1. Associate Professor, Dipartimento di Scienze Agrarie e Forestali, Università degli Studi di Palermo, viale delle Scienze edificio 4, 90128 Palermo, Italy (corresponding author).
2. Caroline and William N. Lehrer Distinguished Chair in Water Engineering and Professor, Dept. of Biological and Agricultural Engineering and Zachry Dept. of Civil Engineering, Texas A&M Univ., 321 Scoates Hall, 2117 TAMU College Station, TX 77843-2117.