Fluctuation in Rainfall

100Mean

Deviation StandardVariance

Variance in rainfall in Singapore

5.61002310

9.149

Variance in rainfall in Edmonton

4.231006.411

4.96

Standard deviation Vs Variance

July Rainfall Pattern

The general pattern of July rainfall in this area is uneven(a skewed distribution). With almost half of the years have no rainfall at all in July.

Medium rainfall is 10 mm and average rainfall is 30 mm. As much as 150-200 mm have been recorded on rare occasions.

Median precipitation• Average precipitation is distorted by rare

instances of high rainfall and does not give a true impression of the generally arid conditions here.

• Mode

• insufficient rainfall leads to crop failure in approximately 2 out of 3 years

• There is approximately a 1 in 3 chance of failure or being damaged because of too much rainfall.

• Flash flooding is likely to be the main environmental hazard because of the unusual occurrence of high rainfall.This, in turn, may lead to erosion by landslip and flow etc.

• Drought may be a hazard if a situation of no rainfall extends over a period of some months.

Variations in the pattern of discharge

•Annual variation - one peak discharge and one low discharge. They are in regular rhythm.

•Long term variation – sudden increase or decrease in discharge; less frequent

Irrigation methods

•basin inundation in times of floods

•build water storage tanks and barrages to store water for use in the low water season

•build irrigation canal networks for areas further away from the river

Cropping patterns

•wet crop (e.g. rice) in period of annual flooding

•dry crops(e.g. wheat) in period of low discharge

Spatial distribution of fields and settlements

•field for wet crops sited near river

•fields for dry crops sited further away from rivers or in higher ground

•settlement are built on higher ground away from river

Impact of Large Water Scheme( more intensive farming will be carried

out)• increases number of cropping• expansion of farmland to marginal area• area of farmland increases• high yielding crops will be selected• productivity/ yield per hectare will increase

Impact of Large Water Scheme• Use more agricultural chemicals (chemical

fertilizers and pesticides)• provision of HEP may encourage

mechanization• the living standard of rural areas will

become higher

( high cost of dam construction and maintenance• irrigation water is an additional production cost• tendency to grow high-priced cash crops to

justify high production cost, reduced production of food crops

• intensification of farm production requires further inputs of fertilizers and other related investments

• loss of farmland for dam building• cost of population migration and compensation

• waterlogging / gleying• excessive evaporation and salinization• reduced nutrient content of irrigation water• intensification of land use due to increased w

ater supplies, over-cultivation and overgrazing, soil quality deterioration

• growth of weeds, pests and diseases• disturb regional distribution of water resourc

es• aquatic life disturbances• encourage the use of more farming chemicals

– water pollution

South-to-North Water Diversion Project

The East line

• 1,150 km diversion line

• 6.8 billion cubic metres of water a year

• 88% can be built by expanding the current canal

• Water to Shangdong by 2005

The Central line

• 1,245 km diversion line

• 40 billion cubic metres of water

• Complete in 2010

• Water to Beijing-Tianji

The West line

• 90 km diversion line

• 5.5 to 10 billion cubic metres of water

• Water to arid western areas

• Important to GO WEST

Water conservation technology

• Dry farming

• Drought-resistant seed

• Windbreak

• Better farming methods to minimize evaporation and soil erosion