1.TITLE 1.1 DATASET IDENTIFICATION Stomatal Resistance 1.4 Revision date of this document 15 Feb 93 2.INVESTIGATORS 2.1 Principal Investigator Dr Simon J. Allen 2.2 Title of investigation Water use by vegetation in the Sahel 2.3 Contacts 2.3.1 2.3.2 2.3.3 2.3.4 2.3.5 Dr C.J. Holwill Institute of Hydrology, Wallingford, England (0491) 38800 CAJH@UK.AC.NWL.IA (0491) 32256 2.4 Requested form of acknowledgement Funding from the Overseas Development Administration is gratefully acknowledged. 3 INTRODUCTION 3.1 Objective/Purpose To determine the evaporation from the herbaceous substrate at the fallow site 3.2 Summary of parameters Stomatal resistance from the herbaceous substrate and underlying soil 3.3 Discussion 4. THEORY OF MEASUREMENTS 5. EQUIPMENT Evaporation chamber measuring relative humidity and temperature 5.1.3 Key Variables Stomatal resistance 5.1.4 Principles of operation Stomatal resistance (and hence evaporation) can be calculated from the slope of vapour density v time 5.1.6 Manufacturer of instrument MP1000 Rotronic temperature and humidity probe Campbell Scientific Inc 14-20 Field St Shepshed, LEICS ENGLAND Tel: 01144509601141 Chamber: Institute of Hydrology Wallingford, England Tel: 0491 38800 5.2 Calibration 5.2.1 Specifications 5.2.1.1 Tolerance Temperature: Input range -40 to 60 deg C Precision 0.1 deg C Humidity: Input range 0-100%RH Precision < 0.5% RH 5.2.3 Other calibration information 6.PROCEDURE 6.2 Spatial Characteristics 6.2.1 Spatial coverage Ten measurements of 0.6*0.44m each at Southern Supersite at fallow site. 6.2.2 Spatial resolution Point measurements 6.3 Temporal Characteristics 6.3.1 Temporal coverage On a number of runs, each lasting for 2/3 days ie no continuous collection throughout SOP 6.3.2 Temporal resolution 2-hourly intervals on days of measurement during daylight hours 7. OBSERVATIONS 7.1 Field notes Fallow measurements were made outside the WAB but as close to the WAB as possible. Data taken over the herbaceous substrate may be affected by long shadows from nearby bushes during the early evening, and to a lesser extent in the morning. Dew in the morning also affects the measurements Each set of data refers too a specific plot, and the mean and standard error of the mean are also given for all the plots. Associated with each plot are the leaf area measurements which were determined at the end of the run. These are given as a separate dataset. The numbering of the leaf area plot measurements corresponds directly to the numbering of the 10 areas in this file. 8. DATA DESCRIPTION 8.2 Type of data 1 observation date 2 time of observation 3 stomatal resistance #1 4 stomatal resistance #2 5 stomatal resistance #3 6 stomatal resistance #4 7 stomatal resistance #5 8 stomatal resistance #6 9 stomatal resistance #7 10 stomatal resistance #8 11 stomatal resistance #9 12 stomatal resistance #10 13 mean stomatal resistance #1-#10 14 standard error of mean 15 revision date 0-3000 0-3000 0-3000 0-3000 0-3000 0-3000 0-3000 0-3000 0-3000 0-3000 0-3000 0-3000 s/m s/m s/m s/m s/m s/m s/m s/m s/m s/m s/m s/m (MISSING = .) 8.3 Sample database record 12SEP92 14:15 103.3 132.2 145.3 110.8 34 15MAR93 99.2 102.1 145.8 123.5 89.9 78.9 88.9 8.4 Data format OBSERVATION DATE: observation was made in the column contains the date on which the format DDMMMYY OBSERVATION TIME: column contains the time when the observations were made, in GMT, in the format HH:MM STOM STOM STOM STOM STOM STOM STOM STOM STOM STOM RES#1 RES#2 RES#3 RES#4 RES#5 RES#6 RES#7 RES#8 RES#9 RES#10 Stomatal Stomatal Stomatal Stomatal Stomatal Stomatal Stomatal Stomatal Stomatal Stomatal resistance resistance resistance resistance resistance resistance resistance resistance resistance resistance for for for for for for for for for for plot plot plot plot plot plot plot plot plot plot #1 (s/m) #2 (s/m) #3 (s/m) #4 (s/m) #5 (s/m) #6 (s/m) #7 (s/m) #8 (s/m) #9 (s/m) #10(s/m) MEAN RES (s/m) Mean stomatal resistance for all plots STD ERR RES Standard error of MEAN RES (s/m) REV DATE revision data for the data 9. DATA MANIPULATION 10. ERRORS Presence of dew during early morning measurements may have an effect on the measurement. 11. NOTES 12. REFERENCES 12.2 Journal Articles and Study Reports W. Koshiek (1981) A rapid-circulation Evaporation Chamber for measuring bulk stomatal resistance. J. Appl. Met., 20, 42-52 Ground Station Documentation 1. INVESTIGATOR 1.1 Dr Simon J. Allen 1.2 Dr Catherine J. Holwill 1.3 16/02/93 1. Stomatal Resistance 2. STATION IDENTIFICATION AND LOCATION 2.1 Southern Supersite Fallow Bush. Nearest village = Sadore 2.2 Station Code 2.3 Latitude 13 14.63' 2.4 Longitude 2 14.65' 2.5 Altitude 250m 2.6 Super Site and WAB SS 3. Data Acquisition 10 aluminium bases were positioned in two parallel rows of five approximately 1-2m apart close to the WAB. Measurements were taken over each of the ten bases at twohourly intervals. The chamber is lowered directly onto the area marked by the base and remains in place by virtue of its weight. Between the base and the bottom of the chamber is a layer of insulating material which keep the system as airtight as possible. The fans remained on continuously throughout the series of measurements and logging of the humidity and temperature data was carried using a Campbell 21x logger. Each measurement lasted approx 2 minutes and in between measurements the temperature and humidity were allowed to return to their normal values. At the end of the measurement period ie after up to 3 days of data had been collected in this manner, the vegetation enclosed by the bases was then cut by hand and the leaf area, fresh weight, and later, dry weight then determined. This data is given in a separate dataset and refers dirctly to these measurements.