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

Southwestern Intermittent and Ephemeral Stream Connectivity

Ephemeral and intermittent streams are abundant in the arid and semiarid landscapes of the Western and Southwestern United States (U.S.). Connectivity of ephemeral and intermittent streams to the relatively few perennial reaches through runoff is a major driver of the ecohydrology of the region. These streams supply water, sediment, nutrients, and biota to downstream reaches and rivers. In addition, they provide runoff to recharge alluvial and regional groundwater aquifers that support baseflow in perennial mainstem stream reaches over extended periods when little or no precipitation occurs. Episodic runoff, as well as groundwater inflow to surface water in streams support limited naturally occurring riparian communities. This paper provides an overview and comprehensive examination of factors affecting the hydrologic, chemical, and ecological connectivity of ephemeral and intermittent streams on perennial or intermittent rivers in the arid and semiarid Southwestern U.S. Connectivity as influenced and moderated through the physical landscape, climate, and human impacts to downstream waters or rivers is presented first at the broader Southwestern scale, and secondly drawing on a specific and more detailed example of the San Pedro Basin due to its history of extensive observations and research in the basin. A wide array of evidence clearly illustrates hydrologic, chemical, and ecological connectivity of ephemeral and intermittent streams throughout stream networks.EPA ORD; USDA-ARS Southwest Watershed Research CenterThis article is a U.S. Government work and is in the public domain in the USA.This item from the UA Faculty Publications collection is made available by the University of Arizona with support from the University of Arizona Libraries. If you have questions, please contact us at [email protected]

Hydrological modeling of green infrastructure to quantify its effect on flood mitigation and water availability in the high school watershed in Tucson, AZ

Green Infrastructure (GI) practices are being implemented in numerous cities to tackle stormwater management issues and achieve co-benefits such as mitigating heat island effects and air pollution, as well as water augmentation, health, and economic benefits. Tucson, Arizona is a fast-growing city in the semiarid region of the southwest United States and provides a unique landscape in terms of urban hydrology and stormwater management, where stormwater is routed along the streets to the nearest ephemeral washes. Local organizations have implemented various GI practices, such as curb cuts, traffic chicanes, roof runoff harvesting, and retention basins, to capture the excess runoff and utilize it on-site. This study models the 3.31 km2 High School watershed in central Tucson using the Automated Geospatial Watershed Assessment (AGWA) tool and the Kinematic Runoff and Erosion (KINEROS2) model. Each parcel in the watershed was individually represented using the KINEROS2 Urban element to simulate small-scale flow-on/flow-off processes. Seven different configurations of GI implementation were simulated using design storms, and we stochastically generated 20 years of precipitation data to understand the effects of GI implementation on flood mitigation and long-term water availability, respectively. The design storm analysis indicates that the configuration designed to mimic the current level of GI implementation, which includes 175 on-street basins and 37 roof runoff harvesting cisterns, has minimum (<2%) influence on runoff volume. Furthermore, the analysis showed that the current level of GI implementation caused an increase (<1%) in peak flows at the watershed outlet but predicted reduced on-street accumulated volumes (>25%) and increased water availability via GI capture and infiltration. When the GI implementation was increased by a factor of two and five, a larger reduction of peak flow (<8% and <22%, respectively) and volume (<3% and <8%, respectively) was simulated at the watershed outlet. The 20-year analysis showed that parcels with roof runoff harvesting cisterns were able to meet their landscape irrigation demands throughout the year, except for the dry months of May and June. Additionally, stormwater captured and infiltrated by the on-street basins could support xeric vegetation for most of the year, except June, where the water demand exceeded volume of water infiltrated in the basins. The current level of GI implementation in the High School watershed may not have significant large-scale impacts, but it provides numerous benefits at the parcel, street, and small neighborhood scales. © 2021 by the authors. Licensee MDPI, Basel, Switzerland.Open access journalThis item from the UA Faculty Publications collection is made available by the University of Arizona with support from the University of Arizona Libraries. If you have questions, please contact us at [email protected]

Importance des corrections radiométriques dues au relief pour les données SAR du satellite ERS-1 : applications à l'hydrologie

[Notes_IRSTEA]bibl., ill., graph. [Departement_IRSTEA]GT [TR1_IRSTEA]GMA1-Fonctionnement hydrologique des bassins et des réseaux hydrographiquesNational audienceThis paper deals with the retrieval of surface soil moisture (0-5 cm) from ERS-1 SAR images in a hilly semi-arid rangeland (Walnut Gulch watershed, Arizona). The main purpose is to enlighten the necessity of calibration of the raw image by correcting for the backscattering area of each pixel. The backscattering area is simulated using a digital elevation model (40m resolution) and the results show that the calibration coefficient has a 8 dB range over the watershed and that the calibrated backscattering coefficient is decreasing with the local incidence angle. The correlation between surface soil moisture measurements and backscattering coefficients is significantly improved when the calibrated data are used, giving a sensitivity of 0.19 dB/% soil moisture. Despite the spatial variability of other parameters affecting the backscattering coefficient (soil roughness, vegetation), this relationship can still be used to detect relative change in surface soil moisture from image ratio technique if we assume constant soil roughness and vegetation properties in time.Ce papier présente une méthode d'utilisation des images SAR du satellite ERS-1 pour la détermination de l'humidité de surface du sol (0-5 cm) en zone semi-aride, sur un bassin versant de l'Arizona (Walnut Gulch). Le principal objectif est de démontrer la nécessité de calibrer les données brutes de l'image en tenant compte de l'aire de rétrodiffusion de chaque pixel. Une nouvelle méthode de correction se basant sur une simulation d'aire à partir d'un MNT (Modèle Numérique de Terrain) est ainsi testé et montre que le coefficient de calibration peut alors varier dans une gamme de 8 dB sur le bassin versant. L'analyse des résultats montre qu'il est également possible de tenir compte de la dépendance angulaire du coefficient de rétrodiffusion avec l'angle d'incidence local. La comparaison des rétrodiffusions brutes et calibrées avec des données de terrain d'humidité du sol permet de montrer l'amélioration de la relation humidité avec les données calibrées et d'en déduire une relation statistique. Une sensibilité de 0.19 dB/% d'humidité est aini déterminé. Malgré la variabilité spatiale d'autres paramètres influant sur le, tels que la rugosité du sol et la quantité de végétation, cette relation permet d'établir, en supposant ces paramètres stables dans le temps, des cartes d'évolution de l'humidité du sol à partir de ratios d'images entre différentes dates

