Alfonso Senatore

Regionalization of the Hargreaves Coefficient for the Assessment of Distributed Reference Evapotranspiration in Southern Italy

AbstractThe Hargreaves equation (HE) is the most reliable and diffused temperature-based method for the estimate of the reference crop evapotranspiration ETo in areas with limited meteorological data. Several studies proposed its further enhancement by adopting correction equations for recalibrating its parameters, specifically the empirical Hargreaves coefficient, C=0.0023. In this paper, a local recalibration for southern Italy is shown, taking as a reference the Food and Agriculture Organization of the United Nations (FAO) Penman-Monteith (PM) equation applied over 137 (34 coastal and 103 inland) meteorological stations, allowing the estimation of 357,920 daily ETo values in the period 1994–2011. Through a regression analysis, the adjusted Hargreaves coefficients (AHC), minimizing the errors for each individual station between the HE and the FAO Penman-Monteith equation, and providing better performances than the original HE applied at the monthly scale, were correlated to the available daily meteorolo...

A model based on cellular automata for the parallel simulation of 3D unsaturated flow

Cellular automata (CA) are discrete dynamic systems that are used for modeling many physical systems. They are often used as an alternative to model and solve large-scale systems where the use of partial differential equations involve complex and computationally expensive simulations. The purpose of this work is to investigate the use of CA based techniques for modeling and parallel simulation of water flux in unsaturated soils. Unsaturated flow processes are an important topic in several branches of hydrology, soil science and agricultural engineering dealing with soil-atmosphere interaction, subsurface flow and transport processes. In this paper a CA model for 3D unsaturated flow simulation is proposed using an extension of the original computational paradigm of cellular automata. This model, aimed at simulating large-scale systems, uses a macroscopic CA approach where local laws with a clear physical meaning govern interactions among automata. Its correctness is proved by CAMELot system, which allows the specification, parallel simulation, visualization, steering and analysis of CA models in the same environment, using a friendly interface and providing at the same time considerable flexibility. The model has been validated with reference multidimensional solutions taken from benchmarks in literature, showing a good agreement, even in the cases where non-linearity was very marked. Furthermore, using some of these benchmarks we present a scalability analysis of the model and different quantization techniques aimed at reducing the number of messages exchanged and the execution time when simulations are characterized by scarce mass interactions.

The SCALEX Campaign: Scale-Crossing Land Surface and Boundary Layer Processes in the TERENO-preAlpine Observatory

AbstractScaleX is a collaborative measurement campaign, collocated with a long-term environmental observatory of the German Terrestrial Environmental Observatories (TERENO) network in the mountainous terrain of the Bavarian Prealps, Germany. The aims of both TERENO and ScaleX include the measurement and modeling of land surface–atmosphere interactions of energy, water, and greenhouse gases. ScaleX is motivated by the recognition that long-term intensive observational research over years or decades must be based on well-proven, mostly automated measurement systems, concentrated in a small number of locations. In contrast, short-term intensive campaigns offer the opportunity to assess spatial distributions and gradients by concentrated instrument deployments, and by mobile sensors (ground and/or airborne) to obtain transects and three-dimensional patterns of atmospheric, surface, or soil variables and processes. Moreover, intensive campaigns are ideal proving grounds for innovative instruments, methods, and...

DISTRIBUTED ESTIMATION OF ACTUAL EVAPOTRANSPIRATION THROUGH REMOTE SENSING TECHNIQUES

Evapotranspiration (ET) is one of the main water balance components, and its actual value appears to be the most difficult to measure directly. Therefore, the choice of reliable models capable of predicting spatially distributed actual ET represents a drought monitoring fundamental aspect. This chapter presents a brief introduction to the main remote sensing methods for ET estimate and, by means of ground ET measurements carried out through eddy covariance systems at three different sites in southern Italy, analyzes the performance given by the Surface Energy Balance Algorithm for Land (SEBAL) model using images of the Moderate Resolution Imaging Spectroradiometer (MODIS) on areas characterized by different physiographic and vegetative conditions (sparse vegetation, crop canopy and high mountain vegetation). The distributed results obtained for different days from summer 2004 to summer 2006 on a wide southern Italian area pointed out generally good ET predictions in the eddy covariance sites, also if some differences arose depending on the type and density of vegetation

Sensitivity of Modeled Precipitation to Sea Surface Temperature in Regions with Complex Topography and Coastlines: A Case Study for the Mediterranean

AbstractAn analysis of the effects of SST representation on precipitation in long-term continuous simulations was carried out for the Mediterranean peninsula of Calabria, Italy, which is characterized by complex coastlines and orography. A parameterization analysis was performed to find an optimal model configuration, using a method where SST fields are directly ingested from NCEP datasets into the Weather Research and Forecasting (WRF) Model lower boundary condition files. The results of the optimal configuration were used for a comparison with recorded precipitation patterns for a very wet period (from November 2008 to January 2009), adopting several interpolation options available in the WRF Preprocessing System. An additional comparison was made against a uniform variation of the original SST fields by e = ±0.5 K. It was found that the interpolation options mainly affect near-coastline SSTs, where methods requiring fewer source data points have several advantages. Effects of SST representation on prec...

