U6115: Climate & Water Tuesday, August 16 2005

““The highest form of human intelligence The highest form of human intelligence is the ability to observe without judgingis the ability to observe without judging””

KrishnamurtiKrishnamurti

““The intuitive mind is a sacred gift and The intuitive mind is a sacred gift and the rational mind is a faithful servant. We the rational mind is a faithful servant. We

have created a society that honors the have created a society that honors the servant and has forgotten the giftservant and has forgotten the gift””

Albert EinsteinAlbert Einstein

““The mind is everything,The mind is everything,what you think you becomewhat you think you become””

BuddhaBuddha

• Water Properties• Heat capacity• latent heat• saturation vapor pressure

• Evaporation• Evaporation• transpiration, mass/energy

balance

• Droughts• Physical and historical impacts

U6115: Climate & WaterU6115: Climate & WaterTuesday, August 16 2005Tuesday, August 16 2005

...Now the wind grew strong and hard,it worked at the rain crust in the corn fields.

Little by little the sky was darkened by the mixing dust, and the wind felt over the earth, loosened the dust and carried it away.

The Grapes of Wrath, John Steinbeck.

Land Land vsvs Ocean breeze Ocean breeze

Heat Capacity – Specific HeatHeat Capacity – Specific Heat

Heat CapacityHeat Capacity

SubstanceHeat Capacity(Calorie/g.°C)

Water 1.00

Sea water 0.94

Air 0.25

Granite 0.20

Change in amount of heatChange in amount of heat (Q): (Q): QQ

Q = M x CQ = M x Cpp x x TTButBut

Mass = Mass = ww x Volume x Volume

Q = Q = ww x V x C x V x Cpp x x TT

Latent Heat - Change of phaseLatent Heat - Change of phaseLiquid Liquid Solid Solid == 80 calories per gram80 calories per gramLiquid Liquid Gas Gas == 540 calories per gram540 calories per gram

Q = Q = ww x V x C x V x CLL

evapotranspiration summarizes all processes that return liquid water back to the atmosphere into water vapor

- evaporation: direct transfer of water from open water bodies- transpiration: indirect transfer of water from root-stomatal system

• Photosynthesis requires water as well as solar energy• of the water taken up by plants, ~95% is returned to the atmosphere through their stomata (only 5% is turned into biomass!)• potential evaporation (PE), i.e. the evaporation rate given an unrestricted water supply - different from actual evaporation• how can the actual evapotranspiration be measured?

• water balance• energy balance• or combination of both

Evapotranspiration

Apart from precipitation, the most significant component of the hydrologic budget is evapotranspiration. Evapotranspiration varies regionally and seasonally; during a drought it varies according to weather and wind conditions

Slightly more than 10% of atmospheric moisture (40,000 bg) is precipitated as rain, sleet, hail, or snow in the conterminous USA. The disposition of this precipitation is illustrated below.

Evapotranspiration

Evapotranspiration: ~ 67%(majority of loss through transpiration: 97%)Runoff: 29%Groundwater outflow: ~2%Consumption: ~2%

Estimates of average statewide evapotranspiration for the conterminous United States range from about 40% of the average annual precipitation in the Northwest and Northeast to about 100% in the Southwest. During a drought, the significance of evapotranspiration is magnified, because evapotranspiration continues to deplete the limited remaining water supplies in water bodies and soils

Evapotranspiration

Estimation of ET1) from the water balancethis approach may suffer from the uncertainties in the numbers, example:

dV/dt = p + rsi - rso - et = 0 et = p + rsi - rso

p = 107±5105 m3/y (±5%)rsi = 109±1.5108 m3/y (±15%)

rso = 9.95108±1.5108 m3/y (±15%)

Here, if we neglect the groundwater inflows and outflows, we can use these values to solve for et.

Evapotranspiration

The results, accumulating the errors as we go, is:The results, accumulating the errors as we go, is:

1.51.5101077±3±3101088 m m33/y/yUnrealistic to expect to be able to quantify Unrealistic to expect to be able to quantify accuratelyaccurately all terms in a water balance all terms in a water balance for a catchment to solve for for a catchment to solve for etet, especially over short periods where storage , especially over short periods where storage changes are both substantial and difficult to measure precisely (or predict).changes are both substantial and difficult to measure precisely (or predict).

Diagnostic Diagnostic NOT predictive approach NOT predictive approach

Estimation of ET2) from the Energy balanceFirst Law of Thermodynamics: conservation of energy (E)Thermodynamic principles hold that the net radiant energy arriving across the boundary of a surface land system (including a very thin top soil layer, vegetation, and immediate surrounding air), must be exactly balanced by other energy fluxes across the boundary and the net change in energy held within the volume.

