sensor COSMOS CRS-1000. Al realizar esta corrección, se observó un incremento en el contenido de humedad del suelo de 1 a 2 % con respecto a los valores estimados con el COSMOS CRS-1000 en todo el periodo de análisis. A pesar de la variabilidad espacial en el contenido de humedad del suelo bajo estudio, se observó que el sensor COSMOS CRS-1000 tiene la capacidad de proveer estimaciones razonables del contenido de la humedad del suelo de manera continua a una profundidad de 0 a 40 cm, en una superficie de alrededor de 30 ha