RSE-08181; No of Pages 16 Remote Sensing of Environment xxx (2012) xxx–xxx Contents lists available at SciVerse ScienceDirect Remote Sensing of Environment journal homepage: www.elsevier.com/locate/rse Use of Landsat thermal imagery in monitoring evapotranspiration and managing water resources Martha C. Anderson a,⁎, Richard G. Allen b, Anthony Morse c, William P. Kustas a a USDA-ARS, Hydrology and Remote Sensing Lab, Bldg. 007, BARC West, Beltsville, MD 20705, United States b University of Idaho, Kimberly Research and Extension Center, Kimberly, ID 83301, United States c Spatial Analysis Group, Boise, ID 83701, United States article info abstract Article history: Freshwater resources are becoming increasingly limited in many parts of the world, and decision makers are Received 16 March 2011 demanding new tools for monitoring water availability and rates of consumption. Remotely sensed thermal- Received in revised form 27 July 2011 infrared imagery collected by Landsat provides estimates of land-surface temperature that allow mapping of Accepted 28 August 2011 evapotranspiration (ET) at the spatial scales at which water is being used. This paper explores the utility of Available online xxxx moderate-resolution thermal satellite imagery in water resource management. General modeling techniques for using land-surface temperature in mapping the surface energy balance are described, including methods Keywords: Evapotranspiration developed to safeguard ET estimates from expected errors in the remote sensing inputs. Examples are provid- Thermal remote sensing ed of how remotely sensed maps of ET derived from Landsat thermal imagery are being used operationally by Landsat water managers today: in monitoring water rights, negotiating interstate compacts, estimating water-use by Water resource management invasive species, and in determining allocations for agriculture, urban use, and endangered species protec- Drought tion. Other applications include monitoring drought and food insecurity, and evaluation of large-scale land-surface and climate models. To better address user requirements for high-resolution, time-continuous ET data, novel techniques have been developed to improve the spatial resolution of Landsat thermal-band imagery and temporal resolution between Landsat overpasses by fusing information from other wavebands and satellites. Finally, a strategy for future modification to the Landsat program is suggested, improving our ability to track changes in water use due to changing climate and growing population. The long archive of global, moderate resolution TIR imagery collected by the Landsat series is unmatched by any other satellite program, and will continue to be an invaluable asset to better management of our earth's water resources. Published by Elsevier Inc. 1. Introduction identify crop water deficits and causes of low food production, and form a major component of our national food security program. Diag- Land-surface evapotranspiration (ET) transfers large volumes of nostic estimates of ET can be used to infer soil moisture conditions — water (and energy, in the form of latent heat) from the soil (evapora- a valuable input to weather, drought, and flood forecast models, and tion) and vegetation (transpiration) into the atmosphere. Accurate, spa- critical to many military applications. On still larger scales, spatial pat- tially distributed information on water use, quantified at the scale of terns in ET play an essential role in mesoscale and general circulation human influence, has been a long-standing critical need for a wide modeling, affecting cycling of water and energy between the land, range of applications. Quantifying ET from irrigated crops is vital to oceans and atmosphere. management of water resources in areas of water scarcity, and detailed Dwindling supplies of fresh water are a problem worldwide, and maps enable managers to more judiciously allocate available water demand for more spatially detailed quantification of ET is growing among agricultural, urban, and environmental uses. The actual rate of as demands on water resources come under increasing competition. water use by vegetation can deviate significantly from potential ET The U.S. Department of the Interior predicts significant water short- rates (as regulated by atmospheric demand for water vapor) due to im- ages throughout the American West resulting from limited supply pacts of drought, disease, insects, vegetation amount and phenology, coupled with explosive population growth. Climate change research and soil texture, fertility and salinity. Satellite-derived indices reflecting suggests this scenario will be echoed around the globe, striking the difference between actual and potential ET are used globally to most severely the