Effects of land-use modification on potential increase of convection: A numerical mesoscale study over south Israel

The current research was designed to examine the potential of modified surf ace conditions in semiarid and and central-southern Israel to enhance conve ctive development and rainfall. The fifth-generation mesoscale model (MM5), coupled with a sophisticated land-surface submodel, is applied for the thr ee-dimensional high resolution simulations of two convective rain case stud ies, on October 27, 1990 and October 18, 1987. Three surface conditions are modeled to examine the relative influence of land-use changes, which are p resent-time land-use (1990s), preirrigation time (1930s), and the hypotheti cal case of extended irrigated agricultural lands. The main conclusion of t he study is that there exists a positive influence of the anthropogenic lan d-use changes on the enhancement of thermal convection and associated rainf all. Modification of surface parameters from semiarid land conditions to cu ltivated lands tends to consistently increase the potential for moist conve ction during the daytime heating hours, as expressed in the evolution of th e PBL structure and the growth of convective available potential energy (CA PE), as well as the area-averaged rainfall. The model seems to accurately r eproduce the observed atmospheric situations and rainfall, lending confiden ce to the assertion that these land-atmosphere effects can be quantified wi th an advanced mesoscale modeling system. This work is the first numerical mesobeta scale 3-D study over the south Israel area with its relatively sha rp spatial change in land use as well as in climatic zone. It is believed t o be a region, possibly the only in the world, where mesoscale surface and planetary boundary layer processes were suggested as causes for observed an ti-desertification gains.