Hydrology: Soil moisture, Rainfall, and Evapotranspiration. Tarendra Lakhankar NOAA-CREST Center, The City University of New York

Transcription

1 Hydrology: Soil moisture, Rainfall, and Evapotranspiration Tarendra Lakhankar NOAA-CREST Center, The City University of New York

2 Overview Hydrology Rainfall Soil moisture Evapotranspiration Experiments Math Examples Soil moisture experiment using moisture meter (Postponed to next week due to cold weather)

3 The Hydrologic Cycle

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5 Rainfall

6 Precipitation Single strongest variable driving hydrologic processes Formed water vapor in the atmosphere rain snow sleet graupel freezing rain hail

7 Droplets become heavy enough to fall Evaporation decreases size of many droplets Droplets increase in size by condensation Droplets form by nucleation Larger drops break up Some droplets increase in size by impact and aggregation Water vapor Rain Drops

8 Point Measurement Rainfall Gauges Network of Rainfall Gauges The number of stations depend on precipitation and its variability Area Measurement Radar, Satellites Source of Data Precipitation Measurements Many other publications, Universities, etc.

9 Rational Method for Watershed Discharge Q = ica Q = Peak discharge, cfs C = Rational method runoff coefficient i = Rainfall intensity, inch/hour A = Drainage area, acre If Q = cubic feet per second, P = inches/hour and A= Acres, Then Q = 1.008CiA Simplified Table of Rational Method Runoff Coefficients (see references below) Ground Cover Runoff Coefficient, C Lawns Forest Cultivated land Meadow Parks, cemeteries Unimproved areas Pasture Residential areas Business areas Industrial areas Asphalt streets Brick streets Roofs Concrete streets

10 Precipitation Measurement

11 Precipitation Measurement

12 Tipping-Bucket: Demonstration

13 Pluviometer A rain gauge (also known as an udometer, pluviometer, or an ombrometer) is a type of instrument used by meteorologists and hydrologists to gather and measure the amount of liquid precipitation over a set period of time.

14 Precipitation Measurement Under Canopy Outside Canopy

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16 Precipitation Measurement

17 Precipitation Measurement

18 Ideal rain gage for rainfall with egg-crate Structure (Dingman, 2002)

19 Rainfall Interception Conifer forests in North America I c = 15-40% of P g Natural teak forests in Thailand I c = 65% of P g Is influenced by rain: amount, duration, intensity, and pattern

20 Simplest method for determining areal average Arithmetic Mean Method P 1 = 10 mm P 2 = 20 mm P 3 = 30 mm 1 P = N N i= 1 P i P 2 P P = = 20 3 mm P 3 Gages must be uniformly distributed Gage measurements should not vary greatly about the mean

21 Isohyetal method Steps Construct isohyets (rainfall contours) Compute area between each pair of adjacent isohyets (A i ) Compute average precipitation for each pair of adjacent isohyets (p i ) Compute areal average using the following formula P 2 P 1 A 1 =5, p 1 = 5 A 2 =18, p 2 = 15 A 3 =12, p 3 = 25 M P = ia = 1 P 1 N A i p i i= 1 A i P i 30 P 3 A 4 =12, p 3 = P = = mm

22 Inverse distance weighting Prediction at a point is more influenced by nearby measurements than that by distant measurements The prediction at an ungaged point is inversely proportional to the distance to the measurement points Steps Compute distance (d i ) from ungaged point to all measurement points. P 2 = 20 d 2 =15 p P 1 =10 d 1 =25 d 3 =10 P 3 =30 Compute the precipitation at the ungaged point using the following formula d 2 ( x x ) + ( y ) 2 12 = y2 Pˆ N i= 1 = N i= 1 P i di 1 di Pˆ = = mm

23 Thiessen polygon method Any point in the watershed receives the same amount of rainfall as that at the nearest gage Rainfall recorded at a gage can be applied to any point at a distance halfway to the next station in any direction Steps in Thiessen polygon method 1. Draw lines joining adjacent gages 2. Draw perpendicular bisectors to the lines created in step 1 3. Extend the lines created in step 2 in both directions to form representative areas for gages 4. Compute representative area for each gage 5. Compute the areal average using the following formula P = 1 A N i= 1 A i P i P = = mm P 2 A 2 P 1 A 1 P 3 A 3 P 1 = 10 mm, A 1 = 12 Km 2 P 2 = 20 mm, A 2 = 15 Km 2 P 3 = 30 mm, A 3 = 20 km 2

