B. Martin-Gorriz

Satellite-Based Method for Estimating the Spatial Distribution of Crop Evapotranspiration: Sensitivity to the Priestley-Taylor Coefficient

This work discusses an operational method for actual evapotranspiration (ET) retrieval from remote sensing, considering a minimum quantity of ancillary data. The method consists in a graphical approach based on the Priestley-Taylor (PT) equation, where the dry soil and non-limiting water conditions are defined by land surface temperature (LST) and vegetation index (VI) space, both retrieved from remote sensing. Using ET tower flux measurements and Landsat 5 TM images of an irrigation scheme in southeast Spain, a sensitivity analysis of ET spatial distribution was performed for the period 2009–2011 with respect to: (i) the shape (trapezoidal or rectangular) of the LST-VI space; and (ii) the value of the PT coefficient, α. The results from ground truth validation were satisfactory, both shapes providing similar performances in estimating ET, with root mean square error ~30 W/m2 and relative difference ~10% with respect to tower-based measurements. Importantly, the best fit with ground data was found for α close to 1, a somewhat different value from the commonly used value of 1.27, indicating that substantial error might arise when using the latter value. Overall, our study underlines the importance of a more precise knowledge of the actual value of α coefficient when using ET retrieval methods based on the LST-VI space.

Seawater desalination for crop irrigation—Current status and perspectives

Abstract Seawater desalination for sustaining agricultural production has been reported as an alternative water source in some Mediterranean countries and its adoption is also being considered in other regions. Desalinated seawater (DSW) can represent a steady water source, which effectively removes the hydrological constraints for crop production under arid and semiarid conditions. This chapter reviews current irrigation experiences with DSW worldwide, analyzing the revealed key issues for its successful implementation, including (1) the main agronomic concerns, such as low nutrient concentration, crop toxicity risk due to high boron and chloride concentration, or the sodicity risk affecting soil physical properties; (2) the energy requirements for DSW production and allocation, the associated greenhouse gas emissions and the derived cost, as the current limiting factors for its agricultural application; and (3) future research for promoting its sustainability and its development perspectives. Additionally, the chapter contains two demonstrative study cases; the first one deals with the planning and development of DSW supply in semiarid south-eastern Spain, while the second focuses on blending strategies for optimizing DSW use together with other available water resources at the farm scale.

Analysis of water markets as an adaptive tool to water scarcity in SE Spain’s agriculture

Abstract. Structural water scarcity is a reality in southeastern Spain, where there has been an important increase in agricultural water demand throughout the last decades, and climate change is producing a progressive reduction of water resources. This scenario will necessarily require the widespread adoption of adaptive measures in irrigated agriculture. These measures may be aimed (1) to increase the water supply (regional transfers, desalination and reuse), (2) to improve the efficiency of water use (irrigation districts modernization), or (3) to manage the demand. Water markets are demand management tools that allow for a more flexible and efficient reallocation of water resources towards higher value users, and thus contribute to improving social welfare by maximizing the income derived from its use, as well as reduce water availability-related hazards and mitigate the economic impacts of drought periods in agriculture. Water markets are allowed by the Spanish water legislation, but there are still numerous gaps on the knowledge about their functioning that must necessarily be covered as an essential starting point to make practical proposals for their improvement. The objective of this study is to describe the current performance of water markets in southeastern (SE) Spain, identifying their limitations and strengths. The activity of water markets in SE Spain over the past three decades has been less than might have been expected given the hydrological conditions and characteristics of the economy of water in the basin, and has been limited almost exclusively to agricultural irrigation. After a characterization of the water markets experiences that have occurred to date, the study shows a preliminary analysis of availability and adequacy of water infrastructure. Especially interesting is the analysis of transaction costs, i.e. those derived from the costs of physical transportation of water and its potential environmental impacts. The analysis of water-energy-CO 2 nexus is also interesting in order to know both the specific energy and the emissions of greenhouse gases associated with water markets, information of strategic interest when assessing the sustainability of water markets over other adaptive measures for irrigated agriculture adaptation to water scarcity, such as seawater desalination or regional water transfers.