Title: Estimating water productivity and assessing irrigation performance of fruit crops by measurements of basin-scale energy balances in the Sao Francisco River Basin, Brazil.

Primary Researcher: Antonio Heriberto de Castro Teixeira
Email address: heriberto.teixeira@wur.nl
Submitted on: October 3, 2006

Start date: 01 March 2004
End date: 20 December 2008

Introduction:

The impacts of human activities on the environment have been mostly studied at the the local scale. Nowadays, the problems start to be considered at the scale of the river basin. Planning the land and water use in a basin is a necessity in a society with increasing water demands that tends to implement this in a disorderly form, resulting in damage to the ecosystem. National development is also associated with water use for irrigation and drainage to meet food demand.
Irrigation managers today are faced with several challenges. They must become aware of the sustainable use of the natural resources. An inadequate water management in agriculture will cause negative impacts on rivers by diffuse pollution, erosion and sedimentation. Fresh water has become the most precious natural resource and global water scarcity forms a major constraint on sustaining and enhancing agricultural productivity. Between 1900 and 1995, the fresh water demand in the world increased six- fold, twice the population growth (Gleick, 1998). Water policy makers have, therefore, to work out strategies for integrated water and environmental management, which rely on the proper knowledge of the basin hydrological and pollution conditions (Bastiaanssen et al., 2003).
An understanding of the natural systems and the physical laws that govern each component of the hydrologic cycle is very important for the irrigation manager. Cropland irrigation is a major consumer of water in semiarid and arid regions and in these areas the effects of soil use modification and the climatic variability of short and medium term upon the river basin and human activities are meaningful. The challenge for science is the interdisciplinary evaluation of meteorological and hydrological processes, the vulnerability of the ecosystems to climate change and the development of models to simulate these integrated processes for the evaluation of development scenarios. Better understanding of these processes on a regional scale is possible with multidisciplinary research as in agro-meteorology, soil physics, irrigation and drainage and geo-information techniques.
Available data sets on agro-meteorology can be used to estimate the crop water requirements by measurements of evapotranspiration for the entire growing seasons. With these agro-meteorological parameters together with production data, the water productivity for specific crops can be determined. Data on soil physics and water applied in irrigation as well as the water that percolated from the root systems are necessary for the water balance so that these data can be integrated in a Geographical Information System. Field data together with remote sensing and GIS can be transformed in water use, water productivity and economic indicators at a regional scale. An integration of data from satellite images, agro-meteorological stations, field and secondary data is used to determine these indicators. The basic parameters required for these analyses are evapotranspiration, gross and effective rainfall, irrigation water supply, crop yield and crop prices.

Aim:

The overall goals of the proposal for the Sao Francisco River Basin are:

- To find parameters associated with energy transfers from irrigated crops and natural vegetation in semiarid region, which can be used to assess evapotranspiration, water productivity and irrigation performance on a regional scale as well as provide new information on the energy balance for vegetation in semi-arid conditions;

- To monitor the daily water requirements and water productivity of the main cash crops of the region, which will lead to recommendations for a more rational and strategic water management with the input of presently available of agro-meteorological stations.

- To find relationship among easily-measured canopy dimension variables and evapotranspiration for later determination of water consumption by the plants, according to the stage of development.

- To use satellite images, ago-meteorological data and Geographic Information System to assess evapotranspiration, water productivity and irrigation performance fot the main irrigated fruit crops of the Sao Francisco River Basin.

Research:

Irrigation is expected to perform in a rational way, based on knowledge of soil water storage capacity, soil water content, crop type and development stage, characteristics of irrigation systems and crop water requirements over the entire growing season.
Water is transferred to the atmosphere due to evapotranspiration (Allen et al., 1998), which is a good indicator of irrigation supply and planning, water rights regulation and river basin hydrological studies.
Experimentally, the calculation of evapotranspiration can be made accurately using weighing lysimeters, eddy correlation techniques and the Bowen ratio method. The use of lysimeters in fruit crops is often not recommended, due to the development of the root system which can attain large depths, so, that the energy balance above the surface seems to be the best way in these situations. With the development of electronic devices and the use of computers, the Bowen ratio and the eddy correlation methods can be relatively easy to use in obtaining the components of the complete energy balance above the vegetation, including the energy used for transporting the water vapor to the atmosphere.
Evapotranspiration estimations through the energy balance in agricultural crops and natural vegetation have been made by the Bowen ratio method (Heilman et al., 1994, 1996; Teixeira et al., 1999, 2002, 2003; Scott et al., 2000; Inman-Bamber & McGlinchey, 2003; Lee et al., 2003) and by eddy correlation technique (Oliver & Sene, 1992; Sene, 1994; Trambouze et al., 1998; Cleverly et al., 2002; Prueguer et al., 2003; Humphreys et al., 2003; Lund & Soegaard, 2003; Villalobos et al., 2004; Testi et al., 2004). Comparisons between the methods of measurements have also been carried out (Unland et al., 1996; Spano et al., 2000, Beringer & Tapper, 2000; Olejnik et al., 2001; Azevedo et al., 2003).
These methods, however, provide only point values for specific sites and fail for estimation of evapotranspiration on a regional scale. This limitation has motivated the development of the use of remotely sensed data from satellites and Geographic Information Systems to evaluate the water vapor lost by large vegetated areas to the atmosphere.
The variability of evapotranspiration in space is due to the wide spatial variability of precipitation, hydraulic characteristics of soils and vegetation types and densities, while the variability in time is due to the variability in climate. The major advantage of remote sensing is that the evapotranspiration on a large scale can be computed without quantifying these complex hydrological processes, providing an excellent means for determining and mapping the spatial and temporal structure of evapotranspiration (Bastiaanssen et al., 1998).
Jackkson et al. (1977) undertook the pioneer work, for assessment of evapotranspiration by remote sensing, with the use of infrared thermometry for estimation of wheat water consumption. After this, various methods for using remote sensing for evapotranspiration calculations have been utilized (Kustas & Norman, 1996; Roerink et al., 1997; Bastiaanssen et al., 2001; Boegh et al., 2004). Procedures for the validation of the models with field data were also undertaken (Bastiaanssen, 1998; Havstad et al., 2000; Roerink et al., 2000; Hamakumara et al., 2003; Jia et al., 2003; Brunsell, 2003).
One of the recent models that use satellite images is the SEBAL (Surface Energy Balance Algorithm for Land) for heterogeneous surfaces. This model involves the spatial variability of the most common agro-meteorological variables and can be applied to various ecosystems (Bastiaanssen et al., 1998). This algorithm was developed for assessment energy partitioning on a regional scale. The relationship between the specters of visible and infrared radiation of areas with big hydrological contrast is the base for SEBAL formulation.
Irrigation performance has been introduced to describe the hydrological behavior of irrigation systems by means of irrigation performance indicators, which involve agro-meteorological data and water delivered. These indicators describe the various aspects of water management (Bos et al., 1994). In South-America, irrigation performance was studied by Bos et al. (1991) and Morabito et al. (1998) in the Tunuiyan Irrigation scheme in Mendoza, Argentina. In Northeast Brazil, Bastiaanssen et al. (2001) utilized low-cost and low-resolution satellite images complemented by agro-meteorological data in monitoring performance of a modern commercial irrigation scheme. The basic input data for these studies were the water applied and information on cropping pattern and agro-meteorological conditions.
The crop water productivity (CPW) is considered to be the crop yield divided by the evapotranspiration or irrigation. To derive options for improvement of CWP, both good estimates of actual marketable crop production and evapotranspiration, and their interactions are needed (Bessembinder et al., 2003). In a recent comprehensive review of crop water productivity for irrigated areas published by Zwart and Bastiaanssen (2004), they concluded that the Bowen ratio and eddy correlation methods for estimating evapotranspiration and crop water productivity are not common in agronomical studies. Instead, they are often used for meteorological and climate studies in which yields are not reported. According to Zwart and Bastiaanssen (2004), many studies on water productivity focus on either determination of crop water use or crop yields, whereas others only consider water applied.
Combining evapotranspiration and production estimations by the SEBAL algorithm and satellite images, the irrigation performance indicators and the water productivity can also be obtained for regional scale. By using a Geographical Information System together with satellite images, maps of the elements of the regional water balance and water productivity can be drawn for the river basin.
This proposed research will be conducted in the Sao Francisco River basin. This basin crosses six Brazilian states, totaling an area around 640,000 km². From this total, roughly 333,000 hectares are irrigated, representing about 10% of the irrigated land. The semi-arid zone, in Northeastern Brazil, comprises 52% of the basin. This region is characterized by a lengthy dry season with an amount of 350 to 800 mm average rainfall concentrated in three to four months with high evapotranspiration rates.
Irrigated agriculture in the semiarid region of the basin constitutes an important activity for the livelihoods of rural communities. The potential for fruit production, in this area, has been confirmed by the continuous expansion of the cultivated land, mainly with fruit crops, especially grapes for table and wine and mango. Associated with this expansion is the competition for water by multiple uses, such as human consumption for urban areas, power generation and irrigation, which has been rising in recent decades.
The region is known as a producer and exporter area of high quality fruits. High productivities are possible because cultivation takes place under conditions of low rainfall and water needs can be supplied through irrigation based on crop water requirements. However, the farmers have limited information on the evapotranspiration in irrigated schemes, which contributes to low irrigation performance and water productivity and also to the impact on the environment. The water applied through irrigation can sometimes deviate significantly from actual crop requirements, because the climatic conditions, irrigation and soil management are often changing. In addition, farming practices and phenological phases are generally not considered in water management during the growing season.
Considering the expansion of fruit crops and the need for a rational irrigation management in Sao Francisco River Basin, the availability of a network of automated agro-meteorological stations recently installed by Embrapa in the semiarid region of the basin, allowing for the determination of the water balance through field data and satellite images, can help the farmers-producers to dimension their irrigation systems and to conduct a rational water management thus contributing to improve the cost/benefit relationships and improved quality of fruits. With improvement in irrigation system performance the impact of the increases of the irrigated areas on the environment can be reduced.
This proposal involves multidisciplinary activities in the semiarid region of the Sao Francisco River Basin with assessment of evapotranspiration and crop coefficients for the main fruit crops; the use of parameters of energy balance components in irrigated and natural vegetation for hydrological contrast, necessary for SEBAL formulation; comparison among different methods of determination of evapotranspiration; analysis of irrigation performance of the main schemes in the region; and development of options to increase Crop Water Productivity of the main fruit crops in the region.

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Future Research

After the validation of SEBAL based on energy transfers, this algorithm together with the network of agro-meteorological stations and a Geographic Information System will be a useful tool to study the water productivity and irrigation performance in the entire Sao Francisco River Basin by making use of historical series. This future research will contribute to a better fruit production with less damage to the ecosystem. The focus of this study will be the evaluation of different irrigation schemess and their impact on water resources, by irrigated agriculture.

External funding

Yes

External Funding Sponsors

Funds are granted by CAPES (Fundacao Coordenacao de Aperfeicoamento de Pessoal de Nivel Superior), Ministry of Education - Brazil and EMBRAPA (Brazilian Corporation for Agricultural Research)..