Total incoming E = Outgoing E + any increase in the body’s internal E (Q)

Evapotranspiration

dQ/dt = Rn - G - H - El

Rn = net (solar) radiation

G = output (conduction) to the ground

H = output (sensible heat) to atmosphere

El = output of latent heat

Estimation of ET2) from the Energy balanceAll matter has internal energy (expressed in calories or joules)a) Sensible heat is the portion of internal energy that is proportional to temperature (heat sensed by contact). The specific heat capacity provides a measure of how a substance’s internal energy changes with temperature

dEu = Cp m dT

Cp = dEu/(dT m)

Water has a specific heat of 1.0 cal/g.°C or 4.2x103 J/kg.°C

b) Latent heat is the amount of internal energy that is released or absorbed during phase change (no change in temperature), at a constant temperature.

v = 2.5 - (2.18 10-3 T) 106 J/kgAt 20°C v = 2.45x106 J/kg

Evapotranspiration

Estimation of ET2) from the Energy balanceThe rate of evaporation can be described, in the context of the energy balance equation, as an energy flux

dQ/dt = Rn - G - H - El

or

El = Rn - G - H - dQ/dt

Since the heat flux is related to the rate of evapotranspiration (through latent heat of vaporization)

et = El/(wv)

We can then substitute this later equation into the previous one:

et = (Rn - G - H - dQ/dt)/(wv)

Evapotranspiration

Estimation of ET2) from the Energy balance

Example: Daily evaporation from a forest on a sunny day (Rn = 200 W/m2)

et = (Rn - G - H - dQ/dt)/(wv)

If we can neglect H and G and assume that T (thermal energy content, Q) within the forest remains approximately constant, then:

et = (Rn)/(wv)

et = (200 W/m2) /(1000kg/m3) (2.5x106 J/kg) = 8.010-8 m/s = 0.7 cm/day

However, we need to consider the state (wetness) of the surface to understand and quantify how the received energy is partitioned.

Evapotranspiration

Estimation of ET2) from the Energy balanceWhen water is in limited supply, the surface becomes warmer than in the wet cases and more energy is removed from the control volume through conduction in the soil and heating of the air.In this case the surface properties, rather than the atmospheric conditions, are controlling the rate of evapotranspiration. (eg. Higher winds and lower saturation will increase evaporation rate, while reduced solar radiation - clouds - will reduce evaporation)

Evapotranspiration

Estimation of ET2) from the Energy balanceRelationship between surface wetness and the partitioning of received energy between evaporation and heating of air and soil

Evapotranspiration

Estimation of ETEstimation of ET2) from the Energy balance2) from the Energy balanceThe rate of The rate of etet that occurs under prevailing solar input and atmospheric properties, that occurs under prevailing solar input and atmospheric properties, if the surface is fully wet, is commonly referred as if the surface is fully wet, is commonly referred as Potential Evapotranspiration Potential Evapotranspiration (PET)(PET).. For a catchment water balance, we are interested in the actual For a catchment water balance, we are interested in the actual etet (rate at which (rate at which water is actually removed).water is actually removed).

When a surface is wet When a surface is wet etet/PET = 1, when it is dry /PET = 1, when it is dry etet/PET ~ 0/PET ~ 0

Evapotranspiration

Large-scale spatial variability in streamflow and storage

Spatial Variability of StreamflowSpatial Variability of Streamflow

Large-scale spatial variability in streamflow is explained by precipitation/evaporation balance to a large extent (~90%) and additional processes to a smaller one (soil water storage, seasonality)

Spatial Variability of StreamflowSpatial Variability of Streamflow

For the Catskill region, the change in evapotranspiration and snowpack amount will offset any increase in precipitation that may occur.

Temporal Variability of StreamflowTemporal Variability of Streamflow

The Concept of DroughtThe Concept of DroughtDrought is a normal, recurrent feature of climate, although many erroneously Drought is a normal, recurrent feature of climate, although many erroneously consider it a rare and random event. It occurs in virtually all climatic zones, consider it a rare and random event. It occurs in virtually all climatic zones, but its characteristics vary significantly from one region to another. Drought but its characteristics vary significantly from one region to another. Drought is a is a temporary aberrationtemporary aberration; it differs from aridity, which is restricted to low ; it differs from aridity, which is restricted to low rainfall regions and is a permanent feature of climate.rainfall regions and is a permanent feature of climate.

Drought, as a normal, recurrent feature of climate, occurs almost everywhere, Drought, as a normal, recurrent feature of climate, occurs almost everywhere, although its features vary from region to region. Defining drought is therefore although its features vary from region to region. Defining drought is therefore difficult; it depends on differences in regions, needs, and disciplinary difficult; it depends on differences in regions, needs, and disciplinary perspectives.perspectives. In Libya In Libya when annual rainfall is less than 180 mm when annual rainfall is less than 180 mm In Bali In Bali after a period of only 6 days without rain! after a period of only 6 days without rain!

