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Emitter discharge of subsurface drip irrigation (SDI) decreases as a result of the overpressure in the soil water at the discharge orifice. In this paper, the variation in dripper discharge in SDI laterals is studied. First, the emitter coefficient of flow variation CV ? was measured in laboratory experiments with drippers of 2 and 4 L/h that were laid both on the soil and beneath it. Additionally, the soil pressure coefficient of variation CV te was measured in buried emitters. Then, the irrigation uniformity was simulated in SDI and surface irrigation laterals under the same operating conditions and uniform soils; sandy and loamy. CV q was similar for the compensating models of both the surface and subsurface emitters. However, CV ? decreased for the 2-L/h non-compensating model in the loamy soil. This shows a possible self-regulation of non-compensating emitter discharge in SDI, due to the interaction between effects of emitter discharge and soil pressure. This resulted in the irrigation uniformity of SDI non-compensating emitters to be greater than surface drip irrigation. The uniformity with pressure-compensating emitters would be similar in both cases, provided the overpressures in SDI are less than or equal to the compensation range lower limit.

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Terrestrial evapotranspiration (ET) is a central process in the climate system, is a major component in the terrestrial water budget, and is responsible for the distribution of water and energy on land surfaces especially in arid and semiarid areas. In order to inform water management decisions especially in scarce water environments, it is important to assess ET vegetation use by differentiating irrigated socio-economic areas and natural ecosystems. The global remote sensing ET product MOD16 has proven to underestimate ET in semiarid regions where ET is very sensitive to soil moisture. The objective of this research was to test whether a modified version of the remote sensing ET model PT-JPL, proven to perform well in drylands at Eddy Covariance flux sites using the land surface temperature as a proxy to the surface moisture status (PT-JPL-thermal), could be up-scaled at regional levels introducing also a new formulation for net radiation from various MODIS products. We applied three methods to track the spatial and temporal characteristics of ET in the World Heritage UNESCO Doñana region: (i) a locally calibrated hydrological model (WATEN), (ii) the PT-JPL-thermal, and (iii) the global remote sensing ET product MOD16. The PT-JPL-thermal showed strong agreement with the WATEN ET in-situ calibrated estimates (ρ = 0.78, ρ 1month-lag = 0.94) even though the MOD16 product did not (ρ = 0.48). The PT-JPL-thermal approach has proven to be a robust remote sensing model for detecting ET at a regional level in Mediterranean environments and it requires only air temperature and incoming solar radiation from climatic databases apart from freely available satellite products.The global water cycle is changing due to the combined effects of climate change and human interventions during the 21st century [1]. One of the greatest challenges is keeping water consumption at sustainable levels, which is more complex due to the increasing population in a context of climate uncertainty [2,3] and 3.5-4.4 billion people estimated under water scarcity conditions in 2050 [4]. Many regions of the world can expect a combination of increasing temperatures (largely increasing evaporative demand) and decreasing precipitation patterns, which leads to increased stress on tackling water demand [5]. A prime example of this is the Mediterranean region, which is consistently projected as a "hotspot" of drying trends and prolonged water scarcity conditions [6,7].The Iberian Peninsula is predicted to be among the most affected areas by severe droughts by the end of the 21st century [8]. In this region, where irrigated agriculture represents over 80% of the total extracted water [9], land use shifts towards higher market-valued crops represent a major driver of change, which will markedly increase water withdrawals [10]. In the Guadalquivir basin in Spain, irrigation water requirements are expected to increase between 15% and 20% by 2050 [11]. This may cause a redistribution of water between the surface and groundwater [12]. Monitoring the variations i...

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