24 Rainfall interpolation in GIS Data are generally available as points with precipitation stored in attribute table.

25 Rainfall maps in GIS Nearest Neighbor Thiessen Polygon Interpolation Spline Interpolation

26 Figure 2.14 Storm Patterns (Histograms)

27 Lets do some calculation Estimate Average precipitation

28 Soil Moisture

29 Meteorological and weather prediction modeling Hydrological modeling Runoff prediction and flood control Reservoir management Soil erosion and mud slide Agriculture applications Improving crop yield Irrigation scheduling Soil Moisture

30 Volumetric vs. Gravimetric Water Content Volumetric Water Content (VWC) Symbol θ Water volume per unit total volume Air 15% Gravimetric Water Content (GWC) Symbol w Water weight per unit dry soil weight Water 35% Soil 50% In situ field measurement methods only measure volumetric water content

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32 Direct Water Content Measurements Gravimetric (w) Technique Sample representative weight of soil Take care to limit water draining/evaporating from soil Weigh sample on balance with adequate accuracy/precision Dry sample at 105 o C for 24 h Allow to cool in desiccators Obtain dry sample weight and take weight Generate volumetric water content Same as gravimetric except soil is sampled with known volume

33 Advantages Simple Direct measurement Can be inexpensive Direct Water Content Measurements Disadvantages Destructive does not account for temporal variability Time consuming Requires precision balance & oven

34 On field how to take sample

35 Measuring in situ Water Content (indirect) Neutron thermalization Neutron probes Dielectric measurement Capacitance/Frequency Domain Reflectometry (FDR) Time Domain Reflectometry (TDR)

36 Neutron Thermalization Probe: How They Work Radioactive source High-energy epithermal neutrons Releases neutrons into soil Interact with H atoms in the soil slowing them down Other common atoms Absorb little energy from neutrons Low-energy detector Slowed neutrons collected thermal neutrons Thermal neutrons directly related to H atoms, water content The probe contains a source of fast neutrons, and the gauge monitors the flux of slow neutrons scattered by the soil. In using the neutron meter, a cased hole in the ground is necessary for lowering the probe to obtain readings.

37 Dielectric Theory: How it works In a heterogeneous medium: Volume fraction of any constituent is related to the total dielectric permittivity Changing any constituent volume changes the total dielectric Because of its high dielectric permittivity, changes in water volume have the most significant effect on the total dielectric Material Dielectric Permittivity Air 1 Soil Minerals 3-7 Organic Matter 2-5 Ice 5 Water 80 Influencing Factors Water Content Water Content Soil Temperature Soil Porosity and Bulk Density Minerals (2:1 clays) Measurement Frequency Air Gaps (Installation swelling soils)

38 Dielectric Mixing Model: FYI The total dielectric of soil is made up of the dielectric of each individual constituent The volume fractions, V x, are weighting factors that add to unity V V b b b b b ε = ε m m + ε a a + ε wθ + ε om om + t V ε V b i i Where ε is dielectric permittivity, b is a constant around 0.5, and subscripts t, m, a, om, i, and w represent total, mineral soil, air, organic matter, ice, and water.

39 Volumetric Water Content and Dielectric Permittivity Rearranging the equation shows water content, θ, is directly related to the total dielectric by θ = 1 ε 0.5 w ε 0.5 t ( ε 0.5 m V m + ε 0.5 a V + ε ε a 0.5 w 0.5 om V om + ε 0.5 i V i ) Take home points Ideally, water content is a simple first-order function of dielectric permittivity Generally, relationship is second-order in the real world Therefore, instruments that measure dielectric permittivity of media can be calibrated to read water content

40 Dielectric Instruments: Time Domain Reflectometry TDR sensors propagate a pulse down a line into the soil, which is terminated at the end by a probe with wave guides. TDR systems measure the determine the water content of the soil by measuring how long it takes the pulse to come back.