Drought should not be viewed as merely a physical phenomenon or natural Drought should not be viewed as merely a physical phenomenon or natural event. Its impacts on society result from the interplay between a natural event event. Its impacts on society result from the interplay between a natural event (less precipitation than expected resulting from natural climatic variability) (less precipitation than expected resulting from natural climatic variability) and the demand people place on water supplyand the demand people place on water supply.

DroughtsDroughts

Operational definitions help people identify the beginning, end, and degree of severity of a drought. To determine the beginning of droughts, operational definitions specify the degree of departure from the average of precipitation or some other climatic variable over some time period. This is usually done by comparing the current situation to the historical average, often based on a 30-year period of record. The threshold identified as the beginning of a drought (e.g., 75% of average precipitation over a specified time period) is usually established somewhat arbitrarily, rather than on the basis of its precise relationship to specific impacts.

Operational definition of droughtsOperational definition of droughts

Meteorological droughtMeteorological drought is usually an expression of is usually an expression of precipitation’s departure from normal over timeprecipitation’s departure from normal over time

Agricultural droughtAgricultural drought occurs when there isn’t enough occurs when there isn’t enough soil moisture to meet the needs of a particular cropsoil moisture to meet the needs of a particular crop

Hydrological droughtHydrological drought refers to deficiencies in surface refers to deficiencies in surface and subsurface water suppliesand subsurface water supplies

Socioeconomic droughtSocioeconomic drought occurs when physical water occurs when physical water shortage affect supply and demand of economic goodsshortage affect supply and demand of economic goods

Drought indices assimilate thousands of bits of data on rainfall, snowpack, Drought indices assimilate thousands of bits of data on rainfall, snowpack, streamflow, and other water supply indicators into a comprehensible big picture. A streamflow, and other water supply indicators into a comprehensible big picture. A drought index value is typically a single number, far more useful than raw data for drought index value is typically a single number, far more useful than raw data for decision making.decision making. Some indices are better suited than others for certain uses. Some indices are better suited than others for certain uses.

Palmer Drought Severity IndexPalmer Drought Severity Index widely used by the U.S. Department of widely used by the U.S. Department of Agriculture to determine when to grant emergency drought assistance (better when Agriculture to determine when to grant emergency drought assistance (better when working with large areas of uniform topography)working with large areas of uniform topography) Surface Water Supply Index Surface Water Supply Index (takes snowpack and other unique conditions into (takes snowpack and other unique conditions into account) account) useful to supplement Palmer values in Western states, with mountainous useful to supplement Palmer values in Western states, with mountainous terrain and the resulting complex regional microclimatesterrain and the resulting complex regional microclimates ..

Drought IndicesDrought Indices

Palmer Drought Severity IndexPalmer Drought Severity Index The PDSI is a meteorological drought index, and it responds to weather conditions that have been abnormally dry or abnormally wet. When conditions change from dry to normal or wet, for example, the drought measured by the PDSI ends without taking into account streamflow, lake and reservoir levels, and other longer-term hydrologic impacts. The PDSI is calculated based on precipitation and temperature data, as well as the local Available Water Content (AWC) of the soil.PDSI is designed for agriculture but does not accurately represent the hydrological impacts resulting from longer droughts. Also, the Palmer Index is applied within the United States but has little acceptance elsewhere.


Palmer ClassificationPalmer Classification4.0 or more extremely wet

3.0 to 3.99 very wet

2.0 to 2.99 moderately wet

1.0 to 1.99 slightly wet

0.5 to 0.99 incipient wet spell

0.49 to -0.49 near normal

-0.5 to -0.99 incipient dry spell

-1.0 to -1.99 mild drought

-2.0 to -2.99 moderate drought

-3.0 to -3.99 severe drought

-4.0 or less extreme drought

Surface Water Supply IndexSurface Water Supply Index The Surface Water Supply Index (SWSI) was The Surface Water Supply Index (SWSI) was developed to complement the Palmer Index for moisture conditions across the state developed to complement the Palmer Index for moisture conditions across the state of Colorado.of Colorado. It is an indicator of surface water conditions and described the index as It is an indicator of surface water conditions and described the index as “mountain water dependent”, in which mountain snowpack is a major componen“mountain water dependent”, in which mountain snowpack is a major componen t.t. Like the Palmer Index, the SWSI is centered on zero and has a range between -4.2 and +4.2 (the index is unique to each basin, which limits interbasin comparisons).


May 2004May 2004

Keetch and Byram Drought Index Keetch and Byram (1968) designed a drought index specifically for fire potential assessment. It is a number representing the net effect of evapotranspiration and precipitation in producing cumulative moisture deficiency in deep duff and upper soil layers. It is a continuous index, relating to the flammability of organic material in the ground.

