Book of Abstracts

28
Study of vulnerability of the Northern Negev agriculture to droughts with the spatially explicit model of
agriculture land-use dynamics
Giora J Kidron, Tiferet Zilberman and Itzhak Benenson, Laboratory of Geosimulation and Spatial Analysis; Dept
of Geography and Human Environment, Tel Aviv University; gkidron@post.tau.ac.il; z.tiferet@gmail.com;
bennya@post.tau.ac.il
Based on the data on precipitation, irrigation and wheat yield during the last 20 years in two kibbutzim in the
northern Negev (Beit Kama and Mishmar HaNegev), we have developed a spatially explicit high-resolution model
of crop dynamics in the northern Negev at the resolution of a single field. The dynamics of crops in the Negev is
defined, primarily, by the irrigation. Based on the field data, crop cycles are estimated, separately for irrigated (e.g.,
potatoes, wheat, carrot) and rain-fed fields (e.g., wheat, legumes), as an autoregression of the second or third order.
The residuals of wheat are regularly used by the Bedouin herds during the critical months of the year (June-
September), when the other sources of sheep food are exhausted. Bedouin husbandry, thus, critically depends on
Jewish farming, and the model enables us to understand the interaction between Jews and Bedouins in the Negev.
The model is calibrated based on precipitation, the irrigation network and crop data (type, yield) collected in each
kibbutz during 1990- 2010. The analysis of the model for different scenarios of climatic change during 2010 ¨C
2030 shows that with the employment of intensive irrigation, crop yield per hectare will drop by only half the
amount in comparison to a hypothetical situation during which no irrigation would have been employed.
Furthermore, the drop in crop yield may be even less substantial when the increase in wheat yield in fields that were
irrigated during the previous year (during potato or carrot cultivation) is accounted for. With the increase in wheat
yield (and subsequently with the increase in the residual wheat used by the Bedouins), the resilience of both
communities, the Jewish and the Bedouin, increases. Yet, as the field capacity is limited and following population
growth, further expansion of the Bedouin agriculture will necessitate intensive husbandry.
Soil evaporation revisited – what controls evaporation dynamics from porous surfaces?
Dani Or; Department of Environmental Systems Science; ETH Zurich; Zurich, Switzerland; dani.or@env.ethz.ch
Evaporation dynamics from soil surfaces reflect interactions between internal liquid and vapor transport, energy
input for phase change, and mass transfer across air boundary layer. The roles of two key interfaces controlling
evaporation dynamics are studied: (1) interactions of wet evaporating surfaces with an air boundary layer; and (2)
the role of a receding drying front. At a critical drying-front depth defined by soil pore-size distribution, capillary
liquid continuity essential to supplying surface evaporation is disrupted and the evaporation rate transitions to
diffusion-controlled stage-2. This characteristic length is modified by evaporation rate, hence reflecting the interplay
of capillary, gravity and viscous forces. For surface-boundary layer interactions, we quantified a nonlinear behavior
of drying porous surfaces responsible for enhanced vapor fluxes from remaining active pores as they become
increasingly isolated (with soil surface drying). Experiments show that in contrast to nearly-constant evaporation
rates at low atmospheric demand (typically