41 Dielectric Instruments: Capacitor/FDR Sensor Basics Sensor probes form a large capacitor Steel needles or copper traces in circuit board are capacitor plates Surrounding medium is dielectric material Electromagnetic (EM) field is produced between the positive and negative plates

42 Typical Capacitor Capacitor Dielectric Material Positive Plate Negative Plate Electromagnetic Field

43 Example: How Capacitance Sensors Function 2 cm Sensor (Side View) 1 cm 0 cm EM Field

44 Question: What Technique is Best for My Research? Answer: It depends on what you want. Every technique has advantages and disadvantages All techniques will give you some information about water content So what are the important considerations? Experimental needs How many sites? How many probes at each site? Current inventory of equipment What instruments are available or can by borrowed Budget How much money can be spent to get the data? Required accuracy/precision Manpower available to work Certification People available certified to work with radioactive equipment

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46 Examples: Applying Techniques to Field Measurement Case: Irrigation scheduling/monitoring Details 20+ sites, measurements from.25 m to 2 m Spread over field system Continuous data collection is desirable Money available for instrumentation Eventually moving to controlling irrigation water Choice Capacitance sensors Good accuracy Inexpensive Easy to deploy and monitor Radio telemetry available to simplify data collection

47 Permanent installation Horizontal insertion Purpose Measure at specific depths Useful to see infiltration fronts, drying depths Technique Dig trench Sensor Installation Install probes into side wall» Installation tools are helpful (see manufacturer)» Ensure NO air gaps between probes and soil Refill trench

48 Push-in and Read Sensors Purpose Spot measurements of VWC Many measurements over large area No need for data on changes in VWC over time Technique Push probe into soil Ensure adequate soil to probe contact Take reading from on-board display Sensor Installation

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50 With Replicates

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53 U.S. Climate Reference Network (USCRN) All 114 Stations Installed/Operational End of FY 08 Installed 7 Pairs (14) Installed Single (92) Awaiting Installation (8)

54 What can I expect to see in the field? Volumetric water Content (%) Rainfall (mm) 0 8/1 8/4 8/7 8/10 8/13 8/16 8/19 8/22 8/25 8/28 8/31 August EC-5 15cm EC-5 30cm EC-5 45cm EC-5 90cm TE-5(WC) 15cm Rain (mm) 0 Data courtesy of W. Bandaranayake and L. Parsons, Univ. of Florida Citrus Research and Education Center

55 USDA Soil Climate Analysis Network (SCAN)

56 Soil Moisture - Microwave Remote Sensing Evolution Active Microwave own energy (Reflection) Passive Microwave Earth energy (Emission) Soil Moisture Sensing Technology High (10 s meter) Regional modeling Field Experiments SEASAT, PBMR, SMMR Low ( Km) Global modeling SIR-C/X-SAR JERS-1, ERS-1 ESTAR, SSM/I RADARSAT-1 ERS-2, ENVISAT AMSR-E 1970s 1980s 1990s 2000 RADARSAT-2 SMOS, METOP 2010 Common wavelength L and C band, which penetrate cloud, rain, and vegetation canopies NPOESS CMIS/VIIRS AQUARIUS SMAP SAOCOM GCOM-W Ground truth SM Missions: FIFE Mansoon 90 OXSOME 90 MACHYDRO 90 HAPEX WASHITA 92 WASHITA 94 SGP 97 SGP 99 SMEX 02 SMEX 03 SMEX 04 SMEX 05

57 Advanced Microwave Scanning Radiometer (AMSR-E) AMSR-E is Advanced Microwave Scanning Radiometer for NASA s Earth Observing System and JAXA of Japan. It s onboard the Aqua satellite of EOS that was successfully launched in May Mission Operational begin Instrument concept AMSR-E Launched December, 2002 Passive microwave radiometer Frequency 6.92, 10.65, 18.7, 23.8, 36.5, 89 GHz Polarization Dual polarization Channels Foot print Angular range Swath 12 channels 5 to 60 km 55 degrees 1445 km

58 SMOS (Soil Moisture and Ocean Salinity) Mission ESA's Soil Moisture and Ocean Salinity (SMOS) mission has been designed to observe soil moisture over the Earth's landmasses and salinity over the oceans. The goal of the SMOS mission is to monitor surface soil moisture with an accuracy of 4% (at km spatial resolution). Mission SMOS Launch November, 2009 Duration Instrument Instrument concept Frequency Number of receivers 69 Receiver spacing Polarization Radiometric resolution Angular range Temporal resolution Minimum 3 years Microwave Imaging Radiometer using Aperture Synthesis - MIRAS Passive microwave 2D-interferometer L-band (21 cm, 1.4 GHz) lambda = cm H & V 35 km at center of field of view 0-55 degrees 3 days revisit at Equator

