Thesis (M.S. - Soils, Water and Engineering)--University of Arizona, 1985. / Includes bibliographical references (leaves 75-77).

Thesis (Ph.D.)--Vrije Universiteit Amsterdam, 2007. / Includes bibliographical references (p.185-202).

Stodmarsh National Nature Reserve includes the largest reedbed in Southern England and is an important habitat for breeding waders and several rare bird species, including Bitterns. A succession of drought years in the 1990s brought the issue of the hydrology and water requirements of the wetland to the attention of managers and there is concern about future water supplies to the reserve. This study aims to calculate the amount of water required by the site in order to maintain optimum habitat conditions. The greatest area of uncertainty in the water balance is the evapotranspiration rate of the reedbeds and therefore a secondary aim is to increase understanding of this flux. Detailed hydrological measurements were carried out over two years to establish the water balance of the site. Evapotranspiration was measured using the Bowen ratio technique, accompanied by additional physiological and meteorological measurements. Results showed that evapotranspiration from reeds was generally less than reference evapotranspiration and that stornatal resistance was the most important factor controlling evapotranspiration rates. The hydrology of the site was modelled using a thirty year historical data series to quantify the return periods of flood and drought conditions of different severity. These were used to predict water resource requirements and availability and confidence limits were attached to the results. In 70% of years, summer deficits in the rainfall-evapotranspiration balance require the addition of water from the Lampen Stream. In 10% of these years, the entire surmner discharge of the Lampen Stream would be insufficient to meet site water requirements and an additional source of water is required. Competition with other water users and limits on abstraction will increase the number of years an additional water source is required. In addition future climate change is likely to increase summer water requirements whilst decreasing resource availability.

Grassland is the dominant vegetation cover of many of the 19 Water Catchment Areas within South Africa. The inappropriate management of some of these grassland catchments by the communities that depend on them for their livelihoods, often results in overgrazed lands with low biomass or invasive alien species. The short grass maintained by grazing policies of many communities results in high storm flows that have an adverse effect on the quantity and quality of runoff and recharge. Catchment-scale water balances depend on accurate estimates of run-off, recharge and evapotranspiration (ET). This study focuses on the ET component of the catchment scale water balance and explores the effect of two different grazing strategies on ET. To achieve this, two contrasting but adjacent quaternary catchments namely: P10A (a high biomass site) and Q91C (a low biomass site) were selected within the Bushman’s River Primary catchment as primary study sites. Within each catchment, a relatively homogenous pixel of 1 km was selected, representing contrasting example of high and low intensity grazing. From an eleven year MODIS leaf area index (LAI) data stack (March 2000 – 2010), 8-day LAI values was extracted for each pixel in each catchment. Using the Penman- Monteith equation, potential evapotranspiration (ET0) was calculated using data from a nearly automatic weather station. Actual evapotranspiration was estimated by adjusting ET0 using the values extracted from the MODIS LAI product. The MODIS LAI ET (ETMODIS) obtained for the eleven year period for both 1 km pixels decreased consistently, reflecting a general trend in declining LAI throughout the Eastern Cape. The highest ETMODIS obtained from P10A was 610.3 mm (2001) and the lowest was 333.1 mm (2009). Then from Q91C the highest ET obtained was 534.7 mm (2006) and the lowest was 266.2 mm (2009). The ETMODIS results were validated for each catchment using the Open Top Chamber (OTC) which sums the water lost from vegetation and soil within the chamber. This validation was conducted during the growing season of 2010–11. Wind speed; relative humidity and temperature were measured both at the inlet and the outlet of the chamber on five clear sunny days for each 1 km pixel. ETa for the same period was compared to the OTC ET (ETOTC) using the regression analysis and a good relationship was observed with the r2 of 0.7065. The relationship observed confirmed that ETOTC closely approximates ETMODIS and that the OTC can be used as a tool to validate MODIS LAI ET on clear, low winds and sunny days. In order to demonstrate proof-of-concept for the use of this modeling of ETMODIS within a Payment for Ecosystem Services framework, the approach was applied to two other quaternary catchments under communal tenure. Within each catchment, three land use scenarios were created for each catchment to reflect potential changes in the standing aboveground biomass. For Scenario 1, the status quo was maintained; for Scenario 2, MODIS pixels representing 28 km in each catchment were selected and the LAI of these pixels was doubled; and for scenario 3, LAI was halved. ETMODIS was calculated for each scenario by adjusting the ET0 data from a nearby automatic weather station with the MODIS LAI product. The results showed that the estimated annual ETMODIS obtained from the high biomass catchment was 111 mm greater than that obtained from the low biomass catchment. When comparing between the scenarios, the annual ETMODIS obtained from scenario 2 was the highest of the 3 scenarios for both sites. These results confirm that increased leaf area results in higher annual ETMODIS. This has a positive long term impact on stream flow, as high grass biomass allows the rainfall to infiltrate the soil and be gradually released to the dams with reduced magnitude of storm flows. This approach has the potential to quantify the benefits to down-stream water users of improving above-ground biomass in catchments.

