(First edition: 1998, this reprint: 2004). This publication presents an updated procedure for calculating reference and crop evapotranspiration from meteorological data and crop coefficients. The procedure, first presented in FAO Irrigation and Drainage Paper No. 24, Crop water requirements, in 1977, allows estimation of the amount of water used by a crop, taking into account the effect of the climate and the crop characteristics. The publication incorporates advances in research and more accurate procedures for determining crop water use as recommended by a panel of high-level experts organised by FAO in May 1990. The first part of the guidelines includes procedures for determining reference crop evapotranspiration according to the FAO Penman-Monteith method. These are followed by updated procedures for estimating the evapotranspiration of different crops for different growth stages and ecological conditions.

Crop evapotranspiration : guidelines for computing crop water requirements

Soil Chemical Analysis

Investigating soil moisture-climate interactions in a changing climate: A review

FLUXNET: A New Tool to Study the Temporal and Spatial Variability of Ecosystem-Scale Carbon Dioxide, Water Vapor, and Energy Flux Densities

A remote sensing surface energy balance algorithm for land (SEBAL)-1. Formulation

1. Opening address of the first George Kovacs Colloquium U. Shamir 2. Heterogeneity and scaling land-atmospheric water and energy fluxes in climate systems E. F. Wood 3. Scale problems in surface fluxes J. C. I . Dooge 4. Remote sensing - inverse modelling approach to determine large scale effective soil hydraulic properties in soil-vegetation-atmospheric systems R. A. Feddes 5. The importance of landscape position in scaling SVAT-models to catchment scale hydro-ecological prediction T. J. Hatton, W. R. Dawes and R. A. Vertessy 6. The influence of subgrid-scale spatial variability on precipitation and soil moisture in an atmospheric GCM D. Entekhabi 7. Modelling the hydrological response to a large scale land use change A. Henderson-Sellers, K. McGuffie and T. B. Durbidge 8. An approach to represent mesoscale (subgrid-scale) fluxes in GCMs demonstrated with simulations of local deforestation in Amazonia R. Avissar and F. Chen 9. A hierarchical approach to the connection of global hydrological and atmospheric models G. W. Kite, E. D. Soulis and N. Kouwen 10. Stochastic downscaling of GCM-output results using atmospheric circulation patterns A. Bardossy 11. Dependencies of spatial variability in fluvial ecosystems on the temporal hydrological variability H. P. Nachtnebel 12. Problems and progress in macroscale hydrological modelling A. Becker 13. Predictability of the atmosphere and climate: towards a dynamical view C. Nicolis 14. From scalar cascades to lie cascades: joint multifractal analysis of rain and cloud processes D. Schertzer and S. Lovejoy 15. Fractals et multifractals appliques a l'etude de la variabilite temporelle des precipitations P. Hubert.

Space and time scale variability and interdependencies in hydrological processes

This paper presents the results of modelsimulations to evaluate drainage designparameters for the Fourth Drainage Project(FDP), Punjab, Pakistan. The SWAP model wasapplied to compute the effects of landdrainage (12 combinations of drain depthand spacing) on soil moisture conditions inthe root zone and their effect on cropyield and soil salinization. For theconditions considered, the selection ofdrain depth is found to be more criticalthan that of drain spacing. Deeper drainsperform technically better in relation tocrop growth and soil salinization. Theoptimum drain depth for the multiplecropping system of the FDP-area was foundto be 2.2 m. This drain depth will producereasonably good crop yields at rather lowdrainage intensity while keeping the rootzone salinity within acceptable limits.This drainage design also maintained thegroundwater table depth below the root zonethroughout the growing season. The outcomeof this study reveals that the drainagedesign criteria applied for the FDP israther conservative with high drainageintensity. The FDP-area can effectively bedrained with a 25 percent lower drainageintensity (q
drain/Δh)provided no operational or maintenanceconstraints are present. However, the finaldecision on the optimum combination ofdrain depth and drain spacing would requirea thorough economical analysis. Thenon-steady state approach proved successfulin analyzing the complex interactionsbetween irrigation and drainage components.It is a valuable tool to optimize thedesign of drainage systems against cropyields and soil salinization.

Evaluating drainage design parameters for the Fourth Drainage Project, Pakistan by using SWAP model: Part II - modeling results

Irrigation water distribution and long-term effects on crop and environment

Part I of this paper described a Galerkin-type finite element approach to the simulation of two-dimensional transient flow in saturated-unsaturated soils considering evaporation and water uptake by roots. The purpose of Part II is to verify the numerical model against field measurements, to compare the-results with those obtained by a finite difference technique, and to show how the finite element method can be applied to complex but realistic two-dimensional flow situations. Two examples are given. The first concerns one-dimensional flow and it compares numerical results with those obtained experimentally in the field from water balance studies on red cabbage (Brassica oleracea L. ‘Rode Herfst’) grown on a clay soil in the presence of a water table. The second example describes two-dimensional flow in a complex field situation in The Netherlands where flow takes place under cropped field conditions through five anisotropic layers. Water is supplied to the system by infiltration from two unlined ditches and is withdrawn from the system by evapotranspiration and by leakage to an underlying pumped aquifier.

Finite Element Analysis of Two-Dimensional Flow in Soils Considering Water Uptake by Roots: II. Field Applications

Data on evaporation to be used in agriculture, hydrology, forestry, etc. are usually supplied by meteorologists. Meteorologists themselves also use evaporation data. Air mass properties determining weather are strongly dependent on the input of water vapour from the surface. So for weather prediction purposes evaporation data, or rather methods to compute evaporation are needed.

Reinder A. Feddes

Papers

Space and time scale variability and interdependencies in hydrological processes

Evaluating drainage design parameters for the Fourth Drainage Project, Pakistan by using SWAP model: Part II - modeling results

Irrigation water distribution and long-term effects on crop and environment

Finite Element Analysis of Two-Dimensional Flow in Soils Considering Water Uptake by Roots: II. Field Applications

Evaporation and weather