59 SMAP ( Soil Moisture Active Passive) Mission SMAP is implemented as a directed mission within the NASA Earth Systematic Mission Program. The SMAP project is managed by the Jet Propulsion Laboratory (JPL) with participation by the Goddard Space Flight Center (GSFC). SMAP will use a combined radiometer and high-resolution radar to measure surface soil moisture and freeze-thaw state, providing new opportunities to enable improvements to weather and climate forecasts, flood prediction and drought monitoring. Mission SMAP Launch March, 2013 Duration Instrument concept 3 years Active microwave - Synthetic Aperture Radar Passive microwave - Radiometer Frequency L-band :1.26 GHz (H) 1.29 GHz (V) Polarization HH, VV,HV H, V, U Radiometric resolution 1-3 km 40 km Angular range Swath width Temporal resolution 40 degrees 1000 km L-band :1.41 GHz global coverage within 3 days at the equator and 2 days at boreal latitudes (>45 N)

60 ASCAT (Advanced SCATterometer) Level 2 Soil Moisture Product The ASCAT soil moisture product is produced by EUMETSAT, using the WARPNRT software originally developed by IPF/TU Wien (Institute of Photogrammetry and Remote Sensing, Vienna University of Technology). Accuracy: The average RMS error of the soil moisture index is about 25%, which corresponds to about m 3 water per m 3 soil, depending on soil type. The ASCAT soil moisture service has been set up to meet the requirements of Numerical Weather Prediction (NWP) applications. Value-added soil moisture products for hydrological users in Europe are currently under development within the Satellite Application Facility in Support to Operational Hydrology and Water Management. Mission ASCAT Operational begins 11 December, 2008 Instrument concept Frequency Polarization Spatial Resolution Active microwave Real aperture radar Radar C-band (5.255 GHz) VV polarization Angular range 25º - 65 º Swath Width 50 km (25 km grid spacing) 550 km Source: km (12.5 km grid spacing)

61 NOAA-CREST Microwave Radiometer Specification: L-Band Radiometer Frequency: 1.40 to 1.55 GHz (SMAP Frequency) polarization : Dual (H, V) Antenna System: 1.5 x 0.7 meters Delivery date: September 2009 Manufacturer: Radiometrics Corporation, Boulder CO. High frequency Radiometers 37, 89 GHz radiometer for snow related research. Research Objective: Improve our understanding of scattering and emission. Evaluate the vegetation (NDVI, VWC) effect on soil moisture. Evaluate spatial and temporal variability of soil moisture. We looking for suitable field location for radiometer.

62 Evaporation

63 Process by which the phase of water is changed from liquid to a vapor. It occurs at the evaporating surface, the contact between water body and overlaying air. Evaporation

64 Evaporation rate is a function of several meteorological and environmental factors The two main factors from an engineering standpoint are: Solar energy: it provides latent heat of vapor Advective energy: it is the ability to transport Evaporation

65 Evaporation Measures Pan evaporation Water budget Correlations to climate data (empirical)

66 Evaporation Pan evaporation method An evaporation pan is a device designed to measure evaporation by monitoring the loss of water in the pan during a given time period, usually one (1) day. Pan coefficient = 0.60 to 0.85 on an annual basis E = pe L c p

67 Standard 4 foot diameter pan

68 Evaporation Correlations to Climate Data General Empirical Formula E= f( eu, ) General Theoretical Formula

69 Empirical Formula for Lake Hefner E = ( e e ) U L o a E L = evaporation rate in inches per day 2. e o = saturation vapor pressure at the water surface in inches of mercury 3. e o8 = vapor pressure in air over the lake at an elevation of 8 m, in inches of mercury 4. U 8 = wind speed over the lake at an elevation of 8 m, in miles per day As an engineer, you have to find an empirical formula for surface waters in your area of interest

70 Empirical Formula for Class A pan E = ( e e )( m + bu ) p o a 1. E p = daily pan evaporation, (in./day) 2. e o = saturation vapor pressure at the water surface, (in. of mercury) 3. e o = atmospheric vapor pressure at air temperature, (in. of mercury) 4. U = wind speed at 6 inches above pan rim, (mpd) 5. n, m, and b = 0.88, 0.37, , respectively. Note: saturated vapor pressure is a function of temperature. n

71 Transpiration Transpiration is the process by which plants transfer water from the root zone to the leaf surface, where it eventually evaporates into atmosphere. The process by which transpiration takes place can be described as follows: Water is extracted by a plants roots, transported upward through its stem and diffused into the atmosphere through stoma.