The KBDI attempts to measure the amount of precipitation necessary to return the soil to full field capacity. It is a closed system ranging from 0 to 800 units (800 is the maximum drought that is possible):


KBDI = 0 - 200KBDI = 0 - 200: Soil moisture and large class : Soil moisture and large class fuel moistures are high and do not contribute much fuel moistures are high and do not contribute much to fire intensity. Typical of spring dormant season to fire intensity. Typical of spring dormant season following winter precipitation.following winter precipitation. KBDI = 200 - 400KBDI = 200 - 400: Typical of late spring, early : Typical of late spring, early growing season. Lower litter and duff layers are growing season. Lower litter and duff layers are drying and beginning to contribute to fire intensity.drying and beginning to contribute to fire intensity. KBDI = 400 - 600KBDI = 400 - 600: Typical of late summer, early : Typical of late summer, early fall. Lower litter and duff layers actively contribute fall. Lower litter and duff layers actively contribute to fire intensity and will burn actively.to fire intensity and will burn actively. KBDI = 600 - 800KBDI = 600 - 800: Often associated with more : Often associated with more severe drought with increased wildfire occurrence. severe drought with increased wildfire occurrence. Intense, deep burning fires with significant Intense, deep burning fires with significant downwind spotting can be expected. Live fuels can downwind spotting can be expected. Live fuels can also be expected to burn actively at these levels.also be expected to burn actively at these levels.

Temporal and spatial distribution Temporal and spatial distribution Drought forecast using combined models Drought forecast using combined models

Drought MonitoringDrought Monitoring

Temporal and spatial distribution Temporal and spatial distribution Drought forecast using combined models Drought forecast using combined models

Drought MonitoringDrought Monitoring

• The Dust Bowl (1933-1940) The Dust Bowl (1933-1940) • The 6-years Texas Drought (1951-1956)The 6-years Texas Drought (1951-1956)

Drought Temporal and spatial variability Drought Temporal and spatial variability


North East Atlantic RegionNorth East Atlantic Region

0

2000

4000

6000

8000

10000

12000

May-31 Aug-39 Oct-47 Jan-56 Mar-64 Jun-72 Aug-80 Nov-88 Feb-97 Apr-05

Date

St. Lawrence streamflow (m3/s)

0

200

400

600

800

1000

1200

1400

1600

1800

2000

Hudson streamflow (m3/s)

St.LawrenceHudson



The Colorado RiverThe Colorado River

Streamflow forecast and historical dataStreamflow forecast and historical data

Discharge - Colorado River

0

20000

40000

60000

80000

100000

120000

140000

Oct-21 Oct-23 Oct-25 Oct-27 Oct-29 Oct-31 Oct-33 Oct-35 Oct-37 Oct-39

Date

(Ft

3/sec)

Discharge

South Texas ReservoirsSouth Texas Reservoirs

Nueces River Stream Flow

0.0E+00

5.0E+08

1.0E+09

1.5E+09

2.0E+09

2.5E+09

3.0E+09

3.5E+09

1910 1920 1930 1940 1950 1960 1970 1980 1990 2000

Year

Stream Flow (m

3/yr)

3 Rivers

Mathis

South Texas ReservoirsSouth Texas Reservoirs

Nueces River Stream Flow

0.0E+00

5.0E+08

1.0E+09

1.5E+09

2.0E+09

2.5E+09

3.0E+09

3.5E+09

1910 1920 1930 1940 1950 1960 1970 1980 1990 2000

Year

Stream Flow (m

3/yr)

3 Rivers

Mathis

0

50000

100000

150000

200000

250000

1/8/56 6/30/61 12/21/66 6/12/72 12/3/77 5/26/83 11/15/88 5/8/94 10/29/99 4/20/05

Year

Volume (AcFt)

Series1


http://drought.unl.edu/dm/thumbnails/12_week.gif

http://drought.unl.edu/dm/thumbnails/12_week.gif

European Conditions 2003-2005European Conditions 2003-2005

Annual temperature deviation in Europe in 2003Annual temperature deviation in Europe in 2003(Temperature deviation, relative to average temperature from 1961-1990)(Temperature deviation, relative to average temperature from 1961-1990)

European Conditions 2005European Conditions 2005

European Conditions 2005European Conditions 2005

Precipitation deficit in Spain since beginning of water year (1 Sept, Precipitation deficit in Spain since beginning of water year (1 Sept, 2004)2004)

97% of Portugal’s territory is affected by “severe” drought conditions97% of Portugal’s territory is affected by “severe” drought conditions

Documents

U6115: Climate & Water Tuesday, August 16 2005