Worldwide assessment of the Penman–Monteith temperature approach for the estimation of monthly reference evapotranspiration

When not all the meteorological data needed for estimating reference evapotranspiration ETo are available, a Penman–Monteith temperature (PMT) equation can be adopted using only measured maximum and minimum air temperature data. The performance of the PMT method is evaluated and compared with the Hargreaves–Samani (HS) equation using the measured long-term monthly data of the FAO global climatic dataset New LocClim. The objective is to evaluate the quality of the PMT method for different climates as represented by the Köppen classification calculated on a monthly time scale. Estimated PMT and HS values are compared with FAO-56 Penman–Monteith ETo values through several statistical performance indices. For the full dataset, the approximated PMT expressions using air temperature alone produce better results than the uncalibrated HS method, and the performance of the PMT method is even more improved adopting corrections depending on the climate class for the estimation of the solar radiation, especially in the tropical climate class.

Regional-scale modeling of reference evapotranspiration: Intercomparison of two simplified temperature- and radiation-based approaches

AbstractTwo regionalized models for the distributed estimation of daily reference evapotranspiration, the temperature-based Hargreaves (HE) and the radiation-based Makkink (MK) equations, are applied in Southern Italy during the years 2007 and 2008. Spatially distributed meteorological inputs, such as air temperature and incoming solar radiation, were derived from geostatistical interpolation of ground data and from the Land Surface Analysis Satellite Application Facility (LSA-SAF) surface radiation product, respectively. Comparison of the latter with 83,394 daily measurements provided by 128 weather stations shows a not negligible seasonal error in daily solar radiation that is corrected by means of a periodic equation. A preliminary local calibration of the MK coefficient highlights its strong dependency on the interactions between moist winds from the Atlantic Ocean and orographic obstructions, leading to two western and eastern subzones. Hence, a regionalization of the MK-adjusted coefficient was perf...

The Open Computing Abstraction Layer for Parallel Complex Systems Modeling on Many-Core Systems

Abstract This article introduces OpenCAL, a new open source computing abstraction layer for multi- and many-core computing based on the Extended Cellular Automata general formalism. OpenCAL greatly simplifies the implementation of structured grid applications, contextually making parallelism transparent to the user. Different OpenMP- and OpenCL-based implementations have been developed, together with a preliminary MPI-based distributed memory version, which is currently under development. The system software architecture is presented and underlying data structures and algorithms described. Numerical correctness and efficiency have been assessed by considering the S c i d d i c a T Computational Fluid Dynamics landslide simulation model as reference example. Eventually, a comprehensive study has been performed to devise the best platform for execution as a function of numerical complexity and computational domain extent. Results obtained have highlighted the OpenCAL’s potential for numerical models development and their execution on the most suitable high-performance parallel computational device.

Accelerating a three-dimensional eco-hydrological cellular automaton on GPGPU with OpenCL

This work presents an effective implementation of a numerical model for complete eco-hydrological Cellular Automata modeling on Graphical Processing Units (GPU) with OpenCL (Open Computing Language) for heterogeneous computation (i.e., on CPUs and/or GPUs). Different types of parallel implementations were carried out (e.g., use of fast local memory, loop unrolling, etc), showing increasing performance improvements in terms of speedup, adopting also some original optimizations strategies. Moreover, numerical analysis of results (i.e., comparison of CPU and GPU outcomes in terms of rounding errors) have proven to be satisfactory. Experiments were carried out on a workstation with two CPUs (Intel Xeon E5440 at 2.83GHz), one GPU AMD R9 280X and one GPU nVIDIA Tesla K20c. Results have been extremely positive, but further testing should be performed to assess the functionality of the adopted strategies on other complete models and their ability to fruitfully exploit parallel systems resources.

The Role of Evapotranspiration in the Framework of Water Resource Management and Planning Under Shortage Conditions

The increased availability of observed data and of advanced techniques for the analysis of meteo-hydrological information allows an even more detailed description of the evolution of global climate. The results showed by the Fourth Assessment Report (FAR) of the International Panel on Climate Change (IPCC, 2007) about the changes that, starting from 1950, are affecting the atmosphere, the cryosphere and the oceans, confirm global warming. The global average surface temperature has increased in the last 100 years by 0.74°C ± 0.18°C, accelerating in the last 50 years (0.13°C ± 0.03°C per decade), especially over land (about 0.27 °C per decade) and at higher northern latitudes. As a consequence, the higher available energy on the surface has speeded up the hydrological cycle. The concentration of the water vapor in the troposphere has increased (1.2 ± 0.3% per decade from 1988 to 2004), while long-period precipitation trends (both positive and negative) in many regions have been observed by analyzing time series from the year 1900 to the year 2005. Changes in temperature and precipitation regimes strongly affect the hydrological cycle. As an example, the increase in temperature has produced a substantial reduction in snow cover in several regions, mainly in spring, and a reduction in the areas covered by seasonal frozen ground (reduction of about 7% in the northern hemisphere over the latter half of the 20th century). Direct long-term measurements of all the main components of the hydrological cycle are not widely available: in order to assess soil moisture long-term changes, due to the lack of direct measurements the primary approach is to calculate Palmer Drought Severity Index, while long-term stream flow gauge records do not cover entirely and uniformly the world, and they present gaps and different record lengths. However, generally stream flow trends are positively correlated to precipitation, while a common effect of climate change is arising independently on precipitation trends: starting from the ‘70s a considerable increase of the frequency of extreme hydrological events (floods and droughts) has been observed. Also concerning actual evapotranspiration, direct measurements over global land areas are still very limited, but already the Third Assessment Report (TAR) reported that actual evapotranspiration increased during the second half of the 20th century over most dry regions of the USA and Russia, and, by means of observed precipitation, temperature,