This study is concerned with the energy balance of a suburban area of south central Vancouver and in particular with the role of evapotranspiration in this balance. In the late summer - early fall of 1977 a measurement program was conducted to determine the energy balance components using the Bowen ratio - energy balance approach. The Bowen ratio was obtained from differential psychrometric measurements taken above mean roof-level. Net radiation was measured directly and the volumetric heat storage was parameterized in terms of net radiation. The results indicate that the Bowen ratio - energy balance approach is applicable to suburban environments. An error analysis developed for the reversing psychrometer system indicates that the errors in the turbulent fluxes were typically 10 - 20%. The turbulent latent heat flux was always a significant and often the dominant energy sink for this 'surface'. This is shown to be largely due to soil moisture replenishment by precipitation and irrigation (especially lawn sprinkling). The turbulent fluxes tended to be in-phase with net radiation during the day. This appears to be a result of the decreasing importance of non-radiative controls (especially the vapour pressure deficit) on evapotranspiration as the land use changes from rural to heavily urbanized. Sustained periods of positive turbulent fluxes were recorded at night, however the Bowen ratio was predominantly negative indicating that only one turbulent flux was positive. The data do not reveal any dependence on wind direction. The influence (if any) of the sea breeze could not be isolated. The equilibrium evapotranspiration rate often closely approximated the measured evapotranspiration. / Arts, Faculty of / Geography, Department of / Graduate

4 pp. / The objective of this and subsequent bulletins in the Turf Irrigation Management Series is to simplify the subject of ET and thereby increase the effective utilization of ET in irrigation management. This bulletin provides some basic background on the related subjects of evaporation and evapotranspiration.

5 pp. / This document describes the procedures used to adjust ETo for use on managed turf surfaces in Arizona.

No description available.

Urban landscapes require irrigation during periods of insufficient rainfall. Significant water use savings may be achieved if landscape irrigation is based on reference evapotranspiration (RET). The objectives of this study were to determine 1.) landscape crop coefficients (K[subscript L]) for landscapes comprised of different vegetation types, 2.) if regional climatic differences affect K[subscript L], and 3.) examine differences in leachate nutrient concentrations from the plant treatments. The K[subscript L] was determined from the ratio of actual evapotranspiration and a modified Penman equation reference. Irrigation quantity was based on 100% replacement of RET. The K[subscript L] were determined for St. Augustinegrass [Stenotaphrum secundatum (Walt.) Kutze.] alone, Red Oak [Quercus shumardii Buckl.] alone, St. Augustinegrass plus Red Oak, native grasses [Muhlenbergia capillaries (Lam.) Trin. and Schizachyrium scoparium (Michx.) Nash], and native grasses plus Red Oak in College Station (CS) and San Antonio (SA) Texas, on a Rader fine sandy loam (mixed, semiactive, thermic Aquic Paleustalfs). Soil was systematically placed into lysimeters containing a drainage system and soil moisture probes. Lysimeters (1136 L) were placed in-ground in a randomized complete block design with three blocks. Soil moisture measurements were made at 0 to 20, 20 to 40, and 40 to 60 cm depths. The K[subscript L] was determined after a rainfall or irrigation event for periods of two to five days. Leachate was analyzed for dissolved organic carbon (DOC), dissolved organic nitrogen (DON), ammonium, nitrate-N, orthophosphate-P, and alkalinity. During the growing seasons of 2007 and 2008, K[subscript L] in San Antonio increased from early-, to mid-, to late-season while in CS the K[subscript L] decreased from early-, to mid-, to late-season. Treatments with nativegrasses in SA had K[subscript L]'s as large as 0.91 in late-season. In CS, soil sodium accumulation caused a decreasing seasonal K[subscript L]. Mean DOC concentration was not different between sites except for tree only treatment which was larger in SA. For mean DON concentrations between sites, only the St. Augustinegrass treatment was larger in CS than in SA. Orthophosphate-P concentrations were larger at SA under the tree alone, nativegrass, and St Augustine plus tree treatments than in CS. Ammonium concentration was similar by site for vegetative treatments.

Revised. (Originally published: 2000). / 4 pp. / Introduction: Local information on evapotranspiration (ET) is now readily available from on-site weather stations and/or public weather networks to assist turfgrass professionals with irrigation management decisions. Proper utilization of ET information can provide accurate estimates of daily water use and thus can assist irrigation managers with the all important decisions of when to apply water and how much water to apply. The concept of ET can be confusing and often is presented in a highly technical manner. The objective of this and subsequent bulletins in the Turf Irrigation Management Series is to simplify the subject of ET and thereby increase the effective utilization of ET in irrigation management. This bulletin provides some basic background on the related subjects of evaporation and evapotranspiration.