72 Transpiration Contributing factors: a. Moisture available b. Vegetation type c. Vegetation density d. Vegetation health

73 Transpiration Measured with phytometer (plant used as a measuring device) Phytometer is a device for measuring transpiration, consisting of a vessel containing soil in which one or more plants are rooted and sealed so that water can escape only by transpiration from the plant. Based on monthly consumptive use (if available) and monthly evaporation T = ET E 1. T = transpiration rate (mm/time) 2. ET = evapotransipiration rate (mm/time) 3. E = Evaporation rate (mm/time)

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75 Evapotranspiration ET = evaporation from soils, plant surfaces, and water bodies combined with water losses through plant leaves Evaporation: net loss of water from a surface resulting from a change in state from liquid to vapor and the net transfer of vapor to the atmosphere Transpiration: net loss of water from plant leaves by evaporation through plant stomata

76 Impacts on Hydrology > 70% of annual PPT in US > 95% in semi-arid and arid regions For dry areas, ET/P ~ 1 Q/P is very small ET is limited by plant water availability For humid areas, ET/P is smaller Q/P is higher ET is limited by energy

77 Evapotranspiration Mass balance S= P R F ET Based on Pan Evaporation ET = ke p k = 0.35 to 0.85 = f(soil/plant condition, location of the pan, wind speed, upwind fetch, and humidity) For example, k = 0.7 if wind speed = km/day, upwind fetch of green crop = 1,000 m, and low relative humidity = percent.

78 Example Assume the following situations for a small watershed in northern Indiana. The six-month seasonal precipitation is 70 cm, runoff is 20 cm, and the change in groundwater storage is 15 cm. What are the monthly evapotransipiration rates? S= P R ET 15= ET ET = = 35 cm/6 month = 5.83 cm/ month

79 Evapotranspiration Irrigation needs based on evapotranspiration 0 Known 0 0 Known S= P+ I R F ET I = ET P

80 Evapotranspiration Potential Evapotranspiration (PET) is the amount of evapotranspiration that would take place under the assumption of an ample supply of moisture at all times. PET is an indication of optimum crop water requirements.

81 Combination Approach Evaporation and Evapotranspiration Can be measured using - evaporation pan - weighing lysimeter Allows for estimation of E from measurements of - Global radiation - Wind speed - Air temperature - Relative humidity

82 Evaporation and Evapotranspiration Reference Evapotranspiration ET 0 Crop evapotranspiration under standard conditions ET KcET 0 For ryegrass Kc mid=1.65 c = Crop evapotranspiration under non-standard conditions(actual evapotranspiration) Radiation Temperature Well watered Wind speed grass Humidity Well watered crop optimal agronomic comditions ET = actual K s ET c Water & environmental stress

83 Evaporation and Evapotranspiration Crop growth stages initial stage. development stage Mid-season stage Late season stage

84 Evaporation and Evapotranspiration Crop Coefficient Crop growth stages Single crop coefficient approaches (K c ) Dual crop coefficient approaches (Kcb+ Ke ) basal crop coefficient (Kcb) soil water evaporation coefficient (K e ) K c =K cb +K e

85 Drought Videos

86 Drought Videos to Watch Western U.S. drought puts big strain on reservoirs (2.56 min) NASA Mega-droughts Projected for American West (2.40 min) NASA launches Earth-observing satellite helps Measuring Soil Moisture Cycle and floods conditions (3.00 min) California's Extreme Drought, Explained The New York Times (3.36 min) Real World: What Is Soil Moisture? (5.28 min)

87 Experiment

88 National Weather Stations in New York

89 Thiessen Method for Average Rain Step 1

90 Thiessen Method for Average Rain Step 2

91 Thiessen Method for Average Rain Step 3

92 Thiessen Method for Average Rain Step 4

93 Soil Moisture Experiment Mark the glass 5 levels. Fill soil in plastic glass 50% Pour the ¼ glass of water in soil. Allow water to infiltrate to soil. Take a moisture meter Check the video how this moisture meter works (Earth Battery) Measure wetness of soil on scale of Pour more water slowly to make soil completely saturate. Estimate approx. how much water you poured to soil get saturate?