Lecture 1: Fundamentals of water 2

Question 1

FLUXES:

Precipitation

Answer 1

Includes rainfall, fog, snow, dew, sleet, rime… (measured in mm)

The most significant hydrological flux in many environments

Variable diurnally, seasonally, inter-annually and in the long term

Highly spatially variable

In most places precipitation is dominated by rainfall

Basic types: convective, orographic, frontal

Question 2

FLUXES:

Precipitation- important characteristics

Answer 2

Seasonality – within the year
Variability → in inter-annual totals
Reliability → consistency in timing and duration
Amount → total volume (depth) of rainfall
Duration → how long the rainfall lasts
Frequency → how often it rains
Intensity → amount per unit time

Question 3

Monitoring climate

Answer 3

Chiquito catchment, Costa Rica : distributed monitoring stations

Monitoring climate (instrumentally : at (or near) the ground)- San Gerardo cloud forest, Costa Rica : instrumental tower

Question 4

Measuring rainfall

Answer 4

standard totalling gauge

tipping bucket (recording) raingauge

space borne radar- ground based rainfall radar

Question 5

Pan tropical rainfall assessments

Answer 5

WORLDCLIM – 1km monthly measured rainfall compiled from 47,554 stations
interpolated using splines with altitude as a co-variable, complied by Hijmans et al (2005)*

b) TROPICLIM- 1km monthly near-surface rainfall based on 8 years of approx. bi-weekly Tropical Rainfall Monitoring Mission (TRMM) 2B31 rainfall rate data, processed by Mulligan (2006).

Question 6

Costa rica

Answer 6

wind-driven rainfall highly variable in tropical mountains according to their eastern exposure

Question 7

Evapo-transpiration

Answer 7

Upward flux from land back to atmosphere

Potential ET controlled by solar radiation, temperature and atmos humidity and wind speed

Actual ET controlled by availability of water (incl surface area)

Comprising:
Free water evaporation
Soil evaporation
Canopy interception loss
Transpiration through stomata

Varies with climate and land surface properties
Used by animals (and plants) for cooling

Loss through stomata in plants during photosynthesis → water productivity (kg/mm) fundamental to agriculture

Question 8

Annual radiation load is highest in the tropics because.

Answer 8

… the same radiation is spread over a much smaller area
(Lambert’s Cosine Law). NOT because the land is further away – the
Solar energy has already travelled 92,900,000 miles (149,476,000
km) from the sun so an extra 4-6 000 km makes no difference).
This sets up a latitudinal gradient in energy that drives the hydrosphere

Question 9

measuring evapotranspiration

Answer 9

evaporation pan (PET)

lysimeter

eddy covariance systems

scintillometers

Question 10

measuring transpiration

Answer 10

Leaf chambers

• thermal sap-flow
• sensors

Question 11

Runoff

Answer 11

The lateral flux of water balance (precipitation minus actual evapotranspiration)

Depends on rate of rainfall vs rate of infiltration (hydro-crossroads)

Overland flow on land

Streamflow/runoff in rivers

Responsible for global river network

Connects landscapes upstream-downstream

Question 12

Through flow

Answer 12

Slow flow through matrix
Faster flow through macropores
Important for redistribution in time and space
Ensures rivers are perennial