Euro-Mediterranean Information System on know-how in the Water sector - Evapotranspiration & soil moisture

Facts and figures about Evapotranspiration and soil moisture

2008-09-02T18:05:52Z

Basics of evapotranspiration

2008-09-02T18:05:52Z

Courtesy of Stevens Water Monitoring Systems, Inc.
Originally published Aug. 2008

Evapotranspiration (ET) represents the loss of water from the Earth’s surface from the combination of direct evaporation and plant transpiration. ET is usually expressed as a rate such as inches per day. Knowledge of ET is important for irrigation scheduling but it is also an important factor for other land use applications such as septic tank drain fields, water shed water budgeting, and climate and weather models. ET can be used as a historical tool but usually it is predicted or used in a forecast to help irrigators optimize irrigation.

Integrated Methodology for Estimating Water Use in Mediterranean Agricultural Areas

2010-04-23T17:51:23Z

Agricultural use is by far the largest consumer of fresh water worldwide, especially in the Mediterranean, where it has reached unsustainable levels, thus posing a serious threat to water resources. Having a good estimate of the water used in an agricultural area would help water managers create incentives for water savings at the farmer and basin level, and meet the demands of the European Water Framework Directive.

This work presents an integrated methodology for estimating water use in Mediterranean agricultural areas. It is based on well established methods of estimating the actual evapotranspiration through surface energy fluxes, customized for better performance under the Mediterranean conditions: small parcel sizes, detailed crop pattern, and lack of necessary data. The methodology has been tested and validated on the agricultural plain of the river Strimonas (Greece) using a time series of Terra MODIS and Landsat 5 TM satellite images, and used to produce a seasonal water use map at a high spatial resolution.

Finally, a tool has been designed to implement the methodology with a user-friendly interface, in order to facilitate its operational use.

NDVI 10-day daily composites

2010-10-27T05:34:08Z

The Normalized Difference Water Index (NDVI) (Gao, 1996) is a satellite-derived index from the Near-Infrared (NIR) and Short Wave Infrared (SWIR) channels. The SWIR reflectance reflects changes in both the vegetation water content and the spongy mesophyll structure in vegetation canopies, while the NIR reflectance is affected by leaf internal structure and leaf dry matter content but not by water content.

Estimating reference evapotranspiration using remote sensing and empirical models in a region with limited ground data availability in Kenya

2011-04-22T16:36:22Z

Evapotranspiration is an important component of the hydrological cycle and its accurate quantiﬁcation is crucial for the design, operation and management of irrigation systems. However, the lack of meteorological data from ground stations is a clear barrier to the proper management of water resources in poor countries, increasing the risks of water scarcity and water conﬂicts. In the presented study, three temperature based ET models are evaluated in the Taita Hills, Kenya, which is a particularly important region from the environmental conservation point of view. The Hargreaves, the Thornthwaite and the BlaneyeCriddle are the three tested methods, given that these are the most recommended approaches when only air temperature data are available. Land surface temperature data, retrieved from the MODIS/Terra sensor are evaluated as an alternative input for the models. One weather station with complete climate datasets is used to calibrate the selected model using the FAO-56 PenmaneMonteith method as a reference. The results indicate that the Hargreaves model is the most appropriate for this particular study area, with an average RMSE of 0.47 mm d1, and a correlation coefﬁcient of 0.67. The MODIS LST product was satisfactorily incorporated into the Hargreaves model achieving results that are consistent with studies reported in the literature using air temperature data collected in ground stations.