arid and semiarid regions that have the least buffer in terms of stored water supply. The Strategic Plan for the U.S. Inte- grated Earth Observation System has identified “Protection and Moni- ⁎ Corresponding author at: Bldg 007, Rm 104 BARC-West, 10300 Baltimore Ave, ” Beltsville, MD 20705, United States. Tel.: +1 301 504 6616; fax: +1 301 505 8931. toring of Water Resources as one of nine application focus areas for E-mail address: [email protected] (M.C. Anderson). earth observation for Societal Benefit. Already, satellite-based ET 0034-4257/$ – see front matter Published by Elsevier Inc. doi:10.1016/j.rse.2011.08.025 Please cite this article as: Anderson, M.C., et al., Use of Landsat thermal imagery in monitoring evapotranspiration and managing water re- sources, Remote Sensing of Environment (2012), doi:10.1016/j.rse.2011.08.025 2 M.C. Anderson et al. / Remote Sensing of Environment xxx (2012) xxx–xxx mapping has been integrated into operational water management food supply from 25% of the world's croplands (399 million ha) programs within the US. Remotely sensed ET has been used to devel- (Thenkabail et al., 2010). Water consumption from irrigated agriculture op water budgets, to monitor aquifer depletion, to understand water is estimated to total about 1200 km3 per year of abstracted water in ad- use change with land use, to optimize irrigation to protect endan- dition to 920 km3 per year of incident rainfall (Thenkabail et al., 2010). gered species habitat, to monitor water rights compliance, and to es- Total water consumption by all agricultural vegetation, both irrigated timate agricultural water use for water-right buy-back programs for and rainfed, is estimated to be 6700 km3 per year (6.7 trillion m3). mitigation and litigation. Based on these successful implementations, Rates of water consumption are governed by a combination of sur- the Western States Water Council (WSWC) has voiced strong support face energy availability (weather and climate), soil water availability for continued nation-wide water data collection using satellite re- (precipitation, irrigation, and shallow water tables), and the amount, mote sensing (www.westgov.org/wswc/-325 nasa position 29oct type and health of the vegetation. Plant water use is regulated by sto- 2010.pdf; landsat.gsfc.nasa.gov/news/news-archive/soc_0023.html). matal aperture, and studies at the leaf, plant and canopy scale have To address these growing needs for ET data, land-surface temper- demonstrated the utility of TIR measurements for assessing plant ature (LST) maps, derived from thermal infrared (TIR) imagery col- water relations (Jones et al., 2002), canopy/stomatal conductance lected by satellites and aircraft, have proven to be a valuable asset (Blonquist et al., 2009; Jones and Leinonen, 2003; Leinonen et al., in mapping ET over large areas. The LST state variable is highly sensi- 2006), and monitoring stomatal closure (Jones and Leinonen, 2003). tive to local moisture conditions and effects of evaporative cooling, These biophysical properties regulate transpiration rates and can be and plays a key role in diagnosing many of the major surface energy highly variable, both spatially and temporally. Evaporation of water balance components, including sensible heat, net radiation, and soil from exposed soil surfaces also has a thermal signature, and can heat flux. For management and monitoring, the TIR band has an ad- lead to small-scale structure in landscape ET. In agricultural and het- vantage over the soil-moisture sensitive microwave band in that TIR erogeneous natural systems, significant variability in ET and LST can can be used to retrieve moisture information at several orders of mag- occur at scales of hundreds of meters or less. nitude higher spatial resolution. Several TIR-based approaches to Moderate-resolution satellite TIR imagery is therefore required to mapping ET have been developed in support of water resource appli- identify the water consumption associated with specific crop types cations, using LST as the primary input (e.g., Allen et al., 2007a; and land holdings, and to provide information relevant to food pro- Bastiaanssen et al., 1998; Su, 2002). The most successful of these in- ducers. This resolution is also needed to study variability in water corporate novel strategies to reduce sensitivity to expected errors in consumption within individual fields and plant communities for the LST retrieval due to atmospheric and emissivity corrections to TIR purposes of improving water-use efficiency of crops, and for identify- imagery. ing particularly water-inefficient (often invasive) species. A typical ir- In this paper, we describe some of these approaches, and demon- rigated field in the western US, for example, has dimensions of strate