Vegetation Water Use Based on a Thermal and Optical Remote Sensing Model in the Mediterranean Region of Doñana

Abstract

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...

CubeSats Enable High Spatiotemporal Retrievals of Crop-Water Use for Precision Agriculture

“…The Priestley-Taylor Jet Propulsion Laboratory (PT-JPL) retrieval model has been evaluated extensively across a wide range of biomes [27,29,30], time scales [14,15,31], and environments [13,28,32]. The model used in this study is a slightly modified version of the original PT-JPL approach described in Fisher et al [27], which requires a minimum of commonly available meteorological forcing and satellite data.…”

“…These biophysical multipliers represent constraints for the surface wetness ( f wet ), fraction of green canopy f g , plant temperature ( f T ), plant moisture ( f M ) and soil moisture ( f SM ). Detailed information behind the specification of the biophysical multipliers, model parameters and model constants can be found in a range of previously published contributions [13,[27][28][29]32] and in Table S1.…”

“…Fisher et al [27] developed a modified approach (referred to as the Priestley-Taylor Jet Propulsion Laboratory model; PT-JPL), that introduced biophysical multipliers to scale potential ET to actual ET using a minimum amount of meteorological data and vegetation parameters derived from optical satellite imagery. The model has been employed at various spatial and temporal resolutions [13][14][15] and has shown good performance across a variety of different biomes [28][29][30][31][32]. It is also the primary ET retrieval algorithm for NASA's ECOSTRESS mission [33].…”

Advances in the Remote Sensing of Terrestrial Evaporation

“…It is these regions where accurate estimation may be of utmost importance to determine water use and management amongst competing sectors. Moyano et al [32] apply the PT-JPL model with dryland thermal modifications to the critical environment of the World Heritage Doñana region of Spain. They demonstrated that the remote sensing retrieval captured in situ measurements, providing confidence that the approach can be used for the ongoing management of these important ecosystems.…”

“…Of course, advances will not be driven solely by just increasing spatial and temporal resolutions. Certainly, one of the most important aspects required to advance the development of evaporation models is our representation of the vegetation components inherent in the partitioning between soil evaporation, interception, and transpiration: an aspect that will benefit not only from resolution improvements, but also new retrieval approaches [32,33,41]. Given the array of existing sensing systems that span the visible, near-infrared, thermal, and microwave spectral ranges, efforts to utilize the varied information to better characterize land surface influences (e.g., plant form and function) are likely to provide further knowledge gains [42][43][44].…”