A GLOBAL RAIN-DRIVEN SOIL EROSION INVESTIGATION BASED ON SIMULATED BREAKPOINT PRECIPITATION

Recent research has highlighted problems with erosion modeling applications that use coarser fixed-interval precipitation data as opposed to breakpoint precipitation data, which better preserves precipitation characteristics such as intensity and duration. Due to their wider availability, erosion modeling applications and risk assessments are typically based on fixed-interval data. However, these applications could be subject to substantial erosion underestimation bias related to time-averaged precipitation. Alternatively, this manuscript presents a novel approach to global-scale erosion assessment based on simulated breakpoint precipitation data. A point-scale stochastic weather generator, CLIGEN, was used to generate precipitation events with characteristics more similar to breakpoint precipitation data than fixed-interval alternatives. An international CLIGEN dataset of climate parameters from more than 10,000 long-term climate stations in numerous countries was evaluated for use in parameterizing CLIGEN simulations. CLIGEN-simulated event characteristics and derived statistics such as annual rainfall erosivity were compared to high-quality, high-resolution NOAA-ASOS precipitation data where available. The Rangeland Hydrology and Erosion Model (RHEM) was used to predict runoff and soil loss based on the same CLIGEN inputs for simple bare soil scenarios with site-specific soil textures taken from the global 250m SoilGrids product. Erosion results were analyzed according to climate type, revealing that predicted distributions of sediment yield and runoff were statistically unique for most global climate types. A multivariate regression model was developed to explore and understand the importance of various precipitation input factors. Peak precipitation intensity was the most critical climate factor for determining sediment yield, and combined CLIGEN precipitation factors had approximately as much predictive power as soil texture. Average annual rainfall erosivity values were calculated for each location and were 25% and 20% greater than values from RUSLE2 and Panagos et al. (2017) estimates, respectively. This finding is in agreement with the latest research on the topic. © 2022 American Society of Agricultural and Biological Engineers.Immediate accessThis item from the UA Faculty Publications collection is made available by the University of Arizona with support from the University of Arizona Libraries. If you have questions, please contact us at [email protected]

Estimation de l'humidité du sol en zone semi-aride au moyen de données SAR ERS-1 dans le cadre d'une approche multi-capteur de suivi du bilan d'énergie

[Departement_IRSTEA]GT [TR1_IRSTEA]GMA1-Fonctionnement hydrologique des bassins et des réseaux hydrographiquesThis paper describes the preliminary results concerning surface soil moisture estimation using ERS-1 SAR data in the framework of the "Walnut Gulch 92" experiment. This experiment was conducted to investigate the potential use of combined visible-thermal-radar remote sensing data to monitor seasonal changes of biophysical parameters and of energy balance in semi-arid rangelands, such as the Walnut Gulch watershed, Arizona. The seven images used here (processed as MLD products by the CCRS) showed that radar backscatter so temporal trend followed quite well surface soil moisture Hs and rainfalls, despite some calibration problems. At this step of the study, a restricted vegetation data set did not allow us to accurately explain the observed radar signal. However, "water cloud model" with standard parameterization showed that vegetation attenuation of soil backscatter could result in a strong dispersion in the so /Hs relationship.L'expérimentation "Walnut Gulch 92" a été menée dans une zone semi-aride de l'Arizona (bassin versant de Walnut Gulch) afin d'étudier les possibilités offertes par la complémentarité de différents domaines spectraux (visible, thermique, radar) pour le suivi de paramètres biophysiques et du bilan d'énergie. Les aspects radar de l'étude présentés ici ont montré une bonne corrélation entre l'évolution de la rétrodiffusion (sept images MLD du CCRS) et l'évolution de l'humidité superficielle du sol Hs et de la pluviométrie, malgré certains problèmes de calibration des images. A cette étape de l'étude, certaines données de végétation manquantes ont empêché d'interpréter complètement le signal radar observé. Cependant, l'utilisation d'un "modèle goutte d'eau" paramétré de manière standard a montré que la végétation pouvait atténuer de manière non négligeable la rétrodiffusion issue du sol et augmenter ainsi la dispersion de la relation so =f(Hs)